Abstract Book

S734

ESTRO 37

maximum dose (Dmax), the average dose (Dav), the percentage of volume receiving more than 1 Gy (V1Gy%), the volume receiving more than 1 Gy in cc (V1Gy cc), the percentage of volume receiving more than 2 Gy (V2Gy%), the volume receiving more than 2 Gy in cc (V2Gy cc). Results The median Dmax and Dav for CB were 5.12 Gy (0-44.01 Gy) and 0.29 (0-27.11 Gy) respectively. The median V1Gy% and V1Gy cc were 6.79% (0-56.75%) and 50.48 cc (0-602.48 cc) respectively. The median V2Gy% and V2Gy cc were 1.56% (0-36.16%) and 11.19 cc (0-434cc) respectively. Conclusion Contralateral breast is an important organ at risk during breast radiotherapy. Indeed, population studies have shown an excess risk of contralateral carcinoma from 1Gy received by the CB. The results of our study show that the CB receives an important dose during 3D conformal radiotherapy with a median volume receiving more than 1Gy of 50 cc reaching up to 600 cc. Contouring the CB as an organ at risk must be systematic to reduce the doses to its level especially for young patients. EP-1342 to evaluate a deformable registration protocol for preoperative PET-CT for breast radiotherapy C. Ambroise 1 , R. Miralbell 1 , D. Di Pasquale 1 , K. Koutsouvelis 1 , O. Fargier-Bochaton 1 , X. Xinzhuo 2 1 hôpitaux Universitaires De Genève, Oncology, Geneva, Switzerland 2 tianjin Union Medical Center, Oncology, Tianjin, China Purpose or Objective Using Velocity© (Varian Medical System) as a deformable image registration (DIR) tool we aimed to assess the quality of a registration protocol between preoperative PET-CT (PrePET-CT) and post-surgery simulation CT (SimCT) before breast cancer irradiation and after Eleven patients (pts) were identified having PrePET-CT and a SimCT all in supine position, arms over the head. Some of them had a SimCT in deep inspiration breath hold. To guide the registration process and measure the quality of DIR, the following anatomical structures were contoured on PrePET-CT and SimCT images: half-body without lung (PRV_Body), anatomic nipples, nipples extended (with 25mm margin) (PRV_NIP) and clavicular head. The rigid protocol was a Velocity auto alignement of all body. The tested protocol (tested_protocol) was realized in two steps. First, a rigid manual nipples registration of the treated breast (Rigid_protocol); second, using the union of the PRV_Body in the region of interest (ROI) and the PRV_NIP (Fig 1a and 1b), a structure guided deformation (SGD) registration was made (Fig.1c). Dice, mean, and maximum distance between structures surfaces of Pre_PET-CT and SimCT were analyzed to quantify the DIR quality. A wilcoxon test was used to perform statistical analysis. conservative surgery. Material and Methods

SimCT with spyglass showing the deformed prePET-CT inside and a good fusion for the breast gland, the skin, the ribs, the lungs and, the nipples. Results The DIR protocol led to better fusion compared to rigid protocol (Fig. 1 d), with Dice, Mean and maximum distance improving at all levels, (see table 1), except for the maximal surface distance of the clavicular head (bony stucture).

Table 1: Deformation image protocol analysis.

Conclusion Velocity© can afford an optimized deformable

registration after lumpectomy helping to get a more accurate definition of the tumor bed before postoperative irradiation in the conservative treatment setting of breast cancer. EP-1344 Long-term reconstruction failure after postmastectomy RT to temporary expander or permanent implant S. Dicuonzo 1 , M. Leonardi 2 , D. Radice 3 , A. Morra 2 , V. Dell'Acqua 2 , M. Gerardi 2 , D. Rojas 4 , A. Surgo 2 , F. Cattani 5 , R. Cambria 5 , C. Fodor 3 , F. De Lorenzi 6 , V. Galimberti 7 , R. Orecchia 8 , B. Jereczek-Fossa 9 1 Dicuonzo Samantha, Division of Radiation Oncology, Milan, Italy 2 European Institute of Oncology, Division of Radiation Oncology, Milan, Italy 3 European Institute of Oncology, Department of Epidemiology and Statistics, Milan, Italy 4 European Institute of Oncology and University of Milan, Division of Radiation Oncology and Department of Oncology and Hemato-onco, Milan, Italy 5 European Institute of Oncology, Unit of Medical Physics, Milan, Italy 6 European Institute of Oncology, Department of Plastic and Reconstructive Surgery, Milan, Italy 7 European Institute of Oncology, Department of Surgery, Milan, Italy 8 European Institute of Oncology and University of Milan, Department of Medical Imaging and Radiation Sciences and Department of Oncology and Hemato-oncology, Milan, Italy 9 European Institute of Oncology and University of Milan, Division of Radiation Oncology and Department of Oncology and Hemato-oncology, Milan, Italy Purpose or Objective Immediate breast reconstruction (IBR) followed by postemastectomy radiotherapy (PMRT) is becoming an integral part of breast cancer treatment, due to younger age of detection and to the trend to offer PMRT to an increasing number of patients (pts) with small tumors or with fewer positive lymph nodes based on the results of

Figure 1: DIR steps details : a) Deep inspiration SimCT with PRV_Body coutoured; b) PrePET-CT with PRV_Body coutoured; c) Exemple of vectors of deformation; d)