S1663
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Material/Methods: Solid Water phantoms (SUN NUCLEAR) were
consistent with the reported literature. Owing to their layered structures, they can be used to verify complex 2D dose distributions near metallic interfaces using radiochromic films or detectors. References: [1] Rivard J. M, Coursey M.B, Hanson F. W, Huq S. M, Ibbott S. G, Mitch G. M, Nath R, Williamson F J. Update of AAPM Task Group No.43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys. 2004; 31(3): 633–673.[2] Baltas D, Geramani K, Ioannidis T. G, Hierholz K, Rogge B, Kolotas C, Sievers K M, Milickovic N, Kober B, Zamboglou N. Comparison of calibration procedures for 192Ir high-dose-rate brachytherapy sources. Int. J. Radiation Oncology Biol. Phys. 1999; 43(3): 653–661. Keywords: Brachytherapy, Phantoms, verification Digital Poster Highlight 3182 MRI-compatible tissue-equivalent lung phantom with dynamic breathing capabilities Giacomo Insero 1 , Immacolata Vanore 1 , Fulvio Ratto 2 , Andrea Profili 3 , Livia Marrazzo 1,4 , Margherita Zani 4 , Ilaria Cupparo 4 , Silvia Calusi 4 , Lucia Cavigli 2 , Michaela Servi 3 , Yary Volpe 3 , Giovanni Romano 1 , Alberto Dalla Mora 5 , Laura Di Sieno 5 , Stefania Pallotta 1,4 1 Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy. 2 Institute of Applied Physics, Italian National Research Council IFAC-CNR, Sesto Fiorentino, Italy. 3 Department of Industrial Engineering, University of Florence, Florence, Italy. 4 Medical Physics Unit, Azienda Ospedaliero Universitaria Careggi, Florence, Italy. 5 Department of Physics, Politecnico di Milano, Milan, Italy Purpose/Objective: Developing an MR-compatible tissue-equivalent lung phantom, capable of replicating steady dynamic breathing. As radiotherapy treatments become increasingly complex, phantoms closely simulating clinical conditions are essential to explore innovative techniques and devices and to perform advanced QA. Material/Methods: The lung phantom consists of a 20 cm-long triangular prism, designed to reproduce anthropomorphic characteristics of the human lung. The lung volume is made of a lung–tissue–mimicking material characterized by a compressible, porous structure with micron-sized air pores, obtained mixing PolyDiMethilSyloxane (PDMS) sponges with agarose hydrogel-in-PDMS emulsion [1].A 3D-printed scaffold houses the phantom. The scaffold includes a movable side, allowing phantom axial compression. This movable side comprises two spherical lesions of different sizes (fig.1a). Both the lesions and the
specifically designed to allow tight insertion of both a LumenCare applicator (ELEKTA) and a Trocar needle (ELEKTA) to minimize potential air gaps. CT images were acquired for the measurement setup (Figure 1), which included a Farmer-type ionization chamber, to perform treatment planning. The Flexisource (ELEKTA) was planned to dwell at the farthest position with a prescription of 3.5 Gy normalized at 10 mm from the dwell point. The doses measured in the ionization chamber were compared with the calculated doses. To validate the measurement accuracy, the correction factor for the needle measurement relative to the LumenCare was calculated. The air kerma strength ranged from 15,162 to 40,047 cGy•cm2/h.
Results: The difference between the calculated and measured mean doses using the LumenCare setup was - 0.6±2.4% (Table 1), which was comparable to the reported differences between measured and TG-43 values [2]. The measured dose using the needle was 7.80±0.07 cGy. The correction factor of the needle measurement relative to the LumenCare was calculated as 1.015±0.01. This value shows excellent agreement with the previously reported correction factor of 1.017±0.002 for a stainless-steel applicator compared with a plastic one [2]. This consistency validates the accuracy of the developed phantom.
Conclusion: The phantom developed in this study enables accurate dose measurements with an uncertainty of ±3%, which is generally acceptable for clinical QA. Furthermore, the phantom accurately measured the specific dose perturbation effects of the metallic applicator, which is
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