S222
Clinical - Breast
ESTRO 2026
study was to achieve nationwide harmonization of clinical and technical hyperthermia protocols in preparation for the prospective RT-HYPE study (clinicaltrials.gov NCT06452485), evaluating postoperative re-irradiation with or without hyperthermia in LRR breast cancer. Material/Methods: A structured three-step consensus process was implemented by the three Dutch radiotherapy centers (Amsterdam UMC, Erasmus MC, Institute Verbeeten) currently delivering hyperthermia combined with re- irradiation. First, an inventory of existing hyperthermia devices, thermometry systems, treatment protocols, and documentation procedures was conducted through on-site audits and structured interviews. Differences and similarities were recorded in a comprehensive item list. Next, consensus was achieved using the Nominal Group Technique, a suitable structured group decision-making process for three participating centers. Four multidisciplinary meetings were held in 2023 to align clinical delivery, quality assurance, and data registration, in accordance with ESHO guidelines for superficial hyperthermia clinical trials. The final step was protocol implementation across all centers from January 2024 onward (Figure 1). Results: All centers employed radiofrequency or microwave hyperthermia systems (70–433.9 MHz) suitable for target depths up to 4 cm, with invasive thermometry applied for targets deeper than 1 cm. Consensus was reached on key treatment parameters, including a 15- minute pre-heating phase followed by 60 minutes of steady-state heating per session, a median target temperature goal of 41–42 °C, and one weekly hyperthermia session shortly after radiotherapy (Table 1). Centers agreed to maintain the standard re- irradiation schedule of 46 Gy in 23 fractions. Institutional differences—such as thermometry type (fiber-optic versus thermocouple) and timing between radiotherapy and hyperthermia—were accepted and will be recorded for subsequent analysis. A uniform documentation framework was established, standardizing registration of temperature, thermal dose (CEM43), and target-related measurement locations.
Conclusion: Incidental axillary lymph nodes on RT planning CT are clinically relevant findings that may aid in early recognition of axillary residual disease. Malignancy was identified in about one-third of cases and was associated with advanced age, prior axillary dissection, higher nodal stage, and advanced pathology. Correlation with USG and PET-CT remains valuable for nodal characterization. Keywords: Breast cancer, Radiotherapy, axillary lymph node Digital Poster 865 Achieving national consensus in thermoradiation protocols for treatment of patients with locoregional recurrent breast cancer in the Netherlands Lisca F Wurfbain 1 , Akke Bakker 2 , Sergio Curto 3 , Martine Franckena-Schouten 3 , Anton Rink 3 , Abi Kanagaratnam 3 , Abdelali Ameziane 3 , Marion Essers 4 , Maaike Schippers 4 , Michelle van Wieren 4 , Rianne Oldenhof - de Kroon 1 , Remko Zweije 1 , Paola Tello Valverde 1 , Annemarie Holtmaat 1 , Willemijn Kolff 1 , Daphne de Vries-Huizing 1 , Joost Verhoeff 1 , Hans Crezee 1 , Desiree van den Bongard 1 1 Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Radiation Oncology, Princess Maxima Center/UMCU, Utrecht, Netherlands. 3 Radiation Oncology, Erasmus MC, Rotterdam, Netherlands. 4 Radiation Oncology, Institute Verbeeten, Tilburg, Netherlands Purpose/Objective: Hyperthermia combined with re-irradiation has shown substantial efficacy in locoregional recurrent (LRR) breast cancer and is one of the standard treatment protocols in the Netherlands. However, variations in hyperthermia delivery, temperature monitoring, and data reporting between Dutch centers hinder consistent outcome evaluation. The objective of this
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