A Matrad-Fluka Framework for the Generation and Monte Carlo Validation of Monoenergetic Proton Range-Shifter Plans
Abstract
Purpose
3D range-modulators (3D-RMs) are a feasible method to enable very fast, ultra-high dose-rate proton irradiation and potentially spare the healthy tissue (FLASH-effect) using one single energy. They can be generated either from a conventional multi-energy plan or even better by utilizing a dedicated range-shifter (RaShi) plan as a base for the 3D-RM design as it already incorporates the additional lateral scattering. This study introduces a framework for the generation of such monoenergetic range-shifter pans in the matRad treatment planning system followed by a dosimetric verification using Monte Carlo (MC) simulations.
Methods
The MatRad treatment-planning-system (Blaise v.2.10.1) was extended with the capability of creating monoenergetic variable-thickness RaShi plans taking into account the additional scattering from the RaShi plates. A one-field proton RaShi plan (with 3mm/2 mm WET lateral and longitudinal spot step respectively) was optimized for a prostate target using the matRad native Pencil-beam algorithm and a single energy of 180 MeV. In order to verify the matRad dose distribution, the FLUKA MC package was modified to incorporate the variable-thickness RaShi plan in one single simulation. For this purpose, a customized simulation workflow was implemented whereby the user “source.f“ routine was adjusted for per-particle, on-the-fly modulation of the RaShi slab body-thickness depending on the thickness-layer the particle belongs to. Finally, the scan-spot weights map from the matRad plan was simulated on the patient CT with FLUKA and both dose distributions were compared.
Results
Both the matRad and FLUKA dose distributions exhibit good homogeneity and conformity. There is a good agreement between them with a 3D Gamma-Index passing-rate (3%/3 mm, local) of 98%.
Conclusion
By successfully implementing in-house user routines in matRad and FLUKA, we have developed a validated workflow for monoenergetic RaShi planning providing a solid foundation for further research and design of 3D range modulators, based on RaShi plans.