Estimation of the Thyroid Secondary Cancer Risk on the Patient of Standard Breast External Beam Radiotherapy

The purpose of this study was to estimate the secondary cancer risk of thyroidin standard radiotherapy methods which are commonly used for breast cancer patients.

A total of 64 breast cancer patients (their age range was around 50 years old) whoreferred to Seyed‑Al‑Shohada hospital (Isfahan, Iran) were included in this study. The radiotherapyof the mentioned patients was performed using 6‑MV photon beams. Dose measurements were alsodone using thermoluminescent dosimeters. Calculation of the risk of developing secondary cancer inthyroid was done using the Biological Effects of Ionizing Radiation Committee VII and recommendedquantity of the International Radiation Protection Commission, excess relative risk.

Themean radiation dose to thyroid for the tangential beams, tangential field with supraclavicular (SC)field, and also a tangential field with SC field in modified radical mastectomy (MRM) were0.883 ± 0.472, 1.512 ± 0.365, and 1.587 ± 0.37, respectively. The risk of developing secondarythyroid cancer over a period of 5 years after breast cancer therapy in the tangential, tangential witha SC field, and also tangential beam with SC field in MRM were 9.974 ± 4.318, 17.891 ± 0.365,and 18.783 ± 4.384, respectively. The mean of the measured thyroid doses in patients treated withtangent fields was significantly lower than the patients under the irradiation of the tangent fields withSC field (P < 0.001).

Using radiation protection equipment is suggested for breastcancer patients who treated with the studied radiotherapy methods.