S1664
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
phantom are halved to accommodate a radiochromic film, which can be fixed either with the movable lesions or with the scaffold. Compression is driven by an MR-compatible pneumatic system (fig.1c). The phantom is connected to an air cylinder with an adjustable stroke length, actuated by controlling the pressure at its two ports. The pneumatic system is powered by the room’s pressurized air supply, stabilized through a pressure reducer. The pressurized air feeds a 5/2-way pneumatic solenoid valve connected to the cylinder through two flow regulators. The electronically-controlled valve timing, the regulated air pressure and flow allow precise control of the phantom’s compression, reproducing a realistic human breathing pattern. Air tubing is extended to keep all non-MR-safe components outside the MRI room.Lung-equivalence and compressibility of the material were evaluated through 4D-CT scans. To assess the phantom motion reproducibility, a draw- wire encoder monitors the phantom compression over extended periods. As a representative use case, a stereotactic RT treatment (54 Gy in 3 fractions) was planned and delivered on the 15mm-diameter lesion, with the film moving synchronously with the lesion.
Conclusion: The phantom demonstrated lung equivalence, reproducible motion, and dosimetric consistency, proving reliable, robust, and suitable for theranostic procedures, including novel technologies as MRI- guided radiotherapy. References: [1] Ratto, Fulvio, et al. "Sponges based on polydimethylsiloxane as pulmonary phantoms for diffuse optics." 2024 Italian Conference on Optics and Photonics (ICOP). IEEE, 2024.This work was partially funded by European Union – Next Generation EU - PNRR - M4C2, investment 1.1 - PRIN 2022 fund - ALPHA id 2022HHZWRS-LS7-PRIN2022 – CUP B53D23020320006 Keywords: lung, phantom, quality assurance (QA)
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Out-of-field doses of a pediatric brain tumor for proton, helium and carbon ion beam therapy Marija Majer 1 , Iva Ambrožová 2 , Željka Knežević 1 , Michał Sądel 3 , Cornelius Bauer 4 , Mercedes Hotvat 1 , Christina Mooshammer 5 , Jonas Mahnke 5 , Hannah Todte 5 , Stefan Schimdt 5,6 , Christina Stengl 5,6 , Pawel Olko 7 , Liliana Stolarczyk 8 , José Vedelago 5,6 1 Radiation Chemistry and Dosimetry Laboratory, Ruđer Bošković Institute (RBI), Zagreb, Croatia. 2 Department of Radiation Dosimetry, Nuclear Physics Institute (NPI), Prague, Czech Republic. 3 Department of Radiation Physics and Dosimetry, Institute of Nuclear Physics (IFJ), Krakov, Poland. 4 Heidelberg Ion Beam Therapy Center (HIT), Heidelberg University Hospital (UKHD), Heidelberg, Germany. 5 Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 6 Department of Radiation Oncology, Heidelberg University Hospital (UKHD), Heidelberg, Germany. 7 Department of Radiation Research and Proton Radiotherapy, Institute of Nuclear Physics (IFJ), Krakov, Poland. 8 Danish Centre for Particle Therapy (DCPT), Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: Although out-of-field doses during proton therapy have been reported to be lower than for photon
Results: CT-scan revealed a material CT# of -750 HU, matching human lung parenchyma (-650 to -850 HU). HU variation (up to 50 HU) across ten respiratory phases scanned through 4D-CT confirms the compression efficacy.Compression reproducibility (fig.2) was assessed for at least 20 minutes using different air pressure supplies, showing stability during the breathing dynamic (deviations < 0.5 mm).The measured isodoses demonstrate that the phantom geometry allows a reliable reconstruction of the dose distribution using radiochromic films (fig.1b).
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