Purpose: A Monte Carlo (MC) beam model and its implementation in a clinical treatment planning system (TPS, Varian Eclipse) are presented for a modified ultra-high dose-rate electron irradiator and FLASH radiotherapy (eFLASH-RT) utilizing clinical accessories and geometry.
Methods: GAMOS MC software modelled the gantry head without scattering foils or targets, representative of the LINAC modifications. Applying a nominal and mean energy of 10MeV, the energy spectrum’s standard deviation (s?) was varied to match the central axis percent depth dose (PDD) profiles of an open field with jaws retracted and measured with Gafchromic film. The beam’s source spot size was 0.5mm. The emittance cone angle (?cone) was determined by equating the quadratic fit between simulated ?cone and resulting lateral spread to the film measured lateral spread at several depths. The beam model and its Eclipse configuration were validated with film measured lateral profiles in air and water, and PDD’s of the open field and clinical applicators. Eclipse produced an oral melanoma treatment for a canine patient as a demonstration.
Results: The GAMOS model agreed best with measured profiles at s?=0.5MeV and ?cone=3.9°±0.2°. The quadratic fit excluded ?cone>4.63° due to obstruction from the primary collimator. The model and its Eclipse configuration agreed with measured profiles (3% for in-water lateral, 4% for in-air lateral, and 3% for PDD’s). The anterior-posterior treatment can spare the tongue (<10% receiving >9Gy) while delivering >90% of the prescribed dose to majority of the tumor volume.
Conclusion: To the best of our knowledge, this is the first functional clinical TPS configured for eFLASH-RT and it can narrow the current gap in FLASH-RT translation from preclinical to clinical implementation. The optimization of dose and dose-rate can determine the quality of eFLASH-RT plans, especially in cases of large animal and human patients involving complex geometries and tissue inhomogeneities.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Norris Cotton Cancer Center seed funding through core grant P30CA023108, seed funding from the Thayer School of Engineering, and grant R01EB024498. Conflict of Interest: Dr. Pogue reports personal fees and Dr. Bruza reports non-financial support from DoseOptics LLC, outside the submitted work.
Treatment Planning, Electron Therapy
TH- External Beam- Electrons: Computational dosimetry: Monte Carlo