ESTRO 38 Abstract book

S713 ESTRO 38

to the whole breast PTV followed by a boost irradiation in 6 fractions, using an alpha/beta ratio of 4 Gy for tumor response, based on the linear-quadratic cell survival model. Dermatological toxicities were assessed and documented in agreement with the Common Toxicity Criteria Adverse Events version 3 (CTCAE v.3.0). Cox regression model and Kaplan-Meier curves were calculated, and the log-rank test was used to evaluate the differences of overall (OS) and disease free (DFS) survival rates between two different modalities of radiotherapy. Results Among 216 patients, 174 received post-operative radiotherapy with Rapid-Arc and 42 patients had Tomotherapy after BCS. All patients tolerated IMRT-SIB without any interruption. The median follow-up was 6.4 years. Four patients (1.85%) in the entire cohort developed late skin complication after IMRT-SIB. For the entire cohort, the 5-year and 7-year OS rates were 94.4% and 93.1% respectively. The 5-year and 7-year DFS rates were 94.9% and 94.0 % respectively. Conclusion There exists no statistically significant difference in the rates of locoregional recurrence and overall survival when comparing RapidArc with Tomotherapy. IMRT-SIB was well tolerated with small late skin complication and good survival rates. EP-1303 Hypofractionated adjuvant radiotherapy in elderly low risk breast cancer patients: loss or gain? A. Fodor 1 , M. Pasetti 1 , P. Mangili 2 , B. Longobardi 2 , F. Zerbetto 1 , L. Perna 2 , I. Dell'Oca 1 , P. Signorotto 2 , R. Tummineri 1 , F. Borroni 1 , C.L. Deantoni 1 , A.M. Deli 1 , N. Slim 1 , A. Chiara 1 , P. Passoni 1 , S. Foti 1 , M. Azizi 1 , C. Fiorino 2 , A. Bolognesi 1 , N.G. Di Muzio 1 1 San Raffaele Scientific Institute, Department of Radiotherapy, Milan, Italy ; 2 San Raffaele Scientific Institute, Medical Physics, Milan, Italy Purpose or Objective The PRIME II trial (Lancet Oncol 2015) and a recent meta- analysis (Radiother Oncol 2017) suggested that adjuvant radiotherapy does not impact overall survival in elderly patients (pts) with low risk breast cancer (LRBC), and therefore could be omitted. We report here the 5-year outcomes in elderly pts with LRBC treated with whole breast hypofractionated adjuvant radiotherapy (RT). Material and Methods One hundred forty five pts 70 years or older, with hormonal receptors positive, Her2-negative status (Luminal A/Luminal B Her2-negative) early stage (pTis- pT1c pN0-1a ≤ 3 positive lymph nodes) breast cancer, treated from 02/2009-05/2013, were included in this analysis. The patients were treated with whole breast radiotherapy to 40 Gy/15 fractions with a multiple- segments 3D-CRT technique, without tumor bed boost. Median age was 73 (70-90) years, 8 pts had ductal carcinoma in situ, 25 lobular invasive carcinoma or combination, 98 ductal invasive carcinoma and 14 other histology (mucinous, tubular, papillary); 70 were right sided and 75 left sided tumors. Hormonal therapy was prescribed in 133/ 145 pts. For possible side effects follow up visits were scheduled for 5 years. Acute toxicity during RT was evaluated with RTOG scale, late toxicity with SOMA-LENT score. Results A median number of 4 (2-6) segments were used to obtain a homogeneous dose distribution. Acute toxicity was: 24.1% G0, 69.0% G1 and 24.1% G2. Half of G2 toxicities were delayed, 7-15 days after RT, and concerned only the inframammary fold; 70% of them had breast volume> 600 cc. Two G2 toxicities were observed in low breast volume pts but with bolus for half therapy. Late toxicity was available for 131 pts: 16 % were G1 edema/dyschromia, rarely persistent over three years, while 7.6% G1 fibrosis/teleangiectasia, starting generally from the third

hypertension and G3 cutaneous 5-y-LTFS (98.5 vs 100%) and between chemotherapy and G3 subcutaneous 5-y- LTFS (98.4 vs 100%). A trend suggesting an impact of taxan-based chemotherapy schedules on G2 subcutaneous late toxicity was observed. Hormonotherapy with Aromatase Inhibitors (AI) was significantly (p>0.0001) associated with worse G2 subcutaneous 5-y-LTFS (75.6% vs 84.6% and 89.1% for Tamoxifen plus LH-RH analogue and Tamoxifen alone respectively). EQD2 was also related to G2 subcutaneous toxicity: in particular, better outcomes were observed in the group of pts treated with 50.4 Gy in 28 fractions (fr) with sequential electron boost of 10 Gy in 4 fr (EQD2 PTV 48.4 Gy, EQD2 BOOST 59.4 Gy). This was probably related to the used technique for boost delivery (electrons vs concomitant boost with tangential fields in the other two groups). In the two groups treated with IMRT and concomitant boost, G2 subcutaneous toxicity was higher in the one with higher EQD2, as expected. An interesting correlation (p=0.001) was also found between nodal status and G2 subcutaneous toxicity: pts with N2-3 disease, who underwent regional lymphadenectomy (with consequent alteration of lymphatic drainage) had a worse outcome compared to pts with N1 disease, where lymphadenectomy rate was lower. This could also be explained by the different technique (hemi-fields) used for pts who needed lymph nodes irradiation (typically pN2- 3). Finally, PTV volume was correlated with G2 skin LTFS (p<0.0001), with a significant difference between values below and above the median (5y-LTFS: 98.4% vs 80.1%). Conclusion Our preliminary data confirm that some factors could be related to higher rates of late toxicity in pts treated for breast cancer. This analysis may represent the basis to develop predictive models of late toxicity. EP-1302 long-term clinical outcomes of IMRT with simultaneous integrated boost for breast cancer H. Lee 1,2 , M. Huang 2,3 1 Ph.D. Program in Environmental and Occupational Medicine- Kaohsiung Medical University and National Health Research Institutes, Radiation Oncology, Kaohsiung, Taiwan ; 2 Kaohsiung Medical University Hospital, Radiation Oncology, Kaohsiung, Taiwan ; 3 Kaohsiung Medical University, Faculty of Medicine- College of Medicine, Kaohsiung, Taiwan Purpose or Objective To report the long-term survival outcomes and late toxicities resulted from intensity modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB) for breast cancer patients after breast conserving surgery (BCS). Material and Methods The study included 216 patients with pathologically proven breast cancer who underwent BCS between 2010 and 2013. The median age was 52 years (Range: 21 to 81). All patients received IMRT-SIB to 2 dose levels simultaneously. They received 50.4 Gy at 1.8 Gy per fraction to the whole breast and 60.2 Gy at 2.15 Gy per fraction to the tumor bed by integral boost. The fractionation scheme was biologically equivalent to the sequential boost-technique comprising 25 fractions of 2 Gy