Adaptation and dosimetric commissioning of a synchrotron-based proton beamline for FLASH experiments

Abstract

Objective. Irradiation with ultra-high dose rates (>40 Gy/s), also known as FLASH irradiation, has the potential to shift the paradigm of radiation therapy because of its reduced toxicity to normal tissues compared to that of conventional irradiations. The goal of this study was to (1) achieve FLASH irradiation conditions suitable for pre-clinical in-vitro and in-vivo biology experiments using our synchrotron-based proton beamline and (2) commission the FLASH irradiation conditions achieved. Approach. To achieve these suitable FLASH conditions, we made a series of adaptations to our proton beamline, including modifying the spill length and size of accelerating cycles, repurposing the reference monitor for dose control, and expanding the field size with a custom double-scattering system. We performed the dosimetric commissioning with measurements using an Advanced Markus chamber and EBT-XD films as well as with Monte Carlo simulations. Main results. Through adaptations, we have successfully achieved FLASH irradiation conditions, with an average dose rate of up to 375 Gy/s. The Advanced Markus chamber was shown to be appropriate for absolute dose calibration under our FLASH conditions with a recombination factor ranging from 1.002 to 1.006 because of the continuous nature of our synchrotron-based proton delivery within a spill. Additionally, the absolute dose measured using the Advanced Markus chamber and EBT-XD films agreed well, with average and maximum differences of 0.32% and 1.63%, respectively. We also performed a comprehensive temporal analysis for FLASH spills produced by our system, which helped us identify a unique relationship between the average dose rate and the dose in our FLASH irradiation. Significance. We have established a synchrotron-based proton FLASH irradiation platform with accurate and precise dosimetry that is suitable for pre-clinical biology experiments. The unique time structure of the FLASH irradiation produced by our synchrotron-based system may shed new light onto the mechanism behind the FLASH effect.

Dosimetric response of Gafchromic™ EBT‐XD film to therapeutic protons

“…A horizontal proton beamline (87.2 MeV) at the MD Anderson Proton Therapy Center was commissioned to deliver dose with different dose rates in either FLASH (>40 Gy/s) or non-FLASH mode. 21,22 Different F I G U R E 2 Illustration of experimental setup using the horizontal proton beamline. The first scatterer was used to broaden the beamlet laterally.…”

“…In the experiment using the research horizontal beamline, the film and the Advanced Markus chamber were irradiated simultaneously with the ion chamber downstream next to the film. In the FLASH mode, the ion collection efficiency of the Advanced Markus chamber was 99.5% (at 300 V), 21 making it suitable for accurate dose measurement in both FLASH and non-FLASH modes of the proton synchrotron.…”

“…The output dose fluctuation (standard deviation/mean) of Gy/MU measured using the Advanced Markus chamber was 1.1% in the FLASH mode and 0.5% in the non-FLASH mode. 21 More details can be found in the commissioning report of the proton FLASH beamline. 21 The experimental setup is shown in Figure 2, and the actual experimental setup can be found in Figure S3 in the Supplementary Materials.…”

“…21 More details can be found in the commissioning report of the proton FLASH beamline. 21 The experimental setup is shown in Figure 2, and the actual experimental setup can be found in Figure S3 in the Supplementary Materials. The order of components in the setup along the beam direction was as follows: plastic water phantom buildup, film, and Advanced Markus chamber without the protection cap.…”

PyMedPhys: A community effort to develop an open, Python-based standard library for medical physics applications

“…Many of these tools are in use clinically at affiliated sites, and additionally, aspects of PyMedPhys are implemented around the world for some applications. Many parties have embraced the gamma analysis module (Castle et al, 2022;Cronholm et al, 2020;Gajewski et al, 2021;Galić et al, 2020;Lysakovski et al, 2021;Milan et al, 2019;Pastor-Serrano & Perkó, 2021;Rodrıǵuez et al, 2020;Spezialetti et al, 2021;Tsuneda et al, 2021;Yang et al, 2022), while implementations of the electron cutout factor module and others (Baltz & Kirsner, 2021;Douglass & Keal, 2021;Rembish, 2021) have also been reported. Additionally, the work has been recognized by the European Society for Radiotherapy and Oncology (ESTRO) and referenced as recommended literature in their 3rd Edition of Core Curriculum for Medical Physics Experts in Radiotherapy (Bert et al, 2021).…”