title: How common is hypothyroidism after external radiotherapy to neck in head and neck cancer patients?
abstract: OBJECTIVE
  To identify the occurrence of clinical and subclinical hypothyroidism among head and neck cancer patients receiving radiation to the neck and to justify routine performing of thyroid function tests during follow-up.
  
  
  METHODS
  This is a prospective nonrandomized study of 45 patients of head and neck cancer, receiving radiotherapy (RT). Thyroid stimulating hormone and T4 estimations were done at baseline and at 4 months and 9 months following RT.
  
  
  RESULTS
  Of the 45 patients, 37(82.2 %) were males and eight (17.8 %) were females. All patients received radiation to the neck to a dose of >40Gy. 35.6% received concurrent chemotherapy. Two patients underwent prior neck dissection. Fourteen patients (31.1%) were found to have clinical hypothyroidism (P value of 0.01). Five (11.1%) patients were found to have subclinical hypothyroidism with a total 19 of 45 (42.2%) patients developing radiation-induced hypothyroidism. Nine of 14 patients with clinical hypothyroidism were in the age group of 51 to 60 years (P=0.0522). Five of 16 patients who received chemoradiation and nine of 29 who received RT alone developed clinical hypothyroidism. Above 40 Gy radiation dose was not a relevant risk factor for hypothyroidism.
  
  
  CONCLUSIONS
  Hypothyroidism (clinical or subclinical) is an under-recognized morbidity of external radiation to the neck which is seen following a minimum dose of 40 Gy to neck. Recognizing hypothyroidism (clinical or subclinical) early and treating it prevents associated complications. Hence, thyroid function tests should be made routine during follow-up.
authors.affiliation: Department of Radiotherapy, MS Ramaiah Medical College, Bengaluru, Karnataka, India.
authors.forename: Nirmala
authors.initials: N
authors.lastname: Srikantia
authors.forename: Karthik S
authors.initials: KS
authors.lastname: Rishi
authors.forename: M G
authors.initials: MG
authors.lastname: Janaki
authors.forename: Ramesh S
authors.initials: RS
authors.lastname: Bilimagga
authors.forename: Arul
authors.initials: A
authors.lastname: Ponni
authors.forename: A G
authors.initials: AG
authors.lastname: Rajeev
authors.forename: Kirthi
authors.initials: K
authors.lastname: Kaushik
authors.forename: Mala
authors.initials: M
authors.lastname: Dharmalingam