Fetus dose calculation during proton therapy of pregnant phantoms using MCNPX and MCNP6.2 codes

TL;DR

This study uses Monte Carlo simulations with MCNPX and MCNP6.2 to accurately estimate fetal dose during proton therapy in pregnant women, highlighting the importance of phantom selection and particle contributions.

Contribution

It provides a comparative analysis of MCNPX and MCNP6.2 codes for fetal dose calculation in pregnant phantoms during proton therapy, including the impact of phantom geometry.

Findings

Fetal dose ranged from 0.4 to 0.8 μSv/Gy depending on the phantom.

Neutrons contributed the majority of the fetal dose, with photons accounting for about 20%.

Differences between code versions and phantoms affected dose estimates by up to 6% and a factor of two, respectively.

Abstract

Radiotherapy of pregnant cancer patients is not common, but when applied accurate assessment of the fetus dose is required, especially since the treatment planning systems are not able and do not allow accurate assessment of out-of-field doses. Proton therapy significantly reduces out-of-field doses, such as dose to the fetus, when compared to the photon radiotherapy techniques and as such could be promising for pregnant cancer patients. Within this study Monte Carlo calculations are performed on the three different computational phantoms representing pregnant women, all in second trimester of pregnancy. Simplified proton beam to the pregnant women brain was modelled, and the total dose equivalent (normalized per target dose) to the fetus was calculated. Between MCNPX and MCNP6.2 code versions we observed up to 6% difference. In this work 3 groups participated and the variation between the groups was 8% and 12% for MCNPX and MCNP6.2, respectively. Depending on the phantom used in the calculations the fetal dose was between 0.4 and 0.8 {\mu}Sv/Gy. Major contribution to the total dose came from the neutrons, with only 20% of the dose coming from photons, while other particles have negligible contributions. Results of the total dose equivalent differ by factor of two, when different phantoms were used, due to geometrical and anatomical characteristics of mother and fetus position.