ESTRO 2025 - Abstract Book

S354

Brachytherapy - Physics

ESTRO 2025

Approximation of TPU applicator as homogeneous water equivalent material showed a better agreement with a gamma passing rate of 98%. A lower gamma passing rates was observed with fomay TPU (97.2%), most likely due its lower density. Conclusion: Ultracur3D® FL 300 resin can be considered a promising material for 3D printed skin brachytherapy applicator as it combines both high flexibility and appropriate dosimetric characteristics

Keywords: 3D printing, innovative materials, dosimetry

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Digital Poster Dosimetry of I-125 seeds according to GEC-ESTRO recommendations at clinical level Frank-Andre Siebert, Hirt Markus UKSH, Clinic of Radiotherapy, Kiel, Germany

Purpose/Objective: This study presents results of source strength measurements of a single clinic for one seed model according to GEC ESTRO guidelines [1]. Calculation of the distribution of LDR source strengths, lacking in the literature [1], is also shown. Material/Methods: This investigation demonstrates dosimetry of I-125 seeds model I25.S17plus-SM (Eckert&Ziegler Bebig GmbH, Berlin, Germany) of class 6 or 7 (range in air kerma strength (RAKR) 0.587-0.637. Over a period of four years, five test seeds per treated patient were measured individually using well type ionization chambers (WIC) prior to implantation. Test seeds of 34 patients (5x34=170 seeds) were included in this study. The test seeds were ordered as loose seeds from the same seed batch as the seeds used for implantation. Two WICs (calibrated in an accredited laboratory) were used: HDR 1000 Plus (Standard Imaging, Middleton, WI) and SourceCheck 4Pi (PTW, Freiburg, Germany). A warm-up period of at least 1h for the WICs was considered before measurements. Cross-calibration between the two WICs was conducted as well. Each of the five test seeds per patient were measured three times using an integration time of 60s. Results of seed dosimetry was evaluated for normal distribution using the Kolmogorov-Smirnov (KS) test in Excel 2019 (Microsoft corporation, Redmond, WA). Results: Each individual test seed was measured three times and the resulting mean value was used in this study, standard deviation (SD) was 0.1%. SD of RAKRs within the five seeds of the same class per patient was in mean 1.6%. The relative RAKR difference in mean was 0.6% for all patients (SD = 1.6%). The RAKR of seeds of two patients were outside the 5% tolerance recommended in [1] (i.e. 5.1% and 7.2%). Testing for normal distribution with KS test of the relative RAKR difference between measurements and certificate with α=0.05, n=34 and a critical value of 0.22743 (one-sample KS table) resulted in a maximum difference of 0.0937 and, thus, shows the distribution is normal (Fig. 1). Estimated time effort for a medical physicist was about 30 mins per patient for RAKR measurements of five seeds.