Bhudatt Paliwal headshot

Bhudatt Paliwal, PhD

Professor Emeritus

Department of Human Oncology

I am a professor emeritus in the Departments of Human Oncology and Medical Physics. I am engaged in clinical physics activities, focusing primarily on emerging applications of magnetic resonance imaging (MRI) in radiation therapy. My work is focused on understanding the impact of MRI-integrated radiation therapy systems on the delivery of radiation therapy. Real-time MR imaging provides high-quality images with superior soft-tissue contrast. This ability has contributed to innovative approaches to managing respiratory and cardiac motion as well as the impact of gastrointestinal processes. New MR acquisition techniques reduce imaging times and provide 3D MR images with a large field of view (FOV) for short breath hold. Image-based breath-hold management for gating promises to be relatively superior to operator guidance.

Real-time MR-guided, on-table adaptive therapy allows the incorporation of anatomical changes within short time periods to optimize treatment plans. The dose from each fraction can be escalated or de-escalated based upon the proximity of nearby critical structures while the patient is on the treatment table. This approach permits replanning to reduce dose to organs at risk while giving a greater dose to the target.


PhD, The University of Texas at Houston, Biophysics (1973)

IAEA Fellow, M.D. Anderson Hospital, (1973)

Fellow, Hahnemann Medical College and Hospital, (1970)

Trainee, Bhabha Atomic Research Centre, Radiological Physics (1965)

MS, Sri Aurobindo International Centre of Education, (1962)

Academic Appointments

Professor Emeritus, Human Oncology (2016–pres.)

Professor, Human Oncology (1983)

Associate Professor, Human Oncology (1979)

Assistant Professor, Human Oncology (1973)

Selected Honors and Awards

Fellow American Society of Radiation Oncology (2013)

The Bhudatt Paliwal Professorship, Department of Human Oncology, University of Wisconsin–Madison (2013)

Ramaiah Naidu Memorial Oration Award of the Association of Medical Physicists of India (2006)

Distinguished Alumni Award, Graduate School of Biomedical Sciences Houston (2005)

William D. Coolidge Award American Association of Physicists in Medicine (2002)

Marvin M.D. Williams Professional Achievement Award, American College of Medical Physics (2002)

Fellow of the American College of Medical Physics (1999)

Fellow of the American Association of Physicists in Medicine (1995)

Fellow of the International Atomic Energy Agency, Vienna (1970–1972)

World Health Organization Fellowship awarded through the Indian Atomic Energy Agency (1964–1965)

Research Focus

MRI-Guided Radiation Therapy, Time Dose Fractionation, Assessment and Prediction of Response in Radiation Therapy

Dr. Bhudatt Paliwal is engaged in clinical physics activities, focusing primarily on emerging applications of magnetic resonance imaging (MRI) in radiation therapy. His work focuses on understanding the impact of MRI-integrated radiation therapy systems on the delivery of radiation therapy.

  • MOSFET dosimeter characterization in MR-guided radiation therapy (MRgRT) Linac Journal of applied clinical medical physics
    Yadav P, Hallil A, Tewatia D, Dunkerley AP, Paliwal B
    2020 Jan;21(1):127-135. doi: 10.1002/acm2.12799. Epub 2019 Dec 18.
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      PURPOSE: With the increasing use of MR-guided radiation therapy (MRgRT), it becomes important to understand and explore accuracy of medical dosimeters in the presence of magnetic field. The purpose of this work is to characterize metal-oxide-semiconductor field-effect transistors (MOSFETs) in MRgRT systems at 0.345 T magnetic field strength.

      METHODS: A MOSFET dosimetry system, developed by Best Medical Canada for in-vivo patient dosimetry, was used to study various commissioning tests performed on a MRgRT system, MRIdian® Linac. We characterized the MOSFET dosimeter with different cable lengths by determining its calibration factor, monitor unit linearity, angular dependence, field size dependence, percentage depth dose (PDD) variation, output factor change, and intensity modulated radiation therapy quality assurance (IMRT QA) verification for several plans. MOSFET results were analyzed and compared with commissioning data and Monte Carlo calculations.

      RESULTS: MOSFET measurements were not found to be affected by the presence of 0.345 T magnetic field. Calibration factors were similar for different cable length dosimeters either placed at the parallel or perpendicular direction to the magnetic field, with variations of less than 2%. The detector showed good linearity (R2 = 0.999) for 100-600 MUs range. Output factor measurements were consistent with ionization chamber data within 2.2%. MOSFET PDD measurements were found to be within 1% for 1-15 cm depth range in comparison to ionization chamber. MOSFET normalized angular response matched thermoluminescent detector (TLD) response within 5.5%. The IMRT QA verification data for the MRgRT linac showed that the percentage difference between ionization chamber and MOSFET was 0.91%, 2.05%, and 2.63%, respectively for liver, spine, and mediastinum.

      CONCLUSION: MOSFET dosimeters are not affected by the 0.345 T magnetic field in MRgRT system. They showed physics parameters and performance comparable to TLD and ionization chamber; thus, they constitute an alternative to TLD for real-time in-vivo dosimetry in MRgRT procedures.

      PMID:31854078 | PMC:PMC6964768 | DOI:10.1002/acm2.12799

      View details for PubMedID 31854078
  • 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

      View details for PubMedID 31682018
  • 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

      View details for PubMedID 30706022
  • 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

      View details for PubMedID 29872602
  • 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

      View details for PubMedID 28168936
  • Dosimetric differences in flattened and flattening filter-free beam treatment plans Journal of medical physics
    Yan Y, Yadav P, Bassetti M, Du K, Saenz D, Harari P, Paliwal BR
    2016 Apr-Jun;41(2):92-9. doi: 10.4103/0971-6203.181636.
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      This study investigated the dosimetric differences in treatment plans from flattened and flattening filter-free (FFF) beams from the TrueBeam System. A total of 104 treatment plans with static (sliding window) intensity-modulated radiotherapy beams and volumetric-modulated arc therapy (VMAT) beams were generated for 15 patients involving three cancer sites. In general, the FFF beam provides similar target coverage as the flattened beam with improved dose sparing to organ-at-risk (OAR). Among all three cancer sites, the head and neck showed more important differences between the flattened beam and FFF beam. The maximum reduction of the FFF beam in the mean dose reached up to 2.82 Gy for larynx in head and neck case. Compared to the 6 MV flattened beam, the 10 MV FFF beam provided improved dose sparing to certain OARs, especially for VMAT cases. Thus, 10 MV FFF beam could be used to improve the treatment plan.

      PMID:27217620 | PMC:PMC4871009 | DOI:10.4103/0971-6203.181636

      View details for PubMedID 27217620
  • Expanding horizons in medical physics: Standardization to visualization and quantitative assessment based personalized treatments Journal of medical physics
    Paliwal BR
    2015 Oct-Dec;40(4):181-2. doi: 10.4103/0971-6203.170795.
  • 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.
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      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
  • Rapid Automated Target Segmentation and Tracking on 4D Data without Initial Contours Radiology research and practice
    Chebrolu VV, Saenz D, Tewatia D, Sethares WA, Cannon G, Paliwal BR
    2014;2014:547075. doi: 10.1155/2014/547075. Epub 2014 Aug 3.
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      Purpose. To achieve rapid automated delineation of gross target volume (GTV) and to quantify changes in volume/position of the target for radiotherapy planning using four-dimensional (4D) CT. Methods and Materials. Novel morphological processing and successive localization (MPSL) algorithms were designed and implemented for achieving autosegmentation. Contours automatically generated using MPSL method were compared with contours generated using state-of-the-art deformable registration methods (using Elastix© and MIMVista software). Metrics such as the Dice similarity coefficient, sensitivity, and positive predictive value (PPV) were analyzed. The target motion tracked using the centroid of the GTV estimated using MPSL method was compared with motion tracked using deformable registration methods. Results. MPSL algorithm segmented the GTV in 4DCT images in 27.0 ± 11.1 seconds per phase (512 × 512 resolution) as compared to 142.3 ± 11.3 seconds per phase for deformable registration based methods in 9 cases. Dice coefficients between MPSL generated GTV contours and manual contours (considered as ground-truth) were 0.865 ± 0.037. In comparison, the Dice coefficients between ground-truth and contours generated using deformable registration based methods were 0.909 ± 0.051. Conclusions. The MPSL method achieved similar segmentation accuracy as compared to state-of-the-art deformable registration based segmentation methods, but with significant reduction in time required for GTV segmentation.

      PMID:25165581 | PMC:PMC4137600 | DOI:10.1155/2014/547075

      View details for PubMedID 25165581
  • 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.
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      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
  • Dosimetric comparison of photon and proton treatment techniques for chondrosarcoma of thoracic spine Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Yadav P, Paliwal BR, Kozak K
    2013 Autumn;38(3):233-7. doi: 10.1016/j.meddos.2013.02.002. Epub 2013 Mar 28.
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      Chondrosarcomas are relatively radiotherapy resistant, and also delivering high radiation doses is not feasible owing to anatomic constraints. In this study, the feasibility of helical tomotherapy for treatment of chondrosarcoma of thoracic spine is explored and compared with other available photon and proton radiotherapy techniques in the clinical setting. A patient was treated for high-grade chondrosarcoma of the thoracic spine using tomotherapy. Retrospectively, the tomotherapy plan was compared with intensity-modulated radiation therapy, dynamic arc photon therapy, and proton therapy. Two primary comparisons were made: (1) comparison of normal tissue sparing with comparable target volume coverage (plan-1), and (2) comparison of target volume coverage with a constrained maximum dose to the cord center (plan-2). With constrained target volume coverage, proton plans were found to yield lower mean doses for all organs at risk (spinal cord, esophagus, heart, and both lungs). Tomotherapy planning resulted in the lowest mean dose to all organs at risk amongst photon-based methods. For cord dose constrained plans, the static-field intensity-modulated radiation therapy and dynamic arc plans resulted target underdosing in 20% and 12% of planning target volume2 volumes, respectively, whereas both proton and tomotherapy plans provided clinically acceptable target volume coverage with no portion of planning target volume2 receiving less than 90% of the prescribed dose. Tomotherapy plans are comparable to proton plans and produce superior results compared with other photon modalities. This feasibility study suggests that tomotherapy is an attractive alternative to proton radiotherapy for delivering high doses to lesions in the thoracic spine.

      PMID:23541524 | DOI:10.1016/j.meddos.2013.02.002

      View details for PubMedID 23541524
  • Feasibility study on effect and stability of adaptive radiotherapy on kilovoltage cone beam CT Radiology and oncology
    Yadav P, Ramasubramanian V, Paliwal BR
    2011 Sep;45(3):220-6. doi: 10.2478/v10019-011-0024-5. Epub 2011 Jul 20.
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      BACKGROUND: We have analyzed the stability of CT to density curve of kilovoltage cone-beam computerized tomography (kV CBCT) imaging modality over the period of six months. We also, investigated the viability of using image value to density table (IVDT) generated at different time, for adaptive radiotherapy treatment planning. The consequences of target volume change and the efficacy of kV CBCT for adaptive planning issues is investigated. MATERIALS AND METHODS.: Standard electron density phantom was used to establish CT to electron density calibrations curve. The CT to density curve for the CBCT images were observed for the period of six months. The kV CBCT scans used for adaptive planning was acquired with an on-board imager system mounted on a "Trilogy" linear accelerator. kV CBCT images were acquired for daily setup registration. The effect of variations in CT to density curve was studied on two clinical cases: prostate and lung.

      RESULTS: The soft tissue contouring is superior in kV CBCT scans in comparison to mega voltage CT (MVCT) scans. The CT to density curve for the CBCT images was found steady over six months. Due to difficulty in attaining the reproducibility in daily setup for the prostate treatment, there is a day-to-day difference in dose to the rectum and bladder.

      CONCLUSIONS: There is no need for generating a new CT to density curve for the adaptive planning on the kV CBCT images. Also, it is viable to perform the adaptive planning to check the dose to target and organ at risk (OAR) without performing a new kV CT scan, which will reduce the dose to the patient.

      PMID:22933960 | PMC:PMC3423744 | DOI:10.2478/v10019-011-0024-5

      View details for PubMedID 22933960
  • Postmastectomy radiotherapy with integrated scar boost using helical tomotherapy Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Rong Y, Yadav P, Welsh JS, Fahner T, Paliwal B
    2012 Autumn;37(3):233-9. doi: 10.1016/j.meddos.2011.09.001. Epub 2012 Feb 24.
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      The purpose of this study was to evaluate helical tomotherapy dosimetry in postmastectomy patients undergoing treatment for chest wall and positive nodal regions with simultaneous integrated boost (SIB) in the scar region using strip bolus. Six postmastectomy patients were scanned with a 5-mm-thick strip bolus covering the scar planning target volume (PTV) plus 2-cm margin. For all 6 cases, the chest wall received a total cumulative dose of 49.3-50.4 Gy with daily fraction size of 1.7-2.0 Gy. Total dose to the scar PTV was prescribed to 58.0-60.2 Gy at 2.0-2.5 Gy per fraction. The supraclavicular PTV and mammary nodal PTV received 1.7-1.9 dose per fraction. Two plans (with and without bolus) were generated for all 6 cases. To generate no-bolus plans, strip bolus was contoured and overrode to air density before planning. The setup reproducibility and delivered dose accuracy were evaluated for all 6 cases. Dose-volume histograms were used to evaluate dose-volume coverage of targets and critical structures. We observed reduced air cavities with the strip bolus setup compared with what we normally see with the full bolus. The thermoluminescence dosimeters (TLD) in vivo dosimetry confirmed accurate dose delivery beneath the bolus. The verification plans performed on the first day megavoltage computed tomography (MVCT) image verified that the daily setup and overall dose delivery was within 2% accuracy compared with the planned dose. The hotspot of the scar PTV in no-bolus plans was 111.4% of the prescribed dose averaged over 6 cases compared with 106.6% with strip bolus. With a strip bolus only covering the postmastectomy scar region, we observed increased dose uniformity to the scar PTV, higher setup reproducibility, and accurate dose delivered beneath the bolus. This study demonstrates the feasibility of using a strip bolus over the scar using tomotherapy for SIB dosimetry in postmastectomy treatments.

      PMID:22365416 | DOI:10.1016/j.meddos.2011.09.001

      View details for PubMedID 22365416
  • Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Yadav P, Kozak K, Tolakanahalli R, Ramasubramanian V, Paliwal BR, Welsh JS, Rong Y
    2012 Summer;37(2):157-62. doi: 10.1016/j.meddos.2011.06.005. Epub 2011 Sep 16.
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      This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

      PMID:21925866 | PMC:PMC3348436 | DOI:10.1016/j.meddos.2011.06.005

      View details for PubMedID 21925866
  • A planning study for palliative spine treatment using StatRT and megavoltage CT simulation Journal of applied clinical medical physics
    Rong Y, Yadav P, Paliwal B, Shang L, Welsh JS
    2010 Oct 30;12(1):3348. doi: 10.1120/jacmp.v12i1.3348.
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      Megavoltage CT (MVCT) simulation on the TomoTherapy Hi·Art system is an alternative to conventional CT for treatment planning in the presence of severe metal artifact. StatRT is a new feature that was implemented on the TomoTherapy operator station for performing online MVCT scanning, treatment planning and treatment delivery in one session. The clinical feasibility of using the StatRT technique and MVCT simulation to palliative treatment for a patient with substantial spinal metallic hardware is described. A patient with metastatic non-small-cell lung cancer involving the thoracic spine underwent conventional kilovoltage CT simulation. The metal artifact due to stainless steel spine-stabilizing rods was too severe for treatment planning, despite attempts to correct using density override. The patient was then re-scanned using MVCT on a tomotherapy unit. Plans were generated using both StatRT and conventional tomotherapy planning (Tomo plan) with different settings for comparison. StatRT planning ran a total of five iterations in a short planning window (10-15 min). Two Tomo plans were generated using: (1) five iterations in the "full scatter" mode, and (2) 300 iterations in the "beamlet" mode. It was noted that the DVH of the StatRT plan was almost identical to the Tomo plan optimized by the "full scatter" mode and the same number of iterations. Dose distribution analysis reveals that these three planning methods yielded comparable doses to heart, lungs and targets. This work also demonstrated that undermodulation can result in a high degree of thread effects. The overall time for the treatment process (including 7 minutes for simulation, 15 minutes for contouring, 10 minutes for planning and 5 minutes for delivery) decreases from hours to around 40 minutes using the StatRT procedure. StatRT is a feasible treatment-planning tool for physicians to scan, contour and treat patients within one hour. This can be particularly beneficial in urgent palliative treatments.

      PMID:21330983 | PMC:PMC5718582 | DOI:10.1120/jacmp.v12i1.3348

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  • Helical tomotherapy versus single-arc intensity-modulated arc therapy: a collaborative dosimetric comparison between two institutions International journal of radiation oncology, biology, physics
    Rong Y, Tang G, Welsh JS, Mohiuddin MM, Paliwal B, Yu CX
    2011 Sep 1;81(1):284-96. doi: 10.1016/j.ijrobp.2010.10.059. Epub 2011 Jan 13.
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      PURPOSE: Both helical tomotherapy (HT) and single-arc intensity-modulated arc therapy (IMAT) deliver radiation using rotational beams with multileaf collimators. We report a dual-institution study comparing dosimetric aspects of these two modalities.

      METHODS AND MATERIALS: Eight patients each were selected from the University of Maryland (UMM) and the University of Wisconsin Cancer Center Riverview (UWR), for a total of 16 cases. Four cancer sites including brain, head and neck (HN), lung, and prostate were selected. Single-arc IMAT plans were generated at UMM using Varian RapidArc (RA), and HT plans were generated at UWR using Hi-Art II TomoTherapy. All 16 cases were planned based on the identical anatomic contours, prescriptions, and planning objectives. All plans were swapped for analysis at the same time after final approval. Dose indices for targets and critical organs were compared based on dose-volume histograms, the beam-on time, monitor units, and estimated leakage dose. After the disclosure of comparison results, replanning was done for both techniques to minimize diversity in optimization focus from different operators.

      RESULTS: For the 16 cases compared, the average beam-on time was 1.4 minutes for RA and 4.8 minutes for HT plans. HT provided better target dose homogeneity (7.6% for RA and 4.2% for HT) with a lower maximum dose (110% for RA and 105% for HT). Dose conformation numbers were comparable, with RA being superior to HT (0.67 vs. 0.60). The doses to normal tissues using these two techniques were comparable, with HT showing lower doses for more critical structures. After planning comparison results were exchanged, both techniques demonstrated improvements in dose distributions or treatment delivery times.

      CONCLUSIONS: Both techniques created highly conformal plans that met or exceeded the planning goals. The delivery time and total monitor units were lower in RA than in HT plans, whereas HT provided higher target dose uniformity.

      PMID:21236598 | DOI:10.1016/j.ijrobp.2010.10.059

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  • The effect and stability of MVCT images on adaptive TomoTherapy Journal of applied clinical medical physics
    Yadav P, Tolakanahalli R, Rong Y, Paliwal BR
    2010 Jul 2;11(4):3229. doi: 10.1120/jacmp.v11i4.3229.
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      Use of helical TomoTherapy-based MVCT imaging for adaptive planning is becoming increasingly popular. Treatment planning and dose calculations based on MVCT require an image value to electron density calibration to remain stable over the course of treatment time. In this work, we have studied the dosimetric impact on TomoTherapy treatment plans due to variation in image value to density table (IVDT) curve as a function of target degradation. We also have investigated the reproducibility and stability of the TomoTherapy MVCT image quality over time. Multiple scans of the TomoTherapy "Cheese" phantom were performed over a period of five months. Over this period, a difference of 4.7% in the HU values was observed in high-density regions while there was no significant variation in the image values for the low densities of the IVDT curve. Changes in the IVDT curves before and after target replacement were measured. Two clinical treatment sites, pelvis and prostate, were selected to study the dosimetric impact of this variation. Dose was recalculated on the MVCTs with the planned fluence using IVDT curves acquired before and after target change. For the cases studied, target replacement resulted in an overall difference of less than 5%, which can be significant for hypo-fractionated cases. Hence, it is recommended to measure the IVDT curves on a monthly basis and after any major repairs/replacements.

      PMID:21081878 | PMC:PMC5720397 | DOI:10.1120/jacmp.v11i4.3229

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  • Glamour of technology Journal of medical physics
    Paliwal BR
    2010 Jul;35(3):129-30. doi: 10.4103/0971-6203.66759.
  • Treatment planning for pulsed reduced dose-rate radiotherapy in helical tomotherapy International journal of radiation oncology, biology, physics
    Rong Y, Paliwal B, Howard SP, Welsh J
    2011 Mar 1;79(3):934-42. doi: 10.1016/j.ijrobp.2010.05.055. Epub 2010 Sep 29.
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      PURPOSE: Pulsed reduced dose-rate radiotherapy (PRDR) is a valuable method of reirradiation because of its potential to reduce late normal tissue toxicity while still yielding significant tumoricidal effect. A typical method using a conventional linear accelerator (linac) is to deliver a series of 20-cGy pulses separated by 3-min intervals to give an effective dose-rate of just under 7 cGy/min. Such a strategy is fraught with difficulties when attempted on a helical tomotherapy unit. We investigated various means to overcome this limitation.

      METHODS AND MATERIALS: Phantom and patient cases were studied. Plans were generated with varying combinations of field width (FW), pitch, and modulation factor (MF) to administer 200 cGy per fraction to the planning target in eight subfractions, thereby mimicking the technique used on conventional linacs. Plans were compared using dose-volume histograms, homogeneity indices, conformation numbers, and treatment time. Plan delivery quality assurance was performed to assess deliverability.

      RESULTS: It was observed that for helical tomotherapy, intrinsic limitations in leaf open time in the multileaf collimator deteriorate plan quality and deliverability substantially when attempting to deliver very low doses such as 20-40 cGy. The various permutations evaluated revealed that the combination of small FW (1.0 cm), small MF (1.3-1.5), and large pitch (∼0.86), along with the half-gantry-angle-blocked scheme, can generate clinically acceptable plans with acceptable delivery accuracy (±3%).

      CONCLUSION: Pulsed reduced dose-rate radiotherapy can be accurately delivered using helical tomotherapy for tumor reirradiation when the appropriate combination of FW, MF, and pitch is used.

      PMID:20884127 | DOI:10.1016/j.ijrobp.2010.05.055

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  • Variability of textural features in FDG PET images due to different acquisition modes and reconstruction parameters Acta oncologica (Stockholm, Sweden)
    Galavis PE, Hollensen C, Jallow N, Paliwal B, Jeraj R
    2010 Oct;49(7):1012-6. doi: 10.3109/0284186X.2010.498437.
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      BACKGROUND: Characterization of textural features (spatial distributions of image intensity levels) has been considered as a tool for automatic tumor segmentation. The purpose of this work is to study the variability of the textural features in PET images due to different acquisition modes and reconstruction parameters.

      MATERIAL AND METHODS: Twenty patients with solid tumors underwent PET/CT scans on a GE Discovery VCT scanner, 45-60 minutes post-injection of 10 mCi of [(18)F]FDG. Scans were acquired in both 2D and 3D modes. For each acquisition the raw PET data was reconstructed using five different reconstruction parameters. Lesions were segmented on a default image using the threshold of 40% of maximum SUV. Fifty different texture features were calculated inside the tumors. The range of variations of the features were calculated with respect to the average value.

      RESULTS: Fifty textural features were classified based on the range of variation in three categories: small, intermediate and large variability. Features with small variability (range ≤ 5%) were entropy-first order, energy, maximal correlation coefficient (second order feature) and low-gray level run emphasis (high-order feature). The features with intermediate variability (10% ≤ range ≤ 25%) were entropy-GLCM, sum entropy, high gray level run emphsis, gray level non-uniformity, small number emphasis, and entropy-NGL. Forty remaining features presented large variations (range > 30%).

      CONCLUSION: Textural features such as entropy-first order, energy, maximal correlation coefficient, and low-gray level run emphasis exhibited small variations due to different acquisition modes and reconstruction parameters. Features with low level of variations are better candidates for reproducible tumor segmentation. Even though features such as contrast-NGTD, coarseness, homogeneity, and busyness have been previously used, our data indicated that these features presented large variations, therefore they could not be considered as a good candidates for tumor segmentation.

      PMID:20831489 | PMC:PMC4091820 | DOI:10.3109/0284186X.2010.498437

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  • Advances in radiation therapy dosimetry Journal of medical physics
    Paliwal B, Tewatia D
    2009 Jul;34(3):108-16. doi: 10.4103/0971-6203.54842.
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      During the last decade, there has been an explosion of new radiation therapy planning and delivery tools. We went through a rapid transition from conventional three-dimensional (3D) conformal radiation therapy to intensity-modulated radiation therapy (IMRT) treatments, and additional new techniques for motion-adaptive radiation therapy are being introduced. These advances push the frontiers in our effort to provide better patient care; and with the addition of IMRT, temporal dimensions are major challenges for the radiotherapy patient dosimetry and delivery verification. Advanced techniques are less tolerant to poor implementation than are standard techniques. Mis-administrations are more difficult to detect and can possibly lead to poor outcomes for some patients. Instead of presenting a manual on quality assurance for radiation therapy, this manuscript provides an overview of dosimetry verification tools and a focused discussion on breath holding, respiratory gating and the applications of four-dimensional computed tomography in motion management. Some of the major challenges in the above areas are discussed.

      PMID:20098555 | PMC:PMC2807673 | DOI:10.4103/0971-6203.54842

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  • Dose calculation on kV cone beam CT images: an investigation of the Hu-density conversion stability and dose accuracy using the site-specific calibration Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Rong Y, Smilowitz J, Tewatia D, Tomé WA, Paliwal B
    2010 Autumn;35(3):195-207. doi: 10.1016/j.meddos.2009.06.001. Epub 2009 Jul 15.
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      Precise calibration of Hounsfield units (HU) to electron density (HU-density) is essential to dose calculation. On-board kV cone beam computed tomography (CBCT) imaging is used predominantly for patients' positioning, but will potentially be used for dose calculation. The impacts of varying 3 imaging parameters (mAs, source-imager distance [SID], and cone angle) and phantom size on the HU number accuracy and HU-density calibrations for CBCT imaging were studied. We proposed a site-specific calibration method to achieve higher accuracy in CBCT image-based dose calculation. Three configurations of the Computerized Imaging Reference Systems (CIRS) water equivalent electron density phantom were used to simulate sites including head, lungs, and lower body (abdomen/pelvis). The planning computed tomography (CT) scan was used as the baseline for comparisons. CBCT scans of these phantom configurations were performed using Varian Trilogy system in a precalibrated mode with fixed tube voltage (125 kVp), but varied mAs, SID, and cone angle. An HU-density curve was generated and evaluated for each set of scan parameters. Three HU-density tables generated using different phantom configurations with the same imaging parameter settings were selected for dose calculation on CBCT images for an accuracy comparison. Changing mAs or SID had small impact on HU numbers. For adipose tissue, the HU discrepancy from the baseline was 20 HU in a small phantom, but 5 times lager in a large phantom. Yet, reducing the cone angle significantly decreases the HU discrepancy. The HU-density table was also affected accordingly. By performing dose comparison between CT and CBCT image-based plans, results showed that using the site-specific HU-density tables to calibrate CBCT images of different sites improves the dose accuracy to approximately 2%. Our phantom study showed that CBCT imaging can be a feasible option for dose computation in adaptive radiotherapy approach if the site-specific calibration is applied.

      PMID:19931031 | DOI:10.1016/j.meddos.2009.06.001

      View details for PubMedID 19931031
  • A comprehensive assessment by tumor site of patient setup using daily MVCT imaging from more than 3,800 helical tomotherapy treatments International journal of radiation oncology, biology, physics
    Schubert LK, Westerly DC, Tomé WA, Mehta MP, Soisson ET, Mackie TR, Ritter MA, Khuntia D, Harari PM, Paliwal BR
    2009 Mar 15;73(4):1260-9. doi: 10.1016/j.ijrobp.2008.11.054.
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      PURPOSE: To assess patient setup corrections based on daily megavoltage CT (MVCT) imaging for four anatomic treatment sites treated on tomotherapy.

      METHOD AND MATERIALS: Translational and rotational setup corrections, based on registration of daily MVCT to planning CT images, were analyzed for 1,179 brain and head and neck (H&N), 1,414 lung, and 1,274 prostate treatment fractions. Frequencies of three-dimensional vector lengths, overall distributions of setup corrections, and patient-specific distributions of random and systematic setup errors were analyzed.

      RESULTS: Brain and H&N had lower magnitude positioning corrections and smaller variations in translational setup errors but were comparable in roll rotations. Three-dimensional vector translational shifts of larger magnitudes occurred more frequently for lung and prostate than for brain and H&N treatments, yet this was not observed for roll rotations. The global systematic error for prostate was 4.7 mm in the vertical direction, most likely due to couch sag caused by large couch extension distances. Variations in systematic errors and magnitudes of random translational errors ranged from 1.6 to 2.6 mm for brain and H&N and 3.2 to 7.2 mm for lung and prostate, whereas roll rotational errors ranged from 0.8 degrees to 1.2 degrees for brain and H&N and 0.5 degrees to 1.0 degrees for lung and prostate.

      CONCLUSIONS: Differences in setup were observed between brain, H&N, lung, and prostate treatments. Patient setup can be improved if daily imaging is performed. This analysis can assess the utilization of daily image guidance and allows for further investigation into improved anatomic site-specific and patient-specific treatments.

      PMID:19251098 | PMC:PMC2749998 | DOI:10.1016/j.ijrobp.2008.11.054

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  • Streaking artifacts reduction in four-dimensional cone-beam computed tomography Medical physics
    Leng S, Zambelli J, Tolakanahalli R, Nett B, Munro P, Star-Lack J, Paliwal B, Chen G
    2008 Oct;35(10):4649-59. doi: 10.1118/1.2977736.
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      Cone-beam computed tomography (CBCT) using an "on-board" x-ray imaging device integrated into a radiation therapy system has recently been made available for patient positioning, target localization, and adaptive treatment planning. One of the challenges for gantry mounted image-guided radiation therapy (IGRT) systems is the slow acquisition of projections for cone-beam CT (CBCT), which makes them sensitive to any patient motion during the scans. Aiming at motion artifact reduction, four-dimensional CBCT (4D CBCT) techniques have been introduced, where a surrogate for the target's motion profile is utilized to sort the cone-beam data by respiratory phase. However, due to the limited gantry rotation speed and limited readout speed of the on-board imager, fewer than 100 projections are available for the image reconstruction at each respiratory phase. Thus, severe undersampling streaking artifacts plague 4D CBCT images. In this paper, the authors propose a simple scheme to significantly reduce the streaking artifacts. In this method, a prior image is first reconstructed using all available projections without gating, in which static structures are well reconstructed while moving objects are blurred. The undersampling streaking artifacts from static structures are estimated from this prior image volume and then can be removed from the phase images using gated reconstruction. The proposed method was validated using numerical simulations, experimental phantom data, and patient data. The fidelity of stationary and moving objects is maintained, while large gains in streak artifact reduction are observed. Using this technique one can reconstruct 4D CBCT datasets using no more projections than are acquired in a 60 s scan. At the same time, a temporal gating window as narrow as 100 ms was utilized. Compared to the conventional 4D CBCT reconstruction, streaking artifacts were reduced by 60% to 70%.

      PMID:18975711 | PMC:PMC2655146 | DOI:10.1118/1.2977736

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  • Clinical implementation of target tracking by breathing synchronized delivery Medical physics
    Tewatia D, Zhang T, Tome W, Paliwal B, Metha M
    2006 Nov;33(11):4330-6. doi: 10.1118/1.2359228.
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      Target-tracking techniques can be categorized based on the mechanism of the feedback loop. In real time tracking, breathing-delivery phase correlation is provided to the treatment delivery hardware. Clinical implementation of target tracking in real time requires major hardware modifications. In breathing synchronized delivery (BSD), the patient is guided to breathe in accordance with target motion derived from four-dimensional computed tomography (4D-CT). Violations of mechanical limitations of hardware are to be avoided at the treatment planning stage. Hardware modifications are not required. In this article, using sliding window IMRT delivery as an example, we have described step-by-step the implementation of target tracking by the BSD technique: (1) A breathing guide is developed from patient's normal breathing pattern. The patient tries to reproduce this guiding cycle by following the display in the goggles; (2) 4D-CT scans are acquired at all the phases of the breathing cycle; (3) The average tumor trajectory is obtained by deformable image registration of 4D-CT datasets and is smoothed by Fourier filtering; (4) Conventional IMRT planning is performed using the images at reference phase (full exhalation phase) and a leaf sequence based on optimized fluence map is generated; (5) Assuming the patient breathes with a reproducible breathing pattern and the machine maintains a constant dose rate, the treatment process is correlated with the breathing phase; (6) The instantaneous average tumor displacement is overlaid on the dMLC position at corresponding phase; and (7) DMLC leaf speed and acceleration are evaluated to ensure treatment delivery. A custom-built mobile phantom driven by a computer-controlled stepper motor was used in the dosimetry verification. A stepper motor was programmed such that the phantom moved according to the linear component of tumor motion used in BSD treatment planning. A conventional plan was delivered on the phantom with and without motion. The BSD plan was also delivered on the phantom that moved with the prescheduled pattern and synchronized with the delivery of each beam. Film dosimetry showed underdose and overdose in the superior and inferior regions of the target, respectively, if the tumor motion is not compensated during the delivery. BSD delivery resulted in a dose distribution very similar to the planned treatments.

      PMID:17153412 | DOI:10.1118/1.2359228

      View details for PubMedID 17153412
  • Inverse planning of energy-modulated electron beams in radiotherapy Medical dosimetry : official journal of the American Association of Medical Dosimetrists
    Gentry JR, Steeves R, Paliwal BA
    2006 Winter;31(4):259-68. doi: 10.1016/j.meddos.2005.03.008.
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      The use of megavoltage electron beams often poses a clinical challenge in that the planning target volume (PTV) is anterior to other radiosensitive structures and has variable depth. To ensure that skin as well as the deepest extent of the PTV receives the prescribed dose entails prescribing to a point beyond the depth of peak dose for a single electron energy. This causes dose inhomogeneities and heightened potential for tissue fibrosis, scarring, and possible soft tissue necrosis. Use of bolus on the skin improves the entrant dose at the cost of decreasing the therapeutic depth that can be treated. Selection of a higher energy to improve dose homogeneity results in increased dose to structures beyond the PTV, as well as enlargement of the volume receiving heightened dose. Measured electron data from a linear accelerator was used as input to create an inverse planning tool employing energy and intensity modulation using bolus (e-IMRT). Using tools readily available in a radiotherapy department, the applications of energy and intensity modulation on the central axis makes it possible to remove hot spots of 115% or more over the depths clinically encountered. The e-IMRT algorithm enables the development of patient-specific dose distributions with user-defined positions of peak dose, range, and reduced dose to points beyond the prescription point.

      PMID:17134665 | DOI:10.1016/j.meddos.2005.03.008

      View details for PubMedID 17134665
  • Clinical implementation of adaptive helical tomotherapy: a unique approach to image-guided intensity modulated radiotherapy Technology in cancer research & treatment
    Welsh JS, Lock M, Harari PM, Tomé WA, Fowler J, Mackie TR, Ritter M, Kapatoes J, Forrest L, Chappell R, Paliwal B, Mehta MP
    2006 Oct;5(5):465-79. doi: 10.1177/153303460600500503.
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      Image-guided IMRT is a revolutionary concept whose clinical implementation is rapidly evolving. Methods of executing beam intensity modulation have included individually designed compensators, static multi-leaf collimators (MLC), dynamic MLC, and sequential (serial) tomotherapy. We have developed helical tomotherapy as an innovative solution to overcome some of the limitations of other IMRT systems. The unique physical design of helical tomotherapy allows the realization of the concepts of adaptive radiotherapy and conformal avoidance. In principle, these advances should improve normal tissue sparing and permit dose reconstruction and verification, thereby allowing significant biologically effective dose escalation. Recent radiobiological findings can be translated into altered fractionation schemes that aim to improve the local control and long-term survival. This strategy is being tested at the University of Wisconsin using helical tomotherapy with its highly precise delivery and verification system along with meticulous and practical forms of immobilization. Innovative techniques such optical guidance, respiratory gating, and ultrasound assessments are being designed and tailored for helical tomotherapy use. The intrinsic capability of helical tomotherapy for megavoltage CT (MVCT) imaging for IMRT image-guidance is being optimized. The unique features of helical tomotherapy might allow implementation of image-guided IMRT that was previously impossible or impractical. Here we review the technological, physical, and radiobiological rationale for the ongoing and upcoming clinical trials that will use image-guided IMRT in the form of helical tomotherapy; and we describe our plans for testing our hypotheses in a rigorous prospective fashion.

      PMID:16981789 | DOI:10.1177/153303460600500503

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  • Helical tomotherapy as a means of delivering accelerated partial breast irradiation Technology in cancer research & treatment
    Hui SK, Das RK, Kapatoes J, Oliviera G, Becker S, Odau H, Fenwick JD, Patel R, Kuske R, Mehta M, Paliwal B, Mackie TR, Fowler JF, Welsh JS
    2004 Dec;3(6):639-46. doi: 10.1177/153303460400300614.
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      A novel treatment approach utilizing helical tomotherapy for partial breast irradiation for patients with early-stage breast cancer is described. This technique may serve as an alternative to high dose-rate (HDR) interstitial brachytherapy and standard linac-based approaches. Through helical tomotherapy, highly conformal irradiation of target volumes and avoidance of normal sensitive structures can be achieved. Unlike HDR brachytherapy, it is noninvasive. Unlike other linac-based techniques, it provides image-guided adaptive radiotherapy along with intensity modulation. A treatment planning CT scan was obtained as usual on a post-lumpectomy patient undergoing HDR interstitial breast brachytherapy. The patient underwent catheter placement for HDR treatment and was positioned prone on a specially designed position-supporting mattress during CT. The planning target volume (PTV) was defined as the lumpectomy bed plus a 20 mm margin. The prescription dose was 34 Gy (10 fx of 3.4 Gy) in both the CT based HDR and on the tomotherapy plan. Cumulative dose-volume histograms (DVHs) were generated and analyzed for the target, lung, heart, skin, pectoralis muscle, and chest wall for both HDR brachytherapy and helical tomotherapy. Dosimetric coverage of the target with helical tomotherapy was conformal and homogeneous. "Hot spots" (> or =150% isodose line) were present around implanted dwell positions in brachytherapy plan whereas no isodose lines higher than 109% were present in the helical tomotherapy plan. Similar dose coverage was achieved for lung, pectoralis muscle, heart, chest wall and breast skin with the two methods. We also compared our results to that obtained using conventional linac-based three dimensional (3D) conformal accelerated partial breast irradiation. Dose homogeneity is excellent with 3D conformal irradiation, and lung, heart and chest wall dose is less than for either HDR brachytherapy or helical tomotherapy but skin and pectoral muscle doses were higher than with the other techniques. Our results suggest that helical tomotherapy can serve as an effective means of delivering accelerated partial breast irradiation and may offer superior dose homogeneity compared to HDR brachytherapy.

      PMID:15560722 | DOI:10.1177/153303460400300614

      View details for PubMedID 15560722
  • Technical note: A novel boundary condition using contact elements for finite element based deformable image registration Medical physics
    Zhang T, Orton NP, Mackie TR, Paliwal BR
    2004 Sep;31(9):2412-5. doi: 10.1118/1.1774131.
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      Deformable image registration is an important tool for image-guided radiotherapy. Physics-model-based deformable image registration using finite element analysis is one of the methods currently being investigated. The calculation accuracy of finite element analysis is dependent on given boundary conditions, which are usually based on the surface matching of the organ in two images. Such a surface matching, however, is hard to obtain from medical images. In this study, we developed a new boundary condition to circumvent the traditional difficulties. Finite element contact-impact analysis was employed to simulate the interaction between the organ of interest and the surrounding body. The displacement loading is not necessarily specified. The algorithm automatically deforms the organ model into the minimum internal energy state. The analysis was performed on CT images of the lung at two different breathing phases (exhalation and full inhalation). The result gave the displacement vector map inside the lung. Validation of the result showed satisfactory agreement in most parts of the lung. This approach is simple, operator independent and may provide improved accuracy of the prediction of organ deformation.

      PMID:15487720 | DOI:10.1118/1.1774131

      View details for PubMedID 15487720
  • Treatment plan optimization incorporating respiratory motion Medical physics
    Zhang T, Jeraj R, Keller H, Lu W, Olivera GH, McNutt TR, Mackie TR, Paliwal B
    2004 Jun;31(6):1576-86. doi: 10.1118/1.1739672.
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      Similar to conventional conformal radiotherapy, during lung tomotherapy, a motion margin has to be set for respiratory motion. Consequently, large volume of normal tissue is irradiated by intensive radiation. To solve this problem, we have developed a new motion mitigation method by incorporating target motion into treatment optimization. In this method, the delivery-breathing correlation is determined prior to treatment plan optimization. Beamlets are calculated by using the CT images at the corresponding breathing phases from a dynamic (four-dimensional) image sequence. With the displacement vector fields at different breathing phases, a set of deformed beamlets is obtained by mapping the dose to the primary phase. Optimization incorporating motion is then performed by using the deformed beamlets obtained by dose mapping. During treatment delivery, the same breathing-delivery correlation can be reproduced by instructing the patient to breathe following a visually displayed guiding cycle. This method was tested using a computer-simulated deformable phantom and a real lung case. Results show that treatment optimization incorporating motion achieved similar high dose conformality on a mobile target compared with static delivery. The residual motion effects due to imperfect breathing tracking were also analyzed.

      PMID:15259662 | DOI:10.1118/1.1739672

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  • IMRT may be used to excess because of its higher reimbursement from Medicare. For the proposition Medical physics
    Paliwal BR
    2004 Jan;31(1):1-2. doi: 10.1118/1.1630968.
  • Application of the spirometer in respiratory gated radiotherapy Medical physics
    Zhang T, Keller H, O'Brien MJ, Mackie TR, Paliwal B
    2003 Dec;30(12):3165-71. doi: 10.1118/1.1625439.
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      The signal from a spirometer is directly correlated with respiratory motion and is ideal for target respiratory motion tracking. However, its susceptibility to signal drift deters its application in radiotherapy. In this work, a few approaches are investigated to control spirometer signal drift for a Bernoulli-type spirometer. A method is presented for rapid daily calibration of the spirometer to obtain a flow sensitivity function. Daily calibration assures accurate airflow measurement and also reduces signal drift. Dynamic baseline adjustment further controls the signal drift. The accuracy of these techniques was studied and it was found that the spirometer is able to provide a long-term drift-free breathing signal. The tracking error is comprised of two components: calibration error and stochastic signal baseline variation error. The calibration error is very small (1% of 3 l) and therefore negligible. The stochastic baseline variation error can be as large as 20% of the normal breathing amplitude. In view of these uncertainties, the applications of spirometers in treatment techniques that rely on breathing monitoring are discussed. Spirometer-based monitoring is noted most suitable for deep inspiration breath-hold but less important for free breathing gating techniques.

      PMID:14713083 | DOI:10.1118/1.1625439

      View details for PubMedID 14713083
  • Benchmarking beam alignment for a clinical helical tomotherapy device Medical physics
    Balog J, Mackie TR, Pearson D, Hui S, Paliwal B, Jeraj R
    2003 Jun;30(6):1118-27. doi: 10.1118/1.1576395.
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      A clinical helical tomotherapy treatment machine has been installed at the University of Wisconsin Comprehensive Cancer Center. Beam alignment has been finalized and accepted by UW staff. Helical tomotherapy will soon be clinically available to other sites. Clinical physicists who expect to work with this machine will need to be familiar with its unique dosimetric characteristics, and those related to the geometrical beam configuration and its verification are described here. A series of alignment tests and the results are presented. Helical tomotherapy utilizes an array of post-patient xenon-filled megavoltage radiation detectors. These detectors have proved capable of performing some alignment verification tests. That is particularly advantageous because those tests can then be automated and easily performed on an ongoing basis.

      PMID:12852536 | DOI:10.1118/1.1576395

      View details for PubMedID 12852536
  • Image guidance for precise conformal radiotherapy International journal of radiation oncology, biology, physics
    Mackie TR, Kapatoes J, Ruchala K, Lu W, Wu C, Olivera G, Forrest L, Tome W, Welsh J, Jeraj R, Harari P, Reckwerdt P, Paliwal B, Ritter M, Keller H, Fowler J, Mehta M
    2003 May 1;56(1):89-105. doi: 10.1016/s0360-3016(03)00090-7.
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      PURPOSE: To review the state of the art in image-guided precision conformal radiotherapy and to describe how helical tomotherapy compares with the image-guided practices being developed for conventional radiotherapy.

      MATERIALS AND METHODS: Image guidance is beginning to be the fundamental basis for radiotherapy planning, delivery, and verification. Radiotherapy planning requires more precision in the extension and localization of disease. When greater precision is not possible, conformal avoidance methodology may be indicated whereby the margin of disease extension is generous, except where sensitive normal tissues exist. Radiotherapy delivery requires better precision in the definition of treatment volume, on a daily basis if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided processes of helical tomotherapy that enable this goal are described.

      RESULTS: Examples of the results of helical tomotherapy processes for image-guided intensity-modulated radiotherapy are presented. These processes include megavoltage CT acquisition, automated segmentation of CT images, dose reconstruction using the CT image set, deformable registration of CT images, and reoptimization.

      CONCLUSIONS: Image-guided precision conformal radiotherapy can be used as a tool to treat the tumor yet spare critical structures. Helical tomotherapy has been designed from the ground up as an integrated image-guided intensity-modulated radiotherapy system and allows new verification processes based on megavoltage CT images to be implemented.

      PMID:12694827 | DOI:10.1016/s0360-3016(03)00090-7

      View details for PubMedID 12694827
  • Anatomic variation of prescription points and treatment volume with fractionated high-dose rate gynecological brachytherapy Journal of applied clinical medical physics
    Elhanafy OA, Das RK, Paliwal BR, Migahed MD, Sakr HA, Elleithy M
    2002 Winter;3(1):1-5. doi: 10.1120/jacmp.v3i1.2586.
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      The purpose of this report is to evaluate the geometric movement (relative to the bony pelvis) and dose variation of brachytherapy reference points in the same patient at repeated high-dose rate (HDR) intracavitary implants. A study was also concluded to find the variation in treatment volume from repeated fractions. Twenty-five consecutive cervical cancer patients (all stages) treated with external beam and fractionated HDR intracavitary implants at the University of Wisconsin were reviewed. Each brachytherapy insertion had a different plan generated prior to treatment delivery. ICRU #38 prescription points (A, B, P, bladder, and rectum) were used. Dose volume histogram was generated and treated volume to the prescription dose was recorded for each fraction. Motion analysis of the various points (from a common origin) in subsequent fractions relative to the first fraction revealed a shift of 2-9 mm in a single plane. Vector analysis revealed the magnitude of the average shift ranged from 10-13 mm. These shifts resulted in a dose difference of >20% for the bladder and rectum points, but < than 8% for the other points. Dose volume histograms revealed that with the change in the anatomy of the cervix and upper vagina during a patient's course of treatment, the treatment volume changes considerably. Thirty-six percent of all patients (9/16) had a reduction in the size of the ovoid during the treatment course. Sixty percent of all patients (15/25) had volume changes <10%. Sixty-two and one half percent of patients (10/16) who did not undergo a reduction of avoid size during the entire course of the treatment had volume change <10%. Since there is a change in the anatomy of the cervix and upper vagina during the course of a treatment along with the irreproducibility of the packing, there is movement of the absolute position of the prescription points between fractions, thus emphasizing the importance of individual dosimetry. Moreover, due to the same reasons, there are significant changes in the treatment volume among implants for the same patient. Volume reduction caused by reduction in ovoid size alone could not be extracted from this study.

      PMID:11817998 | PMC:PMC5724548 | DOI:10.1120/jacmp.v3i1.2586

      View details for PubMedID 11817998

Contact Information

Bhudatt Paliwal, PhD

600 Highland Avenue, K4/314,
Madison, WI 53792