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Year : 2019  |  Volume : 15  |  Issue : 9  |  Page : 296-297

Best paper for medical physicist

Date of Web Publication28-Nov-2019

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How to cite this article:
. Best paper for medical physicist. J Can Res Ther 2019;15, Suppl S2:296-7

How to cite this URL:
. Best paper for medical physicist. J Can Res Ther [serial online] 2019 [cited 2021 May 16];15:296-7. Available from: https://www.cancerjournal.net/text.asp?2019/15/9/296/271701

 > Abstract: A novel approach for voxel based radiobiological evaluation of the two-phase sequential radiotherapy treatment plans with different dose regimens Top

Gaganpreet Singh1,2, Balbir Singh1, Arun S. Oinam2, Rose Kamal1, Deepak Thaper1, Bhumika Handa1, Vivek Kumar1, Narendra Kumar2

1Centre for Medical Physics, Panjab University, 2Department of Radiotherapy, PGIMER, Chandigarh, India, E-mail: [email protected]

Introduction: Plan evaluation in radiotherapy is a critical step where expertise and skills of the radiation oncologist is required before making any decision. Two phase sequential treatment plans with different dose distribution are still difficult to evaluate without appropriate knowledge of radiobiology. Commercial treatment planning systems (TPS) are not capable to solve this kind of problem. To address this problem, the present work introduces a novel approach for voxel based radiobiological evaluation of the two-phase sequential radiotherapy treatment plans with different dose regimens. Methods: A patient of carcinoma prostate was selected randomly for demonstration of proposed approach. For the prostate case, radiotherapy treatment plans were made with the VMAT technique using Eclipse TPS version 11.0 (Varian Medical System, Palo Alto, CA, USA). In the first phase, a dose of 52 Gy in 26 fractions to the PTV and in the second phase, a dose of 19.5 Gy in 3 fractions to the PTV Boost were prescribed in the two phase treatment plans. A MATLAB R2011b (The MathWorks, Natick, MA) based in-house developed program called “Voxel based radiobiology display tool or VRb tool” was used for making the Plan Sum of first and second phase treatment plans exported from the TPS in DICOMRT format. Using VRb tool, physical Dose-Cube (dose distribution) was converted into BED and EQD2-Cube using LQ and LQ-L fractionation correction strategy and tissue specific radio-sensitivity parameters (α/β). The differential and cumulative dose volume histograms (DVHs) were reconstructed from the Plan Sum dose distribution and used for calculation of the tumor control probability (TCP) and normal tissue complication probability (NTCP) using radiobiological formulism. Results: A GUI based fully three dimensional (3D) evaluation of the two-phase sequential radiotherapy treatment plans is provided in the form of: (1) reconstructed physical dose, BED- and EQD2 -colorwash. (2) reconstructed physical dose, BED- and EQD2-volume histograms from the Plan Sum dose distribution respectively. For the prostate case, maximum values for physical dose, EQD2- and BED-Cubes were 74.4 Gy, 94.8 Gy, and 218.7 Gy were obtained respectively. TCP calculated for the target volume was 90.5% and NTCP calculated for bladder and rectum was 0.3% and 0.0% respectively for the Plan Sum. Conclusion: The proposed method is an extension of the VRb tool for two phase sequential radiotherapy treatment plans. It provides an independent platform for radiobiological evaluation of the two phase sequential treatment plans with different dose regimens which will be a promising tool in radiotherapy.

 > Abstract: Radiobiological modelling of clinical data of radiation induced severe acute rectal mucositis resulting from carcinoma cervix radiotherapy: An institutional study Top

Balbir Singh1,2, Gaganpreet Singh3, Arun S. Oinam3, Vivek Kumar1, P. Parsanth2, Rajesh Vashistha2, Manjinder Singh2

1Centre for Medical Physics, Panjab University, 3Department of Radiation Oncology, PGIMER, Chandigarh, 2Department of Radiation Oncology, Max Hospital, Bathinda, Punjab, India, E-mail: [email protected]

Aims and Objective: A normal tissue complication probability (NTCP) model of severe acute rectal mucositis would be highly useful to guide clinical decision making and inform radiotherapy planning. The aim of this study was to calculate the NTCP by determining the radiobiological parameters n, m, TD50, from the fitted dose response curve.The radiobiological model was used for best fit of the observed rectal mucositis toxicity data of the clinical outcomes of the patients which gives dose response sigmoidal shape curve of parameters, where n is the dose-volume relationship parameter, m is a measure of the slope of the sigmoid curve represented by the integral of the normal distribution, TD50 is the uniform dose given to the entire OAR which results in a 50% risk of complication and is the slope of dose response. Materials and Methods: This is a single institutional prospective study of 28 patients of Ca Cervix which were available for rectal mucositis toxicity analysis with median age of 56 years (range 37-73 years). Wipro GE CT machine was used for patient CT planning. Focal Sim Monaco (version 5.11) was used for contouring OARs and normal structures using RTOG guidelines of cervix cancer. XiO TPS (version 5.0) with superposition algorithm was used to create patient IMRT plan with mean coverage of PTV by 95% of the prescribed dose. Patients were evaluated weekly for acute radiation mucositis toxicity and scoring (Grading) as per CTCAE (v4.03) protocol. Radiobiological parameters i.e. n, m, TD50 and were calculated from the sigmoidal dose response curve obtained from the clinical data of ca cervix patients. Indigenous MATLAB® program (version 2011b of Mathworks Inc.) was written to calculate the NTCP using LKB model utilizing radiobiological parameters. Results: Acute radiation toxicity for rectam in Carcinoma of cervix patients was calculated for the end point rectal mucositis. The n, m and TD50, parameters for Grade 1 and Grade 2 rectal mucositis from the fitted sigmoidal dose response curve are found to be 0.04,0.33, 22.89 (μ) ±1.15 (CI. 95%),1.23 and 0.04, 0.16, 40.69(μ) ± 2.04 (CI. 95%), 2.55 respectively and average NTCP for Grade 1 and Grade 2 are found to be 99.84%±0.02 and 89.16%±2,27 respectively. Conclusion: This study presents the fitting parameters for NTCP calculation of Grade-I and Grade-II toxicities of rectal mucositis in the ca cervix patients. Results showed the importance of radiobiological models based on the institutional data for the prediction of normal tissue toxicities which incorporates the socio-economic (health, environment and economic) conditions of the local patient. This study can be further extended for the large number of patients and for different sites.

 > Abstract: Early experience with three dimensional ultrasound based image guided radiotherapy Top

Hitesh Gandhi, Gautam Kumar Sharan, P. Shinde, K. Darekar, R. Mahajan

M. N. Budhrani Cancer Institute, Inlaks and Budhrani Hospital, Pune, Maharashtra, India, E-mail: [email protected]

Aim: To evaluate and compare prostate localization accuracy of Clarity™ 3D ultrasound system compared to on board kV cone beam computed tomography (kV-CBCT) during Prostate radiotherapy and to evaluate absolute Intra-fractional prostate motion from pre-treatment and post treatment 3D ultrasound scan during radiotherapy treatment. Materials and Methods: 15 prostate cancer patients underwent radical treatment were treated with VMAT with 70Gy/28#. All patients were immobilized using vacuum cushion. Established protocol of Full Bladder and empty rectum used for treatment. Planning CT and Reference Ultrasound 3D scan (SIM Scan) were taken at CT Simulator in same setup. Planning CT and Reference 3D USG scan was fused to generate Position reference volume (PRV) on 3D USG scan for prostate localization. During treatment Patient was set at fiducial marker to acquire pretreatment Clarity scan (3D USG GUIDE scan). Variation with respect to plan iso-center was noted. Again patient was set at fiducial marker to acquire pre-treatment Cone beam CT scan. Variation with respect to plan iso-center was noted. Post treatment Clarity 3D USG scan acquired after setting patient on fiducial mark to find out Intra-fraction prostate motion. Cone beam CT scan was acquired for these patients throughout treatment and Clarity scan was acquired on most of the days with an average of 19 days. Total number of pre-treatment and post treatment Clarity scan acquired was 277. Movement of the prostate was assessed by measuring shifts (tracking vs. reference) in the centroid of the PRV delineated. Throughout this study, QA was done using ultrasound phantom on a daily basis to test the calibration prior to the acquisition of patient data. Results: Target verification and patient alignment mean time noted was 93 seconds and 307 Seconds for Clarity system and On-board kV Cone-beam (kVCBCT) respectively. Median absolute Difference between Pre-Treatment Clarity and kVCBCT localization was 5.0 (0.1-39.1), 6.3 (0.1-34.5) mm and 4.4(0.1-36.2) mm along Lateral, Vertical and Longitudinal direction respectively. In overall 277 scans the median intra fraction prostate motion along lateral, vertical and longitudinal directions was 3.0 (0.0-29.7) mm, 2.6 (0.0-22.6) mm and 3.5 (0.0-35.9) mm respectively. Conclusion: Our early experience of Clarity system for image guidance concludes, 3D Ultrasound imaging is time durable compared to kVCBCT. Significant absolute difference between pre treatment 3D ultrasound and kVCBCT of prostate suggest that Ultrasound imaging can potentially reduce the chance of geographical prostate CTV miss. Intra-fraction prostate motion occurred predominantly in the posterior and inferior directions, but was statistically insignificant. Rectal volume changes, bladder volume changes, and patient respiration found to contribute to the Intra-fraction prostate movement. Adequate margin or 4D tracking of prostate will reduce the geometric miss due to intra fractional motion during treatment session. Acquiring ultrasound images requires special skill and expertise which reflects into increased frequency of specific absolute difference of 3D ultrasound scan and kVCBCT.


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