S303
Clinical - Breast
ESTRO 2026
edema, breast pain, fatigue, and pneumonitis observed in 87, 10, 19, 15, and 4 pts, respectively. G3 acute event was observed only in one pt (radiation dermatitis) with no radiotherapy discontinuation. Late side effects included 13 G1 and 3 G2 skin fibrosis, one G2 cardiac and 6 G1 pulmonary events. No late toxicities of G ≥ 3 were reported. Conclusion: To our knowledge, the current analysis represents one of the largest real-world series in this subgroup of pts, including details on RT volumes, doses, and techniques, and confirms the safety of concomitant RT and T-DM1 in the adjuvant setting. References: Salvestrini V, Kim K, Caini S, Alkner S, Ekholm M, Skyttä T, Becherini C, Coles CE, Kaidar-Person O, Offersen B, de Azambuja E, Visani L, Cortes J, Harbeck N, Rugo HS, Isacke CM, Marangoni E, Morandi A, Lambertini M, Poortmans P, Livi L, Meattini I. Safety profile of trastuzumab-emtansine (T-DM1) with concurrent radiation therapy: A systematic review and meta- analysis. Radiother Oncol. 2023 Sep;186:109805. doi: 10.1016/j.radonc.2023.109805. Epub 2023 Jul 10. PMID: 37437610. Keywords: Her2-positive Cancer, Adjuvant radiation, T-DM1 CBCT-guided adaptive ultrahypofractionated whole-breast radiotherapy: a single-center early experience Damir Vu č ini ć 1 , Hrvoje Kau č i ć 1 , Giovanni Ursi 1 , Matea Leki ć 1 , Aleksandar Kova č evi ć 1 , Domagoj Kosmina 1,2 , Blanka Jak š i ć 1 , Dragan Schwarz 1,3 1 Specialty Hospital Radiochirurgia Zagreb, Radiochirurgia Zagreb, Sveta Nedelja, Croatia. 2 Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia. 3 Medical Faculty, University of Pula, Pula, Croatia Purpose/Objective: This study reports the implementation and early clinical experience of adaptive adjuvant whole-breast radiotherapy (ART) delivered using the Fast Forward hypofractionated regimen. The primary objective was to evaluate the feasibility, workflow efficiency, and clinical safety of the ART approach integrating daily CBCT-based plan adaptation with inspiration breath- hold (IBH). Material/Methods: A total of 40 patients treated between February 2024 and September 2025 with ART following breast- Digital Poster 3460 conserving surgery were analyzed. Patient positioning and respiratory motion management were achieved using an inspiration breath-hold (IBH) technique, with
with tumor bed boost and regional nodal irradiation performed when clinically indicated. Tolerance assessment (as per CTCAE v.5 scale) was performed during RT and T-DM1 administration, followed by clinical and radiological evaluations every six months. Data analysis was focused particularly on skin, lung and heart side effects. Results:
From January 2022 to January 2025, a total of 121 pts were included, with a median age of 54 years (IQR: 49- 62). Relevant pts data are summarized in Table 1. At diagnosis, 98 pts had a T1 and T2-stage tumor, while 14 and 9 pts presented with T3 and T4 disease, respectively. Fifty-six (46.3%) pts had node-negative disease. Before the start of RT, pts received a median of 2 cycles (range: 0–6) of adjuvant T-DM1, whereas median total cycles administered was 14 (range: 3-14). Treatment volumes included the residual breast and tumor bed boost after breast-conserving surgery (67%) or the chest wall after mastectomy (33%), with nodal irradiation performed as required (51%). A hypofractionated schedule was prescribed in 75% of whole-breast and in half of postmastectomy irradiation. Patients were treated with IMRT–VMAT (87%) or 3D-CRT (13%) technique. After a median follow-up of 18.5 (IQR:10-27.5) months, acute toxicity was mild (Grade, G ≤ 2), with radiation dermatitis,
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