OBJECTIVE: To develop, optimize, and validate a Mobetron applicator for ultra-high dose rate (UHDR) electron radiotherapy that integrates an electrostatically shielded beam current transformer (BCT) for real-time dose tracking, and to perform a comprehensive experimental assessment of the combined applicator-BCT system in a representative preclinical geometry. Approach: Monte Carlo (MC) simulations using BEAMnrc and DOSRZnrc were used to optimize a 3D-printed applicator for the Mobetron (IntraOp, USA). Applicator wall thickness was varied to suppress out-of-field electron scatter, while the length was adjusted to balance instantaneous dose rate and profile flatness for 6 MeV and 9 MeV UHDR beams. Four conductive materials were evaluated for electrostatic shielding of the BCT, with the requirement of minimizing perturbation to the electron beam.The final design was experimentally validated through an comprehensive test using a microchip phantom for tumor spheroid culture, where MC-predicted doses-scaled via the calibrated, shielded BCT-were compared to radiochromic film measurements. Main Results: A polylactic acid applicator with a 2.5 cm wall thickness minimized out-of-field dose, while a 12.5 cm length provided the best compromise between instantaneous dose rate and lateral dose uniformity. Ultra-thin conductive Kapton ® offered effective electrostatic shielding with <0.15 % loss in beam energy fluence. Experimental validation demonstrated excellent agreement between MC-predicted and measured doses, with deviations of 0.16-1.68 % depending on energy and field size, within experimental uncertainty. Significance: The optimized applicator enables accurate, real-time charge measurement without compromising beam quality, supporting reliable dosimetry for UHDR studies. The external BCT configuration provides flexibility for rapid switching between FLASH and conventional modes, and the simulation-driven framework can be readily extended to other geometries and beam configurations, facilitating broader preclinical and clinical implementation.
Chiasson et al. (Wed,) studied this question.