This study is to prospectively investigate the incidence of hypothyroidism after postoperative radiotherapy and identify risk factors for development of hypothyroidism. Patients with breast cancer treated with surgery followed by radiotherapy is enrolled. Thyroid function was assessed at baseline and different times after radiotherapy. The radiation technique, thyroid dose parameters and hypothyroidism are prospective evaluated, and the dose-effect relationship is analyzed.

Breast cancer patients treated with radiotherapy after surgery are prospectively enrolled. Thyroid function is evaluated mainly by the measurement of thyroid-stimulating hormone (TSH), free triiodo-thyronine (FT3) and free thyroxine (FT4). Thyroid function is regularly assessed before and after radiotherapy. The radiation technique and thyroid dose parameters are assessed. Development of subclinical or biochemical hypothyroidism is noted. The incidence and risk factors of hypothyroidism is analyzed. The dose-volume constraints that correlate with functional impairment of the thyroid in breast cancer patients treated with radiotherapy is discussed.

Inclusion Criteria:

Breast cancer patients at first diagnosis, patients who are treated with radiotherapy after breast conserving surgery or modified radical mastectomy, no medical history of hyperthyroidism, hypothyroidism or thyroiditis, have never taken thyroxine, no thyroid surgery.

Exclusion Criteria:

Absence or ectopic thyroid gland, previous radiotherapy of the neck, diseases of thalamus or pituitary, previous radiotherapy of thalamus or pituitary

Breast cancer patients treated with radiotherapy after surgery are enrolled.