Comparison of EGS4 and MCNP4b Monte Carlo codes for generation of photon phase space distributions for a Varian 2100C

Abstract

Monte Carlo based dose calculation algorithms require input data or distributions describing the phase space of the photons and secondary electrons prior to the patient-dependent part of the beam-line geometry. The accuracy of the treatment plan itself is dependent upon the accuracy of this distribution. The purpose of this work is to compare phase space distributions (PSDs) generated with the MCNP4b and EGS4 Monte Carlo codes for the 6 and 18 MV photon modes of the Varian 2100C and determine if differences relevant to Monte Carlo based patient dose calculations exist. Calculations are performed with the same energy transport cut-off values. At 6 MV, target bremsstrahlung production for MCNP4b is approximately 10% less than for EGS4, while at 18 MV the difference is about 5%. These differences are due to the different bremsstrahlung cross sections used in the codes. Although the absolute bremsstrahlung production differs between MCNP4b and EGS4, normalized PSDs agree at the end of the patient-independent geometry (prior to the jaws), resulting in similar dose distributions in a homogeneous phantom. EGS4 and MCNP4b are equally suitable for the generation of PSDs for Monte Carlo based dose computations.

Suggesting a new design for multileaf collimator leaves based on Monte Carlo simulation of two commercial systems

“…( 19 ) The first stage is computation through the patient‐independent part of the beam‐line apparatus, up to a plane just upstream of the accelerator jaws. This is referred to as the “patient‐independent beam‐line Monte Carlo simulation” or the “patient‐independent simulation”.…”

“…( 9 , 20 ) The incident electrons possessed an energy distribution with a Gaussian outline with a center at 6.5 MeV for 6 MV beam and FWHM of 0.5 MeV (Varian Oncology Systems Ltd.). As with the study by Siebers et al, ( 19 ) the photon energy transport cutoff was set to 0.01 MeV, while the electron kinetic energy cutoff was 0.189 MeV. The simulation runs in the patient‐independent stage used no variance reduction while, for the patient‐specific portion, variance reduction techniques like geometry splitting and Russian roulette were used.…”

Dosimetria dos sistemas de radiocirurgia estereotáxica com aceleradores lineares equipados com colimadores micro multi-lâminas

“…As recomendações de trabalhos anteriores [13,31,32,41] indicam que uma descrição por espaço de fases de feixes clínicos utilizados em radioterapia necessita da ordem de 10 8 "partículas" para fornecer resultados com incerteza estatística adequada.…”

“…O MCNP usa uma base de dados contendo seções de choque do código ITS e os poderes de frenagem que a princípio eram equivalentes aos do ICRU-37 [43] , mas como mostrado por Siebers e colaboradores [41] podiam diferir significativamente, por exemplo, para um alvo de tungstênio. No pacote do MCNP está contido o gerador XGEN para produzir os dados dos diversos materiais e energias.…”

“…computacional, ou mesmo os conjuntos (os chamados "clusters") de computadores [13,31,41] , nos quais diversos processadores são interligados para dividir a tarefa de simulação.…”