Room: Track 3
To develop a megavoltage photon converter for the Advanced Rare Isotope Laboratory (ARIEL) electron beamline at TRIUMF which will enable delivery of ultrahigh dose-rate (FLASH) and spatially-fractionated radiotherapy (SFRT) on a common platform.
The 10MeV section of the ARIEL e-linac is being retrofitted to deliver photon FLASH and SFRT using pulsed and continuous beams. A robust Ta-Al photon converter flange and preclinical treatment apparatus have been designed along with environmental shielding and requisite ancillary systems. Computer-aided design (CAD) model-driven finite-element analysis (ANSYS®) and Monte Carlo (TOPAS, FLUKA) software have been leveraged to simulate 1kW irradiations using various beam parameters to ensure FLASH-compatible dose-rates (>40Gy/s) may be achieved within acceptable physical and thermal constraints. Primary beam and modular SFRT collimators have been designed to meet preclinical delivery goals, including maximization of peak central-axis (CAX) dose and a reduction of off-axis fluence to <1% of CAX beyond the angle subtended by the largest collimator size.
CAX entrance dose rates using a 1cm incident electron beam were calculated to be 290Gy/s and 96Gy/s for 10MV and 8MV photon fields (1x1cm²), respectively. Smaller beam sizes were found to increase dose rates, up to a maximum of 326Gy/s for a 10MV beam with 2mm beam-spot size. Peak dose-rates for a 1.5mm slit SFRT configuration reached 40Gy/s, as is nominally required for FLASH-RT. A Ta target thickness of 1mm provided an optimal trade-off between dose-rate and thermal mass for improved heat conduction to the Ta-Al boundary. Flange geometry and active water-cooling channels ensured peak Al and water temperatures did not exceed their respective operating limits of 300°C and 100°C while the thermal strain remained within tolerable bounds.
The performance of the 10MV ARIEL FLASH-RT photon converter was optimized to deliver FLASH-compatible dose-rates while considering the practical and thermal limitations of the system.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by the National Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and the New Frontiers in Research Fund (NFRFE)