Ultra‐high dose rate dosimetry: Challenges and opportunities for FLASH radiation therapy

Abstract

The clinical translation of FLASH radiotherapy (RT) requires challenges related to dosimetry and beam monitoring of ultra‐high dose rate (UHDR) beams to be addressed. Detectors currently in use suffer from saturation effects under UHDR regimes, requiring the introduction of correction factors. There is significant interest from the scientific community to identify the most reliable solutions and suitable experimental approaches for UHDR dosimetry. This interest is manifested through the increasing number of national and international projects recently proposed concerning UHDR dosimetry. Attaining the desired solutions and approaches requires further optimization of already established technologies as well as the investigation of novel radiation detection and dosimetry methods. New knowledge will also emerge to fill the gap in terms of validated protocols, assessing new dosimetric procedures and standardized methods. In this paper, we discuss the main challenges coming from the peculiar beam parameters characterizing UHDR beams for FLASH RT. These challenges vary considerably depending on the accelerator type and technique used to produce the relevant UHDR radiation environment. We also introduce some general considerations on how the different time structure in the production of the radiation beams, as well as the dose and dose‐rate per pulse, can affect the detector response. Finally, we discuss the requirements that must characterize any proposed dosimeters for use in UDHR radiation environments. A detailed status of the current technology is provided, with the aim of discussing the detector features and their performance characteristics and/or limitations in UHDR regimes. We report on further developments for established detectors and novel approaches currently under investigation with a view to predict future directions in terms of dosimetry approaches, practical procedures, and protocols. Due to several on‐going detector and dosimetry developments associated with UHDR radiation environment for FLASH RT it is not possible to provide a simple list of recommendations for the most suitable detectors for FLASH RT dosimetry. However, this article does provide the reader with a detailed description of the most up‐to‐date dosimetric approaches, and describes the behavior of the detectors operated under UHDR irradiation conditions and offers expert discussion on the current challenges which we believe are important and still need to be addressed in the clinical translation of FLASH RT.

Dual beam‐current transformer design for monitoring and reporting of electron ultra‐high dose rate (FLASH) beam parameters

“… 11 However, BCTs have two main limitations relative to traditional transmission chambers: (1) their inability to monitor the beam's spatial profile (flatness and symmetry) and (2) their utility in monitoring the beam is limited to charged particles only. 13 …”

Absolute dosimetry for FLASH proton pencil beam scanning radiotherapy

“…Dosimetry at UHDR is complicated and it is essential to understand the effects that impact detector response in this radiotherapy modality. An extensive review on detectors used in UHDR beams can be found in 25 . The use of a Faraday cup for the commission of a beam monitor at UHDR has been reported 26 .…”

Radiation Hardness Study of Silicon Carbide Sensors under High-Temperature Proton Beam Irradiations

“…In the experiment described in this work, an SiC membrane sensor was used, produced by the SenSiC company [ 10 ]. SiC membranes have recently demonstrated promising hard X-ray beam position monitoring capabilities [ 11 ], as well as promising ultra-high-dose-rate electron beam dosimetry monitoring capabilities, in the so-called Flash Radiotherapy application [ 12 , 13 ]. These devices are semiconductor PiN junctions: they are composed of a thin, 0.3 m p highly doped ( cm ) layer and a 20 m n low-doped ( cm ) layer on top of a ∼370 m thick n ( cm ) substrate.…”