title: Dosimetric Predictors of Hypothyroidism After Radical Intensity-modulated Radiation Therapy for Non-metastatic Nasopharyngeal Carcinoma.
abstract: To investigate dosimetric predictors of hypothyroidism after radical intensity-modulated radiation therapy (IMRT) for non-metastatic nasopharyngeal carcinoma (NPC).
  
  
  
  Patients with non-metastatic NPC treated with radical IMRT from 2008 to 2013 were reviewed. Serum thyroid function tests before and after IMRT were regularly monitored. Univariable and multivariable analyses were carried out for predictors of biochemical and clinical hypothyroidism.
  
  
  
  In total, 149 patients were recruited. After a median follow-up duration of 3.1 years, 33 (22.1%) and 21 (14.1%) patients developed biochemical and clinical hypothyroidism, respectively. Eight (24.2%) patients who had biochemical hypothyroidism developed clinical hypothyroidism later. Univariable and multivariable analyses revealed that the volume of the thyroid (P=0.002, multivariable), VS60 (the absolute thyroid volume spared from 60 Gy or less) (P<0.001, multivariable) and VS45 (P<0.001, multivariable) of the thyroid were significant predictors of biochemical hypothyroidism. The freedom from biochemical hypothyroidism was longer for those whose VS60 ≥ 10 cm(3) (mean 90.9 versus 62.6 months; P<0.001) and VS45 ≥ 5 cm(3) (mean 91.9 versus 65.2 months; P=0.001). Similarly multivariable analyses revealed that VS60 (P=0.001) and VS45 (P=0.003) were significant predictors of clinical hypothyroidism. The freedom from clinical hypothyroidism was longer for those whose VS60 ≥ 10 cm(3) (91.5 versus 73.3 months; P=0.002) and VS45 ≥ 5 cm(3) (91.5 versus 75.9 months; P=0.007).
  
  
  
  VS60 and VS45 of the thyroid should be considered important dose constraints against hypothyroidism without compromising target coverage during IMRT optimisation for NPC.
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong. Electronic address: vhflee@hku.hk.
authors.forename: V
authors.initials: V
authors.lastname: Lee
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Sum-Yin
authors.initials: SY
authors.lastname: Chan
authors.affiliation: Department of Systems Engineering and Engineering Management, The City University of Hong Kong, Hong Kong.
authors.forename: Cheuk-Wai
authors.initials: CW
authors.lastname: Choi
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: D
authors.initials: D
authors.lastname: Kwong
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Ka-On
authors.initials: KO
authors.lastname: Lam
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Chi-Chung
authors.initials: CC
authors.lastname: Tong
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Chun-Kin
authors.initials: CK
authors.lastname: Sze
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: S
authors.initials: S
authors.lastname: Ng
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: To-Wai
authors.initials: TW
authors.lastname: Leung
authors.affiliation: Department of Clinical Oncology, Queen Mary Hospital, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: A
authors.initials: A
authors.lastname: Lee
mesh_terms: D000328:Adult; D002277:Carcinoma / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology*; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D055815:Young Adult
keywords: Dosimetric predictors; hypothyroidism; intensity-modulated radiation therapy; nasopharyngeal carcinoma