ESTRO 36 Abstract Book

S449 ESTRO 36 2017 _______________________________________________________________________________________________

Department of Oncology and Hemato-oncology, MIlan, Italy Purpose or Objective The aim of the study (partially supported by a research grant from Accuray Inc. entitled “Data collection and analysis of Tomotherapy and CyberKnife breast clinical studies, breast physics studies and prostate study”) is to assess the dosimetric benefit of intensity-modulated radiotherapy (IMRT) in postmastectomy patients with implant–based immediate breast reconstruction (IBR), candidates to locoregional radiotherapy with hypofractionation. Material and Methods Data of the first 121 consecutive post-mastectomy locoregional patients treated with Helical Tomotherapy between May 2012 and May 2015 with a hypofractionated scheme (2.67Gy/fr, 15 fractions) have been prospectively collected. At the time of surgery, all patients underwent IBR using either temporary tissue expander or permanent prosthesis. The impact of immediate breast reconstruction on the planning was analyzed. Treatment plans were scored in terms of coverage of the PTVs (chest wall and supraclavicular region) and sparing of organs at risk (heart, lungs and contralateral breast). The coverage of chest wall and supraclavicular region was evaluated according to the amount of volume receiving the 90% of the prescribed dose (V 90% ) while the sparing of each OAR was evaluated according to the number of satisfied constrains (Tab.1). A plan with optimal coverage of both PTVs had 2 PTV points, while a plan with optimal sparing of all OARs had 4 OARs points. An overall score was assigned to each plan.

versa. The figure outlines the normalized (with respect to the Treatment plans) tallied quantities on patient-by- patient basis. In 8 out of the 40 maximum doses the Treatment plans demonstrated lower absolute doses. For none of the 30 tallied average (or mean) doses the Treatment plans were better than the Auto plans. The average differences over the patient cohort range from - 7% to +36%.

Conclusion Unattended inverse optimization holds great potential for further personalization and tailoring of radiotherapy to particular patient anatomies. It utilizes minimum user time and it can be used at the very minimum as a good starting point for personalized precision radiotherapy. PO-0840 Hypofractionated intensity modulated radiotherapy in patients with immediate breast reconstruction D.P. Rojas 1 , R. Ricotti 2 , M.C. Leonardi 2 , A. Viola 1 , S. Dicuonzo 1 , D. Ciardo 2 , R. Cambria 3 , R. Luraschi 3 , F. Cattani 3 , C. Fodor 2 , A. Morra 2 , V. Dell'Acqua 2 , V. Galimberti 4 , R. Orecchia 5 , B.A. Jereczek-Fossa 1 1 European Institute of Oncology - University of Milan, Department of Radiation Oncology - Department of Oncology and Hemato-oncology, MIlan, Italy 2 European Institute of Oncology, Department of Radiation Oncology, MIlan, Italy 3 European Institute of Oncology, Department of Medical Physics, MIlan, Italy 4 European Institute of Oncology, Department of Surgery, MIlan, Italy 5 European Institute of Oncology - University of Milan, Department of Medical Imaging and Radiation Sciences -

Results 71.1% (86/121) of the 121 post-mastectomy radiotherapy plans had high total scores (total score=6 points) as a result of an optimal coverage of both chest wall and supraclavicular region and optimal sparing of all OARs. The remaining 28.9% (35/121) of plans had a compromised distribution of dose (total score<6 points). In particular, 13.2% (16/121) of plans fully satisfied all the OAR constraint but at a cost of moderate coverage of chest wall (7/121 plans) or supraclavicular region (9/121 plans) target volumes. On the other hand, 13.2% (16/121) of plans fully satisfied coverage of both PTVs compromising the sparing of OARs (heart, ipsilateral lung, or contralateral breast). The residual 2.5% of plans (3/121) had both coverage of PTVs and sparing of OARs compromised. Conclusion In patients having implant-based IBR, IMRT allows optimal treatment plans in more than 2/3 of cases. Superior dosimetric results are even more important when