Helium pencil beam commissioning and beam modeling

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• Picked for Medical Physics (paper of the day, 11 August 2026): Helium pencil beam commissioning and validation study

Abstract

BACKGROUND AND PURPOSE: Helium ions combine reduced lateral scattering compared to protons and a lower fragmentation tail than carbon ions, enabling sharp dose gradients and improved normal tissue sparing. This study reports the commissioning of a scanned helium pencil beam line and validation of its corresponding beam model. MATERIALS AND METHODS: Synchrotron-based helium ion beams were commissioned covering energies from 54.6 to 402.8 MeV/u. Depth-dose curves were measured and absolute dose calibration was performed. Beam optics (spot size, position, and intraspill stability) were evaluated for various spill lengths. A beam model was implemented in the RayStation treatment planning system (TPS) and validated through 2D absolute dose measurements in homogeneous and heterogeneous phantoms and 3D measurements of cubic spread-out Bragg peak fields. Gamma-index analysis and Monte Carlo (MC) simulations with GATE/Geant4 were performed for benchmarking. RESULTS: Measured ranges agreed with MC simulations within ± 0.3 mm. Spot sizes decreased with energy, independently of the spill length. Spot positions remained within ± 0.5 mm and intraspill variations were ≤ 0.2 mm (position) and ≤ 5.4 % (size). TPS-predicted doses agreed within 0.1 %. For 3D validations in homogeneous phantoms, the dose differences were generally within 2 %. Median gamma pass rates exceeded 90 % for 3 %/1.5 mm and 95 % for 5 %/1.5 mm. For the heterogeneous phantom, differences were within -3.2 %. CONCLUSIONS: Stable scanned beam delivery with helium ions was established. Validation demonstrated strong agreement between measurements, TPS calculations, and MC simulations, supporting research and future clinical application.

Abstract as published, via PubMed.