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being in groups of BMI>25kg/m 2 (p=0.006) without statistically significant differences between irradiated areas. The overall 5y survival of our cohort was 81%. There were statistically significant differences between intrinsic subtypes. Triple negative subtype had the worst prognosis (p=0.010), with 5y survival of 67%. These study had a median follow up of 5.25y. Conclusion In our study, triple negative intrinsic subtype is associated with poor survival. Higher BMI is correlated with greater severity of radiodermitis. The results obtained in our study are in agreement with the existing literature. However powered prospective studies are needed in order to clarify if this subgroup of young patients might benefit from a different approach. EP-1354 Once-Weekly Hypofractionated Breast Irradiation (Whbi) For Elderly Breast Cancer I. García Ríos 1 , M.J. Garcia Anaya 1 , A. Fernández Forné 1 , I. Domenech Navarro 1 , C. Jodár López 1 , A. Román Jobacho 1 , A. Otero Romero 1 , R. Ordoñez Marmolejo 1 , R. Correa Generoso 1 , J. Gomez-Millan 1 , M.D. Toledo Serrano 1 , C. Castro Garrido 1 , J.A. Medina Carmona 1 1 HOSPITAL UNIVERSITARIO VIRGEN DE LA VICTORIA, RADIATION ONCOLOGY, Málaga, Spain Purpose or Objective Radiotherapy plays an important role in local control, but also improves survival the breast cancer. More than 50% of breast cancer cases occur in women aged 65 years or more, but adjuvant radiotherapy is often omitted in older women because of concerns over treatment burden or logistical obstacles. Treatment decisions concerning elderly patients are often taken on the basis of disease stage, performance status (PS), comorbidities, and even the availability of social support and transportation. Hypofractionation (HF), which is to deliver a lower nominal total dose in larger and fewer fractions. Theoretically, 5 fractions of 5.7 or 6 Gy are predicted to be equivalent to 50 Gy in 25 fractions in terms of tumor control according to the linear quadratic model (assuming α⁄β ratio values of 3.0 and 4.0 Gy, respectively). Objetive To evaluate local control, early and late reactions and disease-free survival of elderly breast cancer patients treated with adjuvant or definitive once-a-week hypofractionated (HF) radiotherapy (RT) Material and Methods Consecutive series of 260 breast cancer patients underwent once-weekly hypofractionated WBRT after BCS or mastectomia or inoperable elderly patients, from January 2006 to Decembre 2016. Patients were primarily selected to take into account older age and/or poor medical condition and/or logistic issues. They were given 32.5 Gy in 5 fractions (6.5 Gy once a week) until October 2011. Subsequently, they were administered 28,5 Gy in 5 fractions (5,7 Gy once a week). The supraclavicular nodes were irradiated with 27.5 Gy (5.5 Gy once a week). All treatments were delivered over 5 weeks. The modification of the fractionation to a lower dose per fraction was chosen according to the approach of the UK FASTer radiotherapy for breast radiotherapy (FAST) randomized trial. Dose was prescribed following International Commission on Radiation Unit (ICRU) recommendations. Results The median aged 78 (35-89) years. 224 (86%) patients underwent breast-conserving surgery, 36 (14%) patients radical surgery and 4 no surgery. The clinical stage distribution was as follows: I in 103, II in 104, III in 50, and IV in 3 patients. Axillary lymph nodes were positive in 41 % of cases. Early skin reactions were tolerable with no documented Radiation Therapy Oncology Group Grade 3 or higher toxicity. Late effects, mainly subcutaneous fibrosis, were recorded in 221 patients, they were

classified as grade 1 in 85 cases, grade 2 in 18 cases and grade 3 in 7 patients. No toxicity in 111 patients. The patients with 28.5-Gy Gy showed a slightly better cosmetic result, which was the main motivation for the option of this dose reduction midway through our study.Local and distant failure was scored in 32 cases (13,6%). At a median follow-up of 50 months, 169 patients (72%), was alive and disease free, 29 (12,3%) patients die and disease free. Conclusion According to the findings from this retrospective study, the HF-RT schedule is an acceptable alternative for elderly patients, allows a good local control, with acceptable toxicity. EP-1355 The prognostic impact of solid component diameter of tumor in Stage I NSCLC undergoing SBRT T. Itonaga 1 , T. Saitou 1 , M. Okubo 1 , R. Mikami 1 , S. Nogi 1 , T. Koichi 1 1 Tokyo Medical University, Radiology, Shinjuku, Japan Purpose or Objective To evaluate the local control rate impact of the size of the solid component in the tumor for patients with stage I non-small cell lung cancer (NSCLC) who underwent intensity-modulated stereotactic body radiotherapy (SBRT) using compensated filters. Material and Methods This study was approved by the ethical board at the Tokyo Medical University Hospital, and started in 2011. All patients provided written informed consents. Eligible criteria included the following: 1. pathologically proven or clinically diagnosed NSCLC; 2. clinical stage of T1- 2N0M0 according to the 7 th UICC TNM classification; 3. patients who were considered to be unsuitable for surgery due to underlying lung diseases, poor performance status, old age or patient’s refusal. A total number of 48 patients with 50 tumors were enrolled in this study. The median age of patients was 79 years (range, 49-90), the male/female ratio was 30/18, and the stage T1 to T2 ratio was 31 to 19. 95% of the prescribed dose of 75 Gy in 30 fractions was given to 95% of the PTV. In this presentation, we re-measured the maximum tumor diameter (MTD) and the solid component diameter (SCD) according to the 8 th UICC TNM classification. After these tumors were reclassified, local control, overall survival (OS) and local progression-free survival (LFS) rates were recalculated based on the new classification. Prognostic factors were analyzed with uni-variate and multiple variate methods using the Cox proportional hazards regression models among possible prognostic factors of MTD, SCD, Age(>75y), Sex. Results The median MTD and SCD were 21 mm and 19 mm, respectively. 50 tumors were classified into Tis (SCD=0mm, MTD≤30 mm) 2 cases, T1a (SCD≤10 mm) 6 cases, T1b (SCD>10 mm, SCD≤ 20 mm) 24cases, T1c (SCD>20 mm, SCD≤30 mm) 11cases, T2 (Invades visceral pleura, SCD≤30 mm) 2cases, T2a (SCD>30 mm, MTD≤40 mm) 3cases, and T3 (SCD>50 mm, SCD≤40 mm) 2cases according to TNM 8 th edition. During the median follow-up time of 35.9 months (range, 3.8–64.7), the 3-year LFS and OS rates were 82.6% and 87.1%, respectively. In patients with SCD>20 mm, the 3- year LFS rate was significantly lower compared with patients with a 20 mm or less (52.7 vs. 96.0%; p = 0.0008). No significant differences were found in MTD or SCD/MTD ratio. By multivariate analysis, the SCD larger than 20 mm (hazard ratio [HR] = 12.2, p = 0.026) was the only statistically significant indicator of poor LFS rates Electronic Poster: Clinical track: Lung