Exploring Offline Pileup Correction to Improve the Accuracy of Microdosimetric Characterization in Clinical Ion Beams

TL;DR

This paper introduces an offline stochastic resampling algorithm to correct pileup effects in microdosimetric spectra, enhancing measurement accuracy in clinical ion beam therapy.

Contribution

It presents a novel offline correction method for pileup in microdosimetry, adaptable to solid-state detectors in radiotherapy, improving data accuracy without hardware changes.

Findings

Successful pileup correction demonstrated on clinical data

Algorithm reduces pileup counts effectively

Potential to improve microdosimetric measurements in therapy settings

Abstract

Microdosimetry investigates the energy deposition of ionizing radiation at microscopic scales, beyond the assessment capabilities of macroscopic dosimetry. This contributes to an understanding of the biological response in radiobiology, radiation protection and radiotherapy. Microdosimetric pulse height spectra are usually measured using an ionization detector in a pulsed readout mode. This incorporates a charge-sensitive amplifier followed by a shaping network. At high particle rates, the pileup of multiple pulses leads to distortions in the recorded spectra. Especially for gas-based detectors, this is a significant issue, that can be reduced by using solid-state detectors with smaller cross-sectional areas and faster readout speeds. At particle rates typical for ion therapy, however, such devices will also experience pileup. Mitigation techniques often focus on avoiding pileup altogether, while post-processing approaches are rarely investigated. This work explores pileup effects in microdosimetric measurements and presents a stochastic resampling algorithm, allowing for offline simulation and correction of spectra. Initially it was developed for measuring neutron spectra with tissue equivalent proportional counters and is adapted for the use with solid-state microdosimeters in a clinical radiotherapy setting. The algorithm was tested on data acquired with solid-state microdosimeters at the MedAustron ion therapy facility. The successful simulation and reduction of pileup counts is achieved by establishing of a limited number of parameters for a given setup. The presented results illustrate the potential of offline correction methods in situations where a direct pileup-free measurement is currently not practicable.