Clinical implementation of a Monte Carlo treatment planning system

The purpose of this study was to implement the Monte Carlo method for clini cal radiotherapy dose calculations. We used the EGS4/BEAM code to obtain th e phase-space data for 6-20 MeV electron beams and 4, 6, and 15 MV photon b eams for Varian Clinac 1800, 2100C, and 2300CD accelerators. A multiple-sou rce model was used to reconstruct the phase-space data for both electron an d photon beams, which retained the accuracy of the Monte Carlo beam data. T he multiple-source model reduced the phase-space data storage requirement b y a factor of 1000 and the accelerator simulation time by a factor of 10 or more. Agreement within 2% was achieved between the Monte Carlo calculation s and measurements of the dose distributions in homogeneous and heterogeneo us phantoms for various field sizes, source-surface distances, and beam mod ulations. The Monte Carlo calculated electron output factors were within 2% of the measured values for various treatment fields while the heterogeneit y correction factors for various lung and bone phantoms were within 1% for photon beams and within 2% for electron beams. The EGS4/DOSXYZ Monte Carlo code was used for phantom and patient dose calculations. The results were c ompared to the dose distributions produced by a conventional treatment plan ning system and an intensity-modulated radiotherapy inverse-planning system . Significant differences (>5% in dose and >5 mm shift in isodose lines) we re found between Monte Carlo calculations and the analytical calculations i mplemented in the commercial systems. Treatment sites showing the largest d ose differences were for head and neck, lung, and breast cases. (C) 1999 Am erican Association of Physicists in Medicine. [S0094-2405(99)00710-5].