title: Thyroid V50 Highly Predictive of Hypothyroidism in Head-and-Neck Cancer Patients Treated With Intensity-modulated Radiotherapy (IMRT).
abstract: OBJECTIVE
  Radiation-induced hypothyroidism affects a significant number of patients with head-and-neck squamous cell cancer (HNSCC). We examined detailed dosimetric and clinical parameters to better determine the risk of hypothyroidism in euthyroid HNSCC patients treated with intensity-modulated radiation therapy (IMRT).
  
  
  METHODS
  From 2006 to 2010, 75 clinically euthyroid patients with HNSCC were treated with sequential IMRT. The cohort included 59 men and 16 females with a median age of 55 years (range, 30 to 89 y) who were treated to a median dose of 70 Gy (range, 60 to 75 Gy) with concurrent chemotherapy in nearly all (95%) cases. Detailed thyroid dosimetric parameters including maximum dose, mean dose, and other parameters (eg, V50-percent volume receiving at least 50 Gy) were obtained. Freedom from hypothyroidism was evaluated using the Kaplan-Meier method. Univariate and multivariate analyses were conducted using Cox regression.
  
  
  RESULTS
  After a median follow-up period of 50 months, 25 patients (33%) became hypothyroid. On univariate analysis, thyroid V50 was highly correlated with developing hypothyroidism (P=0.035). Other dosimetric paramaters including mean thyroid dose (P=0.11) and maximum thyroid dose (P=0.39) did not reach statistical significance. On multivariate analysis incorporating patient, tumor, and treatment variables, V50 remained highly statistically significant (P=0.037). Regardless of other factors, for V50>60%, the odds ratio of developing hypothyroidism was 6.76 (P=0.002).
  
  
  CONCLUSIONS
  In HNSCC patients treated with IMRT, thyroid V50 highly predicts the risk of developing hypothyroidism. V50>60% puts patients at a significantly higher risk of becoming hypothyroid. This can be a useful dose constraint to consider during treatment planning.
authors.affiliation: *Department of Radiation Oncology, Northwestern University Robert H. Lurie Comprehensive Cancer Center, Chicago, IL †Department of Clinical Oncology, Alexandria University, Alexandria, Egypt.
authors.forename: Sean
authors.initials: S
authors.lastname: Sachdev
authors.forename: Tamer
authors.initials: T
authors.lastname: Refaat
authors.forename: Ian D
authors.initials: ID
authors.lastname: Bacchus
authors.forename: Vythialinga
authors.initials: V
authors.lastname: Sathiaseelan
authors.forename: Bharat B
authors.initials: BB
authors.lastname: Mittal
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007037:Hypothyroidism / Q000209:etiology*; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D011832:Radiation Injuries / Q000209:etiology; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods