Primary and central hypothyroidism after radiotherapy for head-and-neck tumors.
OBJECTIVE
To investigate the incidence of radiotherapy (RT)-induced central and primary hypothyroidism regarding total dose, fractionation, and adjuvant chemotherapy.


METHODS
We retrospectively reviewed the data from 312 patients treated with RT for extracranial head-and-neck tumors between 1964 and 2000. The cervical lymph nodes were irradiated in 197 patients. The radiation doses to the thyroid gland and hypothalamic-pituitary axis were estimated by reconstructing the treatment plans.


RESULTS
Clinical central hypothyroidism (CH) was observed in 17 patients (5.4%); the median clinical latency was 4.8 years. Clinical primary hypothyroidism (PH) was observed in 40 patients (20.3%); the median clinical latency was 3.1 years. Multivariate analysis of clinical CH revealed that fractionation, adjuvant chemotherapy, and total dose to the pituitary were not significant. Multivariate analysis of clinical PH revealed that the total dose to the thyroid (p = 0.043) was significant, but adjuvant chemotherapy, age, and gender were not. Of the patients tested for hypopituitarism, 14 (20.3%) of 69 demonstrated subclinical CH and 17 (27.4%) of 62 demonstrated subclinical PH. The 5-year and 10-year rates of freedom from clinical CH and PH were 97% and 87% and 68% and 67%, respectively. Of the patients tested, the 5-year and 10-year rates of freedom from subclinical CH and PH were 91% and 78% and 71% and 71%, respectively.


CONCLUSIONS
Clinical and subclinical manifestations of late radiation toxicity were observed in the thyroid and hypothalamic-pituitary axis. Although CH did not indicate a dependence on fractionation, adjuvant chemotherapy, or total dose to the pituitary, PH showed a dependence on the total dose to the thyroid gland.
Bhandare
Niranjan
N
Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL 32610, USA.
Kennedy
Laurence
L
Malyapa
Robert S
RS
Morris
Christopher G
CG
Mendenhall
William M
WM
D000367:Age Factors; D017024:Chemotherapy, Adjuvant / Q000009:adverse effects; D003131:Combined Modality Therapy / Q000009:adverse effects; D003920:Diabetes Mellitus; D005260:Female; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000528:radiation effects*; D007037:Hypothyroidism / Q000453:epidemiology / Q000209:etiology*; D015994:Incidence; D008297:Male; D044469:Racial Groups; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D012737:Sex Factors; D013961:Thyroid Gland / Q000528:radiation effects*