The impact of radiation therapy on thyroid function in patient with head and neck tumors

Background. Head and neck cancers (HNC) accounted for 1,518,133 new cases and 510,771 new deaths worldwide. The first reports of hypothyroidism following radiotherapy (RT) for HNC were published in the 1960s. The objective of this study was to ascertain the frequency of thyroiditis in patients with HNC and to establish the threshold of radiation dose volume for radiation-induced hypothyroidism in HNC. Methods. This was a prospective study of 35 patients with HNC treated with IMRT-VMAT. The following characteristics were examined: age, gender, comorbidity, initial tumor site, histology, surgical margin resection, radiation therapy dosage, V40, V50, V60 (percentage of thyroid tissue volume), 95% dose received, mean dose, minimum dose, and maximum dose. Thyroid assessment was performed using ultrasonography of the neck. Thyroid function was determined by TFT tests (TSH, free T3, and free T4), which were done at baseline before treatment and after RT for each case. Results. In this study, the mean age was 57.71 ± 11.43 years, with males comprising 68.6% (24 patients) and females comprising 31.4% (11 patients). Regarding TSH, the results showed that post-RT, the mean level of TSH was significantly higher than pretreatment, with a significant difference (P = 0.009). Regarding fT3, the results showed that post-RT, the mean level of fT3 was significantly lower than pretreatment, with a significant difference (P = 0.007). Regarding fT4, the results showed that post-RT, the mean level of fT4 was significantly lower than pretreatment, with a significant difference (P = 0.015). In addition, the mean 95% dose was 6.8 Gy (median = 4 Gy). The percentages of thyroid tissue volumes at V40, V50, and V60 were 79.47%, 39.28%, and 38.02%, respectively. The incidence of hypothyroidism was 14.3%, and the euthyroid incidence rate was 85.7%. Conclusions. There is a strong correlation between radiation therapy doses exceeding 66 Gy and the occurrence of hypothyroidism. The levels of fT3 and fT4 decreased after RT, while TSH levels increased. In dosimetry, the mean 95% dose was 6.8 Gy. The percentages of thyroid tissue volumes at V40, V50, and V60 were 79.47%, 39.28%, and 38.02%, respectively. The incidence of hypothyroidism was 14.3%, and the euthyroid incidence rate was 85.7%.