S311
Clinical - Breast
ESTRO 2026
normofractionation and 8.6 Gy and 3.5 Gy for hypofractionation and significantly higher with tomotherapy compared with 3D-CRT and VMAT.Conventionally fractionated RT resulted in acute and late higher-grade ( ≥ 3) adverse events of 11% (skin) and 4% (skin and cardiac), respectively. Acute grade ≥ 3 side effects were 8% (skin) with hypofractionation. No higher grade ( ≥ 3) late adverse events were observed in hypofractionated regimens.Even though late skin adverse events were more often in the conventionally fractionated group, this did not reach statistical significance (p=0.056). Regarding RT techniques, only the use of helical tomotherapy was associated with higher incidences of acute grade ≥ 3 skin side effects (p=0.029). With a median follow-up of 45.3 months for the entire cohort, the 1-, and 5-year overall survival rates were 96.1% and 88.7% and local control rates were 100% and 92.5%, respectively. Conclusion: Our long-term findings support the use of moderately hypofractionated RT with volumetric modulated arc therapy as a safe option for bilateral whole breast irradiation in patients with synchronous bilateral breast cancer, demonstrating favorable outcomes. However, prospective data, especially for nodal and bilateral chest wall irradiation involving implants, is still needed. Keywords: hypofractionation, bilateral breast cancer Ultra-Hypofractionation adjuvant radiotherapy with simultaneously integrated boost for breast cancer: Long-Term results from a prospective cohort Maia Dzhugashvili 1 , Juan Antonio Barcia 2 , Escarlata Lopez 3 , Jaume Fernandez Ibiza 4 , Ana Serradilla 5 , Antonio Seral 4 , Sigfredo Romero 1 , Lisellot Torres 1 , Daniela Gonsalves 1 , Loubna Aakki 6 , Raul Hernanz 1 , Castalia Fernandez 1 , Abrahams Ocanto 1 , Jose Begara 7 , Maria Mateos 1 , David Esteban 1 , Evita Krumina 1 , Jose Antonio GonzalezFereira 8 , Jon Andreescu 9 , Antonio Ristori 1 , Juan Jose De la Cruz Troca 10 , Alberto Gomez 11 , Philip Poortmans 12,13 , Ana Belen Bezares 14 , Felipe Counago 1 1 Radiation oncology, GenesisCare, Madrid, Spain. 2 Faculty of Medicine, Universidad Complutence, Madrid, Spain. 3 Radiation oncology, GenesisCare, Granada, Spain. 4 Radiation oncology, GenesisCare, Barcelona, Spain. 5 Radiation oncology, Complejo Hospitalario de Jaen, Jaen, Spain. 6 Radiation oncology, GenesisCare, Alikante, Spain. 7 Radiation oncology, GenesisCare, Malaga, Spain. 8 Radiation oncology, Poster Discussion 3844 GenesisCare, Sevilla, Spain. 9 Radiation oncology, GenesisCare, Cordoba, Spain. 10 Preventive Medicine and Public Health Department, Universidad
and local control, suggesting that dose-intensified RT may offer meaningful clinical benefit even in palliative settings. Therefore, a dose-tailored RT approach that considers each patient’s performance status, disease extent, and treatment tolerance should be emphasized to optimize both efficacy and safety. Keywords: Advanced breast cancer, symptomatic breast cancer
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Hypofractionated and conventionally fractionated radiotherapy for synchronous bilateral breast cancer: Clinical and dosimetric outcomes Eva Meixner 1 , Bahar Cepni 1 , Line Hoeltgen 1 , David Neugebauer 1 , Nathalie Arians 1 , Jakob Liermann 1 , Lars Wessel 1 , Maria Vinsensia 1 , Semi Harrabi 1 , Hanna Waldsperger 1 , Thomas Tessonnier 1 , Juliane Hörner- Rieber 2 , Jürgen Debus 1 1 Department of Radiation Oncology, University Hospital Heidelberg, Heidelberg, Germany. 2 Department of Radiation Oncology, University Hospital Düsseldorf, Düsseldorf, Germany Purpose/Objective: The postoperative irradiation of both breasts in patients with synchronous bilateral breast cancer poses complex technical challenges. The overlapping treatment fields and large target volumes make dosimetry challenging, while data for hypofractionated regimens in this setting is limited. Material/Methods: Bilateral breast cancer patients treated with moderately hypofractionated and conventionally fractionated radiotherapy were identified to evaluate dosimetric parameters, side effects, and oncologic outcomes. Results: Seventy patients treated with a median dose of 50.4 Gy in 28 fractions or 40.05 Gy in 15 fractions using 3D- CRT (28.6%), IMRT (2.9%), VMAT (48.6%) or tomotherapy (20%) were identified. Demographic parameters for both regimens were comparable, except for significant differences regarding younger age and more positive lymph nodes in the conventionally fractionated group.The median PTV volume size was 2451 cm ³ (range: 967-4520cm) in the hypofractionated group and significantly larger than in the conventionally fractionated group of 1876 cm ³ (range: 791-4850cm ³ ).A tumor bed boost was delivered in 52 patients (74.2%), using a simulatenously integrated (n=25) or sequential (n=27) boost with photons (n=33), electrons (n=15) or mixed mode (n=2); two sequential boosts were applied as intraoperative boosts. The median EQD2 lung and heart doses were 8.4 Gy and 4.0 Gy for
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