Non-Invasive Reversible Software-Based Configuration of a Clinically Used Linear Accelerator for Preclinical Electron Flash Radiobiology
Abstract
Purpose
Configuring clinical linear accelerators (LINACs) for ultra-high dose rate (UHDR) electron experiments typically requires invasive hardware modification or manufacturer intervention, limiting accessibility. We developed an independent, non-invasive, software-based configuration of a clinically used TrueBeam LINAC (Varian Medical Systems) that enables reversible switching between preclinical UHDR and conventional clinical (CONV) electron modes.
Methods
Service-mode software was used to configure UHDR delivery by emulating MV photon RF and beam current settings, retracting the photon target and internal monitor chamber, and inserting a clinically unused low-energy electron scattering foil. An external AC current transformer (ACCT) provided pulse monitoring, while an external ion chamber in solid water measured exit dose. Organ-specific collimators and in vitro holders were mounted on the accessory tray. Percent depth dose (PDD), beam profiles, and dose uniformity were evaluated using radiochromic film. Dose-per-pulse (DPP) was varied via gun voltage adjustments and measured at multiple source-to-surface distances. Cross-calibration was performed among film, ACCT, and ion chamber measurements. Output reproducibility was assessed over multi-day irradiation sessions.
Results
UHDR and CONV electron beams showed comparable energies (12.8 MeV vs 11.9 MeV) and matched PDD profiles across mouse-equivalent depths. Maximum DPP exceeded 0.5 Gy in all configurations, reaching ~1.5 Gy for in vivo setups and ~0.7 Gy at extended SSD for tissue culture. Beam flatness and symmetry were comparable between UHDR and CONV modes, supporting organ-specific irradiations and uniform coverage of up to a 5 cm diameter field. Dose calibration demonstrated strong linearity across film, ACCT, and ion chamber measurements (R² > 0.95). Day-to-day output variation was low (CV <4%).
Conclusion
A clinical TrueBeam LINAC can be non-invasively and reversibly configured for accurate, reproducible UHDR electron delivery without hardware modification. This approach enables robust preclinical FLASH radiobiology research on widely available clinical systems and may help expand access to UHDR irradiation platforms.