title: Quantification of masticatory muscle atrophy after high-dose radiotherapy.
abstract: OBJECTIVE
  To determine the rate of change in the cross-sectional area of the masticatory muscles after radiotherapy.
  
  
  METHODS
  Eligible patients had undergone unilateral radiotherapy between 1993 and 2000 and had a baseline CT scan, a comparable follow-up CT scan a minimum of 1 year later, and no recurrence of cancer. Fourteen patients had their CT series scanned into digital image files. Two anatomically selected CT slices were bisected by the midline sagittal plane and stored under randomly assigned file names. Three observers measured the masseter and medial pterygoid areas on two occasions.
  
  
  RESULTS
  The intraobserver reliability of the muscle area measurements was 96.3% for the masseter and 97.1% for the medial pterygoid. The interobserver reliability of the muscle area measurements was 96.7% for the masseter and 96.3% for the medial pterygoid. On the treated side, the muscles received a median dose of 56 Gy (range 47-63) in 2.0-0.4-Gy fractions. With a median follow-up of 2.9 years (range 1-7.6), mixed-effects regression analysis demonstrated a significant area of reduction of -0.17 cm(2)/y (p = 0.0001) for the masseter and -0.13 cm(2)/y (p = 0.001) for the medial pterygoid. The controlled rate of muscle atrophy was 3.9%/y (95% confidence interval 1.4-6.4) for the masseter and 2.3%/y (95% confidence interval -0.6 to 5.1) for the medial pterygoid.
  
  
  CONCLUSIONS
  Standard therapeutic radiation doses appear to cause significant masticatory muscle atrophy.
authors.affiliation: Department of Radiation Oncology, BC Cancer Agency, Vancouver, BC, Canada. anichol@bccancer.bc.ca
authors.forename: Alan M
authors.initials: AM
authors.lastname: Nichol
authors.forename: Sally L
authors.initials: SL
authors.lastname: Smith
authors.forename: Yulia
authors.initials: Y
authors.lastname: D'yachkova
authors.forename: James L
authors.initials: JL
authors.lastname: Robar
authors.forename: Leigh R
authors.initials: LR
authors.lastname: Barrett
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Rolleston
authors.forename: John H
authors.initials: JH
authors.lastname: Hay
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008410:Masticatory Muscles / Q000473:pathology* / Q000528:radiation effects*; D008875:Middle Aged; D009133:Muscular Atrophy / Q000209:etiology* / Q000473:pathology; D010307:Parotid Neoplasms / Q000532:radiotherapy; D011832:Radiation Injuries / Q000209:etiology / Q000473:pathology*; D011874:Radiometry; D011878:Radiotherapy / Q000009:adverse effects; D014057:Tomography, X-Ray Computed; D014067:Tonsillar Neoplasms / Q000532:radiotherapy