Author: Rafael Carballeira, Tianyuan Dai, David J. Gladstone, Philip Von Voigts-Rhetz, Rongxiao Zhang 👨🔬
Affiliation: Shandong Cancer Hospital, Dartmouth College, IntraOp, Thayer School of Engineering, Dartmouth College, University of Missouri 🌍
Purpose: To analyze phase space (PHSP) data generated for Mobetron in FLASH radiotherapy and assess key dosimetric characteristics, including the energy spectrum, scattering angle distribution, and percentage depth dose (PDD) curve. These analyses help validate the beam model for treatment planning systems.
Methods: PHSP files for Mobetron were generated via Monte Carlo simulations. The energy spectrum, scattering angle distribution, and PDD curve were validated against measurements. The PDD curve was obtained using the PHSP file in GAMOS to score dose deposition in a water phantom, ensuring fidelity by comparing simulated and expected dose distributions. This analysis validates the PHSP file as a FLASH RT TPS input for accurate dose calculations using DICOM RT datasets.
Results: The energy spectrum showed minimal deviations around the nominal 9 MeV beam energy. The scattering angle distribution indicated a predominantly forward-directed beam with minor backscatter. The PDD curve displayed a gradual dose buildup, followed by a steep falloff beyond 30 mm—characteristic of an electron beam—with a rapid decline beyond 50 mm, confirming expected penetration depth and attenuation. These findings provide insights into the Mobetron beam’s dosimetric behavior and areas for further study.
Conclusion: Mobetron PHSP files exhibit key dosimetric characteristics crucial for FLASH radiotherapy. The validated PDD curve, energy spectrum, and scattering angle data confirm beam model accuracy. These results establish a framework for comparing experimental data with future Monte Carlo simulations, supporting Mobetron beam model validation in FLASH radiotherapy treatment planning.