Ultra-high dose rate dosimetry for pre-clinical experiments with mm-small proton fields

M Togno; K P Nesteruk; R Schäfer; S Psoroulas; D Meer; M Grossmann; J B Christensen; E G Yukihara; A J Lomax; D C Weber; S Safai

doi:10.1016/j.ejmp.2022.10.019

Ultra-high dose rate dosimetry for pre-clinical experiments with mm-small proton fields

Phys Med. 2022 Dec:104:101-111. doi: 10.1016/j.ejmp.2022.10.019. Epub 2022 Nov 14.

Authors

M Togno¹, K P Nesteruk², R Schäfer³, S Psoroulas³, D Meer³, M Grossmann³, J B Christensen⁴, E G Yukihara⁴, A J Lomax⁵, D C Weber⁶, S Safai³

Affiliations

¹ Center for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland. Electronic address: michele.togno@psi.ch.
² Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, USA.
³ Center for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland.
⁴ Department of Radiation Safety and Security, Paul Scherrer Institut, Villigen, Switzerland.
⁵ Center for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland; Department of Physics, ETH Zurich, Zurich, Switzerland.
⁶ Center for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland; Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland; Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Switzerland.

PMID: 36395638
DOI: 10.1016/j.ejmp.2022.10.019

Abstract

Purpose: To characterize an experimental setup for ultra-high dose rate (UHDR) proton irradiations, and to address the challenges of dosimetry in millimetre-small pencil proton beams.

Methods: At the PSI Gantry 1, high-energy transmission pencil beams can be delivered to biological samples and detectors up to a maximum local dose rate of ∼9000 Gy/s. In the presented setup, a Faraday cup is used to measure the delivered number of protons up to ultra-high dose rates. The response of transmission ion-chambers, as well as of different field detectors, was characterized over a wide range of dose rates using the Faraday cup as reference.

Results: The reproducibility of the delivered proton charge was better than 1 % in the proposed experimental setup. EBT3 films, Al₂O₃:C optically stimulated luminescence detectors and a PTW microDiamond were used to validate the predicted dose. Transmission ionization chambers showed significant volume ion-recombination (>30 % in the tested conditions) which can be parametrized as a function of the maximum proton current density. Over the considered range, EBT3 films, inorganic scintillator-based screens and the PTW microDiamond were demonstrated to be dose rate independent within ±3 %, ±1.8 % and ±1 %, respectively.

Conclusions: Faraday cups are versatile dosimetry instruments that can be used for dose estimation, field detector characterization and on-line dose verification for pre-clinical experiments in UHDR proton pencil beams. Among the tested detectors, the commercial PTW microDiamond was found to be a suitable option to measure real time the dosimetric properties of narrow pencil proton beams for dose rates up to 2.2 kGy/s.

MeSH terms

Protons*
Reproducibility of Results

Substances

Protons