Characteristics of elliptical sources in BEAMnrc Monte Carlo system: Implementation and application

摘要: Recently, several papers noticed that the electron focal spot of a linear accelerator (linac) could be elliptical which would cause dosimetric discrepancies between measurements and Monte Carlo simulations. To resolve mismatch, two source models were developed in BEAMnrc code. The first was parallel beam with uniform distribution where shape primarily considered. other Gaussian whose follows normal distribution. validate models, beams impinged on thin air target. Both successfully reproduced shapes distributions. Then, this study investigated characteristics for 6 MV photon Varian 21EX linac. linac head model implemented BEAMnrc/EGSnrc system commissioned by comparing lateral depth dose profiles to ion chamber acquired from annual quality assurance (QA). It found circular MeV/0.2 cm full width half maximum (FWHM) produces best matches QA data. explore source, employed an ellipticalmore » 0.1 FWHM x axis 0.2 y incident target head. Two compare differences sources. For all sources, planar energy fluences analyzed. This also compared water phantom using DOSXYZnrc user In results, constricted shoulder effect observed both fluence plots when value increased field size is larger than 30x30 cm{sup 2}. same profiles, while profile did not vary much.« less