The probe‐format graphite calorimeter, Aerrow, for absolute dosimetry in ultrahigh pulse dose rate electron beams

Abstract

Purpose The purpose of this investigation is to evaluate the use of a probe‐format graphite calorimeter, Aerrow, as an absolute and relative dosimeter of high‐energy pulse dose rate (UHPDR) electron beams for in‐water reference and depth–dose‐type measurements, respectively. Methods In this paper, the calorimeter system is used to investigate the potential influence of dose per pulses delivered up to 5.6 Gy, the number of pulses delivered per measurement, and its potential for relative measurement (depth–dose curve measurement). The calorimeter system is directly compared against an Advanced Markus ion chamber. The finite element method was used to calculate heat transfer corrections along the percentage depth dose of a 20‐MeV electron beam. Monte Carlo–calculated dose conversion factors necessary to calculate absorbed dose‐to‐water at a point from the measured dose‐to‐graphite are also presented. Results The comparison of Aerrow against a fully calibrated Advanced Markus chamber, corrected for the saturation effect, has shown consistent results in terms of dose‐to‐water determination. The measured reference depth is within 0.5 mm from the expected value from Monte Carlo simulation. The relative standard uncertainty estimated for Aerrow was 1.06%, which is larger compared to alanine dosimetry (McEwen et al. https://doi.org/10.1088/0026-1394/52/2/272) but has the advantage of being a real‐time detector. Conclusion In this investigation, it was demonstrated that the Aerrow probe–type graphite calorimeter can be used for relative and absolute dosimetries in water in an UHPDR electron beam. To the author's knowledge, this is the first reported use of an absorbed dose calorimeter for an in‐water percentage depth–dose curve measurement. The use of the Aerrow in quasi‐adiabatic mode has greatly simplified the signal readout, compared to isothermal mode, as the resistance was directly measured with a high‐stability digital multimeter.

Metrology for advanced radiotherapy using particle beams with ultra-high dose rates

“…To evaluate the suitability of the probe calorimeter as a relative and absolute secondary standard for UHDR pulsed electron beam (Bourgouin et al 2022c), the calorimeter was tested at the UHDR reference electron beam facility at PTB (Bourgouin et al 2022b). In this investigation, the calorimeter was exposed to a range of DPP up to 5.6 Gy.…”

Thermal neutron detection and track recognition method in reference and out-of-field radiotherapy FLASH electron fields using Timepix3 detectors

“…The ICT signal has been cross calibrated against the absolute charge measurement using a Faraday cup and absolute dose to water using alanine dosimeters (Bourgouin et al 2022a). The ICT signal can measure the total charge of individual beam pulses (Schüller et al 2017), which is typically between 30 and 230 nC (Bourgouin et al Bourgouin 2022b,2022c. In addition, a calibrated FlashDiamond detector prototype (Kranzer et al 2022, Bourgouin et al 2022a was placed in the middle of the two Timepix3 pixel detectors, to provide in-water monitoring of the dose rate.…”

The role of standards laboratories in reducing uncertainty in clinical dosimetry: A Canadian perspective

“…Preliminary data indicate that the overall uncertainty on dose determination can be significantly improved from the air kerma-based methods currently in use. Perhaps the best current example of coordinated dosimetry research in response to an emerging beam modality is the joint research project, UHDpulse, where NMI collaborators are trialing several new calorimeter systems for direct use in ultra-high dose rate (i.e., FLASH) and laser-driven particle beams [15][16][17]. At the NRC, work is underway characterize pyroelectric-based calorimeters capable of FLASH dosimetry that can be read out with only an electrometer [18].…”