ESTRO 2025 - Abstract Book

S166

Brachytherapy -Breast

ESTRO 2025

Irene Martínez 1 , Ignacio Visus 1 , Paola Jablonska 1 , Naiara Fuentemilla 2 , Lucia Biscari 1 , Sonia Flamarique 1 , Santiago Pellejero 2 , Raquel Villanueva 3 , Amaya Sola 1 , Ujue Ruiz 1 , Maria Isabel Martínez 1 , Patricia Lorenzana 1 , Libe Amondarain 1 , Darwin Enrique Pozo 1 , Ines Villafranca 3 , Elena Villafranca 1 1 Radiation Oncology, Hospital Universitario de Navarra, Pamplona, Spain. 2 Radio Physics, Hospital Universitario de Navarra, Pamplona, Spain. 3 Radiation Oncology Nurse, Hospital Universitario de Navarra, Pamplona, Spain Purpose/Objective: The 10- and 15-year ipsilateral breast recurrence(IBR) rates following breast conserving surgery(BCS) account for 10 20%. Historically radical mastectomy has been considered the first treatment option in this scenario. The aim of this study was to analyse the impact of APBI with interstitial multicatheter high-dose-rate-BT as salvage treatment after secondary BCS in terms of local control(LC), regional control(RC) and overall survival(OS). Material/Methods: Patients with IBR of tumour<3cm treated with secondary BCS and adjuvant interstitial-BT in our institution were retrospectively reviewed. Interstitial multicatheter-HDR was used in all patients. Two APBI-HDR schemes were used: 32-34Gy in 8-10 twice-daily fractions over 4-5 days. CT image-guided planning was carried out in all cases. CTCAEv.5 was used to assess late toxicity. Study endpoints included IBR-free survival, regional recurrence(RR)-free survival, distant metastases(DM)-free survival, progression-free survival (PFS) and OS. SPSSv.25 and Kaplan-Meier and Log-rank tests were used. Results: A total of 120patients(p) were treated between September 2008-March 2023 in our institution. Median follow-up was 68.5 months(9-188). Mean age at the time of salvage-BT was 63 years (23-74). Most common histology: ductal invasive carcinoma(55.83%). Margins >2mm were present in 75p(62.5%), no ink contact was seen in any case. Median interval of time from primary diagnosis to IBR: 148.5months(21-339). Clinical features: 78 p(65%) had T1 and 4p(3.33%) T2 tumours. The rest were pTis. 33p(27.50%) were luminal-B; 27p(22.50%) luminal-A; 11p(9.17%) triple negative; 6p luminal-HER2+(5%) and 2p(1.67%) HER2+. 93p had grade 1-2 and 22.5%(27p) grade 3 tumours. Brachytherapy characteristics: Median of planes: 2(1-4) and median of catheters: 10(4-18) Median D90PTV 3,76GyPD (1.63-4.96), median V100PTV 94,77%PD (65.77-99.24), medianCI 1,7 (V100 implant/V100PTV) (1.06-3.65) and IH(V150implant/V100implant) 29,46 (16.09-40.70), respectively. Events:12 IBR, 5 RR, and 7 DM. 5 and 10-year IBR-free survival:93,4 and 81,9%, 5 and 10-year RR-FS:93,8 and 93,8%, 5 and 10-year DM-FS:94,8 and 89,3%, 5 and 10-year PFS:88,6 and 71,8%, 5 and 10-year OS: 94.3 and 83%, respectively. There was no statistically significant association between LC or OS, and TN phenotype, high histological grade and margin distance(Table1).