Abstract Book

ESTRO 37

S379

In this setting, 10-year DFI and DSS were 89.7% vs 52.8% and 96.4% vs 85.4 %, respectively. (Fig.1, C-D) Exploring results with respect to the prognostic index and type of surgery, there were significative differences only in BCS group, where 10-year DFI and DSS were 89.9% in score <3 vs 51.9 % in score ≥3 and 97.1% vs 89.9 %; in mastectomy group there was a not significant benefit in patients with score <3. We also analyzed locoregional failure: 10-year DFI was 95.3% in the group with score <3 and 79.1% in the group with score ≥3; this difference was statistically significant only in the BCS group. The same analysis was conducted considering the prognostic index and type of RT treatment. In patients receiving hypofractionated RT without boost, the score did not appear to be of prognostic value for locoregional recurrence, but conversely it did in patients submitted to hypofractionated or conventional RT with boost addition: 10-year DFI for locoregional failure resulted 95.8% in score <3 group and 82.8% in score ≥3 group. (Fig.1, E-F)

Conclusion The prognostic role of the investigated index was confirmed. A score ≥ 3 identifies a group of patients with a higher risk of recurrence particularly when BCS and RT with boost dose to tumor bed was performed. This prognostic index is a valid, economical and reliable tool to predict outcome in breast cancer patients. PO-0740 MR-guided single dose pre-operative radiotherapy in low-risk breast cancer patients: first results J. Vasmel 1 , R. Charaghvandi 1 , A. Houw eling 1 , M. Philippens 1 , W. Veldhuis 2 , P. Van Diest 3 , G. Van Leeuwen 4 , J. Van Gorp 5 , I. Van Dam 1 , A. Witkamp 6 , C. Van der Pol 6 , R. Koelemij 7 , A. Doeksen 7 , E. Theunissen 7 , T. Van Dalen 8 , E. Van der Wall 9 , H. Verkooijen 10 , H. Van den Bongard 1 1 UMC Utrecht, Radiation oncology, Utrecht, The Netherlands 2 UMC Utrecht, Radiology, Utrecht, The Netherlands 3 UMC Utrecht, Pathology, Utrecht, The Netherlands 4 St Antonius hospital, Pathology, Nieuwegein, The Netherlands 5 Diakonessen hospital, Pathology, Utrecht, The Netherlands 6 UMC Utrecht, Surgery, Utrecht, The Netherlands 7 St Antonius hospital, Surgery, Nieuwegein, The Netherlands 8 Diakonessen hospital, Surgery, Utrecht, The Netherlands 9 UMC Utrecht, Medical oncology, Utrecht, The Netherlands 10 UMC Utrecht, Imaging division, Utrecht, The Netherlands Purpose or Objective To evaluate pathologic and radiologic response to single dose pre-operative ablative radiotherapy (RT) in women with low-risk breast cancer.