ESTRO 2024 - Abstract Book

S3708

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

1 Institut Curie, INSERM LITO, Orsay, France. 2 Thales, Avionics, Vélizy-Villacoublay, France. 3 Institut Curie, Radiation Oncology Department, Orsay, France. 4 German Cancer Research Center-DKFZ, Department of Medical Physics in Radiation Oncology, Heidelberg, Germany

Purpose/Objective:

Very High Energy Electrons (VHEE) are a possible radiotherapy modality using electron energies of 100-200 MeV and allowing the treatment of deep-seated tumors, at ultra-high dose-rate delivery (FLASH) and with focused beams. However, there is a lack of research tools for fast treatment planning with these modalities. The aim of this work is to report on the implementation of VHEE modality in the open-source research Treatment Planning System (TPS) environment matRad, and validate it against Monte Carlo simulations. Indeed, a TPS toolkit with VHEE modality could stimulate further pre-clinical investigations and contribute to the gradual introduction of VHEE in clinical practice.

Material/Methods:

Several VHEE pencil beam scanning models (between 100-200 MeV) were introduced into the open-source TPS matRad environment. A double Gaussian model based on Fermi-Eyges theory of multiple Coulomb scattering was first developed [1]; a second model for focused beams, based on published data [2], and enabling a significant reduction of the entrance dose has then been introduced. Various field sizes (up to 15x15cm2) and geometries with clinically relevant heterogeneities (bone and lung) were calculated in matRad and compared with Monte Carlo (MC) simulations using TOPAS/Geant4 toolkit. At last, two representative clinical plans (a brain and a prostate case) were also studied and compared between modalities (divergent vs focused beams and MC simulations).

Results:

The VHEE modality has been fully implemented in matRad with GUI capabilities while preserving all original TPS features. New relevant options include spot lists definition and optimization, and adjustment of the lateral dose calculation cut-off. Unfocused VHEE calculations for a single spot and square fields have been validated in water as well as in phantoms with artificial box-shaped heterogeneities. Dose maps from matRad agree well with TOPAS except behind large interface heterogeneity due to the limitations of the pencil-beam algorithm in accurately predicting electron scattering, as seen in Figure 1. Two clinical cases, brain and prostate, were studied with 4 fields of 100 MeV and 3 fields of 200 MeV correspondingly. An example of the matRad interface with the brain case is shown in Figure 2. Overall, good agreement has been found between matRad and TOPAS, albeit with differences after large heterogeneities. A focused VHEE beam modality has also been defined and validated, showing dose maps in good agreement with previously published Monte Carlo results [2]. Further work includes the implementation of beams with different settings, experimental validation, and development of a dedicated optimization function for FLASH applications.