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Conclusion Most recurrences were observed out-of-field in the same coxal bone.These results suggest that defining the optimal clinical target volume in SBRT forcoxal bone metastasis to obtain sufficient local tumor control is difficult. EP-1690 Radiotherapy for Primary or Recurrent Fibromatosis and Long-term Results S.H. Choi 1 , H.I. Yoon 1 , C.O. Suh 1 1 Yonsei University, Radiation Oncology, SEOUL, Korea Republic of Purpose or Objective Although surgery is the primary treatment for locally invasive or recurrent fibromatosis, radiotherapy (RT) has been suggested for its local control benefits for those with positive margins or recurrent/unresectable tumors. Here, we reported our updated institutional experience of performing RT for this disease entity. Material and Methods We evaluated 47 patients with fibromatosis who treated with RT between 1990 and 2015 and followed for >12 months. Eight patients had received RT to gross tumors, and the other 39 patients were given postoperative RT after single or multiple prior surgeries (R0: 5, R2: 21, R2: 13). A median dose of 54 Gy was prescribed for definitive RT, and 48.6 Gy, 50.4 Gy, 54 Gy were prescribed for R0, R1, R2 resected tumors, respectively. Recurrences were classified as infield, marginal, or outfield, and prognostic factors were evaluated. Results With a median follow-up of 60 months,5-year PFS and OS rates were 87% and 100% from the start of RT. Recurrences were noted in 7 patients (infield 2, marginal 4, outfield 1). Infield recurrences occurred in one who received 40.5 Gy of salvage RT after postoperative recurrence, and one who received 45 Gy for R1 resection after multiple prior operations. All marginal failures were due to insufficient RT field, regardless of RT dose (3 with 45 Gy, 1 with 54 Gy). In multivariate analysis, RT field ≥5cm and dose >45 Gy were noted to be significant (p = 0.039, 0.049, respectively). When we divided patients into 4 subgroups according to RT field (≥5cm) and dose (>45 Gy), the subgroup which met both showed a particularly favorable outcome than the others. Conclusion Given the patients with long-term results, these data show that RT is a valuable option for treating aggressive fibromatosis with 45 Gy or more and large field. It would be necessary to establish a wide radiation field considering all initial tumor extents, especially for the tumors with repetitive recurrences before. For grossly residual tumors, higher dose (50-54 Gy) would be needed for infield control than for clearly removed tumors. EP-1691 Clinical outcomes of radiotherapy for patients with cancer undergoing hemodialysis H. Hirota 1 , S. Kageyama 1 , K. Itou 1 , K. Nihei 1 , K. Karasawa 1 1 Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome HospitalR, Radiation oncology, Bunkyo-ku, Japan Purpose or Objective The number of patients with end-stage renal disease (ESRD) requiring hemodialysis (HD) has increased worldwide. Patients with HD are at higher risk of developing cancer than the general population. Such patients with cancer are frequently elderly, have poor

performance status, and usually cannot tolerate chemotherapy because of its toxicity. Radiotherapy might be applicable to treating cancer in patients on HD, but no evidence of this is available. The present study aimed to determine the effects and tolerability of radiotherapy for treating cancer in patients on HD. Material and Methods We retrospectively evaluated the completion rates of radiotherapy and adverse effects on patients with HD listed in our institutional database between April 2012 and April 2017. The inclusion criteria were as follows: ERSD, age >20 years at the time of receiving radiotherapy, undergoing three sessions per week of stable maintenance HD for >12 weeks before the start of the study period, and continuing HD throughout the course of radiotherapy. Acute and late toxicities were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. Weekly toxicity was graded and recorded in the database. Information about toxicity associated with radiotherapy including dermatitis, oral mucositis, dry mouth, esophagitis, vaginal inflammation, and enterocolitis was collected. Results We analyzed 9 radical and 6 palliative episodes in 15 identified patients. Within the series, the median age was 70 (range, 53-79) years, the median follow-up was 7.8 (range, 1.4-26.4) months, the male to female ratio was 4:1, and the mean duration of HD was 85.3 (range, 4.6-204) months. The primary cancer sites were the head and neck (n=3), blood (n=3), lungs (n=3), and other (n=6). The causes of ESRD were chronic glomerulonephritis (n=5), diabetic nephropathy (n=4), other (n=3), and unknown (n=3). All 15 patients completed the scheduled radiotherapy without a prescribed dose reduction. G3 acute adverse effects developed in two patients, but significant (>G3) acute and late adverse effects did not arise. Conclusion All 15 patients with HD completed the scheduled radiotherapy for cancer without an increase in adverse effects. This is the first report of the effects of radiotherapy on cancer in patients undergoing HD. Additional evidence is needed to establish suitable radiotherapeutic regimes for such patients. EP-1692 Quality of Radiation Oncology Training in Germany: Results from the 2017 survey of the young DEGRO C. Dietzel 1 , K. Jablonska 2 , M. Niyazi 3 , T. Gauer 4 , N. Ebert 5 , C. Ostheimer 1 , D. Krug 6 1 Universitaetsklinikum HalleSaale, Radiation Oncology, Halle, Germany 2 University Cologne, Department of Radio-Oncology & CyberKnife Center, Cologne, Germany 3 University of Munich, Department of Radiation Oncology, Munich, Germany 4 University Medical Center Hamburg-Eppendorf, Department of Radiotherapy and Radio-Oncology, Hamburg, Germany 5 University Hospital C.G. Carus, Department of Radiation Oncology, Dresden, Germany 6 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany Purpose or Objective To evaluate the current situation of young radiation oncologists in Germany with regard to the contents and