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

Tianyuan Dai; Austin M Sloop; Mahbubur R Rahman; Jacob P Sunnerberg; Megan A Clark; Ralph Young; Sebastian Adamczyk; Philip Von Voigts-Rhetz; Chris Patane; Michael Turk; Lesley Jarvis; Brian W Pogue; David J Gladstone; Petr Bruza; Rongxiao Zhang

doi:10.1002/mp.17031

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

Med Phys. 2024 Mar 17. doi: 10.1002/mp.17031. Online ahead of print.

Authors

Tianyuan Dai^{1

2}, Austin M Sloop¹, Mahbubur R Rahman³, Jacob P Sunnerberg¹, Megan A Clark¹, Ralph Young⁴, Sebastian Adamczyk⁴, Philip Von Voigts-Rhetz⁴, Chris Patane⁴, Michael Turk⁴, Lesley Jarvis^{5

6}, Brian W Pogue^{1

6

7}, David J Gladstone^{1

5

6}, Petr Bruza¹, Rongxiao Zhang^{1

5

8}

Affiliations

¹ Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA.
² Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China.
³ UT Southwestern Medical Center, Dallas, Texas, USA.
⁴ IntraOp Medical Corporation, Sunnyvale, California, USA.
⁵ Department of Medicine, Geisel School of Medicine, Dartmouth College, Hanover, New Hampshire, USA.
⁶ Dartmouth Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire, USA.
⁷ Department of Medical Physics, Wisconsin Institutes for Medical Research, University of Wisconsin, Madison, Wisconsin, USA.
⁸ Department of Radiation Medicine, New York Medical College, Valhalla, New York, USA.

PMID: 38493501
DOI: 10.1002/mp.17031

Abstract

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 < 3% for PDDs and profiles. Hundred percent gamma pass rate was achieved for all PDDs and profiles with the criteria of 2 mm/3%. With the criteria of 2 mm/2%, maximum, minimum and mean gamma pass rates were (100.0%, 93.8%, 98.7%) for PDDs and (100.0%, 96.7%, 99.4%) for profiles, respectively.

Conclusions: A validated MC beam model for the UHDR capable Mobetron is presented for the first time. The MC model can be utilized for direct dose calculation or to generate beam modeling input required for treatment planning systems for FLASH-RT planning. The beam model presented in this work should facilitate translational and clinical FLASH-RT for trials conducted on the Mobetron FLASH-IQ platform.

Keywords: FLASH; Monte Carlo; electron; radiotherapy; ultra-high dose rate.

Abstract

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