MCNPX simulation of proton dose distributions in a water phantom

Abstract

Background: This study presents the Monte Carlo N-Particles Transport Code, Extension (MCNPX) simulation of proton dose distributions in a water phantom. Methods:In this study, fluence and dose distributions from an incident proton pencil beam were calculated as a function of depth in a water phantom. Moreover, lateral dose distributions were also studied to understand the deviation among different MC simulations and the pencil beam algorithm. MCNPX codes were used to model the transport and interactions of particles in the water phantom using its built-in "repeated structures" feature. Mesh Tally was used in which the track lengths were distributed in a defined cell and then converted into doses and fluences. Two different scenarios were studied including a proton equilibrium case and a proton disequilibrium case. Results:For the proton equilibrium case, proton fluence and dose in depths beyond the Bragg peak were slightly perturbed by the choice of the simulated particle types. The dose from secondary particles was about three orders smaller, but its simulation consumed significant computing time. This suggests that the simulation of secondary particles may only be necessary for radiation safety issues for proton therapy. For the proton disequilibrium case, the impacts of different multiple Coulomb scattering (MCS) models were studied. Depth dose distributions of a 70 MeV proton pencil beam in a water phantom obtained from MCNPX, Geometry and Track, version 4, and the pencil beam algorithm showed significant deviations between each other, because of different MCS models used. Conclusions: Careful modelling of MCS is necessary when proton disequilibrium exists.( Biomed J 2015;38:414-420)

Fundamentos de Transporte e Cálculo de Dose em Tratamentos com Feixes de Prótons

“…A componente de dose devido a partículas secundárias é cerca de três ordens de grandeza menor. Assim, essas partículas tornam-se importantes para questões de radioproteção, mas não para fins terapêuticos 21 .…”

“…O principal mecanismo de interação dos prótons com a matéria se dá por meio do espalhamento elástico com o campo elétrico dos átomos. O modelo de multiespalhamento coulombiano (MSC) que descreve esse processo foi desenvolvido por Molière em 1947 21 . Devido à natureza estocástica dos eventos, a distribuição de prótons sofre um alargamento espacial e angular ao longo de sua propagação, que pode ser descrito aproximadamente por uma Gaussiana, previsto pela teoria de Fermi-Eyges 24 .…”

“…O efeito do espalhamento angular pode ser notado variando-se o tamanho do alvo considerado 21 . A Figura 6 apresenta as diferenças nos perfis de dose em profundidade para quatro diferentes tamanhos de alvo obtidos com o código MCNP6.…”

MCNPX’S Water Equivalent Thickness Simulation of Material with Different Density via Proton Beam Irradiation

“…On the other hand, Lee et al produce a paper on the MCNPX simulation of proton dose distribution in CT phantoms [13]. Apart from that, Lee C.C et al published a paper on MCNPX of proton dose distribution in water phantom that study the fluence and dose distribution of proton in water phantom [14]. Monte Carlo (MC) technique is preferred among the researcher due to its efficient & accurate WET computation competence to model the model of protons and secondary particles propagation [15][16].…”