ESTRO 2024 - Abstract Book

S3593

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

ESTRO 2024

1672

Proffered Paper

Very High Energy Electrons (VHEE): Treatment planning comparison and machine design

Fabio S D'Andrea 1,2,3 , Roger M Jones 1,2 , Ranald MacKay 3,4 , Robert Chuter 3,4

1 The University of Manchester, Physics and Astronomy, Manchester, United Kingdom. 2 The Cockcroft Institute, Accelerator Science and Technology, Daresbury, United Kingdom. 3 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom. 4 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom

Purpose/Objective:

Very High Energy Electron (VHEE) beams have demonstrated potentially superior dosimetric properties compared to current treatment methods [1, 2, 3]. They show insensitivity to inhomogeneities in water phantoms [4] and can be readily steered electromagnetically. However, VHEE-capable machines do not currently exist. This study aims to inform VHEE machine design by establishing a comprehensive treatment planning framework for VHEE beams ranging from 110 to 240 MeV while exploring FLASH dose rates through minimal beam usage [5]. This is achieved by quantifying the degradation of plan quality within realistic constraints on beam parameters, including beam numbers and energy requirements. We evaluate VHEE's performance concerning anatomical changes (such as weight changes and internal density changes) and compare it to conventional photon Volumetric Modulated Arc Therapy (VMAT) and Intensity-Modulated Proton Therapy (IMPT). This comparative analysis explores VHEE’s clinical potential in relation to existing treatments and addresses the absence of a commercial planning system for VHEE. VHEE beam data were generated through Monte Carlo simulations in TOPAS (v3.9) [6]. Assumptions for beam parameters were derived from literature and data from CERN's CLEAR beamline [7]. VHEE radiotherapy treatment planning was conducted by interfacing an in-house modified version of matRad (an open-source multi-modality radiation treatment planning system (TPS) written in MATLAB) [8] with GATE (v8.1, GEANT4 wrapper) [9]. This integration allowed for plan generation utilising the Monte Carlo dose calculation engine. Two disease sites were investigated: lung and prostate, chosen for their contrasting challenges in radiotherapy (low-density vs. tissue-density regions). Various treatment plan parameters, such as beam number (3-12 beams), spot spacing (0.5 – 2 σ), and energy (110 – 240 MeV), were explored and optimal limits were determined to create robust yet clinically suitable plans. The effects of anatomical changes were also investigated, simulating weight changes and internal changes such as tumour debulking for the lung cohort, and rectal filling in the prostate cohort. VHEE plans were compared to clinical VMAT photon plans and IMPT for both treatment sites. The modified version of the matRad TPS enabled a standardised comparison between different radiation modalities, eliminating inherent biases that arise from using different TPS systems. To assess the impact of these anatomical changes, baseline plans were generated for each modality. A CT with simulated anatomical changes was then imported, and the dose distribution was recalculated using the original beam weightings. Dose metrics, dose-volume histograms (DVHs), and the homogeneity index (HI) were used to compare the quality of plans. Material/Methods: