S1671
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Material/Methods: Measurements were performed at the Centro di Protonterapia di Trento using a Proteus Plus system (IBA, Belgium). EBT-XD films (Ashland, USA) were placed within a stack of near water-equivalent plastic slabs and calibrated at 2 cm depth in a low-LET region (≈0.9 keV/μm) using a square PBS field at multiple doses. A single-spot 100 MeV beam was delivered using a 4 cm WET Lexan range shifter (RS). Films were positioned in the coronal plane between slabs and aligned via orthogonal X-ray imaging with metallic markers. A small gantry rotation (3°) was applied to avoid parallel beam incidence on the film plane and to minimize air-gap effects. Films were digitized using an EPSON v750 scanner (Seiko Epson, Japan) under a One-Scan protocol, and multichannel film dosimetry was applied without additional smoothing or corrections. TPS dose and fluence-averaged LET distributions were obtained using the RayStation Monte Carlo algorithm (RaySearch Laboratories,
exponentially decreasing trend (Figure 2), although some radionuclides display atypical distributions (e.g., 60Co).
Sweden). Results:
Entrance, lateral off-axis, and distal dose regions showed no significant discrepancies between film measurement and TPS. The measured FWHM of the single spot matched TPS predictions within <0.4 mm at all depths, demonstrating accurate modeling of spot broadening with the range shifter.However, in the proximal region of the Bragg peak, the film exhibited under-response due to high LET-induced quenching (fig. 1). Although LET influence in darkening depends on the delivered dose for radiochromic films, strong phenomenological correlation, approximately linear after a threshold, was observed between the dose deficit and the product of fluence averaged LET × Dose (fig. 2), both quantities obtained from TPS, confirming that quenching is linked to the local density of energy deposition rather than LET alone.
Conclusion: This study underlines the importance of i) conducting gamma analyses and ii) determining the chemical composition of the components to characterize the radionuclide content in the component. Ultimately, combining these experimental results with Monte Carlo simulations could help to provide a comprehensive model of induced radionuclide activities. Keywords: Activated components, gamma spectrometry Digital Poster Highlight 3793 Assessment of single-spot proton beam dosimetry with range shifter using EBT-XD film and LET analysis Jaime Reverter Pérez 1 , Roberto Righetto 2 , Antonio López Medina 1 1 Medical physics, Hospital do Meixoeiro de Vigo, Vigo, Spain. 2 Centro di Protonterapia, Ospedale di Santa Chiara, Trento, Italy Purpose/Objective: We aim to evaluate single-spot proton beam dosimetry using EBT-XD radiochromic film in the presence of a range shifter and to identify, quantify, and explain discrepancies with treatment planning system (TPS) calculations, including the role of LET- induced quenching.
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