Thyroid function following radiation therapy in breast cancer patients: risk of radiation-induced hypothyroidism

Radiation exposure to the thyroid gland seems unavoidable in breast cancer (BC) patients receiving radiation therapy (RT) to the supraclavicular (SC) region. Hence, this study aimed to evaluate the effects of SC region RT on thyroid function and the prevalence of radiation-induced hypothyroidism (RIHT) in BC patients at regular intervals post-treatment.

Twenty-one patients with BC were enrolled in this analytical cross-sectional study by simple and convenient sampling, from March 2019 to March 2020. Thyroid function and the prevalence of RIHT were evaluated and compared by measuring the serum of thyroid-stimulating hormone (TSH) and free thyroxine hormone (fT4) levels before radiation therapy (pre-RT) and 3 and 6 months after radiation therapy (post-RT). The patients underwent 3 dimensional conformal. radiation therapy (3D CRT) of breast/chest wall, axillary, and supraclavicular lymph nodes with 50 Gy/25 fractions/5 weeks. The collected data were analyzed using SPSS software (version 20).

Serum levels of TSH increased at 3 and 6 months post-RT, this increase was not statistically significant (p > 0.05). Nevertheless, serum levels of fT4 were significantly elevated at 3 and 6 months post-RT (p < 0.01). A correlation was observed between the follow-up period and the incidence of RIHT, where it was 0% at 3 months and 9.5% at 6 months post-RT. RIHT was not significantly associated with any factors, including patient's age, type of surgery, thyroid gland dose, and thyroid gland volume.

It seems that SC region RT does not have a significant adverse effect on the thyroid function among BC patients at 3 and 6 months post-treatment. Hence, a long-term follow-up with a larger sample size is suggested.