ESTRO 2021 Abstract Book

S953

ESTRO 2021

previously described; it is a novel technique that requires a multidisciplinary approach and a well-organized team. Our objective is to assess the feasibility of this technique in a large public tertiary hospital. Materials and Methods We enrolled postmenopausal women with early-stage breast cancer who were candidates for breast conserving surgery. Inclusion criteria were: age ≥ 50 years, tumor size ≤3 cm, cN0, no evidence of distant metastases, hormonosensitive invasive tumors, her2 negative, ki67<20% and negative margins after lumpectomy. Patients with tumors close to the skin, lobular histology, a known mutation of BRCA, linfovascular invasion, with extensive intraductal carcinoma or multifocal tumors were not included. Catheters were implanted with a free-hand technique intraoperatively with the surgeon assistance once the pathologist ruled out the axillary involvement and the radiologist confirmed the margin status. Tumor bed was marked with radiopaque markers. Forty eight hours after the procedure, CT scan and 3D planning were performed. Once the final pathological report was obtained 72 hours after the lumpectomy, the treatment was administered. APBI was delivered as 34 Gy in 10 bid fractions or 30.1 Gy in 7 bid fractions. Clinical data were prospectively collected during follow up. Results Between 2014 and 2021, 44 patients were treated. All cases were presented in a multidisciplinary committee and evaluated by a radiation oncologist prior to the surgery. Patient, tumor and implant characteristics are shown in Table 1. Median duration of the catheter insertion was 15 minutes, and a median of seven catheters were implanted (range 5-9). Median CTV volume was 28 cc with a median CTV D90 =106.8%.