ESTRO 2025 - Abstract Book

S2875

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

ESTRO 2025

direction as indicated by the CBCT, but we reposition the patient if the offset exceeds ±5 mm in other directions. The impact of isocenter distance variation on the dose gradient is under evaluation.

Keywords: VMAT-TBI, dosimetry robustness, multi-isocenters

References: https://doi.org/10.1016/j.radonc.2024.110366 https://doi.org/10.1016/j.phro.2024.100537

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Digital Poster Hyperthermia to enhance radiotherapy treatments in soft-tissue sarcoma patients: radiobiological evaluations. Marco D'Andrea 1 , Mariagrazia Petrongari 2 , Simona Marzi 1 , Erminia Infusino 1 , Vincenzo Anelli 3 , Pasqualina D'Urso 2 , Giuseppe Sanguineti 2 , Brando Pavoni 4 , Serena Carraro 4 , Jacopo Coletti 4 , Jakob Öden 5 , Antonella Soriani 1 1 Medical Physics, IRCCS Regina Elena National Cancer Institute, Rome, Italy. 2 Radiotherapy, IRCCS Regina Elena National Cancer Institute, Rome, Italy. 3 Radiology, IRCCS Regina Elena National Cancer Institute, Rome, Italy. 4 Med Logix SRL, R&D, Rome, Italy. 5 RaySearch Laboratories, AB, Stockholm, Sweden Purpose/Objective: At the Regina Elena Cancer Institute in Rome eligible soft-tissue sarcoma patients follow a protocol for pre-operative radio-hyperthermia. DCE-MRI images are used to segment the probably hypoxic sub-regions of the tumour. The study aims at assessing the radiobiological effect of the combined treatment in the treated patients. Material/Methods: From pre-treatment MRI examinations, quantitative parametric maps of k trans (volume transfer constant between blood plasma and extra vascular extracellular space) are derived and used to delineate the hypoxic sub-regions of the GTV (gross tumour volume). A pre-operative dose of 50 Gy in 2 Gy/fraction 5 days a week is delivered with 6MV photon beams. HT is delivered once a week within 30 minutes after RT using the radiative superficial system (ALBA ON 4000D) that uses curved micro-strip antennas of sizes ranging from 66 cm 2 to 440 cm 2 , operating at 434 MHz. HT treatment geometry evaluation and temperature map calculation for each patient have been performed with the PLAN2heat software, while the RT treatment has been planned with the Eclipse TPS. Dose and temperature maps have been imported in the RayStation environment, the latter using a dedicated python script. The evaluation of the radio-sensitizing effect of the HT treatments on the target volumes has been carried out with a dedicated python script as described in [1], following the formulation in [2]:

where T is the hyperthermia treatment temperature, t int is the time interval between the end of the radiotherapy irradiation session and the start of the hypertermia session and α x and β x are the radiobiological parameters at temperature x . Values of 4.9 Gy, 1.73, 2.5, 1.5h -1 and 0.5h have been used for α 37 /β 37 , α 41 /α 37 , β 41 /β 37 , μ and t int ,