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Monte Carlo models for dosimetry in photon beam radiotherapy
Author(s) -
Fix Michael K.
Publication year - 2002
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 - 10.1118/1.1464550
Subject(s) - monte carlo method , dosimetry , photon , beam (structure) , physics , computational physics , optics , radiation , photon energy , spectral line , nuclear medicine , statistics , mathematics , medicine , astronomy
On the basis of phase space (PS) data Monte Carlo (MC) beam models for a 6 and 15 MV photon beam have been developed. This PS information was used to develop simple point source beam models. Since these models are lacking in flexibility and show limitations in modeling the beam outside the geometric radiation field a multiple source model (MSM) was developed. Original PS data and those reproduced by the MSM are then compared in terms of fluences and mean energies, which all agree within 1%. MC‐calculated primary photon energy spectra are verified by energy spectra derived from transmission measurements. Comparisons of MC‐calculated depth doses and profiles, using original and reproduced PS data, agree within 1% and 1 mm. Deviations from measured doses are within 1.5% and 1 mm. Additionally, the MSM was supplemented with a model of an 80‐leaf MLC. Using this supplemented MSM, dose distributions are calculated in water phantoms. Two test fields for the step‐and‐shoot technique and two realistic fields delivered with dynamic MLC are investigated. MC‐calculated dose profiles are in excellent agreement with measured data from film dosimetry. To assess spectral changes caused by the MLC, energy spectra in portal planes are calculated for moving slits of different widths. The investigation shows an increase in mean photon energy of up to 16% for the 0.25 cm slit compared to the open beam for 6 MV and of up to 6% for 15 MV, respectively. The supplemented MSM has proven to be a powerful tool for investigational and benchmarking purposes and for IMRT treatment planning.