Calorimeter for Real-Time Dosimetry of Pulsed Ultra-High Dose Rate Electron Beams

Alexandra Bourgouin,Malcolm McEwen,Rafael Kranzer,Andreas Schüller,Thomas Hackel,Ralf-Peter Kapsch,Daniela Poppinga

doi:10.3389/fphy.2020.567340

Abstract

An aluminium calorimeter was investigated as a possible real-time dosimeter for electron beams with ultra-high dose per pulse (DPP) as clinical applied at FLASH radiation therapy (1.5 Gy/pulse). Ion chambers, the most widely used active dosimeter type in conventional external beam radiation therapy, suffer very large ion recombination losses at these conditions. Passive dosimeters, as e.g. alanine, are independent of dose rate but do not provide real-time readout. In this work it is shown that the response of alanine is independent of the DPP in the investigated ultra-high DPP range (up to 2.3 Gy/pulse). Alanine dose measurements were then used to determine the ion recombination correction for an Advanced Markus parallel-plate ion chamber at ultra-high DPP. Ion collection losses larger than 50 % were observed. Therefore, ion chambers are not considered suitable for accurate dosimetry in FLASH radiation therapy. As alternative an aluminium open-to-atmosphere calorimeter, operated in quasi-adiabatic mode was investigated at ultra-high DPP electron radiation. The beam pulse charge, and thus the DPP, was varied to evaluate the linearity of the calorimeter response in the DPP range between 0.3 and 1.8 Gy/pulse. On average, the standard deviation of the calorimeter response was 0.1 %. The response was proportional to the DPP in the investigated range. The average deviation of

Highlights

FLASH radiation therapy is a promising new cancer therapy modality in the early stages of development
Ionization chambers used for dosimetry in conventional radiation therapy are not considered suitable for accurate dosimetry in FLASH radiotherapy
Three detector systems were investigated for the accurate dosimetry of electron beams with ultra-high dose per pulse (DPP)

Summary

Introduction

FLASH radiation therapy is a promising new cancer therapy modality in the early stages of development. A number of studies support the hypothesis that this novel treatment modality could significantly reduce the adverse side effects of radiation therapy on the healthy tissue exposed to Calorimeter for Real-Time FLASH Dosimetry radiation for equal dose delivery [1,2,3,4,5,6], this is the so-called FLASH effect. Most of the pre-clinical studies investigating the FLASH effect have been done so far with electron radiation fields generated by dedicated linear accelerators [7, 8] or modified clinical linear accelerators [9, 10] using radiation pulses of an ultrahigh dose per pulse (DPP). The patient received radiation with electrons in one fraction of 90 ms with 10 pulses of 1.5 Gy/pulse, corresponding to a mean dose rate of ∼167 Gy/s

Methods

Results

Discussion

Conclusion