On the accuracy of Monte Carlo based beam dynamics models for the degrader in proton therapy facilities

TL;DR

This paper compares Monte Carlo simulation codes to evaluate how accurately they model proton beam degradation in therapy facilities, impacting downstream beam dynamics predictions and facility performance understanding.

Contribution

It introduces a comparative analysis of four Monte Carlo codes for modeling a graphite degrader in proton therapy, highlighting their influence on beam dynamics accuracy.

Findings

Different Monte Carlo codes produce varying energy spectra and phase space distributions.

The accuracy of the degrader model significantly affects downstream beam transport predictions.

Simplified routines can be effective but may lack detailed interaction modeling.

Abstract

In a cyclotron-based proton therapy facility, the energy changes are performed by means of a degrader of variable thickness. The interaction of the proton beam with the degrader creates energy tails and increases the beam emittance. A precise model of the degraded beam properties is important not only to better understand the performance of a facility already in operation, but also to support the development of new proton therapy concepts. The exact knowledge of the degraded beam properties, in terms of energy spectrum and transverse phase space, depends on the model used to describe the proton interaction with the degrader material. In this work the model of a graphite degrader has been developed with four Monte Carlo codes: three conventional Monte Carlo codes (FLUKA, GEANT4 and MCNPX) and the multi-purpose particle tracking code OPAL equipped with a simplified Monte Carlo routine. From the comparison between the different codes, we can deduce how the accuracy of the degrader model influences the precision of the beam dynamics model of a possible transport line downstream of the degrader.