End-to-End Verification of an Open-Source Preclinical Electron Flash Treatment Planning System
Abstract
Purpose
Clinical translation of FLASH requires treatment planning systems (TPS) capable of accurately modeling ultra-high dose rate delivery. For FLASH configurations on clinical machines, vendor-provided phase space files are not applicable, thus necessitating individual beam modeling. This work presents end-to-end verification of a Monte Carlo-based electron FLASH TPS with a customized beam model.
Methods
A Varian TrueBeam linac configured for 12 MeV electron FLASH irradiation was modeled using the TOPAS Monte Carlo toolkit and integrated into a Python-based TPS supporting CT/structure import, electron collimator CAD outputs, and 3D dose calculations. Two anterior-posterior single-field bilateral lung irradiation plans with 25 Gy target dose were generated: (1) a 20 × 40 mm² field for end-to-end verification of the TPS using an anatomically realistic mouse phantom, and (2) an anatomy-conformed (lung contoured field plus 1 mm margin) using a mouse CT. For Plan 1, dose was delivered and measured in the lungs at 9.5 mm depth using EBT-XD films. DVHs of the lungs and surrounding organs were calculated for both plans.
Results
For Plan 1, TPS-predicted dose demonstrated good agreement with film measurements in the mouse phantom, achieving gamma pass rates of 92.0% (3%/3 mm) and 100% (5%/5 mm) for an axial profile across the left lung. For Plan 2, DVH analysis showed improved organs-at-risk sparing compared to Plan 1, with mean dose reductions of 72.2%, 44.4%, and 32.8% in the liver, spinal cord, and intestines, respectively, and a more modest reduction in the heart (2.0%) due to its geometric proximity to the lungs.
Conclusion
This work establishes end-to-end dosimetric verification of an electron FLASH TPS using a bilateral lung irradiation plan on an anatomically realistic mouse phantom. The TPS demonstrated accurate dose prediction for FLASH irradiation, enabling a future open-source release to promote accessible FLASH research for its clinical translation.