S272
Clinical - Breast
ESTRO 2026
months when available. Toxicities were graded per CTCAE v5.0. Results: All patients completed SBRT without interruption. The median age was 80 years (range 68–86). Stages included IA (n=1), IIA (n=3), IIIB (n=1), and IV (n=3). The most frequent subtype was Luminal A (n=4), followed by Luminal B (n=2), HER2-positive (n=1), and Triple Negative (n=1). At 3 months, 3 of 5 evaluable patients showed a partial radiologic response, with tumor size reduction from 29 mm to 9–20 mm. No grade ≥ 3 acute or late toxicities were reported, and treatment was well tolerated even in patients with ECOG ≥ 2. At the time of analysis, three patients had not yet reached 12-month imaging follow-up due to recent treatment or clinical status. No local recurrence or distant progression has been observed to date. Conclusion: Single-fraction SBRT (21–24 Gy) appears to be a feasible, safe, and well-tolerated treatment option for patients with inoperable breast cancer, offering encouraging early local control with minimal toxicity. Delivering treatment in a single session may significantly enhance quality of life by avoiding prolonged treatment courses in this vulnerable population. Ongoing follow-up and larger patient inclusion are needed to confirm long-term efficacy and safety outcomes. Keywords: Breast, SBRT Digital Poster Highlight 2322 Updated Follow-up of SBRT as Primary Treatment in Breast Cancer Patients Unfit for Surgery Julia Garcia 1 , Ines Ollinger 1 , Isabela Gaztelu 2 , Carmen Colomina 1 , Santiago Velazquez 3 , Gema Muñiz 3 , Nerea Lopez 3 , Roberto De Haro 1 1 Radiation Oncology, Hospital Universitario Virgen del Rocio, Seville, Spain. 2 Radiation Oncology, Hospital Puerta del Mar, Cadiz, Spain. 3 Hospital Physics, Hospital Universitario Virgen del Rocio, Seville, Spain Purpose/Objective: Surgical resection remains the mainstay of breast cancer management; however, curative treatment becomes challenging when surgery is contraindicated or declined. This study presents the updated follow-up of our previously reported prospective trial, evaluating the feasibility, safety, and early efficacy of Stereotactic Body Radiation Therapy (SBRT) as a definitive local treatment for patients ineligible for surgery. Material/Methods: Between 2023 and 2025, twenty-four female breast cancer patients deemed ineligible for surgery were prospectively evaluated. SBRT was delivered at a total dose of 40 Gy in 5 alternate-day fractions using a
numerically large target volume variations warrant further investigation, but one reason may be that the national nomenclature may not be fully adhered to by some RT departments. On the other hand, small dose variations within the studied fractionation schedules suggest good adherence to national treatment guidelines for left-sided breast tumours. References: NOTE: This work is submitted on behalf of the SKvaRT steering committee. Keywords: radiotherapy register Digital Poster 2307 Single-Fraction Stereotactic Body Radiotherapy for Inoperable Breast Cancer: Updated Early Outcomes and Safety Ines Ollinger 1 , Julia Garcia 1 , Sara Estrella 2 , Maria Sanchez 1 , Isabela Gaztelu 3 , Santiago Velazquez 4 , Gema Muñiz 4 , Nerea Lopez 4 , Roberto De Haro 1 1 Radiation Oncology, Hospital Universitario Virgen de Rocio, Seville, Spain. 2 Radiation Oncology, Hospital Virgen de Puerto, Plasencia, Spain. 3 Radiation Oncology, Hospital Puerta del Mar, Cadiz, Spain. 4 Hospital Physics, Hospital Universitario Virgen de Rocio, Seville, Spain Purpose/Objective: For patients with breast cancer who are not candidates for surgery due to advanced age, comorbidities, or personal preference, curative treatment options remain limited. In this context, Stereotactic Body Radiotherapy (SBRT) offers a non- invasive and highly precise alternative with potential for durable local control. Delivering SBRT in a single fraction may further improve patient comfort and quality of life by minimizing hospital visits and treatment burden, which is particularly valuable for elderly or frail individuals.This study presents the updated follow-up and expanded cohort of our preliminary experience, evaluating the feasibility, safety, and early efficacy of single-fraction SBRT in patients with inoperable breast cancer. Material/Methods: Between 2024 and 2025, eight female patients (aged 68–86 years) with inoperable or metastatic breast cancer were treated with single-fraction SBRT (21–24 Gy). Tumor histologies included invasive ductal, lobular, and HER2-positive subtypes, with stages ranging from I to IV. SBRT was planned using 4D-CT and delivered with a dedicated stereotactic setup without invasive immobilization. Systemic therapy, including chemotherapy, hormonal therapy, or immunotherapy, was administered according to molecular subtype and patient condition. Tumor response was assessed by imaging at 3, 6, and 12
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