ESTRO 2024 - Abstract Book

S723

Clinical - Breast

ESTRO 2024

median prescribed dose was 35 Gy (21-45) in median 5 fractions (3-5). Median volume of treated lesions was 31cc (5-189). Radiotherapy was administered concomitant with systemic therapy only in patients receiving Cdk 4/6 inibitors a 7-day stop was performed before and after SAbR. After a median follow-up of 20 months (3-96) only one patient with liver metastasis developed local recurrence after 7 months from SAbR, 98% of irradiated lesions showed a complete or partial response to treatment. 12 (34%) patients with progression outside the irradiated lesion were retreated with a second course of SAbR continuing the same systemic therapy. No grade ≥3 toxicity was reported. At the time of analysis 31(88,5%) of patients were alive.

Conclusion:

This retrospective analysis of oligo-M BC patients showed an excellent local control after SAbR with a good toxicity profile. This advantage can probably translate in a PFS and OS, with a not negligible, although still theoretical, chance of cure, especially if local therapies are integrated with efficient systemic treatments.

Keywords: oligometastatic breast cancer, SAbR

3200

Digital Poster

Ultra versus moderate-hypofractionation in Partial Breast Irradiation.

Catarina van der Elzen, Alice Alves, Filipa Abreu Martins, João Casalta Lopes, Pedro Meireles, Maria Gabriela Pinto

Centro Hospitalar Universitário de São João, Radioterapia, Porto, Portugal

Purpose/Objective:

The 26 Gy FAST-FORWARD schedule is convenient and substantially less expensive for patients and for health services. It’s consistency of results with earlier hypofractionation trials supports the adoption of 26 Gy in five daily fractions demonstrating non-inferior results in terms of locoregional control and late normal tissue effects when compared to the 5-year results of the UK IMPORT LOW Trial moderate hypofractionation regimen. Partial breast irradiation (PBI) is an alternative treatment for selected patients with early-stage breast cancer, with confirmed non inferiority to whole-breast radiotherapy. We aimed to identify a five-fraction schedule of adjuvant radiation therapy (RT) delivered in 1 week with PBI that is non-inferior in terms of breast acute toxicity as an international standard 15-fraction regimen after primary surgery for early breast cancer.

Material/Methods:

Forty-seven women with early-stage breast cancer, treated between 2020 and 2022, with ultrahypofractionated PBI, were reviewed and compared with our historical cohort of 54 patients treated with moderate hypofractionated PBI. A retrospective study was done of patients at the Radiotherapy Department of Centro Hospitalar Universitário de São João. All patients received adjuvant PBI-3DCRT after lumpectomy, with the prescription of 26Gy in 5 fractions or 40Gy in 15 fractions, once daily, 5 consecutive days. Toxicity was assessed and rated according to the Radiation