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hypothyroidism is a known consequence of external - beam radiotherapy to the neck encompassing a part or whole of the thyroid gland . though hypothyroidism has a significant impact on the quality of life , assessment of thyroid function
is not yet a part of continue follow - up of cancer patients even in long term survivors . as the survival of cancer patients are increasing , the quantification of the incidence of radiation - induced hypothyroidism is gaining importance .
the most common clinical late - effect of the thyroid gland irradiation in patients exposed to therapeutic doses ( 30 - 70 gy ) to the cervical region is primary hypothyroidism .
the aetiology of radiation induced thyroid injury includes vascular damage , parenchymal cell damage and auto - immune reactions . in this non - randomized prospective study , we have tried to evaluate the response of the thyroid gland to radiation by assessing thyroid function before irradiation and at regular intervals after irradiation .
the present study was conducted for a period of 2 years in which thyroid function was assessed in 59 patients managed in a tertiary care centre .
fifty nine euthyroid healthy control samples were also taken , who had not received the neck radiation .
the patients / controls were followed periodically , after the completion of radiation therapy , ( in case of patients ) first at 3 months , then at 6 months , 12 months , 18 months , and finally at 24-month interval .
the following patients were included in the study : patients with histologically proven non - thyroid malignancies , who were destined to receive ebrt to the primary site as well as to the neck and where radiation portals included a part or whole of the thyroid gland , and patients who euthyroid prior to radiation therapy . in this study , we present the incidence of long term hypothyroidism in malignancy patients after radiotherapy to the neck
both serum thyroid stimulating hormone ( tsh ) and t4 levels were prospectively measured to reveal subclinical and clinical hypothyroidism .
serum thyroid stimulating hormone ( tsh ) and t4 levels were assayed by radioimmunoassay method using commercial kits .
the radiotherapy technique employed in this study was the conventional ebrt technique using single daily fractions of 1.8 - 2.0 gy , with 5 fractions per week using teletherapy cobalt 60 units .
blood chemistry , complete blood count , abdominal ultrasonography , chest x - ray , ecg , and thyroid hormone levels ( tsh , t4 levels ) , were evaluated regularly .
if the patients presented with low t4 levels and clinical symptoms of hypothyroidism , thyroxine was prescribed to relieve the hypothyroidism with subsequent monitoring of serum t4 change at least every 3 months .
various predisposing factors as age , gender , tumor status , primary tumor site , treatment modality , total radiation dose , and chemotherapy were examined for any association with the development of hypothyroidism using chi - square tests , or student t - test as appropriate .
meier 's method was used to estimate the time from the initiation of treatment to the development of hypothyroidism .
in this study , we present the incidence of long term hypothyroidism in malignancy patients after radiotherapy to the neck .
both serum thyroid stimulating hormone ( tsh ) and t4 levels were prospectively measured to reveal subclinical and clinical hypothyroidism .
serum thyroid stimulating hormone ( tsh ) and t4 levels were assayed by radioimmunoassay method using commercial kits .
the radiotherapy technique employed in this study was the conventional ebrt technique using single daily fractions of 1.8 - 2.0 gy , with 5 fractions per week using teletherapy cobalt 60 units .
blood chemistry , complete blood count , abdominal ultrasonography , chest x - ray , ecg , and thyroid hormone levels ( tsh , t4 levels ) , were evaluated regularly .
if the patients presented with low t4 levels and clinical symptoms of hypothyroidism , thyroxine was prescribed to relieve the hypothyroidism with subsequent monitoring of serum t4 change at least every 3 months .
various predisposing factors as age , gender , tumor status , primary tumor site , treatment modality , total radiation dose , and chemotherapy were examined for any association with the development of hypothyroidism using chi - square tests , or student t - test as appropriate . the kaplan 
meier 's method was used to estimate the time from the initiation of treatment to the development of hypothyroidism .
the incidence of hypothyroidism after ebrt to neck where radiation portals include part or whole of the thyroid gland was 16.94% , 7 cases had subclinical hypothyroidism ( 11.86% ) and 3 cases had clinical hypothyroidism ( 5.08% ) [ table 1 ] .
incidence of hypothyroidism after ebrt and mean thyroid hormone levels of cases we found no effect of age , gender , primary tumor site , radiation dose and chemotherapy , whether neoadjuvant or concurrent on the development of hypothyroidism .
hypothyroidism covariates evaluated in cases we observed that 15.25% of patients who developed post therapy hypothyroidism did so within the 1 year .
this high rate of early onset of hypothyroidism justifies a policy of early thyroid testing .
the first reported case of hypothyroidism following external - beam radiotherapy for malignancy appeared in literature in 1961 .
we evaluated the incidence of hypothyroidism in cases and controls , which was 16.94% in cases and 3.4% in controls .
the association of hypothyroidism in the patients who had received radiotherapy to the neck was found to be statistically significant ( p value 0.015 ) .
both the hypothyroid patients in the control arm were of the subclinical type ( 3.4% ) . in the case arm ,
7 patients ( 11.86% ) were having subclinical hypothyroidism and 3 patients ( 5.08% ) were having clinical hypothyroidism .
previous studies on the risk of hypothyroidism after neck irradiation have shown that hypothyroidism is more frequent in women than in men . however ,
in our cohort of patients , neither age nor sex was of statistical significance and was in consistence with the results of mercado . in our study , patients with age of < 50 years were having a hypothyroidism incidence of 17.2% ( 5/29 ) and patients with age of 50 years having a hypothyroidism incidence of 16.7% ( 5/30 ) with a p value of 0.61 .
similarly , our incidence of hypothyroidism in male patients was 24% ( 6/25 ) and incidence of hypothyroidism in the female patients was 11.8% ( 4/34 ) with a p value of 0.18 .
radiation dose as a risk factor for the development of hypothyroidism remains controversial . in patients receiving radiotherapy for head and neck cancer , doses exceeding 60 gy
were reported to be associated with an increased rate of hypothyroidism . however , in a prospective study , tell et al .
posner et al . did not find the radiation dose to be a significant factor .
similarly , in our study , the patients who received radiation dose < 45 gy to neck showed incidence of hypothyroidism to the tune of 33.2% , while those receiving radiotherapy doses of 45 gy were having the incidence of hypothyroidism of 15% with a p value of 0.26 which is statistically insignificant . in our study , 35 patients received chemotherapy in addition to radiation as part of their treatment schedule .
posner et al . examined the effect of combination chemotherapy on hypothyroidism in patients with head and neck carcinoma and found no association . in the present study
, we evaluated 59 patients ; with 30 patients having breast carcinoma , 17 patients of head and neck cancer and 12 patients of lymphoma , who had received radiotherapy to the neck , encompassing a part or whole of the thyroid gland .
we detected an incidence of 10% , 23.5% and 25% in breast ca , head and neck carcinoma and lymphoma , respectively .
these findings are similar to the incidences of previously cited literature among the patients of head and neck tumors and hodgkin 's disease .
any predilection of hypothyroidism to a particular tumor site was not statistically significant as our p value was 0.34 . in our study ,
tsh levels did not change in the first 3 months but significantly increased in the subsequent 3 months .
tamura et al . reported that the incidence of high tsh increased from 26% after 2 years to 62% after 6 - 12 years .
thus , two kinds of radiation induced thyroid damage are proposed : subacute damage and late damage .
the former develops in almost all patients , whereas the incidence of the latter varies considerably among different reports .
we conclude from the study of thyroid function in cancer patients treated with radiotherapy to the neck that hypothyroidism ( both subclinical and clinical ) occurs with considerable and poorly acknowledged frequency .
we believe that monitoring thyroid function should become a routine procedure in any oncology clinic managing these patients .
introduction : hypothyroidism is a known consequence of external - beam radiotherapy to the neck encompassing a part or whole of the thyroid gland . in this non - randomized prospective study , we have tried to evaluate the response of the thyroid gland to radiation by assessing thyroid function before irradiation and at regular intervals after irradiation.aims and objectives : the aim of this study were to assess in the cancer patients , who were exposed to the therapeutic external beam radiation , where radiation portals include a part or whole of the thyroid gland : the incidence of primary hypothyroidism , the time required to become hypothyroid , any relation between the total dose for the development of hypothyroidism , and whether there are any patient or treatment - related factors that are predictive for the development of hypothyroidism , including the use of concurrent chemotherapy.materials and methods : this non - randomized , prospective study was conducted for a period of 2 years in which thyroid function was assessed in 59 patients ( cases ) of head and neck cancer , breast cancer , lymphoma patients and other malignancies , who had received radiotherapy to the neck region . 
 59 euthyroid healthy patients ( controls ) were also taken , who had not received the neck irradiation . 
 these patients / controls were assessed periodically for 2 years.results:the incidence of hypothyroidism after external beam radiation therapy ( ebrt ) to neck where radiation portals include part or whole of the thyroid gland was 16.94% , seven cases had subclinical hypothyroidism ( 11.86% ) and three cases had clinical hypothyroidism ( 5.08% ) . 
 mean time for development of hypothyroidism was 4.5 months . 
 there was no effect of age , gender , primary tumor site , radiation dose and chemotherapy , whether neoadjuvant or concurrent with the development of hypothyroidism.conclusion:in summary , we found that thyroid dysfunction is a prevalent , yet easily treatable source of morbidity in patients undergoing radiation therapy to neck where radiation portals include a part or whole of the thyroid gland .