Clinical implementation of a Monte Carlo treatment planning system

TLDR

The study aimed to implement Monte Carlo dose calculations for clinical radiotherapy. The authors used EGS4/BEAM and EGS4/DOSXYZ Monte Carlo codes, applying a multiple‑source model to generate accurate phase‑space data for Varian accelerators and to compute patient and phantom doses, then compared these results to conventional and IMRT planning systems. The multiple‑source model reduced phase‑space storage by 1,000× and simulation time by ≥10×, while Monte Carlo dose calculations agreed within 2% of measurements; however, compared to conventional TPS, MC differed by >5% in dose and >5 mm in isodose lines, especially for head‑and‑neck, lung, and breast cases.

Abstract

The purpose of this study was to implement the Monte Carlo method for clinical radiotherapy dose calculations. We used the EGS4/BEAM code to obtain the phase-space data for 6-20 MeV electron beams and 4, 6, and 15 MV photon beams for Varian Clinac 1800, 2100C, and 2300CD accelerators. A multiple-source model was used to reconstruct the phase-space data for both electron and photon beams, which retained the accuracy of the Monte Carlo beam data. The multiple-source model reduced the phase-space data storage requirement by 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 calculations and measurements of the dose distributions in homogeneous and heterogeneous phantoms for various field sizes, source-surface distances, and beam modulations. The Monte Carlo calculated electron output factors were within 2% of the measured values for various treatment fields while the heterogeneity 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 compared to the dose distributions produced by a conventional treatment planning system and an intensity-modulated radiotherapy inverse-planning system. Significant differences (>5% in dose and >5 mm shift in isodose lines) were found between Monte Carlo calculations and the analytical calculations implemented in the commercial systems. Treatment sites showing the largest dose differences were for head and neck, lung, and breast cases.