First Monte Carlo beam model for ultra‐high dose rate radiotherapy with a compact electron LINAC

Background FLASH radiotherapy based on ultra‐high dose rate (UHDR) is actively being studied by the radiotherapy community. Dedicated UHDR electron devices are currently a mainstay for FLASH studies. Purpose To present the first Monte Carlo (MC) electron beam model for the UHDR capable Mobetron (FLA...

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Bibliographic Details
Published in:Medical physics (Lancaster) 2024-07, Vol.51 (7), p.5109-5118
Main Authors: Dai, Tianyuan, Sloop, Austin M., Rahman, Mahbubur R., Sunnerberg, Jacob P., Clark, Megan A., Young, Ralph, Adamczyk, Sebastian, Von Voigts‐Rhetz, Philip, Patane, Chris, Turk, Michael, Jarvis, Lesley, Pogue, Brian W., Gladstone, David J., Bruza, Petr, Zhang, Rongxiao
Format: Article
Language:English
Subjects:
electron
FLASH
Monte Carlo
radiotherapy
ultra‐high dose rate
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Summary:Background FLASH radiotherapy based on ultra‐high dose rate (UHDR) is actively being studied by the radiotherapy community. Dedicated UHDR electron devices are currently a mainstay for FLASH studies. Purpose To present the first Monte Carlo (MC) electron beam model for the UHDR capable Mobetron (FLASH‐IQ) as a dose calculation and treatment planning platform for preclinical research and FLASH‐radiotherapy (RT) clinical trials. Methods The initial beamline geometry of the Mobetron was provided by the manufacturer, with the first‐principal implementation realized in the Geant4‐based GAMOS MC toolkit. The geometry and electron source characteristics, such as energy spectrum and beamline parameters, were tuned to match the central‐axis percentage depth dose (PDD) and lateral profiles for the pristine beam measured during machine commissioning. The thickness of the small foil in secondary scatter affected the beam model dominantly and was fine tuned to achieve the best agreement with commissioning data. Validation of the MC beam modeling was performed by comparing the calculated PDDs and profiles with EBT‐XD radiochromic film measurements for various combinations of applicators and inserts. Results The nominal 9 MeV electron FLASH beams were best represented by a Gaussian energy spectrum with mean energy of 9.9 MeV and variance (σ) of 0.2 MeV. Good agreement between the MC beam model and commissioning data were demonstrated with maximal discrepancy 
ISSN:0094-2405
2473-4209
2473-4209
DOI:10.1002/mp.17031