The Measurement of Thyroid Absorbed dose by Gafchromic™ EBT۲ Film and Changes in Thyroid Hormone Levels Following Radiotherapy in Patients with Breast Cancer

Background: Radiotherapy is a main method for the treatment of breast cancer. This study aimed to measure the absorbed dose of thyroid gland using Gafchromic EBT۲ film during breast cancer radiotherapy. In addition, the relationship between the absorbed dose and thyroid hormone levels was evaluated. Methods: Forty‑six breast cancer patients, with the age ranged between ۲۵ and ۳۵ years, undergoing external radiotherapy were studied. The patients were treated with ۶ and ۱۸ MV X‑ray beams, and the absorbed thyroid dose was measured by EBT۲ film. Thyroid hormone levels, thyroid‑stimulating hormone (TSH), triiodothyronine (T۳), and thyroxin (T۴), were measured before and after the radiotherapy. Pearson’s, Spearman’s, and Chi‑square tests were performed to evaluate the correlation between the thyroid dose and hormone levels. Results: The mean thyroid dose was ۲۶ ± ۹.۴۵ cGy with the range of ۷.۸۵–۴۸.۳۵ cGy. There were not any significant differences at thyroid hormone levels between preradiotherapy and postradiotherapy (P > ۰.۰۵). There was a significant relationship between increased thyroid absorbed dose and changes in TSH and T۴ levels (P < ۰.۰۵), but it was not significant in T۳ level (P = ۰.۱). Conclusion: Regarding the results, the thyroid absorbed dose can have an effect on its function. Therefore, the thyroid gland should be considered as an organ at risk in breast cancer radiotherapy.

Keywords:

Breast cancer , Gafchromic film , radiotherapy , thyroid gland