ESTRO 2025 - Abstract Book

S835

Clinical - Gynaecology

ESTRO 2025

[2] Potter, R., et al. (2018). The EMB[RACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies. Clinical and Translational Radiation Oncology 9 (2018) 48 60. Doi: https://doi.org/10.1016/j.ctro.2018.01.001 [3] Tan, L., Potter, R., et al. (2019). Change in Pattern of Failure after IGBT for cervical cancer: Analysis from the RetroEMBRACE Study. Int J Radiation Oncol Biol Phys Vol. 104 No. 4 pp 895-904. Doi: https://doi.org/10.1016/j.ijrobp.2019.03.038

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Digital Poster Fast and robust on-line adaptive hyperthermia planning to ensure consistent thermoradiotherapy treatment quality in patients with pelvic tumours. H. P. Kok, J. Crezee Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands Purpose/Objective: Hyperthermia treatments induce tumour radiosensitization by raising the temperature to 40-43°C for ~1h. Clinical application is establised for several malignancies, typically increasing tumour control by ~15% without significantly enhancing side effects. Treatment efficacy roughly doubles with every additional 0.5°C. Pelvic tumours (e.g. cervix, bladder, rectum) are heated using a phased-array system, with multiple phase-amplitude controlled antennas around the patient. This allows focusing, though conformal heating is not possible. Consequently, temperatures at tissue interfaces with large contrast in dielectric properties and blood perfusion (i.e. muscle/fat or muscle/bone) could exceed the pain sensation threshold, requiring adequate adjustments of antenna settings. The exact temperatures are difficult to predict by treatment planning due to large inter-patient variations in tissue properties. Treatments are therefore guided by intraluminal thermometry probes and patient feedback. On-line adjusments are based on operator experience. The number of institutes applying hyperthermia is rapidly increasing, which makes consistent treatment performance increasingly important to ensure operator-independent treatment quality and optimal radiosensitization. To address this need, robust on-line adaptive planning was developed. Material/Methods: We developed on-line re-optimization based on temperature changes induced by phase-amplitude adjustments. Robust prediction of temperature changes was confirmed in a cervical cancer patient by evaluating 100 cases with different dielectric properties and perfusion, randomly selected within the uncertainty ranges. Adaptive planning re optimizes the temperature distribution relative to the distribution predicted with the current phase-amplitude settings. New settings should simultaneously 1)reduce the temperature level at the specified location, 2)maintain tumour heating and 3)induce minimal temperature increase elsewhere to avoid new complaints. The algorithm was compared to adjustments by very experienced operators (golden standard) for 22 cases in 16 cervical cancer patients treated with the 70MHz ALBA-4D system, evaluating local temperature reduction, maximum increase at other potential complaint locations and tumour temperature. Results: Although absolute temperature predictions vary up to several degrees due to inter-patient variation in tissue properties, prediction of temperature changes is robust with variations typically within a few percent (Fig.1). Using these predictions in an on-line inverse re-optimization algorithm yields effective temperature reduction at the complaint location with minimal temperature increase at other locations, while maintaining therapeutic heating. Results are very similar to strategies applied by well-experienced operators (Fig.2), indicating consistent treatment quality. The re-optimization typically takes only ~10 seconds.