ESTRO 36 Abstract Book

S117 ESTRO 36 2017 _______________________________________________________________________________________________

Medicine, Department of Radiation Oncology, Seoul, Korea Republic of 5 Yonsei Cancer Center- Yonsei University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of 6 Samsung Medical Center- Sungkyunkwan University School of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of 7 Proton Therapy Center- National Cancer Center, Department of Radiation Oncology, Goyang, Korea Republic of 8 Bundang CHA Hospital- School of Medicine- CHA University, Department of Radiation Oncology, Seongnam, Korea Republic of 9 Dongsan Medical Center- Keimyung University School of Medicine, Department of Radiation Oncology, Daegu, Korea Republic of 10 Chonbuk National University Hospital, Department of Radiation Oncology, Jeonju, Korea Republic of 11 Ewha Womans University School of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of 12 Ewha Womans University Mokdong Hospital, Department of Radiation Oncology, Seoul, Korea Republic of 13 Gyeongsang National University Hospital- Gyeongsang National University School of medicine, Department of Radiation Oncology, Jinju, Korea Republic of Purpose or Objective This study was performed to identify a subset of patients who may benefit from post-mastectomy radiotherapy (PMRT) among node-negative patients. Material and Methods We retrospectively reviewed 1,828 patients with pT1-2N0 breast cancer, treated with mastectomy without PMRT from 2005 to 2010 at 10 institutions. Univariate and multivariate analyses for locoregional recurrence (LRR) and any first recurrence (AFR) were performed according to clinicopathologic factors and biologic subtypes. Results During a median follow-up period of 5.9 years (range: 0.7– 10.4 years), 98 patients developed AFR (39 cases of isolated LRR, 13 of LRR with synchronous distant metastasis, and 46 of isolated distant metastasis), and 52 patients developed LRR (31 cases of local recurrence, 28 of regional recurrence, and 7 of local and regional recurrence). The 10-year LRR and AFR rates were 3.8% and 7.9%, respectively. Multivariate analysis revealed that an age of ≤ 40 years (hazard ratio [HR], 3.3; p < 0.001) and stage T2 cancer (HR, 1.3; p = 0.013) were independent risk factors for LRR. The 10-year LRR rates were 2.5% with no risk factors, 4.5% with one risk factor, and 12.4% with two risk factors. Multivariate analysis for AFR revealed that an age of ≤ 40 years (HR, 2.6; p < 0.001), stage T2 cancer (HR, 1.3; p < 0.001), and the triple-negative biological subtype (HR, 1.6; p = 0.045) were independent risk factors for AFR. The 10-year AFR rates were 3.9% with no risk factors, 10.6% with one risk factor, and 18.1% with two to three risk factors. Conclusion Mastectomy without PMRT is a sufficient local treatment for pT1-2N0M0 breast cancer. Nevertheless, PMRT might be considered for patients with two or three risk factors, among those of young age, with T2 tumors, and with the triple-negative biological subtype based on LRR and AFR. PV-0236 Impact of radiation therapy delay in patients underwent neoadjuvant chemotherapy and breast surgery S. Silva 1 , A. Pereira 1 , M. Kennya 2 , M. Gustavo 2 , M. Mano 1 1 Instituto do Cancer do Estado de São Paulo Universidade de São Paulo-, Clinical Oncology, São Paulo, Brazil 2 Instituto do Cancer do Estado de São Paulo Universidade de São Paulo-, Radiotherapy, Sao Paulo, Brazil

Purpose or Objective It was proposed that in some patients with early breast cancer (BC) breast-conserving surgery with subsequent irradiation of remaining breast tissue and sentinel lymph nodes (SLN) should provide sustained control over BC and achieving high rates of disease-free survival. Purpose: to evaluate diagnostic accuracy of SPECT-CT with 99mTc-MIBI in predicting non-SLN invasion by BC. To determine efficacy of SPECT-CT (with 99mTc- radiocolloids) visualization of axillary SLN for radiotherapy planning. To determine treatment algorithms based on SPECT-CT examinations with 99mTc-MIBI and 99mTc- radiocolloids in patients with early BC. Material and Methods Accuracy of SPECT-CT in diagnosis of axillary non-SLN invasion (metastases in 2 and more lymph nodes) was prospectively evaluated in 186 primary women with cT1- 3NxM0 BC. Diagnostic results were evaluated by histological examination of removed axillary LN: in 84 cases – by sentinel LN biopsy, in 102 – by standard axillary LN dissection. In 153 BC patients we determined topography of axillary SLN and their relation within standard tangential radiotherapy fields used for breast irradiation after conservative surgery. Distribution of axillary SLN was allocated to following subregions: central(C), anterior pectoral(AP), sub-(SP) intrapectoral (IP), lateral (L), subscapular (SSc), pectoral nodes lying close to thorax wall (Th). Finally, on routine 3D treatment plans of 10 consecutive patients we examined radiation doses absorbed by SLN localized in various axillary subregions and analyzed dose distribution with different fields set up. Results In the first study histological sings of axillary lymph nodes involvement were detected in 66 of 186 evaluated patients, 43 of them had invasion of non-SLN. Sensitivity of hybrid SPECT-CT imaging with 99mTc-MIBI in diagnosis of axillary non-SLN invasion was 93%. This high sensitivity help us to determine women that can be treated by irradiation of SLN without axillary surgery. In 153 women of the second group we used SPECT-CT with radiocolloids to determine topography of SLN. We mentioned following distribution of axillary SLN: C- 64(50.5%), AP–34(26.8%), Th–19(14.9%), L or SSc–10(7.8%). In 17(13.4%) cases SLN were localized both on the I and II(IP, SP) levels. Evaluation of 3D treatment plans demonstrated that standard tangential radiation fields does not cover SLN in 80% cases. In 20% they encompass C, AP, IP, SP nodes. Modification of tangential fields permit effective irradiation of C, AP, IP, SP, L, SSc nodes in all cases. Th LN can be covered only by IMRT technique. Conclusion SPECT-CT with 99mTc-MIBI can effectively diagnose non- SLN invasion by BC and subsequent SPECT-CT with radiocolloids permit accurate planning and irradiation of SLN by extended tangential radiation fields. This strategy can be considered as alternative to treatment with surgical axillary staging. PV-0235 Is there a subset who benefits from PMRT in node-negative breast cancer patients? H.J. PARK 1 , K. Shin 2 , J. Kim 3 , S. Ahn 4 , S. Kim 4 , Y. Kim 5 , W. Park 6 , Y. Kim 7 , S. Shin 8 , J. Kim 9 , S. LEE 10 , K. Kim 11 , K. Park 12 , B. Jeong 13 1 Hanyang University Hospital, Department of Radiation Oncology, Seongdong-gu- Seoul, Korea Republic of 2 Seoul National University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of 3 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of 4 Asan Medical Center- University of Ulsan College of