ESTRO 37 Abstract book

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ESTRO 37

considered to be predictive for acute toxicities. In the group of 276 patients, there were 28 smokers, of whom 10 received a treatment with 50 Gy WBI+ 16 Gy boost. They were matched to a group of 90 non-smoking patients with same radiotherapy. Of all 276 patients 119 had chemotherapy. 26 of these 119 patients had a chemotherapy with Epirubicin, Paclitaxel and Cyclophosphamide and a radiotherapy of 50 Gy WBI +16Gy Boost. They were matched to 58 of the 276 patients who did not receive any chemotherapy, but the same radiotherapy-treatment. Results 3/276 patients(1,08%) had a >110%pdWBI; 33/276(11,95 %) >107%pdWBI; 209/276 (75,72%) 105%-107%pdWBI; 8/276 (2,89 %) < 105%pdWBI. Comparing the CTC-Scores of the different groups, there was no significant differnces between the 3 groups (p>0.05). 3(30%) of the smoking patients had a CTC °1; 7 (70%) a CTC °2 at the end of therapy. 41 (46,06%) of the non smoking patients had a CTC °1; 48 (53,93%) a CTC °2; 1(1.2%) a CTC °3. There was no significant difference between the patients with or without chemotherapy (p=0.8). 11 chemotherapy patients (42%) had a CTC °1 and 15 patients (57,69%) had a CTC °2. Of the 58 patients without chemotherapy 22 (37,93%) showed a CTC °1; 36 (61,01%) had a CTC °2. There was a statistical significant difference in the CTC- Score of the WBI with and without boost (p=0.008). There was no significant difference between the 10 Gy vs 16 Gy boost (p=0,78). Conclusion Modern multiple field tangential WBI 3D-CRT results in a homogenous dose distribution, with dosimetry similar to data published on randomized trials on IMRT. Thus the toxicities are low and within the reported with IMRT. Neither nicotine consumption nor chemotherapy stood in a significant relation with radiodermatitis in this large cohort. While there was a statistic significant difference between the boost vs no boost patients, there was no statistical difference between the of 10 Gy and 16 Gy group. EP-1341 Contralateral breast : A missing organ at risk in breast radiotherapy F. Nejla 1 , C. Ines 1 , M. Wafa 1 , F. Zied 1 , F. Leila 1 , K. Mouna 1 , S. Wicem 1 , D. Jamel 1 1 Hopital Habib Bourguiba, Radiation Oncology, Sfax, Tunisia Purpose or Objective The aim of this study was to determine the dose received by the contralateral breast (CB) during radiotherapy for breast cancer. Material and Methods Between January 2015 and September 2017, 100 newly diagnosed patients with non-metastatic breast cancer were treated with adjuvant radiotherapy in our department. The median age was 50.5 years (23-81 years). The majority of patients had a left breast cancer (68%). All patients received a 3D conformal radiotherapy. The prescribed dose was 66 Gy (2Gy per fraction) after conservative surgery (n=63) and 50 Gy (2Gy per fraction) after modified radical mastectomy (n=37). The contralateral breast was not considered as an organ at risk and we retrospectively contoured it to determine the received dose at its level. We then reported the 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

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) 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).