ESTRO 2025 - Abstract Book

S2618

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

Conclusion: This study demonstrates that Monaco TPS can accurately calculate dose distributions at the portal image level for a variety of phantoms. Additionally, a robust dataset was developed to train DL models for EPID transit dosimetry in radiotherapy.

Keywords: Transit dosimetry, EPID, Radiochromic Films

References: [1] Zhang J. et al. A feasibility study for in vivo treatment verification of IMRT using Monte Carlo dose calculation and deep learning-based modelling of EPID detector response. Radiation Oncology. 2022;17:31. [2] Marini L. et al. Deep learning methods for 2D in-vivo dose reconstruction with EPID detector. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2024;1069:169908. [3] Santos T. A review on radiochromic film dosimetry for dose verification in high energy photon beams. Radiation Physics and Chemistry. 2021;179:109217. [4] Marrazzo L. et al. GafChromic(®) EBT3 films for patient specific IMRT QA using a multichannel approach. Phys Med. 2015;31:1035-42.

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Digital Poster Patient specific verification of steep dose gradients in proton therapy using 3D-printed phantom and Gafchromic film Jenny Gorgisyan 1,2 , Christina Vallhagen Dahlgren 3 , Anneli Edvardsson 1,2 , Patrik Brynolfsson 1,4 , Marcus Bivrén 1 , Adam Aitkenhead 5,6 , Thomas Björk-Eriksson 7,8 , Per Munck af Rosenschöld 1,2 1 Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden. 2 Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 3 The Skandion Clinic, The Skandion Clinic, Uppsala, Sweden. 4 Medical Radiation Physics, Department of Translational Medicine, Lund University, Lund, Sweden. 5 Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, United Kingdom. 6 Division of Cancer Sciences, Faculty of Biology Medicine and Heath, The University of Manchester, Manchester, United Kingdom. 7 Department of Oncology, Institute of Clinical Sciences, Sahlgrenska Academy at the University of Gothenburg, Gothenburg, Sweden. 8 Regional Cancer Centre West, Western Sweden Healthcare Region, Gothenburg, Sweden Purpose/Objective: For medulloblastoma, craniospinal irradiation (CSI, 23.4Gy(RBE)) and tumor bed boost (30.6Gy(RBE)) is given. Hippocampal-sparing is suggested for these patients to minimize cognitive side effects. Hippocampal-sparing proton plans are complex with steep dose gradients which should be carefully verified. Current verification techniques, using 1D/2D ionization chamber arrays with limited spatial resolution, are inadequate for this purpose. The studies’ aim was to develop a verification technique with sufficient resolution to investigate these steep dose gradients in a patient-specific geometry. Material/Methods: A skull was 3D-printed in seven sections using Polyactic Acid (PLA) with 95% fill density and 5% air, based on CT-data from a patient with a CSI target. Double-layer Gafchromic film (Ashland) was inserted between the sections (Fig.1). A three field CSI IMPT treatment plan (head only) was generated in Eclipse (Varian Medical Systems) with steep dose gradients ranging from prescribed dose 23.4 Gy(RBE) to hippocampal mean dose 8.0 Gy(RBE). The plan was recalculated on the phantom and then one fraction (1.8Gy(RBE)) was delivered to the phantom twice. The film was calibrated in both the peak and plateau regions of the Bragg peak and scanning was performed twice (Expression