en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;">Background: Using high energy X-rays (>10 MV) as a radiotherapy boost in treating oropharyngeal cancers (OPC) to reduce mandible radiation exposure may result in deterioration of disease control rates due to re-build-up of X-rays at the tumor surface. Therefore, we retrospectively compared the treatment outcomes and toxicities in OPC patients treated with radiotherapy using 15 MV and/or 4&ndash;6 MV X-rays as a boost. Materials and Methods: Between 2008 and 2014, 63 OPC patients received definitive 3-dimensional conformal radiotherapy. The median total dose was 70.2 (range, 46.8&ndash;75.6) Gy. The median follow-up period for surviving patients was 48 (range, 9&ndash;88) months. Twenty-one patients (33.3%) received a boost employing 15 MV X-ray in at least one beam during treatment, and 42 patients (66.7%) received only 4&ndash;6 MV X-rays. Local control (LC), locoregional control (LRC), disease-free survival (DFS), overall survival (OS) rates and the incidence of osteoradionecrosis (ORN) in the mandible for the two cohorts were estimated using the Kaplan-Meier method and compared using the log-rank test. Results: There were no statistically significant differences between the two cohorts in either treatment outcomes (3-year LC, 81% versus 75% [p=0.742]; 3-year LRC, 71% versus 71% [p=0.925]; 3-year DFS, 66% versus 66% [p=0.934]; 3-year OS, 65% versus 78% [p=0.321]) or incidence of grade >2 ORN in the mandible (9.5% versus 11.9% [p=0.883]). Conclusion: Employing 15 MV X-rays in a boost may provide comparable treatment outcomes to 4&ndash;6 MV X-rays. However, reduction in the incidence of ORN in the mandible was not demonstrated.</div> Oropharyngeal cancer, osteoradionecrosis, radiotherapy. 257 267 http://ijrr.com/browse.php?a_code=A-10-1-725&slc_lang=en&sid=1 H. Kaizu hkaizu1980@ybb.ne.jp 7900319475328460012327 7900319475328460012327 Yes Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan M. Hata 7900319475328460012328 7900319475328460012328 No Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan S. Takano 7900319475328460012329 7900319475328460012329 No Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan T. Kasuya 7900319475328460012330 7900319475328460012330 No Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan G. Nishimura 7900319475328460012331 7900319475328460012331 No Department of Otorhinolaryngology and Head and Neck Surgery, Yokohama City University School of Medicine, Yokohama, Kanagawa, Japan I. Koike 7900319475328460012332 7900319475328460012332 No Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan T. Taguchi 7900319475328460012333 7900319475328460012333 No Department of Otorhinolaryngology and Head and Neck Surgery, Yokohama City University School of Medicine, Yokohama, Kanagawa, Japan N. Oridate 7900319475328460012334 7900319475328460012334 No Department of Radiology, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa, Japan