ESTRO 38 Abstract book

S709 ESTRO 38

grade Baker scale, the aesthetic result was established according to the Harvard scale. Results The treatment plans were compared using dose-volume histograms(DVHs) for planning target volume(PTV) and different OARs. The PTV minimum, mean and maximum doses, V95 (relative volume of breast PTV receiving 95% of the dose), and the dose at OAR were compared between 3DCRT and HT as reported in table 1. PTV coverage with the 95% isodose as expected was better for HT, as this curve fits best to the concave shape of the PTV compared to the 3DCRT(p<0.0001). A deeper analysis, only on the HT group, demonstrated that the more recent tomotherapy planning had a better dosimetry report than a few years ago. It meant a dose reduction in Dmax for ipsilateral lung and heart (p<0.0374 and p<0.0039). Capsular contracture Baker grade1-2: 1patient (HT) and 2pts (3DCRT). As regard, Baker grade3-4, 4pts (HT) and 2pts (3DCRT). An increased contracture rate was observed in patients who underwent 3DCRT (20%) instead of HT (15.15%). The aesthetic result has been classified as follow: “excellent”, “good”, “acceptable” and “poor”.(Figure1)

supine DIBH. The parameters of the partial breast RT arm of the IMPORT LOW trial were applied to each available scan and several dosimetric parameters were collected for comparison including mean heart dose, heart V25 Gy, mean ipsilateral lung dose, ipsilateral lung V20 Gy, and PTV coverage. Results

Among patients with right-sided breast cancer, the supine position was associated with lower mean heart dose while the prone position was associated with lower mean ipsilateral lung dose. In left-sided breast cancer patients, the prone position yielded lower ipsilateral mean lung dose and lung V20 Gy values; while DIBH was associated with a lower mean heart dose and a trend towards lower lung V20 Gy (p=0.058). Conclusion For well-selected women with early breast cancer, the IMPORT LOW trial showed that reducing the treated breast volume is equivalent in efficacy to treating the whole breast. Our results show that incremental reductions in heart and lung dose can be achieved by pairing this approach with alternative patient positioning techniques. Overall, the prone position yields the lowest lung dose, while in left-sided disease, DIBH provides optimal cardiac avoidance. EP-1296 Breast reconstruction and hypofractionated adjuvant radiotherapy: dosimetric and aesthetic analysis. E. Bonzano 1 , M. Guenzi 1 , R. Corvò 1 1 IRCCS Policlinico San Martino and University, Department of Radiation Oncology, Genoa, Italy Purpose or Objective The aim of our study was to analyze dose distribution, target coverage and doses to organs at risk(OAR) in patients(pts) who underwent Postmastectomy Radiotherapy (PMRT) following tissue expander- implant(TE) breast reconstruction and compare different RT techniques: Three Dimensional Conformal Radiation Therapy(3DCRT) and Helical Tomotherapy(HT). The second endpoint was to evaluate patient’s outcome: capsular contracture and aesthetic result. Material and Methods This study was conducted on 53 pts treated from April 2012 to June 2016. PMRT was delivered in a hypofractionated regime of 46 Gy in 20 fractions, 4 times per week. Pts median age was 49y.o.(range 31-78).TE was positioned after mastectomy, progressively inflated, then replaced by a permanent implant, almost 6 months after PMRT. The majority of patients (79.24%) received chemotherapy. Pts started PMRT 3weeks after adjuvant chemotherapy. According to the tumor overexpressed Human Epidermal Growth Factor-2(HER-2) receptor, 24.52% of patients received trastuzumab, as a PMRT concurrent treatment.PMRT was delivered in supine position; 33pts were treated by HT (according to the major complexity to spare OAR), 20pts by 3DCRT. Chest-wall, supraclavicular lymph-nodes, heart, left coronary artery, ipsilateral and contralateral lung, spinal cord, thyroid, contralateral breast and esophagus was delineated. The capsular contracture was evaluated by using the four-