S305
Clinical - Breast
ESTRO 2026
Calmettes, Marseilles, France. 17 Radiation Oncology, Institut Bergonié, Bordeaux, France. 18 Radiation Oncology, Pôle Santé Léonard de Vinci, Chambray-lès- Tours, France. 19 Radiation Oncology, Polyclinique de Limoges – Site Chénieux, Limoges, France. 20 Research & Development Department, Unicancer, Paris, France Purpose/Objective: Thyroid dysfunction is a known late effect of neck irradiation, but its relevance after radiotherapy for breast cancer (BC) is debated [1-2]. This study aimed to evaluate the 5-year incidence of thyroid dysfunction in non-metastatic BC patients treated with adjuvant radiotherapy, including nodal irradiation, and to identify potential risk factors. Material/Methods: This study is a secondary analysis of the French prospective, multicentre, randomised, controlled trial HypoG-01 (NCT03127995). A total of 1059 patients with available DICOM-RT data, treated for early BC between 2016 and 2020 were included. Two radiotherapy regimens were assessed: 40Gy/15fx/3 weeks and 50Gy/25fx/5 weeks. The primary endpoint of the current study was the occurrence of clinical thyroid dysfunction within 5 years of follow-up. Secondary endpoints included the dose–effect relationship and the impact of fractionation. Thyroid dosimetric parameters (volume, Dmean, V5-V50, D2%, D5%) were analyzed. Results: With a median follow-up of 4.8 years, the incidence of clinical thyroid dysfunction was 2.2% (n=23/1058). There was no significant association with supraclavicular nodal irradiation, fractionation, or thyroid dosimetric parameters. However, a higher V5 was observed with IMRT compared with 3D-CRT (p=0.003), whereas V10 was lower with IMRT (p=0.007). Patients who developed thyroid dysfunction had a significantly higher mean Body Mass Index (BMI) compared to those who did not (28.9 vs 26.1 kg/m ² , p=0.023), with 43.5% of affected patients classified as obese. Thyroid dosimetric constraints were met in 97.7% of patients, and delineation was consistent across centers.Table 1. Dosimetric characteristics of the thyroid according to the radiotherapy treatment plan. Thyroid dosimetric results are presented as the median and interquartile range after conversion to EQD2: volume, Dmean, V5 to V50, D2%, D5%. EQD2 thyroid with alpha/beta=3.
validated in a larger patient cohort. References:
1.Offersen, B.V.; Boersma, L.J.; Kirkove, C.; Hol, S.; Aznar, M.C.; Sola, A.B.; Kirova, Y.M.; Pignol, J.P.; Remouchamps, V.; Verhoeven, K.; Weltens, C.; Arenas, M.; Gabrys, D.; Kopek, N.; Krause, M.; Lundstedt, D.; Marinko, T.; Montero, A.; Yarnold, J.; Poortmans, P. ESTRO consensus guideline on target volume delineation for elective radiation therapy of early stage breast cancer, version 1.1. Radiother. Oncol. 2016, 118, 205–208. https://doi.org/10.1016/j.radonc.2015.12.027.2.Galand , A.; Prunaretty, J.; Mir, N.; Morel, A.; Bourgier, C.; Aillères, N.; Azria, D.; Fenoglietto, P. Feasibility study of adaptive radiotherapy with Ethos for breast cancer. Front. Oncol. 2023, 13, 1274082. https://doi.org/10.3389/fonc.2023.1274082 Keywords: adaptive radiotherapy, breast cancer Patterns of thyroid dysfunction after breast cancer treatment: results from the HypoG-01 phase III trial Lisa Ciaptacz 1 , Youssef Ghannam 2 , Thomas Brion 3 , Robabeh Ghodssighassemabadi 4 , Guillaume Auzac 2 , Youlia Kirova 3 , Séverine Racadot 5 , Mohamed Benchalal 6 , Jean-Baptiste Clavier 7 , Claire Charra Brunaud 8 , Anaïs Groulier 9 , Delphine Argo-Leignel 10 , Karine Peignaux-Casasnovas 11 , Ahmed Benyoucef 12 , David Pasquier 13 , Philippe Guilbert 14 , Aurore Goineau 15 , Agnès Tallet-Richard 16 , Adeline Petit 17 , Guillemette Bernadou 18 , Xavier Zasadny 19 , Assia Lamrani 20 , Marie Bergeaud 20 , Stefan Michiels 4 , Sofia Rivera 2 1 Radiation Oncology, CHU Dupuytren, Limoges, France. 2 Radiotherapy, Institut Gustave Roussy, Villejuif, France. 3 Radiation Oncology, Institut Curie, Paris, France. 4 Biostatistics and Epidemiology, Gustave Proffered Paper 3554 Roussy INSERM 1018, Villejuif, France. 5 Radiation Oncology, Centre Leon Berard, Lyon, France. 6 Radiation Oncology, Centre Eugene Marquis, Rennes, France. 7 Radiation Oncology, ICANS – Institut de Cancérologie Strasbourg Europe, Strasbourg, France. 8 Radiation Oncology, Institut de Cancérologie de Lorraine – Alexis Vautrin, Vandoeuvre-lès-Nancy, France. 9 Radiation Oncology, Centre Antoine Lacassagne, Nice, France. 10 Radiation Oncology, Hôpital du Scorff, Lorient, France. 11 Radiation Oncology, Centre Georges François Leclerc, Dijon, France. 12 Radiation Oncology, Centre Henri Becquerel, Rouen, France. 13 Radiation Oncology, Centre Oscar Lambret, Lille, France. 14 Radiation Oncology, Institut Jean Godinot, Reims, France. 15 Radiation Oncology, ICO – Institut de Cancerologie de l’Ouest – Site Paul Papin, Angers, France. 16 Radiation Oncology, Institut Paoli-
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