Recent developments in absolute dosimetry for FLASH radiotherapy

Abstract

Ultra-high dose-rate (UHDR) irradiations, known as FLASH radiotherapy (RT), rely on delivery of therapeutic doses at instantaneous dose-rates several orders of magnitude higher than those currently used in conventional radiotherapy. It has been shown that such an extremely short delivery of radiation leads to remarkable reduction of normal tissue toxicity with respect to conventional dose-rate RT. However, dosimetry at UHDRs is complicated and it is essential to understand the effects that will influence detector response. To date, FLASH RT research has been focused on finding pragmatic solutions that allow the use of UHDR beams in the research setting, but there has been limited focus on absolute dosimetry utilizing primary and secondary standard devices. However, very recently the data on existing standard dosimeters and novel solutions which could serve as secondary standard devices in UHDR dosimetry started emerging. This review provides an overview of the studies that have been conducted employing calorimeters and innovative solutions utilizing ionization chambers.

Electron FLASH radiotherapy in vivo studies. A systematic review

“…Beam monitoring, which is fundamental for clinical LINAC, is performed through an ionization chamber to ensure that the real-time dose delivered matches with what has been planned. However, the commonly available ionization chambers experience a process of saturation with UHDR pulsed beams, and therefore the early experiments with UHDR did not have a beam monitor system able to assure the right beam erogation ( 66 – 68 ).…”

“…These novel tools are able to adequately measure the target dose online ( 74 ). The availability of research dedicated linacs, such as the Sordina IORT Technologies S.p.A. (SIT) ElectronFlash ( 75 ), which guarantee a reliable beam delivery and real time beam monitoring through AC current transformers (ACCT) as well as active dosimetry solutions ( 66 , 70 , 71 , 76 – 78 ), can significantly improve the biological and clinical research in the field of electron FLASH-RT. Moreover, the evaluation of dose distribution is another critical aspect of RT, since in vivo irradiation of inhomogeneous tissues with charged particles does not produce homogeneous dose-distribution.…”

Beam control system and output fine-tuning for safe and precise delivery of FLASH radiotherapy at a clinical linear accelerator

“…Another limitation of this study is reliance of radiochromic film for absolute dose measurements, as these dosimeters have an intrinsic uncertainty of 3%. Recent advancements on FLASH-compatible ion chambers and calorimeters offer promising alternatives for achieving more accurate absolute dose measurements in the future ( 26 ).…”

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

“…Moreover, thanks to ultra-short delivery times in UHDR exposures, uncertainties related to evaluation of heat transfer effects and determination of temperature rise itself will be smaller than in conventional dose rate RT. A recently published review by (Subiel and Romano 2023) provides a detailed overview of calorimeters and their application in UHDR dosimetry together with a list of advantages and disadvantages of calorimetric methods. In addition to calorimetry, Fricke dosimetry is an independent primary standard for absorbed dose to water in UHDR electron beams.…”