SU‐FF‐T‐444: Validation and Benchmark of a Source Model for a Varian 6 MV Photon Beam Using Monte Carlo Calculations

Abstract

Purpose: Validation and benchmarking of a newly‐developed measurement‐driven source model based on Monte Carlo calculations. Method and Materials: A measurement‐driven model using the Dose Planning Method DPM dose calculation algorithm is being developed for use with Varian, Elekta, and Siemens 6 MV and 10 MV photon beams. The present work details the validation and benchmarking for the Varian 6 MV beam. The multi‐source model consists of a primary photon point source, an extra‐focal exponential disk source, and an electron contamination uniform disk source. The model accounts for fluence and off‐axis energy effects due to the flattening filter. Dose calculations for field sizes from 4 cm by 4 cm to 40 cm by 40 cm were performed and tested against the basic beam data measurements. In addition, an IMRT homogeneous plan, a stereotactic lung plan, and an IMRT lung plan were delivered to anthropomorphic phantoms housing TLD and radiographic film dosimeters for benchmark evaluations. Results: Comparisons between calculation and measurement of the PDD and dose profiles for all square field size configurations showed agreement within 2%/2 mm for 90% of the data tested. General agreement at the level of 3%/2mm for 85% of the data tested was found in both of the lung treatment plans. However, calculation of the highly modulated IMRT homogeneous plan showed an underestimation of dose of up to 8% locally in the center of the PTV. Conclusion: This work demonstrates a source model that is robust for the Varian 6 MV photon beam; however, only a simple MLC model that did not include the effects of the rounded leaf ends and interleaf leakage was used. We are currently evaluating a detailed MLC model to improve the agreement with measurement. Conflict of Interest: Work supported by PHS CA010953, CA081647, and R01 CA85181 awarded by NCI, DHHS. © 2009, American Association of Physicists in Medicine. All rights reserved.