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SU‐E‐T‐52: A Monte Carlo Model of the Varian IGRT Couch for RapidArc
Author(s) -
Teke T.,
Gill B.,
Popescu I.A.
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 - 10.1118/1.3612003
Subject(s) - monte carlo method , imaging phantom , hounsfield scale , image guided radiation therapy , ionization chamber , quality assurance , nuclear medicine , radiation treatment planning , medical physics , medicine , medical imaging , computed tomography , physics , radiation therapy , mathematics , radiology , statistics , ionization , ion , external quality assessment , pathology , quantum mechanics
Purpose: To evaluate the impact of the Varian IGRT treatment couch on quality assurance results and to present a Monte Carlo model of the IGRT couch that can be included on both a phantom and patient CT dataset. Methods: Three clinical RapidArc treatment plans were generated for various tumor sites. The correct set of Hounsfield Units for each part of the couch structure was determined experimentally. For each patient three verification plans were produced, one including the thick model of the couch, one including the thin model of the couch and one without any couch included. Monte Carlo dose calculations were performed in a water equivalent phantom for each of these plans. Various values of the physical densities for the couch shell were used. Results were compared to measurements using a calibrated Farmer ionization chamber with an active volume of 0.6 cm̂3. Comparison of RapidArc and Monte Carlo 3D doses was performed using a 3 dimensional Gamma‐factor analysis with a 3%/3mm DTA criteria. Results: Good agreement was observed between chamber measurements and the treatment planning system for each verification plans. Differences as high as 2.6% was observed between the calculated dose by the planning system with and without the couch. The optimal physical density to model the couch shell was determined to be 0.65g/cm̂3 giving the best agreement with both chamber measurements and the planning system with Gamma values below 1 in over 95% of the points considered for all plans. Conclusions: This work indicates the possibility to accurately model the Varian IGRT couch for Monte Carlo RapidArc simulations and to apply it on patient CT dataset.