ESTRO 2025 - Abstract Book

S552

Clinical - Breast

ESTRO 2025

2946

Digital Poster SBRT treatment in inoperable breast cancer (Breast-SBART): a phase I study Carolina De la Pinta 1 , Marina Alarza 2 , Veronica Gamero 3 , Belen Capuz 4 , Rafael Moris 5 , Juan David García 6 , Alejandro De Cozar 1 , Maria Carmen Sabio 7 , Maria Jesus López 8 , Sonia Rivas 9 , Sonsoles Sancho 1 1 Radiation Oncology Department, Ramon y Cajal Hospital, Madrid, Spain. 2 Radiation Oncology Department, Ramón y Cajal Hospital, Madrid, Spain. 3 Radiology Department, Ramon y Cajal Hospital, Madrid, Spain. 4 Medical Physics, Ramon y Cajal Hospital, Madrid, Spain. 5 Medical Physics Department, Ramon y Cajal Hospital, Madrid, Spain. 6 Medical Physics Department, Ramón y Cajal Hospital, Madrid, Spain. 7 Radiation Oncology Departmetn, Ramon y Cajal Hospital, Madrid, Spain. 8 Gynecology Department, Ramon y Cajal Hospital, Madrid, Spain. 9 Surgery Department, Ramon y Cajal Hospital, Madrid, Spain Purpose/Objective: Patients with breast cancer who are unsuitable for surgical resection are typically managed with palliative systemic therapy alone. SBRT can be a solution for this group of patients. Material/Methods: In this open-label single-arm phase I study, safety and tolerability were assessed including toxicity and cosmetic evaluation as the first objective. Secondary endpoints included QoL (based on EORTC QLQ C30), VAS, local control and overall survival. Patients were enrolled 3 by 3 following Fibonacci criteria by dose escalation up to a maximum dose of 40Gy/5 fractions (36 to 40 Gy). In those patients aged 70 years or older, tumors ≤5cm and node-negative were recruited in our center. Follow-up included breast ultrasound at 3 and 6 months. Results: Between March 2021 and October 2024, 10 patients were included (5 refused surgery treatment, 2 was inoperable, and 3 for both reasons). Median age at recruitment was 89.5 years (84-96), all patients were female, and had hormone receptor positive disease; 88.9% received hormone treatment (1 patient declined). After a median follow up of 26,4 months (4-44 months) all patients had excellent tolerance without acute and chronic toxicity greater than G2. There was only one patient with toxicity in subcutaneous cellular tissue G1 at 6 and 9 months of follow-up with a dose of 36Gy in 5 fractions. In the cosmetic evaluation there was no deformity in the treated breast, no increase in hardness, and slight change in skin color in one patient. Pain assessment using the VAS scale was 0 in treatment and follow-up. Best local control included 5 patients with complete response, 2 patients with partial response, and 3 patients with stable disease. No patient had local progression or metastases. OS at median follow-up was 88.89%; one patient died for another reason. Conclusion: SBRT is a reasonable treatment for patients with localized breast cancer. The dose of 40Gy in 5 fractions is safe and tolerable. Based on these data we are working on a phase II study.

Keywords: SBRT, breast cancer

2947

Digital Poster Impact of pre-treatment respiratory training in left breast cancer patients treated with adjuvant radiotherapy using deep inspiration breath hold. Simone Baroni 1 , Luca Frassinelli 1 , Claudio Scaffidi 1,2 , Rachele Petrucci 1 , Nicola Padula 3,4 , Anna Sardo 3 , Erica Prato 1 , Luca Delpiano 1 , Francesco Lucio 3 , Alessia Reali 1