Microdosimetry spectra and RBE of H-1, He-4, Li-7 and C-12 nuclei in water studied with Geant4

TL;DR

This study uses Geant4 simulations to analyze microdosimetry spectra and RBE of various heavy-ion beams in water, providing insights into their potential for cancer therapy.

Contribution

It presents a detailed Monte Carlo model for simulating microdosimetry spectra and RBE of H-1, He-4, Li-7, and C-12 beams, including fragmentation effects and comparisons with experimental data.

Findings

Microdosimetry spectra are well matched with experiments near the Bragg peak.

Helium and lithium beams show promising RBE values for therapy.

Fragmentation reactions significantly influence microdosimetry spectra.

Abstract

A Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) is used to study radiation fields of H-1, He-4, Li-7 and C-12 beams with similar ranges (~160-180 mm) in water. Microdosimetry spectra are simulated for wall-less and walled Tissue Equivalent Proportional Counters (TEPCs) placed outside or inside a phantom, as in experiments performed, respectively, at NIRS, Japan and GSI, Germany. The impact of fragmentation reactions on microdosimetry spectra is investigated for He-4, Li-7 and C-12, and contributions from nuclear fragments of different charge are evaluated for various TEPC positions in the phantom. The microdosimetry spectra measured on the beam axis are well described by MCHIT, in particular, in the vicinity of the Bragg peak. However, the simulated spectra for the walled TEPC far from the beam axis are underestimated. Relative Biological Effectiveness (RBE) of the considered beams is estimated using a modified microdosimetric-kinetic model. Calculations show a similar rise of the RBE up to 2.2-2.9 close to the Bragg peak for helium, lithium and carbon beams compared to the modest values of 1-1.2 at the plateau region. Our results suggest that helium and lithium beams are also promising options for cancer therapy.