Calibration of intensity spectra from fluorescent nuclear track detectors in clinical ion beams

Abstract

Fluorescent nuclear track detectors (FNTDs) can play an important role in determining energy deposition and ionization density on a cellular level in clinical ion beams but due to the considerable variability in detector sensitivity a universal relation between fluorescence intensity and linear energy transfer (LET) might not be applicable. In this study, we present a method to calibrate individually each FNTD from an automated read-out using reference data. This then enables FNTDs to characterize local radiation fields more accurately. We found that the method can be successfully applied to a broad range of radiation fields (clinical proton, helium and carbon ion beams) and that the inclusion criterion for fluorescence intensity is key in matching the detection rate of lower-LET particles. In case of carbon beams, the detection of secondary protons with their distribution in polar angle is, however, critically undermined by their apparent similarity to secondary electron tracks and spurious tracks from detector and readout noise. Further methodological improvements in crystal and readout technology might allow to mitigate this effect.