| [Background and objective]Carcinoma of head and neck is the 5th most common cancer in the world. The incidence of China is 20-30%.Due to the complex anatomy of the head and neck.which including a number of important organs, surgery encounter great difficulties.The surgical injury is huge, therefore radiotherapy take an important position during the treatment of head and neck cancer. The thyroid is the most developed endocrine gland of the body. Due to its anatomical location, it may be exposed to ionizing radiation in external radiotherapy involving head and neck.Radiotherapy can induce thyroid disorders, and hypothyroidism is a common one. Hypothyroidism is induced by the decreased thyroid hormone synthesis and secretion or by the inadequate use of organizations, which result the syndrome of the systemic metabolic decline. According to their different degrees, they are divided into clinical hypothyroidism and subclinical hypothyroidism.Clinical hypothyroidism is defined as a reduction in thyroid hormone, with a concomitant increase in TSH. Subclinical hypothyroidism refers to a state of elevated TSH with the presence of normal levels of thyroid hormone.The purpose of this study was to investigate the radiation-induced damage to the normal thyroid gland.[Methods and materials] From March 2008 to June 2009.53 patients with histopathological iagnosis of head and neck carcinoma from Shandong Provincial Hospital were enrolled in the study. All patients who had history of thyroid diseases,pituitary or hypothalamus diseases, who had previously radiated thyroid prior to treatment, who underwent a thyroidectomy for tumor control, and people with abnormal thyroid function were excluded from this analysis.The average age of the patients was 50.4(range 25—82).Of this group,20 cases were greater than or equal to 60-year-old and 33 cases less than 60 years.36 were men and 17 were women.14 patients had cancer in the Cervical esophageal carcinoma; 3 patients had cancer in the oropharynx;17 patients had cancer in the hypopharynx; 17 patients had cancer in the larynx, the remaining 2 patients had cancer in the cervical metastases. According to the 2002 AJCC staging,12 cases were in stagel;15 cases were in stageⅡ; 23 cases were in stage III and 3 cases were in stage IV.The total dose of radiotherapy was 50-66 grays (Gy) over 5-6.6weeks (2Gy/fraction,5fractions/week).23 patients received chemotherapy using 5-fluorouracil and cisplatin.The thyroid function was examined by the direct chemiluminescence.The serum levels of T3,T4,FT3,FT4 and TSH were obtained for each patient before radiotherapy, at the end of radiotherapy and at 3,6,9,12,18 months after radiotherapy. Reference ranges were 1.3-3.1nmol/L for T3,66-181nmol/L for T4,3.1-6.8pmol/L for FT3,12-22 pool/L for FT4. and 0.27-4.2ulu/ml for TSH. Hypothyroidism was defined as a value of thyroid stimulating hormone (TSH) greater than 4.2 ulu/ml, whether or not symptoms were present.Statistical analysis was carried out by SPSS 17.0, The results were expressed as means±standard deviations. The characteristics of each result were compared using the Student's t-test, and used Fisher's Exact Test to compare the relationship of different factors with the incidence of hypothyroidism,with P<0.05 indicating statistical significance。 [Results]Of the total 53 patients,10 became hypothyroid during the course of follow up. The incidence of hypothyroidism was 18.9%.Among them,6 cases developed subclinical hypothyroidism and 4 clinical hypothyroidism。The average time to detect hypothyroidism was11.7 months (range 3-18 months) after the completion of treatment. Approximately 70% of the cases of hypothyroidism were detected within 12 months. In my study,non-thyroidectomy neck surgery increased the incidence of radiation-induced hypothyroidism .The incidence was 37.55% among the patients who treated with radiation and neck surgery, while it was 10.8% among those treated with radiotherapy alone, with P<0.05. No statistically significant differences were found for such variables as gender, age, combined chemotherapy and smoking。Because of the small sample size, I did not compare compare the relationship of tumor stage with the incidence of developing hypothyroidism.[Conclusion]Radiotherapy for patients with carcinoma of head and neck caused radiation-induced hypothyroidism. The diagnosis was based on laboratory test。With time prolonging after radiotherapy, the incidence of hypothyroidism may increase and some subclinical hypothyroidism may develop into clinical hypothyroidism. Surgery is a risk factor for hypothyroidism, and such variables as gender, age, combined chemotherapy and smoking have no influence on the development of hypothyroidism. Hypothyroidism was defined by the elevated TSH, while the level of T3,T4,FT3 and FT4 determine the degree of hypothyroidism. This article compared the change of T3,T4,FT3 and FT4 after radiotherapy, and concluded that the change of FT4 is more early than other indicators, which will play an important role in the diagnosis of clinical hypothyroidism。Studies have shown that radiation-induced hypothyroidism is a late side effect. It is easy to be confused with tumor associated symptoms. Regular monitoring of thyroid function is very important. The time interval for monitoring has not been decided。According to the NCCN clinical practice guidelines of head and neck carcinomas thyroid function tests should be repeated at 6-12 month intervals after neck radiotherapy, so as to detect thyroid dysfunction in time, and to give timely treatment to reduce the incidence of complications. |
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