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Updated: Jul 2, 2026
Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
Published on: March 11, 2021
Development and evaluation of an in vivo dose-based monitoring system for electron FLASH radiation therapy
Justin DeFrancisco1, Matthew Richeson2, Tomaj Javidtash2
1Department of Radiation Oncology, School of Medicine, Virginia Commonwealth University Health System, Richmond, Virginia, USA.
Background:
FLASH radiotherapy requires further preclinical and clinical investigation to establish its biological effectiveness and define optimal beam parameters. In conventional (CONV) radiotherapy, redundant beam termination systems are a cornerstone ensuring patient safety, yet analogous safeguards for FLASH delivery are not well established, creating a critical barrier to safely enabling such studies.
Purpose:
To develop and evaluate a real-time, in vivo, point-dose monitoring system capable of terminating electron FLASH beam delivery as an additional monitoring system on a modified medical linear accelerator (LINAC).
Methods:
A decommissioned LINAC was modified to deliver electron FLASH beams with stable dose per pulse (DPP) at 300 Hz pulse frequency. A commercial plastic scintillation detector system was adapted through hardware and firmware modifications to enable pulse-based and dose-based beam termination via the LINAC MLC interface. The detector was cross-calibrated against radiochromic film under FLASH conditions. System performance was evaluated through measurements of control accuracy, and detector response as a function of DPP.
Results:
Stable electron FLASH delivery was achieved with an average dose rate of 127.5 14.91 Gy/s and an approximate beam energy of 5.2 MeV. Pulse-based control terminated delivery within +3 pulses of the requested value (requested 1-20 pulses), with overshoot attributable to downstream circuitry latency. Dose-based control agreed with film measurements within 1.11 0.81 Gy for surface-based control (in vivo setup) and -1.45 0.38 Gy at depth (stable dosimetry) (tested dose deliveries between 2-15 Gy). The detector response versus DPP in the FLASH range (0.11-0.78 Gy/p) could be roughly approximated as linear before detector saturation, with only marginal improvement seen when using quadratic fitting.
Conclusion:
A modified scintillation-based system was implemented as a real-time in vivo beam termination mechanism for electron FLASH radiotherapy under stable DPP and specific experimental conditions. While not intended for primary beam control, the system may provide a practical redundant safety layer for mitigating gross delivery errors in experimental and translational FLASH applications.
