Initial experience with an electron FLASH research extension (FLEX) for the Clinac system

Authors

Kyuhak Oh, University of Nebraska Medical Center
Kyle J. Gallagher, University of Nebraska Medical CenterFollow
Megan Hyun, University of Nebraska Medical CenterFollow
Diane Schott, University of Nebraska Medical CenterFollow
Sarah Wisnoskie, University of Nebraska Medical Center
Yu Lei, University of Nebraska Medical CenterFollow
Samuel Hendley, University of Nebraska Medical Center
Jeffrey Wong, University of Nebraska Medical Center
Shuo Wang, University of Nebraska Medical CenterFollow
Brendan Graff, University of Nebraska Medical CenterFollow
Christopher Jenkins, University of Nebraska Medical Center
Frank Rutar, University of Nebraska Medical CenterFollow
Md Ahmed, Varian Medical Systems
Joshua McNeur, Varian Medical Systems
Jeffrey Taylor, Varian Medical Systems
Marty Schmidt, Varian Medical Systems
Lasitha Senadheera, Varian Medical Systems
Wendy Smith, Varian Medical Systems
Subodh M. Lele, University of Nebraska Medical CenterFollow
Ran Dai, University of Nebraska Medical CenterFollow
Dong Jianghu (James), University of Nebraska Medical Center
Y Yan, University of Nebraska Medical CenterFollow
Su-min Zhou, University of Nebraska Medical CenterFollow

Date of this Version

8-22-2023

Citation

J Appl Clin Med Phys. 2023;e14159. https://doi.org/10.1002/acm2.14159

Comments

Open access.

Abstract

Purpose: Radiotherapy delivered at ultra-high-dose-rates (≥40 Gy/s), that is, FLASH, has the potential to effectively widen the therapeutic window and considerably improve the care of cancer patients. The underlying mechanism of the FLASH effect is not well understood, and commercial systems capable of delivering such dose rates are scarce. The purpose of this study was to perform the initial acceptance and commissioning tests of an electron FLASH research product for preclinical studies.

Methods: A linear accelerator (Clinac 23EX) was modified to include a nonclinical FLASH research extension (the Clinac-FLEX system) by Varian, a Siemens Healthineers company (Palo Alto, CA) capable of delivering a 16 MeV electron beam with FLASH and conventional dose rates. The acceptance, commissioning, and dosimetric characterization of the FLEX system was performed using radiochromic film, optically stimulated luminescent dosimeters, and a plane-parallel ionization chamber. A radiation survey was conducted for which the shielding of the pre-existing vault was deemed sufficient.

Results: The Clinac-FLEX system is capable of delivering a 16 MeV electron FLASH beam of approximately 1 Gy/pulse at isocenter and reached amaximum dose rate >3.8 Gy/pulse near the upper accessory mount on the linac gantry. The percent depth dose curves of the 16 MeV FLASH and conventional modes for the 10 × 10 cm² applicator agreed within 0.5 mm at a range of 50% of the maximum dose. Their respective profiles agreed well in terms of flatness but deviated for field sizes >10 × 10 cm². The output stability of the FLASH system exhibited a dose deviation of <1%.Preliminary cell studies showed that the FLASH dose rate (180 Gy/s) had much less impact on the cell morphology of 76N breast normal cells compared to the non-FLASH dose rate (18 Gy/s), which induced large-size cells.

Conclusion: Our studies characterized the non-clinical Clinac-FLEX system as a viable solution to conduct FLASH research that could substantially increase access to ultra-high-dose-rate capabilities for scientists.