ESTRO 2025 - Abstract Book

S2753

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: We conclude that the RP model produces high-quality clinical plans with a high success rate and significantly reduces optimization time. In most cases, the RP plans appear to be Pareto optimal and therefore the question becomes only whether or not the planner wishes to balance the trade-offs differently [2]. In rare cases, however, the model may miss the Pareto surface and it is the responsibility of the physicist to identify these cases and perform additional manual optimization. Pareto optimality is of course not an attribute of RapidPlan itself, but an indication of high quality input data. Implementation of the model in the clinical workflow has raised and standardized the plan quality. References: [1] Ayuthaya IIN, Sanghangthum T, Oonsiri P, et al. Multi-planner validation of RapidPlan knowledge-based model for volumetric modulated arc therapy in prostate cancer. Journal of Applied Clinical Medical Physics. 2024;25(1). doi: 10.1002/acm2.14223 [2] Breedveld S, Craft D, van Haveren R, Heijmen B. Multi-criteria optimization and decision-making in radiotherapy. European Journal of Operational Research. 2019;277(1):1-19. doi: 10.1016/j.ejor.2018.08.019. 1227 Digital Poster HDR brachytherapy vs VMAT with 3D printed bolus in the treatment of skin cancer of large surfaces of the lower extremities Andrei Tšižik, Nikolai Saveljev Radiotherapy, North Estonia Medical Centre, Tallinn, Estonia Purpose/Objective: The aim of this study was to compare two radiotherapy methods (HDR-BT and VMAT) for skin cancer of large surfaces of the lower extremities, used at the North Estonia Medical Center. Material/Methods: Three patients previously treated with HDR-BT or VMAT were replanned for treatment with an alternative method. The HDR-BT plans were calculated using Oncentra system (v.4.6, Elekta Brachytherapy) with an Ir-192 source and TG-43 algorithm. We used a rigid catheter carrier form with a head/neck mask and 4F catheters glued parallel to each other at a distance of 10 mm and 5 mm from the inner surface of the carrier (Fig.1.1). Treatment dose 4 Gy was normalized at 5 mm depth, skin surface dose was in range 110-120% (Fig.1.2). A total dose prescribed to the reference isodose was 16 Gy (EQD2 19 Gy) in 4 fractions twice a week. A 1 cm thick 3D printed bolus was used for VMAT (Fig.2.1). PTV was created by adding a 5 mm wide margin around the skin. VMAT plans were created with the RayStation TPS (v.10A, RaySearch Laboratories AB) to achieve 95% dose coverage to 95% of the volume (Fig.2.2). The total dose is 30Gy (3Gy X 10). Dose calculations were performed using a collapse cone algorithm with a grid size of 2 mm. A 6 MV photon beam was used for treatment. Keywords: radiotherapy planning, automatic planning