Poonam Yadav, MD headshot

Poonam Yadav, PhD

Assistant Professor (CHS)

Department of Human Oncology

I am an assistant professor in the Department of Human Oncology. Much of my current work involves the ViewRay MRIdian System, an MRI-guided radiation therapy machine that enables clinicians to monitor tumors and surrounding tissues during treatment. This technology allows us to adapt to changes in the patient’s anatomy to ensure accurate delivery of radiation. I conduct patient-specific quality assurance and pre-treatment and real-time treatment setup verification. I am also involved in commissioning and acceptance testing of new radiotherapy machines and establishing clinical protocols and planning techniques for various disease sites. My role also includes mentoring radiation oncology physics and radiation oncology residents, physicians, staff and graduate students in clinical practices.


PhD, VIT University (in collaboration with the University of Wisconsin–Madison), Radiation Oncology Physics (2011)

MS, Kurukshetra University, Physics (2004)

BS, Andhra University, Math, Physics and Computer Science (2002)

Academic Appointments

Assistant Professor, Human Oncology (2016)

Research Associate VIT University, VIT University (2006)

Visiting Scholar, Indira Gandhi Atomic Research Center (2006)

Physics Lecturer, Department of Technical Education, Haryana, India (2005)

Research Associate, Department of Physics, Kurukshetra University (2002)

Boards, Advisory Committees and Professional Organizations

International Editor, Journal of Radiotherapy in Practice

Abstract reviewer, Conference of American Association of Physicists in Medicine (2017)

Treasurer and secretary, North Central Chapter of the American Association of Physicists in Medicine

Member, American Association of Physicists in Medicine

Member, American Brachytherapy Society

Member, American College of Radiology

Member, North Central Chapter of the American Association of Physicists in Medicine

Member, Radiological Society of North America

Member, Wisconsin Radiological Society

  • Evaluating dose constraints for radiation induced liver damage following magnetic resonance image guided Stereotactic Body radiotherapy phiRO, February 06, 2021
    Yadav P, Kuczmarska-Haas A, Musunuru HB, BlitzerG, Mahler P, Bassetti M

  • Improved Ipsilateral Breast and Chest Wall Sparing with MR-guided 3-fraction Accelerated Partial Breast Irradiation: A dosimetric study comparing MR-Linac and CT-Linac plans Advances in Radiation Oncology, January 21, 2021
    B.Musunuru HB, Yadav P, Olson SJ, Anderson B

  • In Silico Single-Fraction Stereotactic Ablative Radiotherapy for the Treatment of Thoracic and Abdominal Oligometastatic Disease with Online Adaptive Magnetic Resonance Guidance Advances in Radiation Oncology, January 19, 2021
    Lee SL, Yadav P, van der Kogel AJ, Bayouth J, Bassetti M


  • Use of Stereotactic Magnetic Resonance-Guided Online Adaptive Radiation Therapy for Treatment of a Pelvic Recurrence of Prostate Cancer in a Patient With an Orthotopic Neobladder
  • Radiomic Modeling of Bone Density and Rib Fracture Risk After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer
  • A Predictive Model of 2yDFS During MR-Guided RT Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer Patients
  • The Role of MRI-Guided Radiotherapy for Soft Tissue Sarcomas
  • A multi-institutional comparison of dosimetric data for a 0.35 T MR-linac
  • Defining high-risk elective contralateral neck radiation volumes for oropharynx cancer
  • Synthetic Computed Tomography Generation from 0.35T Magnetic Resonance Images for Magnetic Resonance-Only Radiation Therapy Planning Using Perceptual Loss Models
  • Improved Ipsilateral Breast and Chest Wall Sparing With MR-Guided 3-fraction Accelerated Partial Breast Irradiation: A Dosimetric Study Comparing MR-Linac and CT-Linac Plans
  • In Silico Single-Fraction Stereotactic Ablative Radiation Therapy for the Treatment of Thoracic and Abdominal Oligometastatic Disease With Online Adaptive Magnetic Resonance Guidance
  • Combining Stereotactic Body Radiotherapy and Microwave Ablation Appears Safe and Feasible for Renal Cell Carcinoma in an Early Series
  • Artificial Intelligence in magnetic Resonance guided Radiotherapy: Medical and physical considerations on state of art and future perspectives
  • Delta radiomics for rectal cancer response prediction using low field magnetic resonance guided radiotherapy: an external validation
  • Evaluating dose constraints for radiation induced liver damage following magnetic resonance image guided Stereotactic Body radiotherapy
  • Diagnostic Performance of MRI for Esophageal Carcinoma: A Systematic Review and Meta-Analysis
  • A clinical validation of the MR-compatible Delta<sup>4</sup> QA system in a 0.35 tesla MR linear accelerator
  • Development and evaluation of a GEANT4-based Monte Carlo Model of a 0.35 T MR-guided radiation therapy (MRgRT) linear accelerator
  • Delta Radiomics Analysis for Local Control Prediction in Pancreatic Cancer Patients Treated Using Magnetic Resonance Guided Radiotherapy
  • Combined Immunotherapy and Stereotactic Radiotherapy Improves Neurologic Outcomes in Patients with Non-small-cell Lung Cancer Brain Metastases
  • The quantification and potential impact of dark current on treatments with an MR-guided radiotherapy (MRgRT) system
  • Reduction of cardiac dose using respiratory-gated MR-linac plans for gastro-esophageal junction cancer
  • External Validation of Early Regression Index (ERI<sub>TCP</sub>) as Predictor of Pathologic Complete Response in Rectal Cancer Using Magnetic Resonance-Guided Radiation Therapy
  • MOSFET dosimeter characterization in MR-guided radiation therapy (MRgRT) Linac
  • 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
  • Characterization and longitudinal assessment of daily quality assurance for an MR-guided radiotherapy (MRgRT) linac
  • Impact of adjuvant fractionated stereotactic radiotherapy dose on local control of brain metastases
  • Dosimetric study for spine stereotactic body radiation therapy: magnetic resonance guided linear accelerator versus volumetric modulated arc therapy
  • Cardiac Toxicity in Operable Esophageal Cancer Patients Treated With or Without Chemoradiation
  • MR-based treatment planning in radiation therapy using a deep learning approach
  • Hybrid volumetric modulated arc therapy for chest wall irradiation: For a good plan, get the right mixture
  • Long-term dosimetric stability of multiple TomoTherapy delivery systems
  • Dosimetric aspects of breast radiotherapy with three-dimensional and intensity-modulated radiotherapy helical tomotherapy planning modules
  • Radiation therapy for breast cancer: Literature review
  • Dosimetric differences in flattened and flattening filter-free beam treatment plans
  • Acute Toxicity From Breast Cancer Radiation Using Helical Tomotherapy With a Simultaneous Integrated Boost
  • Dosimetric comparison of photon and proton treatment techniques for chondrosarcoma of thoracic spine
  • Feasibility study on effect and stability of adaptive radiotherapy on kilovoltage cone beam CT
  • Postmastectomy radiotherapy with integrated scar boost using helical tomotherapy
  • Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding
  • A planning study for palliative spine treatment using StatRT and megavoltage CT simulation
  • The effect and stability of MVCT images on adaptive TomoTherapy
  • Development and evaluation of a GEANT4-based Monte Carlo Model of a 0.35 T MR-guided radiation therapy (MRgRT) linear accelerator. Med Phys
    Ullah Khan A, Simiele EA, Lotey R, DeWerd LA, Yadav P
    2021 Feb 08; :
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      PURPOSE: The aim of this work was to develop and benchmark a magnetic resonance(MR)-guided linear accelerator head model using the GEANT4 Monte Carlo (MC) code. The validated model was compared to the treatment planning system (TPS) and was also used to quantify the electron return effect (ERE) at a lung-water interface.

      METHODS: The average energy, including the spread in the energy distribution, and the radial intensity distribution of the incident electron beam were iteratively optimized in order to match the simulated beam profiles and percent depth dose (PDD) data to measured data. The GEANT4 MC model was then compared to the TPS model using several photon beam tests including oblique beams, an off-axis aperture, and heterogeneous phantoms. The benchmarked MC model was utilized to compute output factors (OFs) with the 0.35 T magnetic field turned on and off. The ERE was quantified at a lung-water interface by simulating PDD curves with and without the magnetic field for 6.6x6.6 cm2 and 2.5x2.5 cm2 field sizes. A 2%/2mm gamma criterion was used to compare the MC model with the TPS data throughout this study.

      RESULTS: The final incident electron beam parameters were 6.0 MeV average energy with a 1.5 MeV full width at half maximum (FWHM) Gaussian energy spread and a 1.0 mm FWHM Gaussian radial intensity distribution. The MC-simulated OFs were found to be in agreement with the TPS-calculated and measured OFs, and no statistical difference was observed between the 0.35 T and 0.0 T OFs. Good agreement was observed between the TPS-calculated and MC-simulated data for the photon beam tests with gamma pass rates ranging from 96% to 100%. An increase of 4.3% in the ERE was observed for the 6.6 x 6.6 cm2 field size relative to the 2.5x2.5 cm2 field size. The ratio of the 0.35 T PDD to the 0.0 T PDD was found to be up to 1.098 near lung-water interfaces for the 6.6x6.6 cm2 field size using the MC model.

      CONCLUSIONS: A vendor-independent Monte Carlo model has been developed and benchmarked for a 0.35 T/6 MV MR-linac. Good agreement was obtained between the GEANT4 and TPS models except near heterogeneity interfaces.

      View details for PubMedID 33555052
  • Delta Radiomics Analysis for Local Control Prediction in Pancreatic Cancer Patients Treated Using Magnetic Resonance Guided Radiotherapy. Diagnostics (Basel)
    Cusumano D, Boldrini L, Yadav P, Casà C, Lee SL, Romano A, Piras A, Chiloiro G, Placidi L, Catucci F, Votta C, Mattiucci GC, Indovina L, Gambacorta MA, Bassetti M, Valentini V
    2021 Jan 05; 11 (1):
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      The aim of this study is to investigate the role of Delta Radiomics analysis in the prediction of one-year local control (1yLC) in patients affected by locally advanced pancreatic cancer (LAPC) and treated using Magnetic Resonance guided Radiotherapy (MRgRT). A total of 35 patients from two institutions were enrolled: A 0.35 Tesla T2*/T1 MR image was acquired for each case during simulation and on each treatment fraction. Physical dose was converted in biologically effective dose (BED) to compensate for different radiotherapy schemes. Delta Radiomics analysis was performed considering the gross tumour volume (GTV) delineated on MR images acquired at BED of 20, 40, and 60 Gy. The performance of the delta features in predicting 1yLC was investigated in terms of Wilcoxon Mann-Whitney test and area under receiver operating characteristic (ROC) curve (AUC). The most significant feature in predicting 1yLC was the variation of cluster shade calculated at BED = 40 Gy, with a p-value of 0.005 and an AUC of 0.78 (0.61-0.94). Delta Radiomics analysis on low-field MR images might play a promising role in 1yLC prediction for LAPC patients: further studies including an external validation dataset and a larger cohort of patients are recommended to confirm the validity of this preliminary experience.

      View details for PubMedID 33466307
  • Combined Immunotherapy and Stereotactic Radiotherapy Improves Neurologic Outcomes in Patients with Non-small-cell Lung Cancer Brain Metastases. Clin Lung Cancer
    Enright TL, Witt JS, Burr AR, Yadav P, Leal T, Baschnagel AM
    2020 Nov 10; :
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      BACKGROUND: The purpose of this study was to compare the outcomes of patients with non-small cell lung cancer (NSCLC) brain metastases treated with stereotactic radiotherapy (SRT) alone versus SRT and immune checkpoint inhibitors (ICIs).

      PATIENTS AND METHODS: Patients treated for their first diagnosis of intracranial metastases with SRT or SRT plus ICI were retrospectively identified. Overall survival (OS), local control (LC), distant brain failure (DBF), neurologic death, and rates of radiation necrosis were calculated. Univariate (UVA) and multivariable (MVA) analyses with competing risk analysis were performed.

      RESULTS: Seventy-seven patients with 132 lesions were analyzed, including 44 patients with 68 lesions in the SRT group and 33 patients with 64 lesions in the SRT plus ICI group. There were no differences in baseline factors between groups. Use of ICI predicted for decreased DBF (hazard ratio [HR], 0.45; 95% confidence interval [CI], 0.24-0.84; P = .01), decreased rates of neurologic death (HR, 0.29; 95% CI, 0.10-0.85; P = .02), and better OS (HR, 0.46; 95% CI, 0.23-0.91; P = .03). Two-year LC was 97% for the SRT + ICI group, and 86% for the SRT-alone group (P = .046). Actuarial 2-year DBF was 39% for the SRT + ICI group and 66% for the SRT alone group (P = .016). On MVA, ICI use persisted in predicting lower incidence of neurologic death (HR, 0.25; 95% CI, 0.09-0.72; P = .01) and DBF (HR, 0.47; 95% CI, 0.25-0.85; P = .01) when adjusted for competing risk of death.

      CONCLUSION: In this cohort of patients with NSCLC brain metastases, ICI use combined with SRT predicted for improved LC and OS and decreased DBF and risk of neurologic death.

      View details for PubMedID 33281062
  • The quantification and potential impact of dark current on treatments with an MR-guided radiotherapy (MRgRT) system. J Appl Clin Med Phys
    Shepard AJ, Mittauer KE, Bayouth JE, Yadav P
    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.

      View details for PubMedID 33119933
  • Reduction of cardiac dose using respiratory-gated MR-linac plans for gastro-esophageal junction cancer. Med Dosim
    Lee SL, Mahler P, Olson S, Witt JS, Musunuru HB, Rajamanickam V, Bassetti MF, Yadav P
    2020 Oct 20; :
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      Treatment of locally advanced adenocarcinoma of the gastroesophageal junction (GEJ) with chemoradiation may be associated with high rates of symptomatic cardiac toxicity. Large margins are typically required to ensure coverage of GEJ tumors with free-breathing volumetric modulated arc therapy (VMAT) radiotherapy. The purpose of this study is to determine whether treatment with tighter margins enabled by maximum-inhalation breath hold (MIBH)-gated intensity modulated radiation therapy (IMRT) on an integrated MRI-linear accelerator system (MR-linac) can decrease radiation doses to the heart and cardiac substructures. Ten patients with locally advanced GEJ adenocarcinoma underwent both free breathing 4-dimensional computed tomography (4DCT) and MIBH MRI simulation scans. MR-linac IMRT plans were created with a 3 mm clinical target volume (CTV) to planning target volume (PTV) isotropic margin and 4DCT VMAT plans were created with a 11, 13, and 9 mm CTV to PTV anisotropic margins in the left-right, cranial-caudal, and anterior-posterior directions according to GEJ-specific PTV expansion recommendations by Voncken et al. Prescription dose to PTV was 50.4 Gy in 28 fractions. Dosimetry to the heart and cardiac substructures was compared with paired t test; p < 0.05 was considered significant. Mean PTV on the MR-linac IMRT plans was significantly smaller compared to the 4DCT VMAT plans (689 cm3vs 1275 cm3, p < 0.01). Mean dose to the heart and all cardiac substructures was significantly lower in the MR-linac IMRT plans compared to the 4DCT VMAT plans: heart 20.9 Gy vs 27.8 Gy, left atrium 29.6 Gy vs 39.4 Gy, right atrium 20.5 Gy vs 25.6 Gy, left ventricle 21.6 Gy vs 29.6 Gy, and right ventricle 18.7 Gy vs 25.2 Gy (all p values <0.05). MIBH-gated MR-linac IMRT treatment of locally advanced GEJ adenocarcinoma can significantly decrease doses to the heart and cardiac substructures and this may translate to reduced rates of cardiac toxicity.

      View details for PubMedID 33097372
  • External validation of an early regression index (ERITCP) as predictor of pathological complete response in rectal cancer using MR-guided Radiotherapy. Int J Radiat Oncol Biol Phys
    Cusumano D, Boldrini L, Yadav P, Yu G, Musurunu B, Chiloiro G, Piras A, Lenkowicz J, Placidi L, Broggi S, Romano A, Mori M, Barbaro B, Azario L, Gambacorta MA, De Spirito M, Bassetti MF, Yang Y, Fiorino C, Valentini V
    2020 Aug 03; :
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      PURPOSE: Tumour control probability (TCP)-based Early Regression Index (ERITCP) is a radiobiological parameter that showed promising results in predicting pathological complete response (pCR) on T2-weighted 1.5 Tesla (T) Magnetic Resonance (MR) images of patients with Locally Advanced Rectal Cancer (LARC). This study aims to validate the ERITCP in the context of low T MR-guided Radiotherapy (MRgRT), using images acquired with different magnetic field strength (0.35T) and image contrast (T2/T1). Furthermore, the optimal timing for pCR prediction was estimated, calculating the ERI index at different Biologically Effective Dose (BED) levels.

      METHODS: Fifty-two LARC patients treated with neo-adjuvant chemo-radiotherapy (CRT) were enrolled in this multi-institutional retrospective study. For each patient, a 0.35T T2/T1-weighted MR image was acquired during simulation and on each treatment day. Gross Tumour Volume (GTV) was contoured according to ICRU Report 83 guidelines. According to the original definition, ERITCP was calculated considering the residual tumour volume at BED=25Gy. ERI was also calculated in correspondence of several BED levels: 13, 21, 32, 40, 46, 54, 59 and 67. The predictive performance of the different ERI indices were evaluated in terms of receiver operating characteristic (ROC) curve. The robustness of ERITCP with respect to the inter-observer variability was also evaluated considering two operators and calculating the intra-class correlation index (ICC).

      RESULTS: Fourteen patients showed pCR. ERITCP correctly 47/52 cases (accuracy=90%), showing good results in terms of sensitivity (86%), specificity (92%), NPV (95%) and PPV (80%). The analysis at different BED levels has shown that the best predictive performance is obtained when this parameter is calculated at the BED=25 Gy (AUC=0.93). ERITCP results to be robust with respect inter-observer variability (ICC=0.99).

      CONCLUSION: This study confirmed the validity and the robustness of ERITCP as pCR predictor in the context of low Tesla MRgRT, individuating 25Gy as the best BED level to perform predictions.

      View details for PubMedID 32758641
  • MOSFET dosimeter characterization in MR-guided radiation therapy (MRgRT) Linac. J Appl Clin Med Phys
    Yadav P, Hallil A, Tewatia D, Dunkerley DAP, Paliwal B
    2020 Jan; 21 (1): 127-135
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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.

      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. Med Phys
    Mittauer KE, Yadav P, Paliwal B, Bayouth JE
    2020 Feb; 47 (2): 317-330
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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.

      View details for PubMedID 31682018
  • Characterization and longitudinal assessment of daily quality assurance for an MR-guided radiotherapy (MRgRT) linac. J Appl Clin Med Phys
    Mittauer KE, Dunkerley DAP, Yadav P, Bayouth JE
    2019 Nov; 20 (11): 27-36
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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.

      View details for PubMedID 31633882
  • Impact of adjuvant fractionated stereotactic radiotherapy dose on local control of brain metastases. J Neurooncol
    Musunuru HB, Witt JS, Yadav P, Francis DM, Kuczmarska-Haas A, Labby ZE, Bassetti MF, Howard SP, Baschnagel AM
    2019 Nov; 145 (2): 385-390
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      PURPOSE: The aim of this study was to determine whether a higher biological effective dose (BED) would result in improved local control in patients treated with fractionated stereotactic radiotherapy (FSRT) for their resected brain metastases.

      METHODS: Patients with newly diagnosed brain metastases without previous brain radiotherapy were retrospectively reviewed. Patients underwent surgical resection of at least one brain metastasis and were treated with adjuvant FSRT, delivering 25-36 Gy in 5-6 fractions. Outcomes were computed using Kaplan-Meier survival analysis and univariate analysis.

      RESULTS: Fifty-four patients with 63 post-operative cavities were included. Median follow-up was 16 months (3-60). Median metastasis size at diagnosis was 2.9 cm (0.6-8.1) and median planning target volume was 19.7 cm3 (6.3-68.1). Two-year local control (LC) was 83%. When stratified by dose, 2 years LC rate was 95.1% in those treated with 30-36 Gy in 5-6 fractions (BED10 of 48-57.6 Gy10) versus 59.1% lesions treated with 25 Gy in 5 fractions (BED10 of 37.5 Gy10) (p < 0.001). LC was not associated with resection cavity size. One year overall survival was 68.7%, and was independent of BED10. Symptomatic radiation necrosis occurred in 7.9% of patients and was not associated with dose.

      CONCLUSION: In the post-operative setting, high-dose FSRT (BED10 > 37.5 Gy10) were associated with a significantly higher rate of LC compared to lower BED regimens. Overall, 25 Gy in 5 fractions is not an adequate dose to control microscopic disease. If selecting a 5-fraction regimen, 30 Gy in five fractions appears to provide excellent tumor bed control.

      View details for PubMedID 31606876
  • Dosimetric study for spine stereotactic body radiation therapy: magnetic resonance guided linear accelerator versus volumetric modulated arc therapy. Radiol Oncol
    Yadav P, Musunuru HB, Witt JS, Bassetti M, Bayouth J, Baschnagel AM
    2019 09 24; 53 (3): 362-368
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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.

      View details for PubMedID 31553704
  • Cardiac Toxicity in Operable Esophageal Cancer Patients Treated With or Without Chemoradiation. Am J Clin Oncol
    Witt JS, Jagodinsky JC, Liu Y, Yadav P, Kuczmarska-Haas A, Yu M, Maloney JD, Ritter MA, Bassetti MF, Baschnagel AM
    2019 08; 42 (8): 662-667
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      PURPOSE: The purpose of this study was to evaluate predictors of cardiac events in esophageal cancer patients treated with neoadjuvant chemoradiotherapy (NA CRT) followed by surgery compared with surgery alone.

      MATERIALS AND METHODS: We retrospectively identified patients treated for esophageal cancer between 2006 and 2016. A total of 123 patients were identified; 70 were treated with surgery alone, and 53 were treated with NA CRT. Cardiac events were scored based on Common Terminology Criteria for Adverse Events (version 4.03), and dosimetric data was compiled for all patients who received radiation. Univariate analysis and multivariable analysis (MVA) were performed to identify predictors of cardiac events. Competing risk of death regression was performed to a model the cumulative incidence of cardiac events.

      RESULTS: The overall rates of grade ≥3 cardiac events were 24.5% in the NA CRT group versus 10% in the surgery group (P=0.04). On MVA, use of NA CRT (P<0.01, hazard ratio [HR]: 3.45, 95% confidence interval [CI]: 1.35-9.09) predicted for grade ≥3 cardiac events, though no dosimetric variable predicted for grade ≥3 cardiac events or overall survival. On MVA, NA CRT predicted for pericardial effusions of any grade (P<0.01, HR: 3.70, 95% CI: 1.67-8.33). The V45 Gy was the most significant predictor of pericardial effusions (P=0.012, HR: 1.03, 95% CI: 1.01-1.06) CONCLUSIONS:: NA CRT significantly increased the rate of grade ≥3 cardiac events compared with patients treated with surgery alone. Although no dosimetric parameter predicted for grade ≥3 cardiac events or survival, the V45 Gy predicted for pericardial effusions.

      View details for PubMedID 31313677
  • MR-based treatment planning in radiation therapy using a deep learning approach. J Appl Clin Med Phys
    Liu F, Yadav P, Baschnagel AM, McMillan AB
    2019 Mar; 20 (3): 105-114
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      PURPOSE: To develop and evaluate the feasibility of deep learning approaches for MR-based treatment planning (deepMTP) in brain tumor radiation therapy.

      METHODS AND MATERIALS: A treatment planning pipeline was constructed using a deep learning approach to generate continuously valued pseudo CT images from MR images. A deep convolutional neural network was designed to identify tissue features in volumetric head MR images training with co-registered kVCT images. A set of 40 retrospective 3D T1-weighted head images was utilized to train the model, and evaluated in 10 clinical cases with brain metastases by comparing treatment plans using deep learning generated pseudo CT and using an acquired planning kVCT. Paired-sample Wilcoxon signed rank sum tests were used for statistical analysis to compare dosimetric parameters of plans made with pseudo CT images generated from deepMTP to those made with kVCT-based clinical treatment plan (CTTP).

      RESULTS: deepMTP provides an accurate pseudo CT with Dice coefficients for air: 0.95 ± 0.01, soft tissue: 0.94 ± 0.02, and bone: 0.85 ± 0.02 and a mean absolute error of 75 ± 23 HU compared with acquired kVCTs. The absolute percentage differences of dosimetric parameters between deepMTP and CTTP was 0.24% ± 0.46% for planning target volume (PTV) volume, 1.39% ± 1.31% for maximum dose and 0.27% ± 0.79% for the PTV receiving 95% of the prescribed dose (V95). Furthermore, no significant difference was found for PTV volume (P = 0.50), the maximum dose (P = 0.83) and V95 (P = 0.19) between deepMTP and CTTP.

      CONCLUSIONS: We have developed an automated approach (deepMTP) that allows generation of a continuously valued pseudo CT from a single high-resolution 3D MR image and evaluated it in partial brain tumor treatment planning. The deepMTP provided dose distribution with no significant difference relative to a kVCT-based standard volumetric modulated arc therapy plans.

      View details for PubMedID 30861275
  • Hybrid volumetric modulated arc therapy for chest wall irradiation: For a good plan, get the right mixture. Phys Med
    Balaji K, Yadav P, BalajiSubramanian S, Anu Radha C, Ramasubramanian V
    2018 Aug; 52: 86-92
    • More

      PURPOSE: To find the optimal dose weighting for hybrid volumetric modulated arc therapy (H-VMAT), a combination of conventional 3DCRT and VMAT plans for left sided chest wall and supraclavicular radiation therapy.

      METHODS & MATERIALS: 20 left-sided breast cancer patients who received adjuvant radiotherapy were considered for this study. To find the optimal weighting, 5 H-VMAT plans were generated for each study case by combining different dose proportions of 3DCRT and VMAT plans including: 90% 3DCRT/10% VMAT, 80% 3DCRT/20% VMAT, 70% 3DCRT/30% VMAT, 60% 3DCRT/40% VMAT, 50% 3DCRT/50% VMAT. Further field-in-field, optimal H-VMAT and VMAT alone plans were compared.

      RESULTS: All H-VMAT plans achieved the expected target coverage. A higher conformity index was achieved for 50% 3DCRT/50% VMAT plan, while better homogeneity index was achieved for 80% 3DCRT/20% VMAT plan. Mean and low doses were less in 90% 3DCRT/10% VMAT plan. Compared with other proportions, 80% 3DCRT/20% VMAT and 70% 3DCRT/30% VMAT weighted H-VMAT plans achieved balanced results for PTVs and OARs.

      CONCLUSION: The optimal dose mixture for H-VMAT technique is 70% to 80% for 3DCRT and 20% to 30% for VMAT. The optimal H-VMAT achieved balanced results for the PTVs and OARs compared with field-in-field and VMAT alone plans.

      View details for PubMedID 30139614
  • Long-term dosimetric stability of multiple TomoTherapy delivery systems. J Appl Clin Med Phys
    Smilowitz JB, Dunkerley D, Hill PM, Yadav P, Geurts MW
    2017 May; 18 (3): 137-143
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      The dosimetric stability of six TomoTherapy units was analyzed to investigate changes in performance over time and with system upgrades. Energy and output were tracked using monitor chamber signal, onboard megavoltage computed tomography (MVCT) detector profile, and external ion chamber measurements. The systems (and monitoring periods) include three Hi-Art (67, 61, and 65 mos.), two TomoHDA (31 and 26 mos.), and one Radixact unit (11 mos.), representing approximately 10 years of clinical use. The four newest systems use the Dose Control Stability (DCS) system and Fixed Target Linear Accelerator (linac) (FTL). The output stability is reported as deviation from reference monitor chamber signal for all systems and/or from an external chamber signal. The energy stability was monitored using relative (center versus off-axis) MVCT detector signal (beam profile) and/or the ratio of chamber measurements at 2 depths. The clinical TomoHDA data were used to benchmark the Radixact stability, which has the same FTL but runs at a higher dose rate. The output based on monitor chamber data of all systems is very stable. The standard deviation of daily output on the non-DCS systems was 0.94-1.52%. As expected, the DCS systems had improved standard deviation: 0.004-0.06%. The beam energy was also very stable for all units. The standard deviation in profile flatness was 0.23-0.62% for rotating target systems and 0.04-0.09% for FTL. Ion chamber output and PDD ratios supported these results. The output stability on the Radixact system during extended treatment delivery (20, 30, and 40 min) was comparable to a clinical TomoHDA system. For each system, results are consistent between different measurement tools and techniques, proving not only the dosimetric stability, but also these quality parameters can be confirmed with various metrics. The replacement history over extended time periods of the major dosimetric components of the different delivery systems (target, linac, and magnetron) is also reported.

      View details for PubMedID 28464517
  • Dosimetric aspects of breast radiotherapy with three-dimensional and intensity-modulated radiotherapy helical tomotherapy planning modules. Med Dosim
    Yadav P, Yan Y, Ignatowski T, Olson A
    2017 Spring; 42 (1): 42-46
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      In this work, we investigated the dosimetric differences between the intensity-modulated radiotherapy (IMRT) plans and the three-dimensional (3D) helical plans based on the TomoTherapy system. A total of 15 patients with supine setup were randomly selected from the data base. For patients with lumpectomy planning target volume (PTV), regional lymph nodes were also included as part of the target. For dose sparing, the significant differences between the helical IMRT and helical 3D were only found in the heart and contralateral breast. For the dose to the heart, helical IMRT reduced the maximum point dose by 6.98Gy compared to the helical 3D plan (p = 0.01). For contralateral breast, the helical IMRT plans significantly reduced the maximum point dose by 5.6Gy compared to the helical 3D plan. However, compared to the helical 3D plan, the helical IMRT plan increased the volume for lower dose (13.08% increase in V5Gy, p = 0.01). In general, there are no significant differences in dose sparing between helical IMRT and helical 3D plans.

      View details for PubMedID 28129971
  • Radiation therapy for breast cancer: Literature review. Med Dosim
    Balaji K, Subramanian B, Yadav P, Anu Radha C, Ramasubramanian V
    2016; 41 (3): 253-7
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      Concave shape with variable size target volume makes treatment planning for the breast/chest wall a challenge. Conventional techniques used for the breast/chest wall cancer treatment provided better sparing of organs at risk (OARs), with poor conformity and uniformity to the target volume. Advanced technologies such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) improve the target coverage at the cost of higher low dose volumes to OARs. Novel hybrid techniques present promising results in breast/chest wall irradiation in terms of target coverage as well as OARs sparing. Several published data compared these technologies for the benefit of the breast/chest wall with or without nodal volumes. The aim of this article is to review relevant data and identify the scope for further research in developing optimal treatment plan for breast/chest wall cancer treatment.

      View details for PubMedID 27545009
  • Dosimetric differences in flattened and flattening filter-free beam treatment plans. J Med Phys
    Yan Y, Yadav P, Bassetti M, Du K, Saenz D, Harari P, Paliwal BR
    2016 Apr-Jun; 41 (2): 92-9
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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.

      View details for PubMedID 27217620
  • Acute Toxicity From Breast Cancer Radiation Using Helical Tomotherapy With a Simultaneous Integrated Boost. Technol Cancer Res Treat
    Wojcieszynski AP, Olson AK, Rong Y, Kimple RJ, Yadav P
    2016 Apr; 15 (2): 257-65
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      PURPOSE: To evaluate 2 simultaneous integrated boost treatment planning techniques using helical tomotherapy for breast conserving therapy with regard to acute skin toxicity and dosimetry.

      METHODS: Thirty-two patients were studied. The original approach was for 16 patients and incorporated a directional block of the ipsilateral lung and breast. An additional 16 patients were planned for using a modified approach that incorporates a full block of the ipsilateral lung exclusive of 4 cm around the breast. Dose-volume histograms of targets and critical structures were evaluated. Skin toxicity monitoring was performed throughout treatment and follow-up using the Common Terminology Criteria for Adverse Events.

      RESULTS: Treatment was well tolerated with patients receiving a median dose of 59.36 Gy. Of the 16 patients in both groups, 8 had grade 2 erythema immediately after radiation. On 3-week follow-up, 10 and 7 patients in the original and modified groups showed grade 1 erythema. On 3- and 6-month follow-up, both groups had minimal erythema, with all patients having either grade 0 or 1 symptoms. No grade 2 or 3 toxicities were reported. Mean treatment time was 7.5 and 10.4 minutes using the original and modified methods. Adequate dose coverage was achieved using both methods (V95 = 99.5% and 98%). Mean dose to the heart was 10.5 and 1.8 Gy, respectively (P < .01). For right-sided tumors, the original and modified plans yielded a mean of 8.8 and 1.1 Gy (P < .01) versus 11.7 and 2.4 Gy for left-sided tumors (P < .01). The mean dose to the ipsilateral lung was also significantly lower in the modified plans (11.8 vs. 5.0 Gy, P < .01).

      CONCLUSIONS: Tomotherapy is capable of delivering homogeneous treatment plans to the whole breast and lumpectomy cavity using simultaneous integrated boost treatment. Using the treatment methods described herein, extremely low doses to critical structures can be achieved without compromising acute skin toxicity.

      View details for PubMedID 25780060
  • Dosimetric comparison of photon and proton treatment techniques for chondrosarcoma of thoracic spine. Med Dosim
    Yadav P, Paliwal BR, Kozak K
    2013; 38 (3): 233-7
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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.

      View details for PubMedID 23541524
  • Feasibility study on effect and stability of adaptive radiotherapy on kilovoltage cone beam CT. Radiol Oncol
    Yadav P, Ramasubramanian V, Paliwal BR
    2011 Sep; 45 (3): 220-6
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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.

      View details for PubMedID 22933960
  • Postmastectomy radiotherapy with integrated scar boost using helical tomotherapy. Med Dosim
    Rong Y, Yadav P, Welsh JS, Fahner T, Paliwal B
    2012; 37 (3): 233-9
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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.

      View details for PubMedID 22365416
  • Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding. Med Dosim
    Yadav P, Kozak K, Tolakanahalli R, Ramasubramanian V, Paliwal BR, Welsh JS, Rong Y
    2012; 37 (2): 157-62
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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.

      View details for PubMedID 21925866
  • A planning study for palliative spine treatment using StatRT and megavoltage CT simulation. J Appl Clin Med Phys
    Rong Y, Yadav P, Paliwal B, Shang L, Welsh JS
    2010 Oct 30; 12 (1): 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.

      View details for PubMedID 21330983
  • The effect and stability of MVCT images on adaptive TomoTherapy. J Appl Clin Med Phys
    Yadav P, Tolakanahalli R, Rong Y, Paliwal BR
    2010 Jul 02; 11 (4): 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.

      View details for PubMedID 21081878

Contact Information

Poonam Yadav, PhD

600 Highland Avenue,
Madison, WI 53792