Measurement of fluence, LET, and dose in a carbon ion spread-out Bragg-peak using fluorescent nuclear track detectors and an automated reader

TL;DR

This study evaluates fluorescent nuclear track detectors for measuring fluence, LET, and dose in a carbon ion spread-out Bragg peak, highlighting their accuracy and limitations in particle-energy quantification.

Contribution

It demonstrates the feasibility of using FNTDs with an automated reader to quantify ion beam parameters, identifying key sources of uncertainty and improvements over traditional methods.

Findings

Primary ion track densities matched reference data

Detector sensitivity uncertainty affects LET and dose accuracy

Proton fluence underestimated due to angular distribution effects

Abstract

For the assessment of radiation effects of clinical ion-beams, dosimetry has to be complemented by information on particle-energy distribution or related quantities. Fluorescence nuclear track detectors made from C,Mg-doped alumina single crystals allow for the quantification of ion track density and energy loss on a single-track basis. In this study, their feasibility and accuracy to quantify fluence, linear-energy-transfer (LET) distributions, and eventually dose for a spread-out carbon ion Bragg peak was investigated. We found that the primary ions track densities agreed well with the reference data, but the determination of the individual detector sensitivity represented a major source of uncertainty in LET (and dose) assessment. While low-LET fragments in the beam are not contributing to this dose significantly, their number of was largely underestimated by approximately a factor three. The effect was most pronounced for protons where the measured fluence deviates at least an order of magnitude. We conclude that this is mainly caused by the wide angular distribution of protons in a carbon beam. The use of a dedicated FNTD reader device and semi-automated workflow improved outcome due to the considerably larger amount of data available as compared to a state-of-the-art multi-purpose confocal laser scanning microscope.