ESTRO 36 Abstract Book

S345 ESTRO 36 _______________________________________________________________________________________________

11 Associazione Italiana Radioterapia Oncologica, intraoperative radiotherapy working group, -, Italy Purpose or Objective To assess the outcome after salvage breast conservative surgery (BCS) and additional partial irradiation (PBI) with intraoperative electrons (IORT) in patients previously treated with BCS and whole breast irradiation. Material and Methods From 1999 and 2015, 115 patients affected by in-breast recurrence (IBTR) were treated with salvage BCS and IORT in 8 Italian centers. Data were collected centrally and entered in a dedicated database. The study was promoted and supported by the IORT Working Group of Italian Association of Radiation Oncology (AIRO). Patients gave informed consent for the use of anonymized data for research and training purposes. Efficacy of re-treatment was evaluated by means of second IBTR and distant metastases (DM) rates. Tolerability was assessed based on the incidence of postoperative complications. Systemic treatment was given according to biologic profile and institution’s policy. Results Median time to salvage BCS was 122 months (12-334). Site of IBTR was the same as the index tumor in 44.3% of cases. Median age at first BCS was 56 (37-76), while at salvage BCS was 62 years (40-81). Patients received lumpectomy only in 53% of cases, while axillary dissection was performed in 3.2% of cases. The remaining patients had sentinel node biopsy. In 43.4% of cases, the size of recurrence was comprised between 1 and 2 cm. The majority of patients had positive hormonal receptors, 22.6% had grade 3 tumors and in about half of the cases Ki-67 was higher than 20%. Regarding technical characteristics, IORT dose was 18-21 Gy in 82.6% of cases, median collimator size was 5 cm (3- 6 cm), median electron energy was 7 MeV. Main postoperative complications after IORT delivery consisted of lyponecrosis ( 4.3%), hematoma (6.9%), seroma (8.7%), edema (6.9%), infection (2.6%). At a median follow-up after IBTR of 56 months (13-124 months), 73.6% of patients were alive. Second IBTR rate was 11.3%. Distant metastases rate was 2.6%. Three patients died of distant disease progression (2.6%). Contralateral breast cancer occurred in 2.6% of cases, while 0.9% developed second new primaries in distant sites. Conclusion The study population included patients from 8 institutions who had resectable IBTR and either refused salvage mastectomy or were offered the second BCS, including PBI, as a valid alternative. Local control obtained with IORT was comparable to that previously described in literature, which ranges between 7% and 32%, with a mean value of about 10%. Multivariate analysis to identify prognostic factors for a better selection of patients is ongoing. PO-0662 Target therapy and hypofractionated whole breast radiotherapy: an unexpected protective factor. M.C. De Santis 1 , F. Di Salvo 2 , F. Bonfantini 3 , S. Di Cosimo 4 , E.D. Mantero 1 , V. Riboldi 1 , M. Dispinzieri 1 , F. Soncini 1 , V. Cosentino 3 , G. Bianchi 4 , M. Gennaro 5 , M. Sant 2 , R. Valdagni 6 , E. Pignoli 3 , L. Lozza 1 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiotherapy Department, Milan, Italy 2 Fondazione IRCCS Istituto Nazionale dei Tumori, Analytic Epidemiology and Health Impact Unit, Milan, Italy 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics Unit, Milan, Italy 4 Fondazione IRCCS Istituto Nazionale dei Tumori, Oncology Department, Milan, Italy 5 Fondazione IRCCS Istituto Nazionale dei Tumori, Breast Surgery Unit, Milan, Italy 6 Fondazione IRCCS Istituto Nazionale dei Tumori,

Results Between 6/2012 and 11/2015, 48 pts were treated with re-PBI. Median time to recurrence was 137.3 months ( range: 25.6-319 months). Prescription dose was 37.05 Gy in 13 fractions. 9 pts were treated with Tomotherapy and 39 pts with VERO. Median age was 60.7 years. The patterns of recurrences were as follows: in 37 cases site of recurrence was the same as the index tumor (true/marginal miss), while in the remaining 17 cases recurrence occurred far from the index quadrant across the breast (elsewhere in breast reappearance). Acute toxicity was moderate: no acute toxicity >G2 was observed at the end of the treatment (erythema G1 in 48% of pts; desquamation G1 in 2% of pts; edema G2 in 8% of pts). Late toxicity according to LENT/SOMA was available for 15/48 patients (Tab.1). All but one had G1-G2 toxicity: one patient experienced G3 retraction. Overall, median follow-up after first relapse was 22.1 months. 45 pts are alive without disease while 3 pts showed distant metastasis (DM). Median time to DM event was 12 months and 3/3 have had true/marginal miss local recurrence with Second conservative surgery combined with additional radiotherapy represents a feasible alternative to mastectomy. None of the patients relapsed locally. Furthermore, good acute toxicity profile and an acceptable early chronic toxicity were observed, although longer follow-up and higher number of pts are needed to confirm these results. PO-0661 Intraoperative partial breast re-irradiation: a multicenter study of the AIRO IORT Working Group M.C. Leonardi 1 , G.B. Ivaldi 2 , M. Alessandro 3 , G. Catalano 4 , A. Ciabattoni 5 , C. Fillini 6 , M. Guenzi 7 , L. Tomio 8 , D.P. Rojas 9 , M. Augugliaro 9 , C. Fodor 1 , C. Sangalli 1 , F. Rossetto 1 , B.A. Jereczek –Fossa 9 , R. Orecchia 10 , AIRO IORT Working Group 11 1 European Institute of Oncology, Department of Radiation Oncology, MIlan, Italy 2 Fondazione Salvatore Maugeri, Oncology Unit, Pavia, Italy 3 Ospedale di Città di Castello, Radioterapia Oncologica, Città di Castello, Italy 4 Multimedica Holding Clinical Institute, Unit of Radiotherapy, Castellanza, Italy 5 San Filippo Neri Hospital, Department of Radiotherapy, Rome, Italy 6 Azienda Ospedaliera Santa Croce e Carle, Department of Radiation Oncology, Cuneo, Italy 7 IRCC Azienda Ospedaliero-Universitaria San Martino IST, UOC Oncologia Radioterapica, Genoa, Italy 8 Santa Chiara Hospital, Radiotherapy Unit, Trento, Italy 9 European Institute of Oncology - University of Milan, Department of Radiation Oncology - Department of Oncology and Hemato-oncology, Milan, Italy 10 European Institute of Oncology - University of Milan, Department of Medical Imaging and Radiation Sciences - Department of Oncology and Hemato-oncology, Milan, Italy high Ki-67. Conclusion