ESTRO 2021 Abstract Book

S954

ESTRO 2021

Conclusion At our institution, the intraoperative insertion of the catheters adds 15 minutes to the lumpectomy, while allowing direct visualization of the tumor bed, minimizing geographic failures, the number of catheters inserted and the CTV volume. It avoids secondary procedures and the treatment is administered with definitive pathological data. It is a feasible technique, and requires a multidisciplinary team to implement it. PO-1147 Whole breast Radiotherapy in cT1-2 cN0 with pN+ sentinel nodes: preliminary results of LISEN trial M. Borgia 1,2 , C. Rosa 3,4 , L.A. Ursini 4 , M. Nuzzo 4 , M. Di Tommaso 4 , F.C. Di Guglielmo 4 , D. Brocco 5 , A. Grassadonia 5 , S. Tavoletta 6 , S. Grossi 7 , D. Genovesi 4,5 , L. Caravatta 4 1 SS. Annunziata Hospital, Department of Radiation Oncology , Chieti, Italy; 2 G. D’Annunzio University, Department of Neuroscience, Imaging and Clinical Sciences, Chieti, Italy; 3 G. D’Annunzio University, Department of Neuroscience, Imaging and Clinical Sciences, Chieti, Italy; 4 SS. Annunziata Hospital, Department of Radiation Oncology, Chieti, Italy; 5 G. D’Annunzio University, Medical Oncology Unit, Department of Experimental and Clinical Sciences, Chieti, Italy; 6 G Bernabeo Hospital, Division of Surgical Senology, Ortona (CH), Italy; 7 Division of Surgical Senology, Division of Surgical Senology, Ortona (CH), Italy Purpose or Objective Sentinel lymph node (SLN) replaced axillary lymph node dissection (ALND) in clinically and pathologically node-negative early breast cancer (BC) patients, sparing ALND morbidity. Axillary management remains unclear when SLN results positive in cN0 BC patients. The ACOSOG Z0011 trial represented a revolution in this scenario, with ALND omission in SLN+ patients, although criticized for the non-uniformity of radiation fields (WBRT or high tangent with/without axillary) with potential bias. From these perspectives, we conducted the LISEN trial where WBRT was planned with tangential fields without nodal irradiation in patients with Z0011 characteristics. Materials and Methods Inclusion criteria were: female patients with histologically proven BC, cT1-2cN0, planned BCS, no neoadjuvant therapy. Patients were stratified in two groups according to micrometastatic (pN1mic) and macrometastatic lymph nodes status (no isolated tumor cells) (pN1a). Tangential fields WBRT was mandatory. Adjuvant systemic therapy was administered according to staging and tumor biology. Time to Regional Recurrence (RR), in terms of breast, axillary and supraclavicular relapse, and distant metastases (DM) were analyzed, measured from time of surgery until the first regional and distant recurrence, respectively. Results From May 2011 to June 2019, 199 BC patients were enrolled in the LISEN trial. All patients underwent BCS and SLN biopsy. Eighteen patients (9%) were excluded for nodal sampling or ALND or pN0i+. Other 37 patients (18.6%) were omitted from analyses for non-RT delivery (refusal, older age, comorbidities) or nodal RT for extracapsular extension; data were missing for 11 (5.6%). We reported our results on 133 patients, 41 patients (30.8%) pN1mic and 92 (69.2%) pN1a. Patients and tumor characteristics are reported in Table 1. The median total number of removed lymph nodes was 2, with a median number of histologically positive nodes of 1. At a median follow-up of 50 months (range=5-91 months) RR occurred in only two patients (1.5%) as breast relapse, one in the pN1a group and the other in the pN1mic with also axillary recurrence. Both patients also reported