Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

TL;DR

This study evaluates how polyethylene range compensators affect tumor dose in carbon-ion radiotherapy, finding that their impact is generally marginal and can be partly offset by secondary particle effects, with a small potential dose reduction.

Contribution

The paper introduces a two-component model to quantify the influence of polyethylene on carbon-ion dose attenuation and incorporates it into treatment planning, providing practical dose impact estimates.

Findings

Polyethylene causes 0.1-0.3%/cm dose attenuation.

RBE-weighted dose can decrease by up to 3%.

Typical clinical impact is within 1% dose reduction.

Abstract

\item[Purpose] A recent study revealed that polyethylene (PE) would cause extra carbon-ion attenuation per range shift by 0.45\%/cm due to compositional differences in nuclear interactions. The present study aims to assess the influence of PE range compensators on tumor dose in carbon-ion radiotherapy. \item[Methods] Carbon-ion radiation was modeled to be composed of primary carbon ions and secondary particles, for each of which the dose and the relative biological effectiveness (RBE) were estimated at a tumor depth in the middle of spread-out Bragg peak. Assuming exponential behavior for attenuation and yield of these components with depth, the PE effect on dose was calculated for clinical carbon-ion beams and was partly tested by experiment. The two-component model was integrated into a treatment-planning system and the PE effect was estimated in two clinical cases. \item[Results] The attenuation per range shift by PE was 0.1\%--0.3\%/cm in dose and 0.2\%--0.4\%/cm in RBE-weighted dose, depending on energy and range-modulation width. This translates into reduction of RBE-weighted dose by up to 3\% in extreme cases. In the treatment-planning study, however, the effect on RBE-weighted dose to tumor was typically within 1\% reduction. \item[Conclusions] The extra attenuation of primary carbon ions in PE was partly compensated by increased secondary particles for tumor dose. In practical situations, the PE range compensators would normally cause only marginal errors as compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response.