Development and characterization of a 1-2 MeV electron beam platform with magnetic focusing and steering for shallow high-dose-rate irradiation

OBJECTIVE: To develop and experimentally characterize a 1--2~MeV electron linac platform with magnetic focusing and steering for superficial FLASH-compatible irradiation and electronically tunable spatial dose modulation. APPROACH: A preclinical 1-2 MeV electron linac was equipped with a solenoid for magnetic focusing and nested saddle-type scanning magnets for two-dimensional beam steering. Three-dimensional magnetic-field maps were computed in Opera and imported into a TOPAS Monte Carlo model incorporating the accelerator geometry, titanium exit foil, air gap, and water phantom for dose scoring. Dose distributions were measured using Gafchromic EBT-XD film. Film measurements of spot size, lateral dose profiles, and percentage depth-dose curves were compared with Monte Carlo simulations. Multi-spot dose patterns were generated by varying scanning-magnet field strength, and peak spacing, peak-to-valley dose ratio, and dose rate versus repetition frequency were quantified. MAIN RESULTS: In the solenoid focused configuration, the measured beam size was approximately 2 cm at the 80% isodose diameter, compared with approximately 6 cm for the unfocused reference beam at the exit window. In this focused-beam configuration, the measured dose rate reached 40 Gy/s at 16 Hz and 125 Gy/s at 50 Hz. The measured full-width-at-half-maximum (FWHM) of the focused beam was 1.26 cm in the X direction and 1.39 cm in the Y direction, and the TOPAS model agreed with EBT-XD film measurements to within about 4% in the high-dose region. Magnetic steering generated tunable three-spot shallow dose distributions with peak-to-peak spacing up to approximately 2.9 cm and a maximum peak-to-valley dose ratio of 28.0. By superposition of adjacent scanned beam positions, the system also produced a broadened shallow field with a 95% D max flat-top width of approximately 2.46 cm. SIGNIFICANCE: The results demonstrate that a compact low-energy electron linac can provide a useful platform for FLASH-compatible superficial irradiation and electronically controlled spatial dose modulation in a regime where shallow dose confinement is advantageous.