MMC - A HIGH-PERFORMANCE MONTE-CARLO CODE FOR ELECTRON-BEAM TREATMENTPLANNING

The macro Monte Carlo (MMC) method has been developed to improve the s peed of traditional Monte Carlo (Me) high-energy electron transport ca lculations without loss in accuracy. The MMC algorithm uses results de rived from conventional Me simulations of electron transport through m acroscopic spheres of various radii and consisting of a variety of med ia. Based on these results, electrons are transported in macroscopic s teps through the absorber. The absorber geometry is represented by a t hree-dimensional (3D) density matrix, typically derived from computer tomographic (CT) data. Energy lost by the electrons along their paths through the absorber is scored in a 3D dose matrix. Transport of secon dary electrons and bremsstrahlung photons is taken into account. Major modifications of the original implementation of the MMC algorithm hav e resulted in an improved version of the code, resolving earlier probl ems with electron transport across interfaces of different materials, and running at a substantially higher speed. Furthermore, the code has been integrated into a clinical 3D treatment planning system. MMC res ults are in good agreement with results from conventional MC codes and are obtained with a speed gain of about one order of magnitude for cl inically relevant irradiation situations. Calculation times to obtain a relative statistical accuracy of 2% per dose grid voxel for small el ectron field sizes are short enough to be routinely useful in radiothe rapy clinics on present day affordable workstation computers. Consider ing speed, accuracy and memory requirements, MMC is a promising altern ative to currently available electron dose planning algorithms.