ESTRO 2024 - Abstract Book

S162

Brachytherapy - Breast

ESTRO 2024

chemotherapy (NACT) followed by conservative breast surgery and adjuvant external beam radiotherapy in terms of local control (LC), regional control (RC) and overall survival (OS).

Material/Methods:

Patients with locally advanced breast cancer (clinical stage T1-T4 N+) who received NACT followed by conservative breast surgery (either with axillary lymph node dissection or sentinel lymph node biopsy) and adjuvant radiotherapy plus HD-BT boost in our institution were retrospectively reviewed. The main NACT scheme included epirubicin-cyclophosphamide and sequential taxol with or without anti-HER2 therapy according to the HER2 status. With the exception of triple negative subtype, the majority of patients received adjuvant systemic treatment (hormonotherapy and/or chemotherapy/anti-HER2 therapy), according to the standard of care.

Main radiation therapy schemes were 50Gy in 25 fractions (until 2016) and from 2016 onwards, moderate hypofractionation (42.56Gy in 16 fractions or 40.05Gy in 15 fractions).

Brachytherapy: interstitial multicatheter high-dose rate was used in all patients and 15 Gy in 3 twice-daily fractions over 2 days was the main scheme. CT image-guided planning was carried out in all cases. Toxicity analysis: To classify late toxicity we relied on the use of CTCAEv.5 scales. Statistical analysis: study endpoints included 5- and 8-year ipsilateral breast recurrence (IBR) free survival, regional recurrence (RR) free survival, distant metastases (DM) free survival, progression-free survival (PFS) and overall survival (OS). Kaplan-Meier and Log-rank tests were used. For statistical analysis SPSS v.25 was used.

Results:

A total of 144 patients (p) treated between September 2008 and April 2022 were included. Median follow-up was 63 months (3-169). Mean age at the time of HD-BT boost was 49.7 years (23-74). Most common tumor histology was ductal invasive carcinoma (98%).

Clinical stage: 51 p (35.42%) had T1 tumours, 71p (49.31%) T2, 21p T3 (14.58%) and 1p (0.7%) T4. 69p (47.9%) were N0, 62p (43.06%) were N1, and 13p (9%) were N2 or more, at diagnosis.

Tumour phenotype: 36 patients (25%) had triple negative tumours; 30% Luminal-HER2; 12.5% HER2 and the rest were Luminal. Histologic grade: 5.5% (8p) were grade 1, 41.6% (60p) grade 2 and 52.8% (76p) grade 3 tumours.

Brachytherapy characteristics: Main dosimetric results: median D90 PTV 106.83% PD (72.99-115.77), median V100 PTV 94.9% PD (52.28-99.58), median CI 1.67 (V100 implant/V100PTV) (1.01-2.83) and IH (V150implant/V100implant) 29.95 (20.7-42.6), respectively. Tumoral response: After primary systemic therapy, 44p (30.5%) had pathological complete response (pCR).

Events: 9 ipsilateral breast recurrences (IBR), 8 regional recurrences (RR), and 22 distant metastases (DM). Survival and prognostic factors:

5 and 8-year IBR-free survival was 94.2 and 90.4%,

5 and 8-year regional-free survival was 97.5 and 90%,

5 and 8-year DM-free survival were 87.2 and 82.3 %,

5 and 8-year progression-free survival were 85.6 and 77.8%

5 and 8-years overall survival (OS) and 90.3 and 84.1%, respectively.