ESTRO 2025 - Abstract Book

S442

Clinical - Breast

ESTRO 2025

Conclusion: In this large BC series, RT-related fatigue onset was reported in a minority of cases. CLAS values seem to be negatively affected by HT and treatment toxicity. The positive impact of CT on RT-related fatigue was probably due to the CLAS low values at T0 of chemo-treated patients that progressively increased during the RT course (<0.001) (Table 1).

Keywords: ADJUVANT RADIOTHERAPY; FATIGUE; BREAST CANCER

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Digital Poster Adding a sequential nodal boost in high-risk primary breast cancer – a retrospective study of radiotherapy planning and outcomes Marianne Vogsen 1,2,3 , Marie Louise Holm Milo 4,5 , Agnethe Langborg Rudbeck 1,3 , Else Maae 6 , Stine Elleberg Petersen 7 , Mette Holck Nielsen 1 , Mette Skovhus Thomsen 8 , Birgitte Vrou Offersen 2 1 Oncology, Odense University Hospital, Odense, Denmark. 2 Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark. 3 Clinical Research, University of Southern Denmark, Odense, Denmark. 4 Oncology, Aalborg University Hospital, Aalborg, Denmark. 5 Department of Clinical Medicine, Aalborg University, Aalborg, Denmark. 6 Oncology, Lillebaelt Hospital, Vejle, Denmark. 7 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 8 Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: To describe radiotherapy planning and follow-up in patients who received a sequential nodal boost as a supplement to standard loco-regional radiotherapy after high-risk breast cancer (BC) in a period without national guidelines for a nodal boost. Material/Methods: The study included patients from four Danish radiotherapy centres who received adjuvant radiotherapy to the breast or chest wall and locoregional lymph nodes with an additional sequential nodal boost between 2016 and 2023. Data on the patients, tumours, radiotherapy, reasons for nodal boost, and follow-up were extracted from the medical files and dose-planning systems at all centres. If clinically feasible, nodal biopsies were performed. Descriptive statistics were used to characterise the patients and their prognosis. Results: In total, 124 patients had at least one nodal boost volume. The median age was 55 (range 26-87), and most patients had neoadjuvant systemic treatment (71%). About 40% had HER2 normal and ER-negative/low disease. Standard radiotherapy was prescribed as 50Gy/25fr (40%) and 40Gy/15fr (60%). The main indication for the nodal boost was regional lymph nodes beyond surgical reach detected on pre-surgical FDG-PET/CT (73%), in other imaging modalities (14%) or during radiotherapy planning (7%), and the remaining due to non-radical axillary node dissection (6%). Malignancy was confirmed by biopsy in 40% of the patients. In total, 168 nodal boost volumes were delivered, up to five volumes per patient. The distribution of involved nodes was level I (4%), level II (15%), level III (27%), level IV (10%), supraclavicular level outside level IV (9%), internal mammary nodes (32%), and interpectoral space (4%). Most nodes received 16Gy/8fr (57%) or 10Gy/5fractions (40%), primarily as photon therapy (79%). At a median follow-up of 3.5 years (range 0.8-9.6), 30% (37/124) had a BC event. The median time from BC diagnosis to any BC-related event was 1.4 years (range 0.4-6.7). Three patients had local or loco-regional recurrence, whereas the remaining 34 patients had either synchronous or distant failure only (92%). Of those, 26/34 (60%) had HER2 normal and ER-negative/low disease, and 27/34 (80%) have died. The median time from BC diagnosis to BC-related death was 2.1 years (range 0.8-6.1).