S2606
Radiobiology - Radiobiological modelling
ESTRO 2026
Digital Poster 4296 Translational In Vitro Model for Ir-192 Interventional Radiotherapy (Modern Brachytherapy): Setup Validation and Dose Distribution Analysis Enrico Rosa 1,2 , Benedetta Niccolini 3 , Riccardo Di Santo 4 , Bruno Fionda 1 , Maria Vaccaro 1 , Elisa Placidi 1 , Marco De Spirito 1,5 , Elisabetta Tabolacci 3,6 , Luca Tagliaferri 1,7 , Gabriele Ciasca 5 1 Dipartimento di Diagnostica per Immagini e Radioterapia Oncologica, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 2 Department of Theoretical and Applied Sciences, eCampus University, Rome, Italy. 3 Dipartimento di Sanità Pubblica e Scienze della Vita, Università Cattolica del Sacro Cuore, Rome, Italy. 4 Department of Life Science, Health, and Health Professions, UniLink Campus, Rome, Italy. 5 Dipartimento di Neuroscienze, Università Cattolica del Sacro Cuore, Rome, Italy. 6 Dipartimento di Sanità Pubblica e Scienze della Vita, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 7 Dipartimento di Scienze Radiologiche, Università Cattolica del Sacro Cuore, Rome, Italy Purpose/Objective: Interventional radiotherapy (IRT; modern brachytherapy) with high- dose-rate (HDR) Ir-192 sources is a highly localized modality used in several oncological applications. Reliable in vitro models are essential to reproduce clinical irradiation geometries and investigate radiobiological responses under controlled conditions [1]. This study validates a custom setup for in vitro IRT exposure, focusing on the accuracy of dose distributions through combined computational and experimental dosimetry. Material/Methods: An experimental setup reproducing clinical HDR IRT geometry was realized using an Ir-192 source and standard multiwell plates. Two IRT catheters were positioned on the plate, and four dwell positions (two per catheter) were activated over selected wells to create reference dose regions for benchmarking. A planning CT scan of the setup was acquired to generate an ad hoc treatment plan and corresponding dose distribution. Dose was normalized at the bottom surface of the selected wells, corresponding to the cell- adherent layer, by prescribing so that 100% of the prescription dose was at the geometric center of the well bottom, located approximately 8 mm below the plate top for a standard 96-well flat- bottom plate. To simulate the presence of a cell culture, each selected well was filled with 200 µL of culture medium prior to irradiation. Dose distributions were calculated with the TG-43 formalism [2] (homogeneous water approximation) and with the Collapsed Cone Convolution (CCC) algorithm in Oncentra Brachy, according to the TG-186 formalism [3], which accounts for heterogeneities and material density variations. Experimental validation used Gafchromic™ EBT3 films placed at the well bottoms, and films were scanned and analyzed by triple-channel dosimetry in ImageJ after calibration with reference doses. Results: The three dose distributions, two calculated (TG-43 and TG-186/CCC) and one measured, showed good agreement, with differences of 2– 5% that tended to increase with distance from the sources (i.e., toward the center of the multiwell plate) (Figure). However, discrepancies between calculated and measured dosimetric maps, as well as between TG-43 and TG-186, were not statistically significant, considering uncertainties from the computational models and film-based dosimetry. Conclusion: This setup provides a reliable and reproducible platform for in vitro validation of IRT dose delivery. The concordance among dose distributions from TG-43, TG-186, and EBT3 film measurements supports the dosimetric robustness of the in vitro system and its
Radioembolization Therapy with T(rep)=1.5 h and α / β = 10 for lesion [4]. Results: For EBRT results, theoretical BED is 48 Gy, while the MAESTRO® calculation is 48.52±13.30, showing full agreement. For RLT, the results are 0.97±0.70 Gy for the first set and 0.96±0.72 Gy for the second. The cumulative dose is equal to 48.06±13.30 Gy and 50.58±11.92 Gy, respectively. Conclusion: Theoretical and software-based calculations show strong consistency. In this case, the cumulative BED confirms that EBRT provides the dominant dose contribution. This approach demonstrates the feasibility of cumulative dose evaluation in patients previously treated with EBRT, particularly for OARs with potentially impaired physiological function. Such analysis supports the optimization of safe and effective radiopharmaceutical administration in theranostic oncology.
References: [1] Bilgin G."Current and future directions in theranostics for neuroendocrine prostate cancer."Cancer Treatment Reviews (2025).[2] Rahbar K."Is the vision of radioligand therapy for prostate cancer becoming a reality? An overview of the phase III VISION trial and its importance for the future of theranostics."Journal of Nuclear Medicine (2019).[3] Nath R."AAPM recommendations on dose prescription and reporting methods for permanent interstitial brachytherapy for prostate cancer: Report of Task Group 137."Medical physics (2009).[4] Cremonesi M."Radioembolisation with 90Y-microspheres: dosimetric and radiobiological investigation for multi-cycle treatment."European journal of nuclear medicine and molecular imaging (2008). Keywords: Theranostics, 177Lu-PSMA, EBRT
Made with FlippingBook - Share PDF online