Treatment outcomes of (chemo) radiotherapy for oropharyngeal cancers: influence of the use of 15 MV X-rays in radiation boost

Background: using high energy x-rays (>10 mv) as a radiotherapy boost in treatingoropharyngeal cancers (opc) to reduce mandible radiation exposure may result inbackground: using high energy x-rays (>10 mv) as a radiotherapy boost in treatingoropharyngeal cancers (opc) to reduce mandible radiation exposure may result indeterioration of disease control rates due to re-build-up of x-rays at the tumorsurface. therefore, we retrospectively compared the treatment outcomes andtoxicities in opc patients treated with radiotherapy using 15 mv and/or 4–6 mv xraysas a boost. materials and methods: between 2008 and 2014, 63 opc patientsreceived definitive 3-dimensional conformal radiotherapy. the median total dosewas 70.2 (range, 46.8–75.6) gy. the median follow-up period for surviving patientswas 48 (range, 9–88) months. twenty-one patients (33.3%) received a boostemploying 15 mv x-ray in at least one beam during treatment, and 42 patients(66.7%) received only 4–6 mv x-rays. local control (lc), locoregional control (lrc),disease-free survival (dfs), overall survival (os) rates and the incidence ofosteoradionecrosis (orn) in the mandible for the two cohorts were estimated usingthe kaplan-meier method and compared using the log-rank test. results: therewere no statistically significant differences between the two cohorts in eithertreatment 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 mayprovide comparable treatment outcomes to 4–6 mv x-rays. however, reduction inthe incidence of orn in the mandible was not demonstrated.