Estimation of the thyroid secondary cancer risk on the patient of standard breast external beam radiotherapy

Introduction: The purpose of this study was to estimate the secondary cancer risk of thyroid for standard radiotherapy methods which are commonly used for breast cancer patients. Materials and Methods: Sixty-four breast cancer patients (their age range was around ۵۰ years old) who referred to Seyed- Al- Shohada hospital (Isfahan, Iran) were included in this study. The radiotherapy of the mentioned patients was performed using ۶ MV photon beams. Dose measurements were also done using thermoluminescent dosimeters (TLD). Calculation of the risk of developing secondary cancer in thyroid, was done using the Biological Effected of Ionizing Radiation Committee (BEIR VII) and recommended quantity of International Radiation Protection Commission (ICRP), Excess Relative Risk (ERR). Results: The mean radiation dose to thyroid for the tangential beams, tangential field with Supraclavicular field, and also tangential field with Supraclavicular field in mastectomy (MRM) were ۰.۸۸۳ ± ۰.۴۷۲, ۱.۵۱۲ ± ۰.۳۶۵ and ۱.۵۸۷ ± ۰.۳۷, respectively. The risk of developing secondary thyroid cancer over a period of ۵ years after breast cancer therapy in the tangential, tangential with supraclavicular field, and also tangential beams with supraclavicular field in MRM was ۹.۹۷۴ ± ۴.۳۱۸, ۱۷.۸۹۱ ± ۰.۳۶۵ and ۱۸.۷۸۳ ± ۴.۳۸۴, respectively. The mean of the measured thyroid doses in patients treated with tangent fields was significantly lower than the patients under the irradiation of the tangent fields with supraclavicular field (P <۰.۰۰۱). Conclusion: Using radiation protection equipment is suggested for breast cancer patients who treated with the studied radiotherapy methods.