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Comparison of dose calculation algorithms with Monte Carlo methods for photon arcs
Author(s) -
Chow James C. L.,
Wong Eugene,
Chen Jeff Z.,
Van Dyk Jake
Publication year - 2003
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 - 10.1118/1.1601331
Subject(s) - monte carlo method , imaging phantom , isocenter , photon , physics , monte carlo method for photon transport , computational physics , dosimetry , beam (structure) , optics , nuclear medicine , mathematics , hybrid monte carlo , markov chain monte carlo , statistics , medicine
The objective of this study is to seek an accurate and efficient method to calculate the dose distribution of a photon arc. The algorithms tested include Monte Carlo, pencil beam kernel (PK), and collapsed cone convolution (CCC). For the Monte Carlo dose calculation, EGS4/DOSXYZ was used. The SRCXYZ source code associated with the DOSXYZ was modified so that the gantry angle of a photon beam would be sampled uniformly within the arc range about an isocenter to simulate a photon arc. Specifically, photon beams (6/18 MV, 4 × 4 and 10 × 10 cm 2 ) described by a phase space file generated by BEAM (MCPHS), or by two point sources with different photon energy spectra (MCDIV) were used. These methods were used to calculate three‐dimensional (3‐D) distributions in a PMMA phantom, a cylindrical water phantom, and a phantom with lung inhomogeneity. A commercial treatment planning system was also used to calculate dose distributions in these phantoms using equivalent tissue air ratio (ETAR), PK and CCC algorithms for inhomogeneity corrections. Dose distributions for a photon arc in these phantoms were measured using a RK ion chamber and radiographic films. For homogeneous phantoms, the measured results agreed well ( ∼ 2 % error) with predictions by the Monte Carlo simulations (MCPHS and MCDIV) and the treatment planning system for the 180 ° and 360 ° photon arcs. For the dose distribution in the phantom with lung inhomogeneity with a 90 ° photon arc, the Monte Carlo calculations agreed with the measurements within 2%, while the treatment planning system using ETAR, PK and CCC underestimated or overestimated the dose inside the lung inhomogeneity from 6% to 12%.