Development and characterization of a 1-2 MeV electron beam platform with magnetic focusing and steering for shallow...

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 (MC) 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 MC simulations. Multi-spot dose patterns were generated by varying scanning-magnet field strength, and peak spacing, peak-to-valley dose ratio, and dose rate as a function of repetition frequency were quantified.Main Results.In the solenoid-focused configuration, the beam size at the 80% isodose diameter was reduced from approximately 6 cm without solenoid focusing to 2 cm, and the measured dose rate reached 125 Gy s-1at 50 Hz. The measured full-width-at-half-maximum of the focused beam was 1.26 cm in theXdirection and 1.39 cm in theYdirection, 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%Dmaxflat-top width of 2.46 cm.Significance.The results demonstrate that a compact low-energy electron linac can provide a useful platform for studying FLASH-compatible superficial irradiation and electronically controlled spatial dose modulation in a regime where shallow dose confinement is advantageous.