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Author Notes:

Serdar Charyyev, PhD, Department of Radiation Oncology, Stanford University School of Medicine, 875 Blake Wilbur Dr, Palo Alto, CA 94304, Tel: +1 (650)-724-9779, Email: charyyev@stanford.edu

CRediT: Serdar Charyyev: conceptualization, methodology, software, formal analysis, data acquisition, writing – original draft; Chih-Wei Chang: data curation, formal analysis, resources, software, writing – review and editing; Mingyao Zhu: formal analysis, data acquisition, writing – review and editing; Liyong Lin: conceptualization, data acquisition, resources, writing – review and editing; Katja Langen: data acquisition, writing – review and editing, supervision, resources; Anees Dhabaan: conceptualization, formal analysis, methodology, data acquisition, supervision, writing – original draft.

This article initially appeared on Cornell University's arXiv preprint website, a non-profit, open-access archive for scholarly articles (https://doi.org/10.48550/arXiv.2208.05037).

Katja Langen, PhD is an Associate Editor of the International Journal of Particle Therapy. The authors have no additional conflicts of interest to disclose.


Research Funding:

The authors have no funding to disclose.


  • commissioning
  • proton therapy

Characterization of 250 MeV Protons from the Varian ProBeam PBS System for FLASH Radiation Therapy.


Journal Title:

Int J Part Ther


Volume 9, Number 4


, Pages 279-289

Type of Work:

Article | Final Publisher PDF


Shoot-through proton FLASH radiation therapy has been proposed where the highest energy is extracted from a cyclotron to maximize the dose rate (DR). Although our proton pencil beam scanning system can deliver 250 MeV (the highest energy), this energy is not used clinically, and as such, 250 MeV has yet to be characterized during clinical commissioning. We aim to characterize the 250-MeV proton beam from the Varian ProBeam system for FLASH and assess the usability of the clinical monitoring ionization chamber (MIC) for FLASH use. We measured the following data for beam commissioning: integral depth dose curve, spot sigma, and absolute dose. To evaluate the MIC, we measured output as a function of beam current. To characterize a 250 MeV FLASH beam, we measured (1) the central axis DR as a function of current and spot spacing and arrangement, (2) for a fixed spot spacing, the maximum field size that achieves FLASH DR (ie, > 40 Gy/s), and (3) DR reproducibility. All FLASH DR measurements were performed using an ion chamber for the absolute dose, and irradiation times were obtained from log files. We verified dose measurements using EBT-XD films and irradiation times using a fast, pixelated spectral detector. R90 and R80 from integral depth dose were 37.58 and 37.69 cm, and spot sigma at the isocenter were σx = 3.336 and σy = 3.332 mm, respectively. The absolute dose output was measured as 0.343 Gy*mm2/MU for the commissioning conditions. Output was stable for beam currents up to 15 nA and gradually increased to 12-fold for 115 nA. Dose and DR depended on beam current, spot spacing, and arrangement and could be reproduced with 6.4% and 4.2% variations, respectively. Although FLASH was achieved and the largest field size that delivers FLASH DR was determined as 35 × 35 mm2, the current MIC has DR dependence, and users should measure dose and DR independently each time for their FLASH applications.

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©2023 The Author(s)

This is an Open Access work distributed under the terms of the Creative Commons Attribution 3.0 Unported License (https://creativecommons.org/licenses/by/3.0/).
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