title: Evaluation of clinical hypothyroidism risk due to irradiation of thyroid and pituitary glands in radiotherapy of nasopharyngeal cancer patients.
abstract: BACKGROUND
  Radiation-induced thyroid dysfunction after radiotherapy for nasopharyngeal cancer (NPC) has been reported. This study investigated the radiation effects of the thyroid and pituitary glands on thyroid function after radiotherapy for NPC.
  
  
  METHODS
  Sixty-five NPC patients treated with radiotherapy were recruited. Baseline thyroid hormone levels comprising free triiodothyronine (fT3), free thyroxine (fT4) and thyroid-stimulating hormone (TSH) were taken before treatment and at 3, 6, 12 and 18 months. A seven-beam intensity-modulated radiotherapy plan was generated for each patient. Thyroid and pituitary gland dose volume histograms were generated, dividing the patients into four groups: high (>50 Gy) thyroid and pituitary doses (HTHP group); high thyroid and low pituitary doses (HTLP group); low thyroid and high pituitary doses; and low thyroid and pituitary doses. Incidence of hypothyroidism was analysed.
  
  
  RESULTS
  Twenty-two (34%) and 17 patients (26%) received high mean thyroid and pituitary doses, respectively. At 18 months, 23.1% of patients manifested various types of hypothyroidism. The HTHP group showed the highest incidence (83.3%) of hypothyroidism, followed by the HTLP group (50%).
  
  
  CONCLUSIONS
  NPC patients with high thyroid and pituitary gland doses carried the highest risk of abnormal thyroid physiology. The dose to the thyroid was more influential than the pituitary dose at 18 months after radiotherapy, and therefore more attention should be given to the thyroid gland in radiotherapy planning.
authors.affiliation: Cancer Hospital, Shantou University Medical College, Shantou, Guangdong, China.
authors.forename: Zhixiong
authors.initials: Z
authors.lastname: Lin
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Wang
authors.forename: Wenjia
authors.initials: W
authors.lastname: Xie
authors.forename: Zhining
authors.initials: Z
authors.lastname: Yang
authors.forename: Kaijun
authors.initials: K
authors.lastname: Che
authors.forename: Vincent W C
authors.initials: VW
authors.lastname: Wu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015984:Causality; D015897:Comorbidity; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D007037:Hypothyroidism / Q000453:epidemiology*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000453:epidemiology* / Q000532:radiotherapy*; D010902:Pituitary Gland / Q000528:radiation effects*; D011832:Radiation Injuries / Q000453:epidemiology*; D020266:Radiotherapy, Conformal / Q000706:statistics & numerical data*; D018570:Risk Assessment; D013961:Thyroid Gland / Q000528:radiation effects*; D016896:Treatment Outcome
keywords: head and neck; hypothyroidism; nasopharyngeal carcinoma; radiation oncology