title: Factors influencing the parotid function in nasopharyngeal carcinoma treated with parotid-sparing radiotherapy.
abstract: BACKGROUND
  To evaluate the factors influencing post-irradiation parotid gland function in nasopharyngeal cancer treated with parotid-sparing radiotherapy.
  
  
  METHODS
  This study consisted of 45 patients with nasopharyngeal cancer treated with radiotherapy including 3D conformal radiotherapy, intensity-modulated radiotherapy and high-dose-rate brachytherapy. The mean follow-up time was 37.5 months (range: 15-50 months). Objective parotid gland function was assessed by series sialoscintigraphy pre-irradiation and post-irradiation at 1, 6, 12 and 18 months. Subjective salivary function was recorded by the LENT/SOMA system. Wilcoxon signed-rank test was used to compare the secretion ratio (SR) of parotid gland before and after treatment. Mann-Whitney rank-sum test was used to determine the factors influencing the post-irradiated SR. Chi-square test was used to compare the correlation between subjective grading of xerostomia and objective grading of parotid glands.
  
  
  RESULTS
  There was a significant difference between the pre-irradiation and post-irradiation parotid gland's SR at 1 (0.30 versus 0.01, P < 0.05) and 6 months (0.03 versus 0.08, P < 0.05). However, there was no significant difference compared with the pre-irradiation SR at 12 (0.30 versus 0.20, P > 0.05) and 18 months (0.30 versus 0.18, P > 0.05). There was significant correlation between subjective and objective salivary function (P = 0.024) at 12 months after radiotherapy. The factor that impacted the preservation of parotid function was mean dose to the parotid gland >38.0 Gy (P < 0.05).
  
  
  CONCLUSIONS
  Our results demonstrated that parotid function could recover 1 year after treatment with parotid-sparing radiotherapy in patients with nasopharyngeal cancer. The most important factor that influenced parotid function was the mean dose to the parotid gland.
authors.affiliation: Department of Radiation Oncology, Chung Shan Medical University Hospital, Taichung, Taiwan. p53_tw@yahoo.com.tw
authors.forename: Wen-Shan
authors.initials: WS
authors.lastname: Liu
authors.forename: Steve Pai-Hsun
authors.initials: SP
authors.lastname: Lee
authors.forename: Jong-Kang
authors.initials: JK
authors.lastname: Lee
authors.forename: Mao-Chang
authors.initials: MC
authors.lastname: Su
authors.forename: Gin-Den
authors.initials: GD
authors.lastname: Chen
authors.forename: Hong-Shen
authors.initials: HS
authors.lastname: Lee
authors.forename: Huei
authors.initials: H
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy / Q000009:adverse effects; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000503:physiopathology / Q000532:radiotherapy*; D010306:Parotid Gland / Q000503:physiopathology* / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D014987:Xerostomia / Q000209:etiology