John Bayouth, PhD

John Bayouth, PhD

Professor

Department of Human Oncology

I am a tenured professor in the Department of Human Oncology at the University of Wisconsin in Madison. Nationally, I have served in the presidential chain of both the American Association of Physics in Medicine (AAPM) and the Society of Directors of Academic Medical Physics Programs (SDAMPP) and within various committees of the American Society of Radiation Oncology (ASTRO), the Radiological Society of North America (RSNA) and the American Board of Radiology (ABR).

For several years, I have investigated the clinical impact of advanced treatment approaches in radiation oncology, including intensity modulation radiation therapy treatment (IMRT) planning, image-guided radiation therapy (IGRT), respiratory-gated imaging and radiation therapy and functional imaging for treatment planning and response to therapy. My primary area of research is acquisition and analysis of 4DCT images to quantify longitudinal pulmonary functional changes following radiation therapy, and I am currently the principle investigator (PI) of an NCI funded (R01 CA166703) Investigator Initiated Clinical Trial open at UW-Madison (UW16037), whose goal is to design and deliver radiation treatment plans that will improve pulmonary function of radiation therapy patients.

Beginning in 2013, I worked on the clinical development and implementation of MRI-guided Co-60 radiation therapy (ViewRay) at UW-Madison. This program is creating novel research in IGRT, as patients are imaged daily and during treatment delivery, demonstrating the indication for and enabling execution of online adaptation of treatment delivery and providing a wealth of tumor and normal tissue response information.

Education

Research Fellow, MD Anderson, Houston, TX, Radiation Physics (1993-1994)

PhD, MD Anderson, Houston, TX, Radiation Physics (1993)

MS, Kansas State University, Manhattan, Kansas, Nuclear Engineering (1991)

BS, Kansas State University, Manhattan, Kansas, Nuclear Engineering (1988)

Academic Appointments

Professor , Human Oncology (2013)

Selected Honors and Awards

Fellow, American Association of Physicists in Medicine (2014)

Boards, Advisory Committees and Professional Organizations

Member, American Board of Radiology (Therapeutic Radiological Physics) (1997-pres.)

Research Focus

Quantifying and minimizing normal tissue toxicities during and following radiation therapy

Enabling cancer patients to survive their disease with the highest possible quality of life

 

Our group uses medical images to quantitatively characterize tumors and normal tissues. Tissue characterization changes that occur during therapy provide an indication for adapting therapy; we hypothesize that this form of personalized medicine will lead to improved effectiveness of radiation therapy, measured by increased overall survival and reduced normal tissue toxicity.

Improving Pulmonary Function following Radiation Therapy

Radiation is highly damaging to healthy lung tissue. Our group is using information about the patient’s healthy lung tissue to design radiation treatments that may reduce the side effects of radiation therapy to lung tumors. We have established a clinical trial that is set out to determine if subjects who have been treated with radiation therapy plans designed to spare high ventilation regions have superior preservation of pulmonary function compared to those treated with standard radiation dose distributions. Four-dimensional computed tomographic imaging (4DCT) will be used to determine lung tissue elasticity, as required for ventilation. Lung tissue elasticity maps at three months after RT will be compared to those prior to RT and used to quantify the change in the lung elasticity maps. Reduced lung tissue elasticity is defined in this study as a >6 percent reduction in expansion when compared to the baseline; the amount of lung tissue showing a >6 percent reduction is the metric for our primary endpoint and will be tested for a significant difference between the two arms.

images from a 4DCT scan; one at inhale, one at exhale, and the subsequent ventilation map derived from those images

The figure shows images from a 4DCT scan; one at inhale, one at exhale and the subsequent ventilation map derived from those images. The ventilation map shows regions of the lung where lung function is high, so we hope to avoid these regions during treatment delivery.

MRI-guided Adaptive Radiation Therapy

MRI-guided radiation therapy provides a method by which we are able to observe daily changes in the patient’s internal anatomy. This can be caused by many factors, ranging from reduction in tumor size to differing amounts of content in the stomach, bladder and bowels. Consequently, radiation treatment plans based on an image acquired weeks prior to radiation delivery may not adequately represent the patient’s anatomy on a daily basis.

 

MRI-guided Adaptive Radiation Therapy is a process through which we can identify these anatomical changes and adapt the patient’s treatment on a daily basis, which can produce a substantial improvement in the radiation dose distribution. The image below shows a Dose Volume Histogram for two treatment plans, the original plan and an adaptive plan. The adaptive plan shows much better radiation dose delivery to the gross tumor volume (GTV) and planning tumor volume (PTV) when compared to the original plan. The doses to normal tissues are also reduced with the adaptive plan. We are investigating novel planning techniques to make this process robust and effective.

Dose Volume Histogram for two treatment plans, the original plan and an adaptive plan.

 

Tomotherapy Motion Compensation

Tumor and normal tissue motion during respiration creates many unique challenges in radiation therapy planning and treatment delivery. Most strategies to account for this motion assume the patient’s breathing pattern remains consistent during the entire course of treatment, which may be as long as eight weeks. Unfortunately, humans do not breath as consistently as mechanical phantoms that medical physicists like to use to simulate this behavior. The image below shows variation in tumor position during normal respiration. Note that the tumor motion is large (nearly 10 mm) but also changes substantially from one breath to the next.

 

Consequently, we require more sophisticated techniques for managing respiratory motion. Through collaborative research with Accuray, Inc., we intend to develop and validate a motion compensation system on the Tomotherapy delivery platform.graphical depiction of variation in patient breathing pattern during radiation treatment

MRI-guided Radiation Therapy

MRI is an excellent imaging modality for visualization of soft tissues. This is particularly useful for tumors of the abdomen, such as pancreatic cancer shown below.  The left image shows the patient’s anatomy during exhale, while the image on the right shows the anatomical change during a maximum inspiration breath hold (MIBH). In the MIBH image we can see motion of nearly all the soft tissue, providing us superior ability to align the tumor during our treatment delivery. We are analyzing the clinical impact of using these treatment planning and delivery techniques and our patient’s ability to comply with self-guided breathing maneuvers.

Pancreatic cancer shown here. The left image shows the patient’s anatomy during exhale, while the image on the right shows the anatomical change during a maximum inspiration breath hold (MIBH). 

Patient-Specific Response-Informed Treatment Planning

Changes to the patient occur during the course of radiation treatment, which can be eight weeks. Some of the changes are morphological (tumor size and/or position) and some are physiological (metabolic activity, inflammation, oxygenation, perfusion, etc.). We are developing imaging techniques to quantify these changes that occur during the patient’s treatment process. The results of these studies are then being used to design subsequent treatments that exploit the observed changes.  This enables a new type of precision radiation therapy that we hope will significantly improve patient outcomes.

 

The image below shows an example of patient-specific response-informed treatment planning. This patient has highly functioning lung tissue in the apex of the right upper lobe. While this is an uncommon region of the lung to demonstrate high levels of ventilation, this knowledge enables us to design radiation treatment plans to avoid delivering doses in the high functioning lung (as shown in the second row of images). We are imaging these patients after radiation treatment as well to determine how much improvement can be accomplished using this novel therapeutic approach.

The image shows an example of patient-specific response-informed treatment planning.

  • AAPM Task Group 198 Report: An Implementation Guide for TG 142 Quality Assurance of Medical Accelerators Medical physics
    Hanley J, Dresser S, Simon W, Flynn R, Klein EE, Letourneau D, Liu C, Yin F, Arjomandy B, Ma L, Aguirre F, Jones J, Bayouth J
    2021 May 25. doi: 10.1002/mp.14992. Online ahead of print.
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      The charges on this task group (TG) were as follows: (1) provide specific procedural guidelines for performing the tests recommended in TG 142; (2) provide estimate of the range of time, appropriate personnel, and qualifications necessary to complete the tests in TG 142; (3) provide sample daily, weekly, monthly, or annual quality assurance (QA) forms. Many of the guidelines in this report are drawn from the literature and are included in the references. When literature was not available, specific test methods reflect the experiences of the TG members (for example, a test method for door interlock is self-evident with no literature necessary). In other cases, the technology is so new that no literature for test methods was available. Given broad clinical adaptation of volumetric modulated arc therapy (VMAT), which is not a specific topic of TG 142, several tests and criteria specific to VMAT were added.

      PMID:34036590 | DOI:10.1002/mp.14992


      View details for PubMedID 34036590
  • Combining Stereotactic Body Radiotherapy and Microwave Ablation Appears Safe and Feasible for Renal Cell Carcinoma in an Early Series Clinical genitourinary cancer
    Blitzer GC, Wojcieszynski A, Abel EJ, Best S, Lee FT, Hinshaw JL, Wells S, Ziemlewicz TJ, Lubner MG, Alexander M, Yadav P, Bayouth JE, Floberg J, Cooley G, Harari PM, Bassetti MF
    2021 Apr 20:S1558-7673(21)00095-1. doi: 10.1016/j.clgc.2021.04.010. Online ahead of print.
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      Microwave (MW) ablation and stereotactic body radiation therapy (SBRT) are both used in treating inoperable renal cell carcinoma (RCC). MW ablation and SBRT have potentially complementary advantages and limitations. Combining SBRT and MW ablation may optimize tumor control and toxicity for patients with larger (> 5 cm) RCCs or those with vascular involvement. Seven patients with RCC were treated at our institution with combination of SBRT and MW ablation, median tumor size of 6.4 cm. Local control was 100% with a median follow-up of 15 months. Four patients experienced grade 2 nausea during SBRT. Three patients experienced toxicities after MW ablation, 2 with grade 1 hematuria and 1 with grade 3 retroperitoneal bleed/collecting system injury. Median eGFR (estimated glomerular filtration rate) preceding and following SBRT and MW ablation was 69 mL/min/1.73 m2 and 68 mL/min/1.73 m2 (P = .19), respectively. In patients who are not surgical candidates, larger RCCs or those with vascular invasion are challenging to treat. Combination treatment with SBRT and MW ablation may balance the risks and benefits of both therapies and demonstrates high local control in our series. MW ablation and SBRT have potentially complementary advantages and limitations.

      PMID:34024743 | DOI:10.1016/j.clgc.2021.04.010


      View details for PubMedID 34024743
  • Effects of variable-width jaw motion on beam characteristics for Radixact Synchrony® Journal of applied clinical medical physics
    Ferris WS, Culberson WS, Smilowitz JB, Bayouth JE
    2021 May;22(5):175-181. doi: 10.1002/acm2.13234. Epub 2021 Mar 29.
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      PURPOSE: Radixact Synchrony corrects for target motion during treatment by adjusting the jaw and MLC positions in real time. As the jaws move off axis, Synchrony attempts to adjust for a loss in output due to the un-flattened 6 MV beam by increasing the jaw aperture width. The purpose of this work was to assess the impact of the variable-width aperture on delivered dose using measurements and simulations.

      METHODS: Longitudinal beam profile measurements were acquired using an Edge diode with static gantry. Jaw-offset peak, width, and integral factors were calculated for profiles with the jaws in the extreme positions using both variable-width (Synchrony) and fixed-width apertures. Treatment plans with target motion and compensation were compared to planned doses to study the impact of the variable aperture on volumetric dose.

      RESULTS: The jaw offset peak factor (JOPF) for the Synchrony jaw settings were 0.964 and 0.983 for the 1.0- and 2.5-cm jaw settings, respectively. These values decreased to 0.925 and 0.982 for the fixed-width settings, indicating that the peak value of the profile would decrease by 7.5% compared to centered if the aperture width was held constant. The IMRT dose distributions reveal similar results, where gamma pass rates are above tolerance for the Synchrony jaw settings but fall significantly for the fixed-width 1-cm jaws.

      CONCLUSIONS: The variable-width behavior of Synchrony jaws provides a larger output correction for the 1-cm jaw setting. Without the variable-aperture correction, plans with the 1-cm jaw setting would underdose the target if the jaws spend a significant amount of time in the extreme positions. This work investigated the change in delivered dose with jaws in the extreme positions, therefore overall changes in dose due to offset jaws are expected to be less for composite treatment deliveries.

      PMID:33779041 | PMC:PMC8130229 | DOI:10.1002/acm2.13234


      View details for PubMedID 33779041
  • A clinical validation of the MR-compatible Delta<sup>4</sup> QA system in a 0.35 tesla MR linear accelerator Journal of applied clinical medical physics
    Desai V, Bayouth J, Smilowitz J, Yadav P
    2021 Apr;22(4):82-91. doi: 10.1002/acm2.13216. Epub 2021 Mar 5.
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      PURPOSE: To validate an MR-compatible version of the ScandiDos Delta4 Phantom+ on a 0.35T MR guided linear accelerator (MR-Linac) system and to determine the effect of plan complexity on the measurement results.

      METHODS/MATERIALS: 36 clinical treatment plans originally delivered on a 0.35T MR linac system were re-planned on the Delta4 Phantom+ MR geometry following our clinical quality assurance (QA) protocol. The QA plans were then measured using the Delta4 Phantom+ MR and the global gamma pass rates were compared to previous results measured using a Sun Nuclear ArcCHECK-MR. Both 3%/3mm and 2%/2mm global gamma pass rates with a 20% dose threshold were recorded and compared. Plan complexity was quantified for each clinical plan investigated using 24 different plan metrics and each metric's correlation with the overall 2%/2mm global gamma pass rate was investigated using Pearson correlation coefficients.

      RESULTS: Both systems demonstrated comparable levels of gamma pass rates at both the 3%/3mm and 2%/2mm level for all plan complexity metrics. Nine plan metrics including area, number of active MLCs, perimeter, edge metric, leaf segment variability, complete irradiation area outline, irregularity, leaf travel index, and unique opening index were moderately (|r| > 0.5) correlated with the Delta4 2%/2mm global gamma pass rates whereas those same metrics had weak correlation with the ArcCHECK-MR pass rates. Only the perimeter to area ratio and small aperture score (20 mm) metrics showed moderate correlation with the ArcCHECK-MR gamma pass rates.

      CONCLUSIONS: The MR-compatible version of the ScandiDos Delta4 Phantom+ MR has been validated for clinical use on a 0.35T MR-Linac with results being comparable to an ArcCHECK-MR system in use clinically for almost five years. Most plan complexity metrics did not correlate with lower 2%/2mm gamma pass rates using the ArcCHECK-MR but several metrics were found to be moderately correlated with lower 2%/2mm global gamma pass rates for the Delta4 Phantom+ MR.

      PMID:33666360 | PMC:PMC8035559 | DOI:10.1002/acm2.13216


      View details for PubMedID 33666360
  • Task Group 284 Report: Magnetic Resonance Imaging Simulation in Radiotherapy: Considerations for Clinical Implementation, Optimization, and Quality Assurance Medical physics
    Glide-Hurst CK, Paulson ES, McGee K, Tyagi N, Hu Y, Balter J, Bayouth J
    2021 Jan 1. doi: 10.1002/mp.14695. Online ahead of print.
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      The use of dedicated magnetic resonance simulation (MR-SIM) platforms in Radiation Oncology has expanded rapidly, introducing new equipment and functionality with the overall goal of improving the accuracy of radiation treatment planning. However, this emerging technology presents a new set of challenges that need to be addressed for safe and effective MR-SIM implementation. The major objectives of this report are to provide recommendations for commercially available MR simulators, including initial equipment selection, siting, acceptance testing, quality assurance, optimization of dedicated radiation therapy specific MR-SIM workflows, patient-specific considerations, safety, and staffing. Major contributions include guidance on motion and distortion management as well as MRI coil configurations to accommodate patients immobilized in the treatment position. Examples of optimized protocols and checklists for QA programs are provided. While the recommendations provided here are minimum requirements, emerging areas and unmet needs are also highlighted for future development.

      PMID:33386620 | DOI:10.1002/mp.14695


      View details for PubMedID 33386620
  • The quantification and potential impact of dark current on treatments with an MR-guided radiotherapy (MRgRT) system Journal of applied clinical medical physics
    Shepard AJ, Mittauer KE, Bayouth JE, Yadav P
    2020 Dec;21(12):54-61. doi: 10.1002/acm2.13059. Epub 2020 Oct 29.
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      PURPOSE: Dark current radiation produced during linac beam-hold has the potential to lead to unplanned dose delivered to the patient. With the increased usage of motion management and step-and-shoot IMRT deliveries for MR-guided systems leading to increased beam-hold time, it is necessary to consider the impact of dark current radiation on patient treatments.

      METHODS: The relative dose rate due to dark current for the ViewRay MRIdian linac was measured longitudinally over 15 months (June 2018-August 2019). Ion chamber measurements were acquired with the linac in the beam-hold state and the beam-on state, with the ratio representing the relative dark current dose rate. The potential contribution of the dark current dose to the overall prescription was retrospectively analyzed for 972 fractions from 83 patients over the same time period. The amount of time spent in the beam-hold state was combined with the monthly measured relative dark current dose rate to estimate the dark current dose contribution.

      RESULTS: The relative dark current dose rate compared to the beam-on dose rate was 0.12% ± 0.027%. In a near worst-case estimation, the dark current dose contribution accounted for 0.90% ± 0.67% of the prescription dose across all fractions (3.61% maximum). Gantry and MLC motion between segments accounted for 87% of the dark current contribution, with the remaining 13% attributable to gating during segment delivery. The largest dark current contributions were associated with plans delivering a small dose per treatment segment.

      CONCLUSIONS: The dark current associated with new clinical treatment units should be considered prior to treatment delivery to ensure it will not lead to dosimetric inaccuracies. For the MRIdian linac system investigated in this work, the contribution from dark current remained relatively low, though users should be cognizant of the larger potential dosimetric contribution for plans with small doses per segment.

      PMID:33119933 | PMC:PMC7769391 | DOI:10.1002/acm2.13059


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  • Responses to the 2018 and 2019 "One Big Discovery" Question: ASTRO Membership's Opinions on the Most Important Research Question Facing Radiation Oncology…Where Are We Headed? International journal of radiation oncology, biology, physics
    Dominello MM, Sanders T, Anscher M, Bayouth J, Brock KK, Carlson DJ, Hugo G, Joseph S, Knisely J, Mendonca MS, Mian OY, Moros EG, Singh AK, Yu JB
    2021 Jan 1;109(1):38-40. doi: 10.1016/j.ijrobp.2020.08.032. Epub 2020 Aug 14.
  • Evaluation of radixact motion synchrony for 3D respiratory motion: Modeling accuracy and dosimetric fidelity Journal of applied clinical medical physics
    Ferris WS, Kissick MW, Bayouth JE, Culberson WS, Smilowitz JB
    2020 Sep;21(9):96-106. doi: 10.1002/acm2.12978. Epub 2020 Jul 21.
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      The Radixact® linear accelerator contains the motion Synchrony system, which tracks and compensates for intrafraction patient motion. For respiratory motion, the system models the motion of the target and synchronizes the delivery of radiation with this motion using the jaws and multi-leaf collimators (MLCs). It was the purpose of this work to determine the ability of the Synchrony system to track and compensate for different phantom motions using a delivery quality assurance (DQA) workflow. Thirteen helical plans were created on static datasets from liver, lung, and pancreas subjects. Dose distributions were measured using a Delta4® Phantom+ mounted on a Hexamotion® stage for the following three case scenarios for each plan: (a) no phantom motion and no Synchrony (M0S0), (b) phantom motion and no Synchrony (M1S0), and (c) phantom motion with Synchrony (M1S1). The LEDs were placed on the Phantom+ for the 13 patient cases and were placed on a separate one-dimensional surrogate stage for additional studies to investigate the effect of separate target and surrogate motion. The root-mean-square (RMS) error between the Synchrony-modeled positions and the programmed phantom positions was <1.5 mm for all Synchrony deliveries with the LEDs on the Phantom+. The tracking errors increased slightly when the LEDs were placed on the surrogate stage but were similar to tracking errors observed for other motion tracking systems such as CyberKnife Synchrony. One-dimensional profiles indicate the effects of motion interplay and dose blurring present in several of the M1S0 plans that are not present in the M1S1 plans. All 13 of the M1S1 measured doses had gamma pass rates (3%/2 mm/10%T) compared to the planned dose > 90%. Only two of the M1S0 measured doses had gamma pass rates > 90%. Motion Synchrony offers a potential alternative to the current, ITV-based motion management strategy for helical tomotherapy deliveries.

      PMID:32691973 | PMC:PMC7497925 | DOI:10.1002/acm2.12978


      View details for PubMedID 32691973
  • Modeling the impact of out-of-phase ventilation on normal lung tissue response to radiation dose Medical physics
    Wallat EM, Flakus MJ, Wuschner AE, Shao W, Christensen GE, Reinhardt JM, Baschnagel AM, Bayouth JE
    2020 Jul;47(7):3233-3242. doi: 10.1002/mp.14146. Epub 2020 Apr 13.
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      PURPOSE: To create a dose-response model that predicts lung ventilation change following radiation therapy, and examine the effects of out-of-phase ventilation.

      METHODS: The dose-response model was built using 27 human subjects who underwent radiation therapy (RT) from an IRB-approved trial. For each four-dimensional computed tomography, two ventilation maps were created by calculating the N-phase local expansion ratio (LERN ) using most or all breathing phases and the 2-phase LER (LER2 ) using only the end inspiration and end expiration breathing phases. A polynomial regression model was created using the LERN ventilation maps pre-RT and post-RT and dose distributions for each subject, and crossvalidated with a leave-one-out method. Further validation of the model was performed using 15 additional human subjects using common statistical operating characteristics and gamma pass rates.

      RESULTS: For voxels receiving 20 Gy or greater, there was a significant increase from 52% to 59% (P = 0.03) in the gamma pass rates of the LERN model predicted post-RT Jacobian maps to the actual post-RT Jacobian maps, relative to the LER2 model. Additionally, accuracy significantly increased (P = 0.03) from 68% to 75% using the LERN model, relative to the LER2 model.

      CONCLUSIONS: The LERN model was significantly more accurate than the LER2 model at predicting post-RT ventilation maps. More accurate post-RT ventilation maps will aid in producing a higher quality functional avoidance treatment plan, allowing for potentially better normal tissue sparing.

      PMID:32187683 | DOI:10.1002/mp.14146


      View details for PubMedID 32187683
  • Validation of an MR-guided online adaptive radiotherapy (MRgoART) program: Deformation accuracy in a heterogeneous, deformable, anthropomorphic phantom Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
    Mittauer KE, Hill PM, Bassetti MF, Bayouth JE
    2020 May;146:97-109. doi: 10.1016/j.radonc.2020.02.012. Epub 2020 Mar 6.
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      BACKGROUND AND PURPOSE: To investigate deformable image registration (DIR) and multi-fractional dose accumulation accuracy of a clinical MR-guided online adaptive radiotherapy (MRgoART) program, utilizing clinically-based magnitudes of abdominal deformation vector fields (DVFs).

      MATERIALS AND METHODS: A heterogeneous anthropomorphic multi-modality abdominal deformable phantom was comprised of MR and CT anatomically-relevant materials. Thermoluminescent dosimeters (TLDs) were affixed within regions of interest (ROIs). CT and MR simulation scans were acquired. CT was deformed to MR for dose calculations. MRgoART was executed on a MR-linac (MRIdian) for 5 Gy/5 fractions. Before each fraction, a deformation was applied. Ground truth was known for ROI volume, TLD position, and TLD dose measured by an accredited dosimetry calibration laboratory. To validate the range of applied deformations, phantom DVFs were compared to DVFs of clinical abdominal MRgoART fractions. MR-MR deformation accuracy was quantified through dice similarity coefficient (DSC), Hausdorff distance (HD), mean distance-to-agreement (MDA), and as mean-absolute-error (MAE) for CT-MR-MR deformation. Arithmetic-summation of calculated dose at respective TLD positions and deform-accumulated dose (MIM) was compared to TLD measured dose, respectively. MR-MR deformation statistics were quantified for MRIdian and MIM.

      RESULTS: Mean phantom DVFs were 5.0 ± 2.9 mm compared to mean DVF of clinical abdominal patients at 5.2 ± 3.0 mm. Respective mean DSC, HD, MDA was 0.93 ± 0.03, 0.74 ± 0.80 cm, 0.08 ± 0.03 cm for MRIdian and 0.93 ± 0.03, 0.54 ± 0.27 cm, 0.08 ± 0.03 cm for MIM (N = 80 ROIs). Mean MAE was 20.5 HU. Respective mean and median dose differences were 0.3%, -0.3% for arithmetic-summation and 4.1%, 0.6% for deformed-accumulation. Maximum differences were 0.21 Gy (arithmetic-summation), 0.31 Gy (deformed-accumulation).

      CONCLUSIONS: MRgoART deformation and dosimetric accuracy has been benchmarked for mean fractional DVFs of 5 mm in a multiple-rigid-body deformable phantom. Deformation accuracy was within TG132 criteria and clinically acceptable end-to-end MRgoART dosimetric agreement was observed for this phantom. Further efforts are needed in validation of deform-accumulated dose.

      PMID:32146260 | DOI:10.1016/j.radonc.2020.02.012


      View details for PubMedID 32146260
  • N-Phase Local Expansion Ratio for Characterizing Out-of-Phase Lung Ventilation IEEE transactions on medical imaging
    Shao W, Patton TJ, Gerard SE, Pan Y, Reinhardt JM, Durumeric OC, Bayouth JE, Christensen GE
    2020 Jun;39(6):2025-2034. doi: 10.1109/TMI.2019.2963083. Epub 2019 Dec 30.
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      Out-of-phase ventilation occurs when local regions of the lung reach their maximum or minimum volumes at breathing phases other than the global end inhalation or exhalation phases. This paper presents the N-phase local expansion ratio (LER N ) as a surrogate for lung ventilation. A common approach to estimate lung ventilation is to use image registration to align the end exhalation and inhalation 3DCT images and then analyze the resulting correspondence map. This 2-phase local expansion ratio (LER2) is limited because it ignores out-of-phase ventilation and thus may underestimate local lung ventilation. To overcome this limitation, LER N measures the maximum ratio of local expansion and contraction over the entire breathing cycle. Comparing LER2 to LER N provides a means for detecting and characterizing locations of the lung that experience out-of-phase ventilation. We present a novel in-phase/out-of-phase ventilation (IOV) function plot to visualize and measure the amount of high-function IOV that occurs during a breathing cycle. Treatment planning 4DCT scans collected during coached breathing from 32 human subjects with lung cancer were analyzed in this study. Results show that out-of-phase breathing occurred in all subjects and that the spatial distribution of out-of-phase ventilation varied from subject to subject. For the 32 subjects analyzed, 50% of the out-of-phase regions on average were mislabeled as low-function by LER2 (high-function threshold of 1.1, IOV threshold of 1.05). 4DCT and Xenon-enhanced CT of four sheep showed that LER8 is more accurate than LER2 for measuring lung ventilation.

      PMID:31899418 | PMC:PMC7316305 | DOI:10.1109/TMI.2019.2963083


      View details for PubMedID 31899418
  • STAT-ART: The Promise and Practice of a Rapid Palliative Single Session of MR-Guided Online Adaptive Radiotherapy (ART) Frontiers in oncology
    Mittauer KE, Hill PM, Geurts MW, Costa AD, Kimple RJ, Bassetti MF, Bayouth JE
    2019 Oct 22;9:1013. doi: 10.3389/fonc.2019.01013. eCollection 2019.
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      This work describes a novel application of MR-guided online adaptive radiotherapy (MRgoART) in the management of patients whom urgent palliative care is indicated using statum-adaptive radiotherapy (STAT-ART). The implementation of STAT-ART, as performed at our institution, is presented including a discussion of the advantages and limitations compared to the standard of care for palliative radiotherapy on conventional c-arm linacs. MR-based treatment planning techniques of STAT-ART for density overrides and deformable image registration (DIR) of diagnostic CT to the treatment MR are also addressed.

      PMID:31696053 | PMC:PMC6817496 | DOI:10.3389/fonc.2019.01013


      View details for PubMedID 31696053
  • Characterization of positional accuracy of a double-focused and double-stack multileaf collimator on an MR-guided radiotherapy (MRgRT) Linac using an IC-profiler array Medical physics
    Mittauer KE, Yadav P, Paliwal B, Bayouth JE
    2020 Feb;47(2):317-330. doi: 10.1002/mp.13902. Epub 2019 Dec 29.
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      PURPOSE: With advance magnetic resonance (MR)-guided online adaptive radiotherapy (MRgoART) relying on calculation-based intensity-modulated radiation therapy (IMRT) quality assurance (QA), accurate and sensitive QA of the multileaf collimator (MLC) becomes an increasingly essential component for routine machine QA. As such, it is important to assure compliance with the AAPM TG142 guidelines to supplement calculation-based QA methods for an online adaptive radiotherapy program. We have developed and implemented an efficient and highly sensitive QA procedure using an ionization chamber profiler (ICP) array to enable real-time characterization of the positional accuracy of a double-focused and double-stacked MLC on a clinical MR-guided radiotherapy (MRgRT) system and to supplement calculation-based QA for an MRgoART program.

      METHODS: An in-house MR-compatible jig was used to position the ICP (detector resolution 5 mm on X/Y axis) at an extended SDD of 108.4 cm to enable each MLC leaf (8.3 mm leaf width at isocenter) to be uniquely determined by two neighboring ion chambers. The MRgRT linac system utilizes a novel jawless, double-focused, and double-stacked MLC design such that the upper bank (MLC1) and lower bank (MLC2) are offset by half a leaf width. Positional accuracy was characterized by three methods: single bank half-beam block (HBB) at central axis, forward slash diagonal (FSD), and backslash diagonal (BSD) at off-axis. Measurements were performed for each bank in which each leaf occludes half of a detector. A corresponding reference field with the MLC retracted from occlusion was measured. The sensitivities of HBB, FSD, and BSD were evaluated by introducing 0.5-2.5 mm of known errors in 0.5 mm increments, in both positive and negative directions. The relationship between detector response and MLC error was established. Over a 6-month longitudinal assessment, we have evaluated MLC performance with weekly QA of HBB among cardinal angles, and monthly QA of FSD and BSD.

      RESULTS: A strong correlation was found between detector response of percentage dose difference and MLC positional error introduced (N = 350 introduced errors) for both HBB and FSD/BSD with coefficient of determination of 0.999 and 0.977, respectively. The relationship between detector response to MLC positional change was found to be 20.65%/mm for HBB and 11.14%/mm for FSD and BSD. At baseline, the mean MLC positional accuracy averaged across all leaves was 0.06 ± 0.27 mm (HBB), 0.04 ± 0.52 mm (FSD), -0.06 ± 0.51 mm (BSD). The mean MLC positional accuracy relative to baseline over the 6-month assessment was found to be highly reproducible at 0.00 ± 0.12 mm (HBB; N = 28 weeks), -0.02 ± 0.19 mm (FSD; N = 6 months), -0.03 ± 0.19 mm (BSD; N = 6 months).

      CONCLUSIONS: Positional accuracy of a novel jawless, double-focused, double-stacked MLC has been characterized and monitored over 6 months with an efficient, highly sensitive, and robust method using an ICP array. This routine QA method supplements calculation-based IMRT QA for an online adaptive radiotherapy program. Longitudinal assessment demonstrated no-drift in the MLC calibration. A highly reproducible jig setup allowed the validation of MLC positional accuracy to be within TG142 criteria of ±1 mm for 99% of measurements (i.e., 100% HBB, 95% BSD, 95% FSD) over the 6-month assessment.

      PMID:31682018 | DOI:10.1002/mp.13902


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  • Characterization and longitudinal assessment of daily quality assurance for an MR-guided radiotherapy (MRgRT) linac Journal of applied clinical medical physics
    Mittauer KE, Dunkerley AP, Yadav P, Bayouth JE
    2019 Nov;20(11):27-36. doi: 10.1002/acm2.12735. Epub 2019 Oct 21.
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      PURPOSE: To describe and characterize daily machine quality assurance (QA) for an MR-guided radiotherapy (MRgRT) linac system, in addition to reporting a longitudinal assessment of the dosimetric and mechanical stability over a 7-month period of clinical operation.

      METHODS: Quality assurance procedures were developed to evaluate MR imaging/radiation isocenter, imaging and patient handling system, and linear accelerator stability. A longitudinal assessment was characterized for safety interlocks, laser and imaging isocenter coincidence, imaging and radiation (RT) isocentricity, radiation dose rate and output, couch motion, and MLC positioning. A cylindrical water phantom and an MR-compatible A1SL detector were utilized. MR and RT isocentricity and MLC positional accuracy was quantified through dose measured with a 0.40 cm2 x 0.83 cm2 field at each cardinal angle. The relationship between detector response to MR/RT isocentricity and MLC positioning was established through introducing known errors in phantom position.

      RESULTS: Correlation was found between detector response and introduced positional error (N = 27) with coefficients of determination of 0.9996 (IEC-X), 0.9967 (IEC-Y), 0.9968 (IEC-Z) in each respective shift direction. The relationship between dose (DoseMR/RT+MLC ) and the vector magnitude of MLC and MR/RT positional error (Errormag ) was calculated to be a nonlinear response and resembled a quadratic function: DoseMR/RT+MLC [%] = -0.0253 Errormag [mm]2 - 0.0195 Errormag [mm]. For the temporal assessment (N = 7 months), safety interlocks were functional. Laser coincidence to MR was within ±2.0 mm (99.6%) and ±1.0 mm (86.8%) over the 7-month assessment. IGRT position-reposition shifts were within ±2.0 mm (99.4%) and ±1.0 mm (92.4%). Output was within ±3% (99.4%). Mean MLC and MR/RT isocenter accuracy was 1.6 mm, averaged across cardinal angles for the 7-month period.

      CONCLUSIONS: The linac and IGRT accuracy of an MR-guided radiotherapy system has been validated and monitored over seven months for daily QA. Longitudinal assessment demonstrated a drift in dose rate, but temporal assessment of output, MLC position, and isocentricity has been stable.

      PMID:31633882 | PMC:PMC6839363 | DOI:10.1002/acm2.12735


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  • Dosimetric study for spine stereotactic body radiation therapy: magnetic resonance guided linear accelerator versus volumetric modulated arc therapy Radiology and oncology
    Yadav P, Musunuru HB, Witt JS, Bassetti M, Bayouth J, Baschnagel AM
    2019 Sep 24;53(3):362-368. doi: 10.2478/raon-2019-0042.
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      Background Stereotactic body radiation therapy (SBRT) given in 1-5 fractions is an effective treatment for vertebral metastases. Real-time magnetic resonance-guided radiotherapy (MRgRT) improves soft tissue contrast, which translates into accurate delivery of spine SBRT. Here we report on clinical implementation of MRgRT for spine SBRT, the quality of MRgRT plans compared to TrueBeam based volumetric modulated arc therapy (VMAT) plans in the treatment of spine metastases and benefits of MRgRT MR scan. Patients and methods Ten metastatic lesions were included in this study for plan comparison. Lesions were spread across thoracic spine and lumbosacral spine. Three fraction spine SBRT plans: 27Gy to planning target volume (PTV) and 30Gy to gross tumor volume (GTV) were generated on the ViewRay MRIdian Linac system and compared to TrueBeamTM STx based VMAT plans. Plans were compared using metrics such as minimum dose, maximum dose, mean dose, ratio of the dose to 50% of the volume (R50), conformity index, homogeneity index and dose to the spinal cord. Results MRIdian plans achieved equivalent target coverage and spinal cord dose compared to VMAT plans. The maximum and minimum PTV doses and homogeneity index were equivalent for both planning systems. R50 was lower for MRIdian plans compared to VMAT plans, indicating a lower spread of intermediate doses with MRIdian system (5.16 vs. 6.11, p = 0.03). Conclusions MRgRT can deliver high-quality spine SBRT plans comparable to TrueBeam volumetric modulated arc therapy (VMAT) plans.

      PMID:31553704 | PMC:PMC6765155 | DOI:10.2478/raon-2019-0042


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  • Task Group 174 Report: Utilization of [<sup>18</sup> F]Fluorodeoxyglucose Positron Emission Tomography ([<sup>18</sup> F]FDG-PET) in Radiation Therapy Medical physics
    Das SK, McGurk R, Miften M, Mutic S, Bowsher J, Bayouth J, Erdi Y, Mawlawi O, Boellaard R, Bowen SR, Xing L, Bradley J, Schoder H, Yin F, Sullivan DC, Kinahan P
    2019 Oct;46(10):e706-e725. doi: 10.1002/mp.13676. Epub 2019 Sep 6.
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      The use of positron emission tomography (PET) in radiation therapy (RT) is rapidly increasing in the areas of staging, segmentation, treatment planning, and response assessment. The most common radiotracer is 18 F-fluorodeoxyglucose ([18 F]FDG), a glucose analog with demonstrated efficacy in cancer diagnosis and staging. However, diagnosis and RT planning are different endeavors with unique requirements, and very little literature is available for guiding physicists and clinicians in the utilization of [18 F]FDG-PET in RT. The two goals of this report are to educate and provide recommendations. The report provides background and education on current PET imaging systems, PET tracers, intensity quantification, and current utilization in RT (staging, segmentation, image registration, treatment planning, and therapy response assessment). Recommendations are provided on acceptance testing, annual and monthly quality assurance, scanning protocols to ensure consistency between interpatient scans and intrapatient longitudinal scans, reporting of patient and scan parameters in literature, requirements for incorporation of [18 F]FDG-PET in treatment planning systems, and image registration. The recommendations provided here are minimum requirements and are not meant to cover all aspects of the use of [18 F]FDG-PET for RT.

      PMID:31230358 | DOI:10.1002/mp.13676


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  • MRI-linac systems will replace conventional IGRT systems within 15 years Medical physics
    Bayouth JE, Low DA, Zaidi H
    2019 Sep;46(9):3753-3756. doi: 10.1002/mp.13657. Epub 2019 Jun 30.
  • The Dosimetric and Temporal Effects of Respiratory-Gated, High-Dose-Rate Radiation Therapy in Patients With Lung Cancer Technology in cancer research & treatment
    Rouabhi O, Gross B, Bayouth J, Xia J
    2019 Jan 1;18:1533033818816072. doi: 10.1177/1533033818816072.
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      PURPOSE: To evaluate the dosimetric and temporal effects of high-dose-rate respiratory-gated radiation therapy in patients with lung cancer.

      METHODS: Treatment plans from 5 patients with lung cancer (3 nongated and 2 gated at 80EX-80IN) were retrospectively evaluated. Prescription dose for these patients varied from 8 to 18 Gy/fraction with 3 to 5 treatment fractions. Using the same treatment planning criteria, 4 new treatment plans, corresponding to 4 gating windows (20EX-20IN, 40EX-40IN, 60EX-60IN, and 80EX-80IN), were generated for each patient. Mean tumor dose, mean lung dose, and lung V20 were used to assess the dosimetric effects. A MATLAB algorithm was developed to compute treatment time.

      RESULTS: Mean lung dose and lung V20 were on average reduced between -16.1% to -6.0% and -20.0% to -7.2%, respectively, for gated plans when compared to the corresponding nongated plans, and between -5.8% to -4.2% and -7.0% to -5.4%, respectively, for plans with smaller gating windows when compared to the corresponding plans gated at 80EX-80IN. Treatment delivery times of gated plans using high-dose rate were reduced on average between -19.7% (-0.10 min/100 MU) and -27.2% (-0.13 min/100 MU) for original nongated plans and -15.6% (-0.15 min/100 MU) and -20.3% (-0.19 min/100 MU) for original 80EX-80IN-gated plans.

      CONCLUSION: Respiratory-gated radiation therapy in patients with lung cancer can reduce lung dose while maintaining tumor dose. Because treatment delivery during gated therapy is discontinuous, total treatment time may be prolonged. However, this increase in treatment time can be offset by increasing the dose delivery rate. Estimation of treatment time may be helpful in selecting patients for respiratory gating and choosing appropriate gating windows.

      PMID:30803374 | PMC:PMC6313263 | DOI:10.1177/1533033818816072


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  • A Multi-Institutional Experience of MR-Guided Liver Stereotactic Body Radiation Therapy Advances in radiation oncology
    Rosenberg SA, Henke LE, Shaverdian N, Mittauer K, Wojcieszynski AP, Hullett CR, Kamrava M, Lamb J, Cao M, Green OL, Kashani R, Paliwal B, Bayouth J, Harari PM, Olsen JR, Lee P, Parikh PJ, Bassetti M
    2018 Aug 23;4(1):142-149. doi: 10.1016/j.adro.2018.08.005. eCollection 2019 Jan-Mar.
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      PURPOSE: Daily magnetic resonance (MR)-guided radiation has the potential to improve stereotactic body radiation therapy (SBRT) for tumors of the liver. Magnetic resonance imaging (MRI) introduces unique variables that are untested clinically: electron return effect, MRI geometric distortion, MRI to radiation therapy isocenter uncertainty, multileaf collimator position error, and uncertainties with voxel size and tracking. All could lead to increased toxicity and/or local recurrences with SBRT. In this multi-institutional study, we hypothesized that direct visualization provided by MR guidance could allow the use of small treatment volumes to spare normal tissues while maintaining clinical outcomes despite the aforementioned uncertainties in MR-guided treatment.

      METHODS AND MATERIALS: Patients with primary liver tumors or metastatic lesions treated with MR-guided liver SBRT were reviewed at 3 institutions. Toxicity was assessed using National Cancer Institute Common Terminology Criteria for Adverse Events Version 4. Freedom from local progression (FFLP) and overall survival were analyzed with the Kaplan-Meier method and χ2 test.

      RESULTS: The study population consisted of 26 patients: 6 hepatocellular carcinomas, 2 cholangiocarcinomas, and 18 metastatic liver lesions (44% colorectal metastasis). The median follow-up was 21.2 months. The median dose delivered was 50 Gy at 10 Gy/fraction. No grade 4 or greater gastrointestinal toxicities were observed after treatment. The 1-year and 2-year overall survival in this cohort is 69% and 60%, respectively. At the median follow-up, FFLP for this cohort was 80.4%. FFLP for patients with hepatocellular carcinomas, colorectal metastasis, and all other lesions were 100%, 75%, and 83%, respectively.

      CONCLUSIONS: This study describes the first clinical outcomes of MR-guided liver SBRT. Treatment was well tolerated by patients with excellent local control. This study lays the foundation for future dose escalation and adaptive treatment for liver-based primary malignancies and/or metastatic disease.

      PMID:30706022 | PMC:PMC6349638 | DOI:10.1016/j.adro.2018.08.005


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  • The VAMPIRE challenge: A multi-institutional validation study of CT ventilation imaging Medical physics
    Kipritidis J, Tahir BA, Cazoulat G, Hofman MS, Siva S, Callahan J, Hardcastle N, Yamamoto T, Christensen GE, Reinhardt JM, Kadoya N, Patton TJ, Gerard SE, Duarte I, Archibald-Heeren B, Byrne M, Sims R, Ramsay S, Booth JT, Eslick E, Hegi-Johnson F, Woodruff HC, Ireland RH, Wild JM, Cai J, Bayouth JE, Brock K, Keall PJ
    2019 Mar;46(3):1198-1217. doi: 10.1002/mp.13346. Epub 2019 Feb 1.
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      PURPOSE: CT ventilation imaging (CTVI) is being used to achieve functional avoidance lung cancer radiation therapy in three clinical trials (NCT02528942, NCT02308709, NCT02843568). To address the need for common CTVI validation tools, we have built the Ventilation And Medical Pulmonary Image Registration Evaluation (VAMPIRE) Dataset, and present the results of the first VAMPIRE Challenge to compare relative ventilation distributions between different CTVI algorithms and other established ventilation imaging modalities.

      METHODS: The VAMPIRE Dataset includes 50 pairs of 4DCT scans and corresponding clinical or experimental ventilation scans, referred to as reference ventilation images (RefVIs). The dataset includes 25 humans imaged with Galligas 4DPET/CT, 21 humans imaged with DTPA-SPECT, and 4 sheep imaged with Xenon-CT. For the VAMPIRE Challenge, 16 subjects were allocated to a training group (with RefVI provided) and 34 subjects were allocated to a validation group (with RefVI blinded). Seven research groups downloaded the Challenge dataset and uploaded CTVIs based on deformable image registration (DIR) between the 4DCT inhale/exhale phases. Participants used DIR methods broadly classified into B-splines, Free-form, Diffeomorphisms, or Biomechanical modeling, with CT ventilation metrics based on the DIR evaluation of volume change, Hounsfield Unit change, or various hybrid approaches. All CTVIs were evaluated against the corresponding RefVI using the voxel-wise Spearman coefficient r S , and Dice similarity coefficients evaluated for low function lung ( DSC low ) and high function lung ( DSC high ).

      RESULTS: A total of 37 unique combinations of DIR method and CT ventilation metric were either submitted by participants directly or derived from participant-submitted DIR motion fields using the in-house software, VESPIR. The r S and DSC results reveal a high degree of inter-algorithm and intersubject variability among the validation subjects, with algorithm rankings changing by up to ten positions depending on the choice of evaluation metric. The algorithm with the highest overall cross-modality correlations used a biomechanical model-based DIR with a hybrid ventilation metric, achieving a median (range) of 0.49 (0.27-0.73) for r S , 0.52 (0.36-0.67) for DSC low , and 0.45 (0.28-0.62) for DSC high . All other algorithms exhibited at least one negative r S value, and/or one DSC value less than 0.5.

      CONCLUSIONS: The VAMPIRE Challenge results demonstrate that the cross-modality correlation between CTVIs and the RefVIs varies not only with the choice of CTVI algorithm but also with the choice of RefVI modality, imaging subject, and the evaluation metric used to compare relative ventilation distributions. This variability may arise from the fact that each of the different CTVI algorithms and RefVI modalities provides a distinct physiologic measurement. Ultimately this variability, coupled with the lack of a "gold standard," highlights the ongoing importance of further validation studies before CTVI can be widely translated from academic centers to the clinic. It is hoped that the information gleaned from the VAMPIRE Challenge can help inform future validation efforts.

      PMID:30575051 | PMC:PMC6605778 | DOI:10.1002/mp.13346


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  • FissureNet: A Deep Learning Approach For Pulmonary Fissure Detection in CT Images IEEE transactions on medical imaging
    Gerard SE, Patton TJ, Christensen GE, Bayouth JE, Reinhardt JM
    2019 Jan;38(1):156-166. doi: 10.1109/TMI.2018.2858202. Epub 2018 Aug 10.
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      Pulmonary fissure detection in computed tomography (CT) is a critical component for automatic lobar segmentation. The majority of fissure detection methods use feature descriptors that are hand-crafted, low-level, and have local spatial extent. The design of such feature detectors is typically targeted toward normal fissure anatomy, yielding low sensitivity to weak, and abnormal fissures that are common in clinical data sets. Furthermore, local features commonly suffer from low specificity, as the complex textures in the lung can be indistinguishable from the fissure when the global context is not considered. We propose a supervised discriminative learning framework for simultaneous feature extraction and classification. The proposed framework, called FissureNet, is a coarse-to-fine cascade of two convolutional neural networks. The coarse-to-fine strategy alleviates the challenges associated with training a network to segment a thin structure that represents a small fraction of the image voxels. FissureNet was evaluated on a cohort of 3706 subjects with inspiration and expiration 3DCT scans from the COPDGene clinical trial and a cohort of 20 subjects with 4DCT scans from a lung cancer clinical trial. On both data sets, FissureNet showed superior performance compared with a deep learning approach using the U-Net architecture and a Hessian-based fissure detection method in terms of area under the precision-recall curve (PR-AUC). The overall PR-AUC for FissureNet, U-Net, and Hessian on the COPDGene (lung cancer) data set was 0.980 (0.966), 0.963 (0.937), and 0.158 (0.182), respectively. On a subset of 30 COPDGene scans, FissureNet was compared with a recently proposed advanced fissure detection method called derivative of sticks (DoS) and showed superior performance with a PR-AUC of 0.991 compared with 0.668 for DoS.

      PMID:30106711 | PMC:PMC6318012 | DOI:10.1109/TMI.2018.2858202


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  • Quantifying ventilation change due to radiation therapy using 4DCT Jacobian calculations Medical physics
    Patton TJ, Gerard SE, Shao W, Christensen GE, Reinhardt JM, Bayouth JE
    2018 Oct;45(10):4483-4492. doi: 10.1002/mp.13105. Epub 2018 Aug 31.
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      PURPOSE: Regional ventilation and its response to radiation dose can be estimated using four-dimensional computed tomography (4DCT) and image registration. This study investigated the impact of radiation therapy (RT) on ventilation and the dependence of radiation-induced ventilation change on pre-RT ventilation derived from 4DCT.

      METHODS AND MATERIALS: Three 4DCT scans were acquired from each of 12 subjects: two scans before RT and one scan 3 months after RT. The 4DCT datasets were used to generate the pre-RT and post-RT ventilation maps by registering the inhale phase image to the exhale phase image and computing the Jacobian determinant of the resulting transformation. The ventilation change between pre-RT and post-RT was calculated by taking a ratio of the post-RT Jacobian map to the pre-RT Jacobian map. The voxel-wise ventilation change between pre- and post-RT was investigated as a function of dose and pre-RT ventilation.

      RESULTS: Lung regions receiving over 20 Gy exhibited a significant decrease in function (3.3%, P < 0.01) compared to those receiving less than 20 Gy. When the voxels were stratified into high and low pre-RT function by thresholding the Jacobian map at 10% volume expansion (Jacobian = 1.1), high-function voxels exhibited 4.8% reduction in function for voxels receiving over 20 Gy, a significantly greater decline (P = 0.037) than the 2.4% reduction in function for low-function voxels. Ventilation decreased linearly with dose in both high-function and low-function regions. High-function regions showed a significantly larger decline in ventilation (P ≪ 0.001) as dose increased (1.4% ventilation reduction/10 Gy) compared to low-function regions (0.3% ventilation reduction/10 Gy). With further stratification of pre-RT ventilation, voxels exhibited increasing dose-dependent ventilation reduction with increasing pre-RT ventilation, with the largest pre-RT Jacobian bin (pre-RT Jacobian between 1.5 and 1.6) exhibiting a ventilation reduction of 4.8% per 10 Gy.

      CONCLUSIONS: Significant ventilation reductions were measured after radiation therapy treatments, and were dependent on the dose delivered to the tissue and the pre-RT ventilation of the tissue. For a fixed radiation dose, lung tissue with high pre-RT ventilation experienced larger decreases in post-RT ventilation than lung tissue with low pre-RT ventilation.

      PMID:30047588 | PMC:PMC6220845 | DOI:10.1002/mp.13105


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  • Responses to the 2017 "1 Million Gray Question": ASTRO Membership's Opinions on the Most Important Research Question Facing Radiation Oncology International journal of radiation oncology, biology, physics
    Dominello MM, Keen JC, Beck TF, Bayouth J, Knisely J, Carlson DJ, Mendonca MS, Mian O, Brock KK, Anscher M, Hugo G, Moros EG, Singh AK, Yu JB
    2018 Oct 1;102(2):249-250. doi: 10.1016/j.ijrobp.2018.06.045. Epub 2018 Jul 10.
  • A New Era of Image Guidance with Magnetic Resonance-guided Radiation Therapy for Abdominal and Thoracic Malignancies Cureus
    Mittauer K, Paliwal B, Hill P, Bayouth JE, Geurts MW, Baschnagel AM, Bradley KA, Harari PM, Rosenberg S, Brower JV, Wojcieszynski AP, Hullett C, Bayliss RA, Labby ZE, Bassetti MF
    2018 Apr 4;10(4):e2422. doi: 10.7759/cureus.2422.
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      Magnetic resonance-guided radiation therapy (MRgRT) offers advantages for image guidance for radiotherapy treatments as compared to conventional computed tomography (CT)-based modalities. The superior soft tissue contrast of magnetic resonance (MR) enables an improved visualization of the gross tumor and adjacent normal tissues in the treatment of abdominal and thoracic malignancies. Online adaptive capabilities, coupled with advanced motion management of real-time tracking of the tumor, directly allow for high-precision inter-/intrafraction localization. The primary aim of this case series is to describe MR-based interventions for localizing targets not well-visualized with conventional image-guided technologies. The abdominal and thoracic sites of the lung, kidney, liver, and gastric targets are described to illustrate the technological advancement of MR-guidance in radiotherapy.

      PMID:29872602 | PMC:PMC5985918 | DOI:10.7759/cureus.2422


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  • An analysis of the ArcCHECK-MR diode array's performance for ViewRay quality assurance Journal of applied clinical medical physics
    Ellefson ST, Culberson WS, Bednarz BP, DeWerd LA, Bayouth JE
    2017 Jul;18(4):161-171. doi: 10.1002/acm2.12107. Epub 2017 Jun 6.
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      The ArcCHECK-MR diode array utilizes a correction system with a virtual inclinometer to correct the angular response dependencies of the diodes. However, this correction system cannot be applied to measurements on the ViewRay MR-IGRT system due to the virtual inclinometer's incompatibility with the ViewRay's multiple simultaneous beams. Additionally, the ArcCHECK's current correction factors were determined without magnetic field effects taken into account. In the course of performing ViewRay IMRT quality assurance with the ArcCHECK, measurements were observed to be consistently higher than the ViewRay TPS predictions. The goals of this study were to quantify the observed discrepancies and test whether applying the current factors improves the ArcCHECK's accuracy for measurements on the ViewRay. Gamma and frequency analysis were performed on 19 ViewRay patient plans. Ion chamber measurements were performed at a subset of diode locations using a PMMA phantom with the same dimensions as the ArcCHECK. A new method for applying directionally dependent factors utilizing beam information from the ViewRay TPS was developed in order to analyze the current ArcCHECK correction factors. To test the current factors, nine ViewRay plans were altered to be delivered with only a single simultaneous beam and were measured with the ArcCHECK. The current correction factors were applied using both the new and current methods. The new method was also used to apply corrections to the original 19 ViewRay plans. It was found the ArcCHECK systematically reports doses higher than those actually delivered by the ViewRay. Application of the current correction factors by either method did not consistently improve measurement accuracy. As dose deposition and diode response have both been shown to change under the influence of a magnetic field, it can be concluded the current ArcCHECK correction factors are invalid and/or inadequate to correct measurements on the ViewRay system.

      PMID:28681448 | PMC:PMC5874930 | DOI:10.1002/acm2.12107


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  • The effect of Optune™ Tumor Treating Fields transducer arrays on skin radiation dose during radiotherapy Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia
    Bender E, Kozak K, Howard S, Hayes L, Bayouth J, Robins HI
    2017 Aug;42:172-175. doi: 10.1016/j.jocn.2017.04.002. Epub 2017 Apr 17.
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      A Phase 3 clinical study demonstrated that the addition of 200kHz Tumor Treating Fields (TTF) to temozolomide in the post-radiation (RT) phase of therapy in newly diagnosed glioblastoma increases progression free and overall survival (resulting in FDA and European Union approval). Preclinical studies have demonstrated the ability of TTF to act as a radiosensitizer, suggesting concurrent TTF and RT may have clinical utility. The removal and replacement of TTF transducer arrays from the scalps of patients on a daily basis, i.e., just before and after RT treatments, would be extremely cumbersome. Based on these considerations, phantom studies of the effect of Optune (TM) transducer arrays on radiation dose distribution were performed to evaluate the feasibility of leaving arrays in place during RT. Film measurements were performed using Gafchromic EBT3 film and an Epson 11000XL scanner. Film calibration was done based on the ratio of the red to blue color channel data. A Siemens Oncor linear accelerator operating at 6MV, 10cm×10cm field size, and 100cm source-to-film distance was used for all measurements. For each exposure, two films were stacked, providing planes of measurement that were ∼0.1 and 0.4mm in depth. Data accrued demonstrated that radiation attenuation should not be a clinically significant issue. However, TTF transducer arrays were found to cause both a radiation bolus effect, as well as an increased exit dose effect. These studies predict increased skin toxicity, which merits significant caution for further clinical development of this combination.

      PMID:28427800 | DOI:10.1016/j.jocn.2017.04.002


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  • Dosimetric Comparison of Real-Time MRI-Guided Tri-Cobalt-60 Versus Linear Accelerator-Based Stereotactic Body Radiation Therapy Lung Cancer Plans Technology in cancer research & treatment
    Wojcieszynski AP, Hill PM, Rosenberg SA, Hullett CR, Labby ZE, Paliwal B, Geurts MW, Bayliss RA, Bayouth JE, Harari PM, Bassetti MF, Baschnagel AM
    2017 Jun;16(3):366-372. doi: 10.1177/1533034617691407. Epub 2017 Feb 7.
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      PURPOSE: Magnetic resonance imaging-guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging-guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging-guided radiation therapy plans and internal target volume-based plans utilizing volumetric-modulated arc therapy.

      MATERIALS AND METHODS: Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging-guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared.

      RESULTS: Planning tumor volumes trended larger for volumetric-modulated arc therapy-based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging-guided plans ( P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% ( P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL ( P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 ( P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 ( P = .98).

      CONCLUSION: Magnetic resonance imaging-guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy-based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

      PMID:28168936 | PMC:PMC5616053 | DOI:10.1177/1533034617691407


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  • Using [(18)F]Fluorothymidine Imaged With Positron Emission Tomography to Quantify and Reduce Hematologic Toxicity Due to Chemoradiation Therapy for Pelvic Cancer Patients International journal of radiation oncology, biology, physics
    McGuire SM, Bhatia SK, Sun W, Jacobson GM, Menda Y, Ponto LL, Smith BJ, Gross BA, Bayouth JE, Sunderland JJ, Graham MM, Buatti JM
    2016 Sep 1;96(1):228-39. doi: 10.1016/j.ijrobp.2016.04.009. Epub 2016 Apr 19.
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      PURPOSE: The purpose of the present prospective clinical trial was to determine the efficacy of [(18)F]fluorothymidine (FLT)-identified active bone marrow sparing for pelvic cancer patients by correlating the FLT uptake change during and after chemoradiation therapy with hematologic toxicity.

      METHODS AND MATERIALS: Simulation FLT positron emission tomography (PET) images were used to spare pelvic bone marrow using intensity modulated radiation therapy (IMRT BMS) for 32 patients with pelvic cancer. FLT PET scans taken during chemoradiation therapy after 1 and 2 weeks and 30 days and 1 year after completion of chemoradiation therapy were used to evaluate the acute and chronic dose response of pelvic bone marrow. Complete blood counts were recorded at each imaging point to correlate the FLT uptake change with systemic hematologic toxicity.

      RESULTS: IMRT BMS plans significantly reduced the dose to the pelvic regions identified with FLT uptake compared with control IMRT plans (P<.001, paired t test). Radiation doses of 4 Gy caused an ∼50% decrease in FLT uptake in the pelvic bone marrow after either 1 or 2 weeks of chemoradiation therapy. Additionally, subjects with more FLT-identified bone marrow exposed to ≥4 Gy after 1 week developed grade 2 leukopenia sooner than subjects with less marrow exposed to ≥4 Gy (P<.05, Cox regression analysis). Apparent bone marrow recovery at 30 days after therapy was not maintained 1 year after chemotherapy. The FLT uptake in the pelvic bone marrow regions that received >35 Gy was 18.8% ± 1.8% greater at 30 days after therapy than at 1 year after therapy. The white blood cell, platelet, lymphocyte, and neutrophil counts at 1 year after therapy were all lower than the pretherapy levels (P<.05, paired t test).

      CONCLUSIONS: IMRT BMS plans reduced the dose to FLT-identified pelvic bone marrow for pelvic cancer patients. However, reducing hematologic toxicity is challenging owing to the acute radiation sensitivity (∼4 Gy) and chronic suppression of activity in bone marrow receiving radiation doses >35 Gy, as measured by the FLT uptake change correlated with the complete blood cell counts.

      PMID:27319286 | PMC:PMC4982822 | DOI:10.1016/j.ijrobp.2016.04.009


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  • Impact of temporal probability in 4D dose calculation for lung tumors Journal of applied clinical medical physics
    Rouabhi O, Ma M, Bayouth J, Xia J
    2015 Nov 8;16(6):110-118. doi: 10.1120/jacmp.v16i6.5517.
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      The purpose of this study was to evaluate the dosimetric uncertainty in 4D dose calculation using three temporal probability distributions: uniform distribution, sinusoidal distribution, and patient-specific distribution derived from the patient respiratory trace. Temporal probability, defined as the fraction of time a patient spends in each respiratory amplitude, was evaluated in nine lung cancer patients. Four-dimensional computed tomography (4D CT), along with deformable image registration, was used to compute 4D dose incorporating the patient's respiratory motion. First, the dose of each of 10 phase CTs was computed using the same planning parameters as those used in 3D treatment planning based on the breath-hold CT. Next, deformable image registration was used to deform the dose of each phase CT to the breath-hold CT using the deformation map between the phase CT and the breath-hold CT. Finally, the 4D dose was computed by summing the deformed phase doses using their corresponding temporal probabilities. In this study, 4D dose calculated from the patient-specific temporal probability distribution was used as the ground truth. The dosimetric evaluation matrix included: 1) 3D gamma analysis, 2) mean tumor dose (MTD), 3) mean lung dose (MLD), and 4) lung V20. For seven out of nine patients, both uniform and sinusoidal temporal probability dose distributions were found to have an average gamma passing rate > 95% for both the lung and PTV regions. Compared with 4D dose calculated using the patient respiratory trace, doses using uniform and sinusoidal distribution showed a percentage difference on average of -0.1% ± 0.6% and -0.2% ± 0.4% in MTD, -0.2% ± 1.9% and -0.2% ± 1.3% in MLD, 0.09% ± 2.8% and -0.07% ± 1.8% in lung V20, -0.1% ± 2.0% and 0.08% ± 1.34% in lung V10, 0.47% ± 1.8% and 0.19% ± 1.3% in lung V5, respectively. We concluded that four-dimensional dose computed using either a uniform or sinusoidal temporal probability distribution can approximate four-dimensional dose computed using the patient-specific respiratory trace.

      PMID:26699562 | PMC:PMC5691019 | DOI:10.1120/jacmp.v16i6.5517


      View details for PubMedID 26699562
  • Characterization of a 0.35T MR system for phantom image quality stability and in vivo assessment of motion quantification Journal of applied clinical medical physics
    Saenz DL, Yan Y, Christensen N, Henzler MA, Forrest LJ, Bayouth JE, Paliwal BR
    2015 Nov 8;16(6):30-40. doi: 10.1120/jacmp.v16i6.5353.
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      ViewRay is a novel MR-guided radiotherapy system capable of imaging in near real-time at four frames per second during treatment using 0.35T field strength. It allows for improved gating techniques and adaptive radiotherapy. Three cobalt-60 sources (~ 15,000 Curies) permit multiple-beam, intensity-modulated radiation therapy. The primary aim of this study is to assess the imaging stability, accuracy, and automatic segmentation algorithm capability to track motion in simulated and in vivo targets. Magnetic resonance imaging (MRI) characteristics of the system were assessed using the American College of Radiology (ACR)-recommended phantom and accreditation protocol. Images of the ACR phantom were acquired using a head coil following the ACR scanning instructions. ACR recommended T1- and T2-weighted sequences were evaluated. Nine measurements were performed over a period of seven months, on just over a monthly basis, to establish consistency. A silicon dielectric gel target was attached to the motor via a rod. 40 mm total amplitude was used with cycles of 3 to 9 s in length in a sinusoidal trajectory. Trajectories of six moving clinical targets in four canine patients were quantified and tracked. ACR phantom images were analyzed, and the results were compared with the ACR acceptance levels. Measured slice thickness accuracies were within the acceptance limits. In the 0.35 T system, the image intensity uniformity was also within the ACR acceptance limit. Over the range of cycle lengths, representing a wide range of breathing rates in patients imaged at four frames/s, excellent agreement was observed between the expected and measured target trajectories. In vivo canine targets, including the gross target volume (GTV), as well as other abdominal soft tissue structures, were visualized with inherent MR contrast, allowing for preliminary results of target tracking.

      PMID:26699552 | PMC:PMC5691014 | DOI:10.1120/jacmp.v16i6.5353


      View details for PubMedID 26699552
  • Gadoxetate for direct tumor therapy and tracking with real-time MRI-guided stereotactic body radiation therapy of the liver Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
    Wojcieszynski AP, Rosenberg SA, Brower JV, Hullett CR, Geurts MW, Labby ZE, Hill PM, Bayliss RA, Paliwal B, Bayouth JE, Harari PM, Bassetti MF
    2016 Feb;118(2):416-8. doi: 10.1016/j.radonc.2015.10.024. Epub 2015 Nov 25.
    • More

      SBRT is increasingly utilized in liver tumor treatment. MRI-guided RT allows for real-time MRI tracking during therapy. Liver tumors are often poorly visualized and most contrast agents are transient. Gadoxetate may allow for sustained tumor visualization. Here, we report on the first use of gadoxetate during real-time MRI-guided SBRT.

      PMID:26627702 | DOI:10.1016/j.radonc.2015.10.024


      View details for PubMedID 26627702
  • Flattening filter-free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group Journal of applied clinical medical physics
    Xiao Y, Kry SF, Popple R, Yorke E, Papanikolaou N, Stathakis S, Xia P, Huq S, Bayouth J, Galvin J, Yin F
    2015 May 8;16(3):5219. doi: 10.1120/jacmp.v16i3.5219.
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      This report describes the current state of flattening filter-free (FFF) radiotherapy beams implemented on conventional linear accelerators, and is aimed primarily at practicing medical physicists. The Therapy Emerging Technology Assessment Work Group of the American Association of Physicists in Medicine (AAPM) formed a writing group to assess FFF technology. The published literature on FFF technology was reviewed, along with technical specifications provided by vendors. Based on this information, supplemented by the clinical experience of the group members, consensus guidelines and recommendations for implementation of FFF technology were developed. Areas in need of further investigation were identified. Removing the flattening filter increases beam intensity, especially near the central axis. Increased intensity reduces treatment time, especially for high-dose stereotactic radiotherapy/radiosurgery (SRT/SRS). Furthermore, removing the flattening filter reduces out-of-field dose and improves beam modeling accuracy. FFF beams are advantageous for small field (e.g., SRS) treatments and are appropriate for intensity-modulated radiotherapy (IMRT). For conventional 3D radiotherapy of large targets, FFF beams may be disadvantageous compared to flattened beams because of the heterogeneity of FFF beam across the target (unless modulation is employed). For any application, the nonflat beam characteristics and substantially higher dose rates require consideration during the commissioning and quality assurance processes relative to flattened beams, and the appropriate clinical use of the technology needs to be identified. Consideration also needs to be given to these unique characteristics when undertaking facility planning. Several areas still warrant further research and development. Recommendations pertinent to FFF technology, including acceptance testing, commissioning, quality assurance, radiation safety, and facility planning, are presented. Examples of clinical applications are provided. Several of the areas in which future research and development are needed are also indicated.

      PMID:26103482 | PMC:PMC5690108 | DOI:10.1120/jacmp.v16i3.5219


      View details for PubMedID 26103482
  • Interobserver and intermodality variability in GTV delineation on simulation CT, FDG-PET, and MR Images of Head and Neck Cancer Jacobs journal of radiation oncology
    Anderson CM, Sun W, Buatti JM, Maley JE, Policeni B, Mott SL, Bayouth JE
    2014 Sep;1(1):006.
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      PURPOSE: To compare the interobserver and intermodality differences in image-based identification of head and neck primary site gross tumor volumes (GTV). Modalities compared include: contrast-enhanced CT, F-18 fluorodeoxyglucose positron emission tomography (PET/CT) and contrast-enhanced MRI.

      METHODS AND MATERIALS: Fourteen patients were simulated after immobilization for all 3 imaging modalities (CT, PET/CT, MRI). Three radiation oncologists (RO) contoured GTVs as seen on each modality. The GTV was contoured first on the contrast-enhanced CT (considered the standard), then on PET/CT, and finally on post-contrast T1 MRI. Interobserver and intermodality variability were analyzed by volume, intersection, union, and volume overlap ratio (VOR).

      RESULTS: Analysis of RO contours revealed the average volume for CT-, PET/CT-, and MRI-derived GTVs were 45cc, 35cc and 49cc, respectively. In 93% of cases PET/CT-derived GTVs had the smallest volume and in 57% of cases MRI-derived GTVs had the largest volume. CT showed the largest variation in target definition (standard deviation amongst observers 35%) compared to PET/CT (28%) and MRI (27%). The VOR was largest (indicating greatest interobserver agreement) in PET/CT (46%), followed by MRI (36%), followed by CT (34%). For each observer, the least agreement in GTV definition occurred between MRI & PET/CT (average VOR = 41%), compared to CT & PET/CT (48%) and CT & MRI (47%).

      CONCLUSIONS: A nonsignificant interobserver difference in GTVs for each modality was seen. Among three modalities, CT was least consistent, while PET/CT-derived GTVs had the smallest volumes and were most consistent. MRI combined with PET/CT provided the least agreement in GTVs generated. The significance of these differences for head & neck cancer is important to explore as we move to volume-based treatment planning based on multi-modality imaging as a standard method for treatment delivery.

      PMID:25568889 | PMC:PMC4283948


      View details for PubMedID 25568889
  • Impact of spot size on plan quality of spot scanning proton radiosurgery for peripheral brain lesions Medical physics
    Wang D, Dirksen B, Hyer DE, Buatti JM, Sheybani A, Dinges E, Felderman N, TenNapel M, Bayouth JE, Flynn RT
    2014 Dec;41(12):121705. doi: 10.1118/1.4901260.
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      PURPOSE: To determine the plan quality of proton spot scanning (SS) radiosurgery as a function of spot size (in-air sigma) in comparison to x-ray radiosurgery for treating peripheral brain lesions.

      METHODS: Single-field optimized (SFO) proton SS plans with sigma ranging from 1 to 8 mm, cone-based x-ray radiosurgery (Cone), and x-ray volumetric modulated arc therapy (VMAT) plans were generated for 11 patients. Plans were evaluated using secondary cancer risk and brain necrosis normal tissue complication probability (NTCP).

      RESULTS: For all patients, secondary cancer is a negligible risk compared to brain necrosis NTCP. Secondary cancer risk was lower in proton SS plans than in photon plans regardless of spot size (p = 0.001). Brain necrosis NTCP increased monotonically from an average of 2.34/100 (range 0.42/100-4.49/100) to 6.05/100 (range 1.38/100-11.6/100) as sigma increased from 1 to 8 mm, compared to the average of 6.01/100 (range 0.82/100-11.5/100) for Cone and 5.22/100 (range 1.37/100-8.00/100) for VMAT. An in-air sigma less than 4.3 mm was required for proton SS plans to reduce NTCP over photon techniques for the cohort of patients studied with statistical significance (p = 0.0186). Proton SS plans with in-air sigma larger than 7.1 mm had significantly greater brain necrosis NTCP than photon techniques (p = 0.0322).

      CONCLUSIONS: For treating peripheral brain lesions--where proton therapy would be expected to have the greatest depth-dose advantage over photon therapy--the lateral penumbra strongly impacts the SS plan quality relative to photon techniques: proton beamlet sigma at patient surface must be small (<7.1 mm for three-beam single-field optimized SS plans) in order to achieve comparable or smaller brain necrosis NTCP relative to photon radiosurgery techniques. Achieving such small in-air sigma values at low energy (<70 MeV) is a major technological challenge in commercially available proton therapy systems.

      PMID:25471952 | DOI:10.1118/1.4901260


      View details for PubMedID 25471952
  • Patient-specific biomechanical model for the prediction of lung motion from 4-D CT images IEEE transactions on medical imaging
    Fuerst B, Mansi T, Carnis F, Salzle M, Zhang J, Declerck J, Boettger T, Bayouth J, Navab N, Kamen A
    2015 Feb;34(2):599-607. doi: 10.1109/TMI.2014.2363611. Epub 2014 Oct 16.
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      This paper presents an approach to predict the deformation of the lungs and surrounding organs during respiration. The framework incorporates a computational model of the respiratory system, which comprises an anatomical model extracted from computed tomography (CT) images at end-expiration (EE), and a biomechanical model of the respiratory physiology, including the material behavior and interactions between organs. A personalization step is performed to automatically estimate patient-specific thoracic pressure, which drives the biomechanical model. The zone-wise pressure values are obtained by using a trust-region optimizer, where the estimated motion is compared to CT images at end-inspiration (EI). A detailed convergence analysis in terms of mesh resolution, time stepping and number of pressure zones on the surface of the thoracic cavity is carried out. The method is then tested on five public datasets. Results show that the model is able to predict the respiratory motion with an average landmark error of 3.40 ±1.0 mm over the entire respiratory cycle. The estimated 3-D lung motion may constitute as an advanced 3-D surrogate for more accurate medical image reconstruction and patient respiratory analysis.

      PMID:25343757 | DOI:10.1109/TMI.2014.2363611


      View details for PubMedID 25343757
  • Spatial mapping of functional pelvic bone marrow using FLT PET Journal of applied clinical medical physics
    McGuire SM, Menda Y, Ponto LB, Gross B, TenNapel M, Smith BJ, Bayouth JE
    2014 Jul 8;15(4):129–136. doi: 10.1120/jacmp.v15i4.4780.
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      The purpose of this study was to determine the ability of regions identified with bony landmarks on CT imaging to accurately represent active bone marrow when compared to FLT PET imaging. These surrogate regions could then be used to create a bone marrow sparing radiation therapy plan when FLT PET imaging is not available. Whole body (WB) FLT PET images were obtained of 18 subjects prior to chemoradiation therapy. The FLT image of each subject was registered to a CT image acquired for that subject to obtain anatomic information of the pelvis. Seventeen regions were identified based on features of the pelvic bones, sacrum, and femoral heads. The probability of FLT uptake being located in each of 17 different CT-based regions of the bony pelvis was calculated using Tukey's multiple comparison test. Statistical analysis of FLT uptake in the pelvis indicated four distinct groups within the 17 regions that had similar levels of activity. Regions located in the central part of the pelvis, including the superior part of the sacrum, the inner halves of the iliac crests, and the L5 vertebral body, had greater FLT uptake than those in the peripheral regions (p-value < 0.05). We have developed a method to use CT-defined pelvic bone regions to represent FLT PET-identified functional bone marrow. Individual regions that have a statistically significant probability of containing functional bone marrow can be used as avoidance regions to reduce radiation dose to functional bone marrow in radiation therapy planning. However, because likely active bone marrow regions and pelvic targets typically overlap, patient-specific spatial detail may be advantageous in IMRT planning scenarios and may best be provided using FLT PET imaging.

      PMID:25207403 | PMC:PMC4161980 | DOI:10.1120/jacmp.v15i4.4780


      View details for PubMedID 25207403
  • An Almost Linear Time Algorithm for Field Splitting in Radiation Therapy Computational geometry : theory and applications
    Wu X, Dou X, Bayouth JE, Buatti JM
    2013 Aug 1;46(6):673-687. doi: 10.1016/j.comgeo.2012.11.001.
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      In this paper, we study an interesting geometric partition problem, called optimal field splitting, which arises in Intensity-Modulated Radiation Therapy (IMRT). In current clinical practice, a multi-leaf collimator (MLC) with a maximum leaf spread constraint is used to deliver the prescribed intensity maps (IMs). However, the maximum leaf spread of an MLC may require to split a large intensity map into several overlapping sub-IMs with each being delivered separately. We develop a close-to-linear time algorithm for solving the field splitting problem while minimizing the total complexity of the resulting sub-IMs, thus improving the treatment delivery efficiency. Meanwhile, our algorithm strives to minimize the maximum beam-on time of those sub-IMs. Our basic idea is to formulate the field splitting problem as computing a shortest path in a directed acyclic graph, which expresses a special "layered" structure. The edge weights of the graph satisfy the Monge property, which enables us to solve this shortest path problem by examining only a small portion of the graph, yielding a close-to-linear time algorithm. To minimize the maximum beam-on time of the resulting sub-IMs, we consider an interesting min-max slope path problem in a monotone polygon which is solvable in linear time. The min-max slope path problem may be of interest in its own right. Experimental results based on real medical data and computer generated IMs showed that our new algorithm runs fast and produces high quality field splitting results.

      PMID:24999294 | PMC:PMC4078263 | DOI:10.1016/j.comgeo.2012.11.001


      View details for PubMedID 24999294
  • 3-Dimensional magnetic resonance spectroscopic imaging at 3 Tesla for early response assessment of glioblastoma patients during external beam radiation therapy International journal of radiation oncology, biology, physics
    Muruganandham M, Clerkin PP, Smith BJ, Anderson CM, Morris A, Capizzano AA, Magnotta V, McGuire SM, Smith MC, Bayouth JE, Buatti JM
    2014 Sep 1;90(1):181-9. doi: 10.1016/j.ijrobp.2014.05.014. Epub 2014 Jun 28.
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      PURPOSE: To evaluate the utility of 3-dimensional magnetic resonance (3D-MR) proton spectroscopic imaging for treatment planning and its implications for early response assessment in glioblastoma multiforme.

      METHODS AND MATERIALS: Eighteen patients with newly diagnosed, histologically confirmed glioblastoma had 3D-MR proton spectroscopic imaging (MRSI) along with T2 and T1 gadolinium-enhanced MR images at simulation and at boost treatment planning after 17 to 20 fractions of radiation therapy. All patients received standard radiation therapy (RT) with concurrent temozolomide followed by adjuvant temozolomide. Imaging for response assessment consisted of MR scans every 2 months. Progression-free survival was defined by the criteria of MacDonald et al. MRSI images obtained at initial simulation were analyzed for choline/N-acetylaspartate ratios (Cho/NAA) on a voxel-by-voxel basis with abnormal activity defined as Cho/NAA ≥2. These images were compared on anatomically matched MRSI data collected after 3 weeks of RT. Changes in Cho/NAA between pretherapy and third-week RT scans were tested using Wilcoxon matched-pairs signed rank tests and correlated with progression-free survival, radiation dose and location of recurrence using Cox proportional hazards regression.

      RESULTS: After a median follow-up time of 8.6 months, 50% of patients had experienced progression based on imaging. Patients with a decreased or stable mean or median Cho/NAA values had less risk of progression (P<.01). Patients with an increase in mean or median Cho/NAA values at the third-week RT scan had a significantly greater chance of early progression (P<.01). An increased Cho/NAA at the third-week MRSI scan carried a hazard ratio of 2.72 (95% confidence interval, 1.10-6.71; P=.03). Most patients received the prescription dose of RT to the Cho/NAA ≥2 volume, where recurrence most often occurred.

      CONCLUSION: Change in mean and median Cho/NAA detected at 3 weeks was a significant predictor of early progression. The potential impact for risk-adaptive therapy based on early spectroscopic findings is suggested.

      PMID:24986746 | PMC:PMC4183193 | DOI:10.1016/j.ijrobp.2014.05.014


      View details for PubMedID 24986746
  • A dose homogeneity and conformity evaluation between ViewRay and pinnacle-based linear accelerator IMRT treatment plans Journal of medical physics
    Saenz DL, Paliwal BR, Bayouth JE
    2014 Apr;39(2):64-70. doi: 10.4103/0971-6203.131277.
    • More

      ViewRay, a novel technology providing soft-tissue imaging during radiotherapy is investigated for treatment planning capabilities assessing treatment plan dose homogeneity and conformity compared with linear accelerator plans. ViewRay offers both adaptive radiotherapy and image guidance. The combination of cobalt-60 (Co-60) with 0.35 Tesla magnetic resonance imaging (MRI) allows for magnetic resonance (MR)-guided intensity-modulated radiation therapy (IMRT) delivery with multiple beams. This study investigated head and neck, lung, and prostate treatment plans to understand what is possible on ViewRay to narrow focus toward sites with optimal dosimetry. The goal is not to provide a rigorous assessment of planning capabilities, but rather a first order demonstration of ViewRay planning abilities. Images, structure sets, points, and dose from treatment plans created in Pinnacle for patients in our clinic were imported into ViewRay. The same objectives were used to assess plan quality and all critical structures were treated as similarly as possible. Homogeneity index (HI), conformity index (CI), and volume receiving <20% of prescription dose (DRx) were calculated to assess the plans. The 95% confidence intervals were recorded for all measurements and presented with the associated bars in graphs. The homogeneity index (D5/D95) had a 1-5% inhomogeneity increase for head and neck, 3-8% for lung, and 4-16% for prostate. CI revealed a modest conformity increase for lung. The volume receiving 20% of the prescription dose increased 2-8% for head and neck and up to 4% for lung and prostate. Overall, for head and neck Co-60 ViewRay treatments planned with its Monte Carlo treatment planning software were comparable with 6 MV plans computed with convolution superposition algorithm on Pinnacle treatment planning system.

      PMID:24872603 | PMC:PMC4035618 | DOI:10.4103/0971-6203.131277


      View details for PubMedID 24872603
  • Feasibility of using nonflat photon beams for whole-breast irradiation with breath hold Journal of applied clinical medical physics
    Wang Y, Vassil A, Tendulkar R, Bayouth J, Xia P
    2014 Jan 6;15(1):4397. doi: 10.1120/jacmp.v15i1.4397.
    • More

      Removing a flattening filter or replacing it with a thinner filter alters the characteristics of a photon beam, creating a forward peaked intensity profile to make the photon beam nonflat. This study is to investigate the feasibility of applying nonflat photon beams to the whole-breast irradiation with breath holds for a potential of delivery time reduction during the gated treatment. Photon beams of 6 MV with flat and nonflat intensity profiles were commissioned. Fifteen patients with early-stage breast cancer, who received whole-breast radiation without breathing control, were retrospectively selected for this study. For each patient, three plans were created using a commercial treatment planning system: (a) the clinically approved plan using forward planning method (FP); (b) a hybrid intensity-modulated radiation therapy (IMRT) plan where the flat beam open fields were combined with the nonflat beam IMRT fields using direct aperture optimization method (mixed DAO); (c) a hybrid IMRT plan where both open and IMRT fields were from nonflat beams using direct aperture optimization (nonflat DAO). All plans were prescribed for ≥ 95% of the breast volume receiving the prescription dose of 50 Gy (2.0 Gy per fraction). In comparison, all plans achieved a similar dosimetric coverage to the targeted volume. The average homogeneity index of the FP, mixed DAO, and nonflat DAO plans were 0.882 ± 0.024, 0.879 ± 0.023, and 0.867 ± 0.027, respectively. The average percentage volume of V105 was 57.66% ± 5.21%, 34.67% ± 4.91%, 41.64% ± 5.32% for the FP, mixed, and nonflat DAO plans, respectively. There was no significant difference (p &gt; 0.05) observed for the defined endpoint doses in organs at risk (OARs). In conclusion, both mixed DAO and nonflat DAO plans can achieve similar plan quality as the clinically approved FP plan, measured by plan homogeneity and endpoint doses to the ORAs. Nonflat beam plans may reduce treatment time in breath-hold treatment, especially for hypofractionated treatment.

      PMID:24423835 | PMC:PMC5711254 | DOI:10.1120/jacmp.v15i1.4397


      View details for PubMedID 24423835
  • A computer aided treatment event recognition system in radiation therapy Medical physics
    Xia J, Mart C, Bayouth J
    2014 Jan;41(1):011713. doi: 10.1118/1.4852895.
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      PURPOSE: To develop an automated system to safeguard radiation therapy treatments by analyzing electronic treatment records and reporting treatment events.

      METHODS: CATERS (Computer Aided Treatment Event Recognition System) was developed to detect treatment events by retrieving and analyzing electronic treatment records. CATERS is designed to make the treatment monitoring process more efficient by automating the search of the electronic record for possible deviations from physician's intention, such as logical inconsistencies as well as aberrant treatment parameters (e.g., beam energy, dose, table position, prescription change, treatment overrides, etc). Over a 5 month period (July 2012-November 2012), physicists were assisted by the CATERS software in conducting normal weekly chart checks with the aims of (a) determining the relative frequency of particular events in the authors' clinic and (b) incorporating these checks into the CATERS. During this study period, 491 patients were treated at the University of Iowa Hospitals and Clinics for a total of 7692 fractions.

      RESULTS: All treatment records from the 5 month analysis period were evaluated using all the checks incorporated into CATERS after the training period. About 553 events were detected as being exceptions, although none of them had significant dosimetric impact on patient treatments. These events included every known event type that was discovered during the trial period. A frequency analysis of the events showed that the top three types of detected events were couch position override (3.2%), extra cone beam imaging (1.85%), and significant couch position deviation (1.31%). The significant couch deviation is defined as the number of treatments where couch vertical exceeded two times standard deviation of all couch verticals, or couch lateral/longitudinal exceeded three times standard deviation of all couch laterals and longitudinals. On average, the application takes about 1 s per patient when executed on either a desktop computer or a mobile device.

      CONCLUSIONS: CATERS offers an effective tool to detect and report treatment events. Automation and rapid processing enables electronic record interrogation daily, alerting the medical physicist of deviations potentially days prior to performing weekly check. The output of CATERS could also be utilized as an important input to failure mode and effects analysis.

      PMID:24387505 | DOI:10.1118/1.4852895


      View details for PubMedID 24387505
  • Respiratory effort correction strategies to improve the reproducibility of lung expansion measurements Medical physics
    Du K, Reinhardt JM, Christensen GE, Ding K, Bayouth JE
    2013 Dec;40(12):123504. doi: 10.1118/1.4829519.
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      PURPOSE: Four-dimensional computed tomography (4DCT) can be used to make measurements of pulmonary function longitudinally. The sensitivity of such measurements to identify change depends on measurement uncertainty. Previously, intrasubject reproducibility of Jacobian-based measures of lung tissue expansion was studied in two repeat prior-RT 4DCT human acquisitions. Difference in respiratory effort such as breathing amplitude and frequency may affect longitudinal function assessment. In this study, the authors present normalization schemes that correct ventilation images for variations in respiratory effort and assess the reproducibility improvement after effort correction.

      METHODS: Repeat 4DCT image data acquired within a short time interval from 24 patients prior to radiation therapy (RT) were used for this analysis. Using a tissue volume preserving deformable image registration algorithm, Jacobian ventilation maps in two scanning sessions were computed and compared on the same coordinate for reproducibility analysis. In addition to computing the ventilation maps from end expiration to end inspiration, the authors investigated the effort normalization strategies using other intermediated inspiration phases upon the principles of equivalent tidal volume (ETV) and equivalent lung volume (ELV). Scatter plots and mean square error of the repeat ventilation maps and the Jacobian ratio map were generated for four conditions: no effort correction, global normalization, ETV, and ELV. In addition, gamma pass rate was calculated from a modified gamma index evaluation between two ventilation maps, using acceptance criterions of 2 mm distance-to-agreement and 5% ventilation difference.

      RESULTS: The pattern of regional pulmonary ventilation changes as lung volume changes. All effort correction strategies improved reproducibility when changes in respiratory effort were greater than 150 cc (p < 0.005 with regard to the gamma pass rate). Improvement of reproducibility was correlated with respiratory effort difference (R = 0.744 for ELV in the cohort with tidal volume difference greater than 100 cc). In general for all subjects, global normalization, ETV and ELV significantly improved reproducibility compared to no effort correction (p = 0.009, 0.002, 0.005 respectively). When tidal volume difference was small (less than 100 cc), none of the three effort correction strategies improved reproducibility significantly (p = 0.52, 0.46, 0.46 respectively). For the cohort (N = 13) with tidal volume difference greater than 100 cc, the average gamma pass rate improves from 57.3% before correction to 66.3% after global normalization, and 76.3% after ELV. ELV was found to be significantly better than global normalization (p = 0.04 for all subjects, and p = 0.003 for the cohort with tidal volume difference greater than 100 cc).

      CONCLUSIONS: All effort correction strategies improve the reproducibility of the authors' pulmonary ventilation measures, and the improvement of reproducibility is highly correlated with the changes in respiratory effort. ELV gives better results as effort difference increase, followed by ETV, then global. However, based on the spatial and temporal heterogeneity in the lung expansion rate, a single scaling factor (e.g., global normalization) appears to be less accurate to correct the ventilation map when changes in respiratory effort are large.

      PMID:24320544 | PMC:PMC3843762 | DOI:10.1118/1.4829519


      View details for PubMedID 24320544
  • Continuous localization technologies for radiotherapy delivery: Report of the American Society for Radiation Oncology Emerging Technology Committee Practical radiation oncology
    D'Ambrosio DJ, Bayouth J, Chetty IJ, Buyyounouski MK, Price RA, Correa CR, Dilling TJ, Franklin GE, Xia P, Harris ER, Konski A
    2012 Apr-Jun;2(2):145-50. doi: 10.1016/j.prro.2011.10.005. Epub 2011 Nov 18.
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      PMID:24175000 | PMC:PMC3808750 | DOI:10.1016/j.prro.2011.10.005


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  • Equivalent-quality unflattened photon beam modeling, planning, and delivery Journal of applied clinical medical physics
    Huang Y, Flynn RT, Siochi AC, Bayouth JE
    2013 Jul 8;14(4):4211. doi: 10.1120/jacmp.v14i4.4211.
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      The clinical application of the flattening filter-free photon beam (FFF) has enjoyed greater use due to its advantage of reduced treatment time because of the increased dose rate. Its unique beam characteristics, along with the very high-dose rate, require a thorough knowledge of the capability and accuracy in FFF beam modeling, planning, and delivery. This work verifies the feasibility of modeling an equivalent quality unflattened photon beam (eqUF), and the dosimetric accuracy in eqUF beam planning and delivery. An eqUF beam with a beam quality equivalent to a conventional 6 MV photon beam with the filter in place (WF) was modeled for the Pinnacle3 TPS and the beam model quality was evaluated by gamma index test. Results showed that the eqUF beam modeling was similar to that of the WF beam, as the overall passing rate of the 2%/2 mm gamma index test was 99.5% in the eqUF beam model and 96% in the WF beam model. Hypofractionated IMRT plans were then generated with the same constraints using both WF and eqUF beams, and the similarity was evaluated by DVH comparison and generalized 3D gamma index test. The WF and eqUF plans showed no clinically significant differences in DVH comparison and, on average &gt; 98% voxels passed the 3%/3 mm 3D gamma index test. Dosimetric accuracy in gated phantom delivery was verified by ion chamber and film measurements. All ion chamber measurements at the isocenter were within 1% of calculated values and film measurements passed the 3 mm/3% gamma index test with an overall passing rate &gt; 95% in the high-dose and low-gradient region in both WF and eqUF cases. Treatment plan quality assurance (QA), using either measurement-based or independent calculation-based methods of ten clinically treated eqUF IMRT plans were analyzed. In both methods, the point dose differences were all within 2% difference. In the relative 2D dose distribution comparison, &gt;95% points were within 3% dose difference or 3 mm DTA.

      PMID:23835385 | PMC:PMC5714540 | DOI:10.1120/jacmp.v14i4.4211


      View details for PubMedID 23835385
  • Reproducibility of intensity-based estimates of lung ventilation Medical physics
    Du K, Bayouth JE, Ding K, Christensen GE, Cao K, Reinhardt JM
    2013 Jun;40(6):063504. doi: 10.1118/1.4805106.
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      PURPOSE: Lung function depends on lung expansion and contraction during the respiratory cycle. Respiratory-gated CT imaging and image registration can be used to estimate the regional lung volume change by observing CT voxel density changes during inspiration or expiration. In this study, the authors examine the reproducibility of intensity-based estimates of lung tissue expansion and contraction in three mechanically ventilated sheep and ten spontaneously breathing humans. The intensity-based estimates are compared to the estimates of lung function derived from image registration deformation field.

      METHODS: 4DCT data set was acquired for a cohort of spontaneously breathing humans and anesthetized and mechanically ventilated sheep. For each subject, two 4DCT scans were performed with a short time interval between acquisitions. From each 4DCT data set, an image pair consisting of a volume reconstructed near end inspiration and a volume reconstructed near end exhalation was selected. The end inspiration and end exhalation images were registered using a tissue volume preserving deformable registration algorithm. The CT density change in the registered image pair was used to compute intensity-based specific air volume change (SAC) and the intensity-based Jacobian (IJAC), while the transformation-based Jacobian (TJAC) was computed directly from the image registration deformation field. IJAC is introduced to make the intensity-based and transformation-based methods comparable since SAC and Jacobian may not be associated with the same physiological phenomenon and have different units. Scan-to-scan variations in respiratory effort were corrected using a global scaling factor for normalization. A gamma index metric was introduced to quantify voxel-by-voxel reproducibility considering both differences in ventilation and distance between matching voxels. The authors also tested how different CT prefiltering levels affected intensity-based ventilation reproducibility.

      RESULTS: Higher reproducibility was found for anesthetized mechanically ventilated animals than for the humans for both the intensity-based (IJAC) and transformation-based (TJAC) ventilation estimates. The human IJAC maps had scan-to-scan correlation coefficients of 0.45 ± 0.14, a gamma pass rate 70 ± 8 without normalization and 75 ± 5 with normalization. The human TJAC maps had correlation coefficients 0.81 ± 0.10, a gamma pass rate 86 ± 11 without normalization and 93 ± 4 with normalization. The gamma pass rate and correlation coefficient of the IJAC maps gradually increased with increased smoothing, but were still much lower than those of the TJAC maps.

      CONCLUSIONS: The transformation-based ventilation maps show better reproducibility than the intensity-based maps, especially in human subjects. Reproducibility was also found to depend on variations in respiratory effort; all techniques were better when applied to images from mechanically ventilated sheep compared to spontaneously breathing human subjects. Nevertheless, intensity-based techniques applied to mechanically ventilated sheep were less reproducible than the transformation-based applied to spontaneously breathing humans, suggesting the method used to determine ventilation maps is important. Prefiltering of the CT images may help to improve the reproducibility of the intensity-based ventilation estimates, but even with filtering the reproducibility of the intensity-based ventilation estimates is not as good as that of transformation-based ventilation estimates.

      PMID:23718615 | PMC:PMC3676396 | DOI:10.1118/1.4805106


      View details for PubMedID 23718615
  • Optimal co-segmentation of tumor in PET-CT images with context information IEEE transactions on medical imaging
    Song Q, Bai J, Han D, Bhatia S, Sun W, Rockey W, Bayouth JE, Buatti JM, Wu X
    2013 Sep;32(9):1685-97. doi: 10.1109/TMI.2013.2263388. Epub 2013 May 16.
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      Positron emission tomography (PET)-computed tomography (CT) images have been widely used in clinical practice for radiotherapy treatment planning of the radiotherapy. Many existing segmentation approaches only work for a single imaging modality, which suffer from the low spatial resolution in PET or low contrast in CT. In this work, we propose a novel method for the co-segmentation of the tumor in both PET and CT images, which makes use of advantages from each modality: the functionality information from PET and the anatomical structure information from CT. The approach formulates the segmentation problem as a minimization problem of a Markov random field model, which encodes the information from both modalities. The optimization is solved using a graph-cut based method. Two sub-graphs are constructed for the segmentation of the PET and the CT images, respectively. To achieve consistent results in two modalities, an adaptive context cost is enforced by adding context arcs between the two sub-graphs. An optimal solution can be obtained by solving a single maximum flow problem, which leads to simultaneous segmentation of the tumor volumes in both modalities. The proposed algorithm was validated in robust delineation of lung tumors on 23 PET-CT datasets and two head-and-neck cancer subjects. Both qualitative and quantitative results show significant improvement compared to the graph cut methods solely using PET or CT.

      PMID:23693127 | PMC:PMC3965345 | DOI:10.1109/TMI.2013.2263388


      View details for PubMedID 23693127
  • Image guided radiation therapy (IGRT) technologies for radiation therapy localization and delivery International journal of radiation oncology, biology, physics
    Santos DL, Popple R, Agazaryan N, Bayouth JE, Bissonnette J, Bucci MK, Dieterich S, Dong L, Forster KM, Indelicato D, Langen K, Lehmann J, Mayr N, Parsai I, Salter W, Tomblyn M, Yuh TC, Chetty IJ
    2013 Sep 1;87(1):33-45. doi: 10.1016/j.ijrobp.2013.02.021. Epub 2013 May 7.
  • Optimal field-splitting algorithm in intensity-modulated radiotherapy: evaluations using head-and-neck and female pelvic IMRT cases Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Dou X, Kim Y, Bayouth JE, Buatti JM, Wu X
    2013 Spring;38(1):12-7. doi: 10.1016/j.meddos.2012.05.001. Epub 2012 Jul 25.
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      To develop an optimal field-splitting algorithm of minimal complexity and verify the algorithm using head-and-neck (H&N) and female pelvic intensity-modulated radiotherapy (IMRT) cases. An optimal field-splitting algorithm was developed in which a large intensity map (IM) was split into multiple sub-IMs (≥2). The algorithm reduced the total complexity by minimizing the monitor units (MU) delivered and segment number of each sub-IM. The algorithm was verified through comparison studies with the algorithm as used in a commercial treatment planning system. Seven IMRT, H&N, and female pelvic cancer cases (54 IMs) were analyzed by MU, segment numbers, and dose distributions. The optimal field-splitting algorithm was found to reduce both total MU and the total number of segments. We found on average a 7.9 ± 11.8% and 9.6 ± 18.2% reduction in MU and segment numbers for H&N IMRT cases with an 11.9 ± 17.4% and 11.1 ± 13.7% reduction for female pelvic cases. The overall percent (absolute) reduction in the numbers of MU and segments were found to be on average -9.7 ± 14.6% (-15 ± 25 MU) and -10.3 ± 16.3% (-3 ± 5), respectively. In addition, all dose distributions from the optimal field-splitting method showed improved dose distributions. The optimal field-splitting algorithm shows considerable improvements in both total MU and total segment number. The algorithm is expected to be beneficial for the radiotherapy treatment of large-field IMRT.

      PMID:22835649 | PMC:PMC3997753 | DOI:10.1016/j.meddos.2012.05.001


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  • Dosimetric properties of a beam quality-matched 6 MV unflattened photon beam Journal of applied clinical medical physics
    Huang Y, Siochi RA, Bayouth JE
    2012 Jul 5;13(4):3701. doi: 10.1120/jacmp.v13i4.3701.
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      The purpose of this study was to report the characteristics of an equivalent quality unflattened (eqUF) photon beam in clinical implementation and to provide a generalized method to describe unflattened (UF) photon beam profiles. An unflattened photon beam with a beam quality equivalent to the corresponding flat 6 MV photon beam (WF) was obtained by removing the flattening filter from a Siemens ONCOR Avant-Garde linear accelerator and adjusting the photon energy. A method independent from the WF beam profile was presented to describe UF beam profiles and other selected beam characteristics were examined. The short-term beam stability was examined by dynamic beam profiles, recorded every 0.072 s in static and gated delivery, and the long-term stability was evidenced by the five-year clinical quality assurance records. The dose rate was raised fivefold using the eqUF beam. The depth of maximum dose (d(max)) shifted 3 mm deeper, but the percent depth dose beyond d(max) was very similar to that of the WF beam. The surface dose and out-of-field dose were lower, but the penumbra was slightly wider. The variation in head scatter and phantom scatter with changes in field size was smaller; the variation in the profile shape with change in depth was also smaller. The eqUF beam is stable 0.072 s after the beam is turned on, and the five-year beam stability was comparable to that of the WF beam. A fivefold dose rate increase was observed in the eqUF beam with similar beam characteristics to other reported UF beam data except for a deeper dmax and a slightly wider penumbra. The initial and long-term stability of the eqUF beam profile is on parity with the WF beam. The UF beam profile can be described in the generalized method independently without relying on the WF beam profile.

      PMID:22766941 | PMC:PMC5716519 | DOI:10.1120/jacmp.v13i4.3701


      View details for PubMedID 22766941
  • Reproducibility of registration-based measures of lung tissue expansion Medical physics
    Du K, Bayouth JE, Cao K, Christensen GE, Ding K, Reinhardt JM
    2012 Mar;39(3):1595-608. doi: 10.1118/1.3685589.
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      PURPOSE: Lung function depends on lung expansion and contraction during the respiratory cycle. Respiratory-gated CT imaging and 3D image registration can be used to locally estimate lung tissue expansion and contraction (regional lung volume change) by computing the determinant of the Jacobian matrix of the image registration deformation field. In this study, the authors examine the reproducibility of Jacobian-based measures of lung tissue expansion in two repeat 4DCT acquisitions of mechanically ventilated sheep and free-breathing humans.

      METHODS: 4DCT image data from three white sheep and nine human subjects were used for this analysis. In each case, two 4DCT studies were acquired for each subject within a short time interval. The animal subjects were anesthetized and mechanically ventilated, while the humans were awake and spontaneously breathing based on respiratory pacing audio cues. From each 4DCT data set, an image pair consisting of a volume reconstructed near end inspiration and a volume reconstructed near end exhalation was selected. The end inspiration and end exhalation images were registered using a tissue volume preserving deformable registration algorithm and the Jacobian of the registration deformation field was used to measure regional lung expansion. The Jacobian map from the baseline data set was compared to the Jacobian map from the followup data by measuring the voxel-by-voxel Jacobian ratio.

      RESULTS: In the animal subjects, the mean Jacobian ratio (baseline scan Jacobian divided by followup scan Jacobian, voxel-by-voxel) was 0.9984±0.021 (mean ± standard deviation, averaged over the entire lung region). The mean Jacobian ratio was 1.0224±0.058 in the human subjects. The reproducibility of the Jacobian values was found to be strongly dependent on the reproducibility of the subject's respiratory effort and breathing pattern.

      CONCLUSIONS: Lung expansion, a surrogate for lung function, can be assessed using two or more respiratory-gated CT image acquisitions. The results show that good reproducibility can be obtained in anesthetized, mechanically ventilated animals, but variations in respiratory effort and breathing patterns reduce reproducibility in spontaneously-breathing humans. The global linear normalization can globally compensate for breathing effort differences, but a homogeneous scaling does not account for differences in regional lung expansion rates. Additional work is needed to develop compensation procedures or normalization schemes that can account for local variations in lung expansion during respiration.

      PMID:22380392 | PMC:PMC3306443 | DOI:10.1118/1.3685589


      View details for PubMedID 22380392

Contact Information

John Bayouth, PhD


600 Highland Avenue, K4/B78
Madison, WI 53792-0600