ESTRO 2025 - Abstract Book

S509

Clinical - Breast

ESTRO 2025

Results: The 36 panel members (24 from Europe and 12 from US) included radiation/clinical (n=14) and medical oncologists (n=1), breast (n=18) and plastic surgeons (n=1), and medical physicists (n=2). The female/male ratio was 1. In 2 rounds (June 24 and September 24), panel members answered 97 non-demographic questions. Overall, a consensus was achieved in 81.4% of the questions. Regarding treatment options (n=35), salvage mastectomy is not the only standard treatment (100% agreement) and 2 nd BCT can be presented as a valuable option (100%). Postmenopausal women with a non-metastatic 2 nd iBCE, tumor size ≤20 mm, HR+, HER2-, cancer-free interval ≥60 months, are good candidates for 2 nd BCT (95.2%). Regarding general questions (n=7), pre-treatment distant metastatic work-up is considered mandatory (77.1%) while clinical and radiological surveillance after 2 nd BCT are the same as for 1 st BCT (100%). For 2 nd breast surgery (n=16), 1 st and 2 nd iBCEs being in (or close to) the same quadrant is not a contra-indication for 2 nd BCT (100%); after SM, immediate reconstruction with autologous reconstruction is reasonable (93.8%). For axillary evaluation (n=11), a sentinel biopsy can be offered to patients with prior sentinel procedure (90.6%); in case of sentinel biopsy for the primary, an axillary dissection for invasive 2 nd iBTE is not advised (96.8%). Regarding breast re-irradiation (n=18), it is recommended to be done (94.1%); proof levels for using interstitial brachytherapy or external radiation therapy are acceptable (90.9% and 84%, respectively). Regarding specific questions, the occurrence of 2 nd iBCE in the context of oligometastatic disease is not a contra-indication for a 2 nd BCT (91.2%). Conclusion: This International DELPHI consensus for 2 nd iBCE strongly recommends consideration of 2 nd BCT as an alternative to SM and provides important guidance for physicians. Subsequently, the patients’ perspectives remain crucial in the decision-making process regarding salvage treatment options. Poster Discussion A phase I-II dose escalation study of stereotactic ablative body radiation therapy for breast cancer (NCT03585621) Danny Vesprini 1,2 , Daniel Palhares 1,2 , Merrylee McGuffin 1 , Sandi Bosnic 1 , Dylan Breitkreutz 1,2 , Hanbo Chen 1,2 , Ezra Hahn 3,2 , Irene Karam 1,2 , Claire McCann 1 , Hany Soliman 1,2 , Eileen Rakovitch 1,2 , Justin Lee 4,5 1 Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Canada. 2 Radiation Oncology, University of Toronto, Toronto, Canada. 3 Radiation Oncology, Princess Margaret Cancer Centre, Toronto, Canada. 4 Radiation Oncology, Juravinski Cancer Centre, Hamilton, Canada. 5 Radiation Oncology, McMaster University, Hamilton, Canada Purpose/Objective: Assess the maximum tolerated dose and acute toxicities of stereotactic ablative body radiotherapy (SABR) for intact breast cancer to help inform a clinically acceptable dose for future randomized trials. Material/Methods: This prospective Phase I-II dose escalation trial enrolled breast cancer patients who declined or were not candidates for surgery (medically inoperable, unresectable, metastatic) and were deemed appropriate for breast SABR as a primary treatment modality. Eligible patients had cT1-T4 unifocal tumours, were N0-N2, and had M0 or M1 disease. Radiation was delivered twice weekly using VMAT. There were 4 dose levels (DL; 36, 40, 44 and 48Gy in 4 fractions). Acute toxicity was recorded and monitored for up to 12 weeks post treatment. According to the stopping rule, if more than 2 patients experienced grade 3 or higher toxicity within 12 weeks post treatment (excluding grade 3 skin toxicity) at a specified DL, all remaining patients would have been treated at the last tolerated dose, otherwise accrual would proceed to the next DL. Acute toxicities including desquamation, erythema, edema and pain as per Keywords: breast cancer recurrence, DELPHI consensus 2120