A Monte Carlo Treatment Planning Interface for Quantitative Preclinical Electron Flash Radiotherapy
Abstract
Purpose
Robust and quantitative treatment planning remains a critical barrier to reproducible preclinical FLASH radiotherapy (FLASH-RT) research. We developed and validated a Monte Carlo–based treatment planning interface (TPI) for electron FLASH beams, enabling accurate absolute dose prediction in realistic heterogeneous preclinical geometries.
Methods
A TPI originally designed for orthovoltage treatments was adapted for FLASH-RT, providing CT-based segmentation, customizable beam definitions, automated EGSnrc Monte Carlo input generation, and three-dimensional dose analysis. Beam models for 6 and 9 MeV electron FLASH beams from a Mobetron were implemented using phase spaces generated with EGSnrc. A heterogeneous mouse phantom was fabricated using dual-nozzle 3D printing with tissue-equivalent ABS (soft tissue), PLA (bone), and air (lung), and designed to accommodate alanine pellets, Gafchromic film, and a plastic scintillation detector (PSD). Treatment plans were generated from the phantom CT, and Monte Carlo dose predictions were benchmarked against experimental measurements under FLASH delivery conditions. Dose calibration was performed using alanine pellets in a reference geometry with beam output normalized by a shielded beam current transformer.
Results
The FLASH-adapted TPI successfully generated three-dimensional dose distributions using Mobetron phase-space inputs. Monte Carlo predictions demonstrated excellent agreement with measurements in heterogeneous geometry. Mean absolute dose differences measured with the PSD were 0.94% for 6 MeV and 1.38% for 9 MeV beams while alanine measurements showed mean errors of 2.74% and 2.63% respectively, confirming accurate absolute dose prediction across detectors.
Conclusion
This work presents the first integration of Mobetron electron FLASH phase spaces into a treatment planning interface validated in heterogeneous preclinical geometries. The demonstrated end-to-end accuracy meets accepted clinical electron beam commissioning tolerances for comparable end-to-end tests. This platform provides a robust, quantitative foundation for preclinical FLASH-RT studies and supports the translational development of clinically relevant FLASH research.