ESTRO 36 Abstract Book

S340 ESTRO 36 _______________________________________________________________________________________________

with lymphovascular invasion. LRR was compared for the three groups in multivariable analysis with correction of pN stage. Patients in the BCT and the ME only group showed a significant higher risk for LRR compared to the ME+RT group (HR 3.29, p 0.037 and HR 4.45, p 0.020 respectively). Ten year BCSS was 87 %, 84 % and 75 % for the BCT, ME+RT and ME only group, respectively. BC-specific mortality increased with higher pT and pN stages (HR 1.59, p 0.006 and HR 1.82, p < 0.0001, respectively). Patients with an axillary lymph node dissection (HR 2.81, p 0.016) and with lymphovascular invasion (HR 1.72, p 0.053) had lower BCSS. Adjuvant chemotherapy administration was a protective factor for BC-specific mortality (HR 0.58, p 0.024). Multivariable analysis was conducted to assess differences between the three groups with correction for pT, pN, lymphovascular invasion, lymph node dissection and adjuvant chemotherapy. Patients in the ME only group had significant lower BCSS compared to the BCT and the ME+RT group (HR 1.84, p 0.047 and HR 2.88, p 0.003, respectively). No significant differences were observed for the comparison of BCT versus ME+RT. BCSS curves for the three groups as estimated from the multivariable model are presented in figure 1.

end of radiotherapy and then every year. The association between possible risk factors and development of early and late complications was identified using multivariate logistic regression analysis. Results After a median follow-up of 65,4 (12-84,8) mos the rate of local failure at 5 years was 2,25%. RTOG acute toxicity was: G0 in 164 pts (37%), G1 in 220 pts (49,8%), G2 in 53 pts (12%) and G3 in 5 pts (1,2%). In 9 pts a delayed toxicity ≥G2 was detected at 1-3 weeks after the end of radiotherapy. We observed a strong correlation between acute toxicity ≥G2 and breast volume (p=0,0001), with best cut-off 866 cc derived from ROC analysis . Another important correlation was found with chemotherapy (p=0,003), particularly if concomitant (p=0,017). 99 pts (22,5%) showed edema and/or hyperpigmentation at 6 months after treatment and then the rate decreased over time until disappear, without new events. On the contrary, the rate of pts who presented fibrosis and telangiectasia was neglectable at 6 months (0,68%) but increased over time to become 6.5% at 5 years. The use of build up bolus in more than 7 fractions (p=0,0003), breast volume (p=0,0006), age<56 years (p=0,021), and previous axillary dissection (p=0,0004) were the most important predictable factors for edema and hyperpigmentation, while the development of fibrosis and telangiectasia was correlated with acute toxicity (p=0,0115) (Fig. I) and the presence of edema at 6 months (p=0,0006) (Fig II).

Conclusion TNBC patients treated with ME without adjuvant RT showed significant lower BCSS compared to patients treated with BCT or ME+RT and significant more LRR compared to ME+RT when corrected for known clinicopathological prognostic factors. PO-0651 Five year outcome and soft tissue toxicity of breast cancer hypofractionated adjuvant radiotherapy F. Zerbetto 1 , A. Fodor 1 , C. Sini 2 , P. Mangili 2 , M. Pasetti 1 , P. Signorotto 2 , C. Fiorino 1 , I. Dell'Oca 1 , A. Chiara 1 , A.M. Deli 1 , N. Slim 1 , B. Noris Chiorda 1 , C.L. Deantoni 1 , C. Gumina 1 , M. Azizi 1 , G. Rossi 1 , S. Foti 1 , P. Passoni 1 , A. Bolognesi 1 , N.G. Di Muzio 1 1 San Raffaele Scientific Institute, Department of Radiotherapy, Milano, Italy 2 San Raffaele Scientific Institute, Medical Physics, Milano, Italy Purpose or Objective To report the local control and soft tissues toxicity, in breast cancer patients (pts) treated with hypofractionated adjuvant radiotherapy (HRT), 40 Gy in 15 fractions (2,67 Gy/fraction), after breast conservative surgery (BCS), with a 5-years median follow-up. Material and Methods From February 2009 and October 2011, 442 pts were treated with HRT after BCS. Local tumor relapse was defined as recurrence of cancer at irradiated breast. The acute toxicity was evaluated during RT treatment by RTOG scale. Late side effects as edema, fibrosis, hyperpigmentation and telangiectasia, were individually assessed, using SOMA-LENT score, at 6 months from the

Conclusion In our experience HRT is a safe treatment with high rate of 5 year local control, as reported in literature, and low toxicity. The predicting factors of toxicity emerged from our analysis could help to better manage the breast HRT in terms of cosmetic result. PO-0652 Risk factors for complications of post- mastectomy radiotherapy on implant-based reconstructed breast M. Ogita 1,2 , J. Kawamori 2 , K. Sekiguchi 3 , N. Nagura 4 , R. In 4 , A. Yoshida 4 , H. Yamauchi 4 , Y. Iwahira 5