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SU‐E‐T‐410: Clinical Application of Dose Reconstruction Based on Full‐Scope Monte Carlo Calculations
Author(s) -
Yeo I,
Xu Q,
Chen Y,
Jung J,
Kim J
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612364
Subject(s) - imaging phantom , monte carlo method , nuclear medicine , dosimetry , voxel , image guided radiation therapy , medical imaging , biomedical engineering , medicine , computer science , computer vision , artificial intelligence , mathematics , statistics
Purpose: To reconstruct dose delivered to a deformable phantom from images acquired by an electronic portal imaging device (EPID) using a full‐scope Monte Carlo based non‐iterative reconstruction method we have developed and to evaluate the delivered dose to the deformed organs using the resulting reconstructed dose. Methods: A deformable prostate phantom was embedded into a 20cm‐deep and 40cm‐wide water phantom. The phantom was CT scanned and the anatomical models of prostate, seminal vesicles, and rectum were contoured. A coplanar 4‐field IMRT plan was used for this study. The XVMC Monte Carlo code, XVMC, was used for verification of planned dose in phantom and calculation of dose response by EPID. Organ deformation was simulated by inserting a “transrectal” balloon containing 20ml of water and air. A new CT scan was obtained and the deformed structures were contoured. The IMRT plan was delivered to the two phantoms and integrated EPID images were respectively acquired. Dose reconstruction was performed using these images with calculated EPID responses. The deformed phantom was registered to the original phantom using an in‐house developed software based on the Demons algorithm. The transfer matrix for each voxel was obtained and used to correlate the two sets of the reconstructed dose to generate a cumulative reconstructed dose on the original phantom. Results: Forwardly calculated planning dose in the original phantom was compared to the cumulative reconstructed dose from EPID in the original phantom. The prescribed 200 cGy isodose lines showed little difference with respect to the “prostate” and “seminal vesicles”, but appreciable difference (3%) was observed at 210cGy dose level. Conclusions: The results validate our dose reconstruction method for EPID dosimetry. Organ deformation resulted small but observable dose changes in the target and critical structure. This study was in part supported by Varian Medical Systems, Inc.