Spatially fractionated radiotherapy with very high energy electron pencil beam scanning

Journal article

Objective. To evaluate spatially fractionated radiation therapy (SFRT) for very-high-energy electrons (VHEEs) delivered with pencil beam scanning. Approach. Radiochromic film was irradiated at the CERN linear electron accelerator for research using 194 MeV electrons with a step-and-shoot technique, moving films within a water tank. Peak-to-valley dose ratios (PVDRs), depths of convergence (PVDR ⩽ 1.1), peak doses, and valley doses assessed SFRT dose distribution quality. A Monte Carlo (MC) model of the pencil beams was developed using TOPAS and applied to a five-beam VHEE SFRT treatment for a canine glioma patient, compared to a clinical 6 MV VMAT plan. The plans were evaluated based on dose-volume histograms, mean dose, and maximum dose to the planning target volume (PTV) and organs at risks (OARs). Main results. Experimental PVDR values were maximized at 15.5 ± 0.1 at 12 mm depth for 5 mm spot spacing. A DOC of 76.5, 70.7, and 56.6 mm was found for 5, 4, and 3 mm beamlet spacings, respectively. MC simulations and experiments showed good agreement, with maximum relative dose differences of 2% in percentage depth dose curves and less than 3% in beam profiles. Simulated PVDR values reached 180 ± 4, potentially achievable with reduced leakage dose. VHEE SFRT plans for the canine glioma patient showed a decrease in mean dose (>16%) to OARs while increasing the PTV mean dose by up to 15%. Lowering beam energy enhanced PTV dose homogeneity and reduced OAR maximum doses. Significance. The presented work demonstrates that pencil beam scanning SFRT with VHEEs could treat deep-seated tumors such as head and neck cancer or lung lesions, though small beam size and leakage dose may limit the achievable PVDR.

Authors: Fischer, J; Hart, A; Bedriová, N; Krim, D; Clements, N

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Publishing
• Journal: Physics in Medicine & Biology
• Volume: 70
• Issue: 1
• Article number: 015011
• Publication date: 2024-12-24
• Acceptance date: 2024-11-13
• DOI: 10.1088/1361-6560/ad9232
• EISSN: 1361-6560
• ISSN: 0031-9155
• Language: English
• Keywords: treatment planning; very-high energy electrons; spatially fractionated radiation therapy; radiotherapy; film dosimetry; Monte Carlo simulations