Assessment of Radiation-induced Secondary Cancer Risks in Breast Cancer Patients Treated with 3D Conformal Radiotherapy

In this survey, radiation-induced secondary cancer risks (SCRs) have been assessed in irradiated organs following three-dimensional conformal radiation therapy (3D-CRT) of breast cancer using the Biological Effects of Ionizing Radiation (BEIR) VII models.
Sixty patients with left-sided breast cancer, who were treated with a total breast dose of 50 Gy in 2 Gy fractions were chosen for this study. Differential dose volume histograms (dDVHs) were retrieved, and values of mean organs dose were computed. Second cancer risks for the heart, ipsilateral lung, liver, thyroid, and contralateral were estimated using both excess relative risk (ERR) and excess absolute risks (EAR) models as proposed by the BEIR VII committee of the U.S National Academy of Sciences.
The mean organ dose values of these 60 patients were 6.8, 15.9, 3.7, 4.5, and 1.5 Gy in the thyroid, ipsilateral lung, contralateral breast, heart, and liver, respectively. Based on the BEIR VII models, ERR was estimated to be 21.2, 5.0, 1.6, and 1.4 Gy-1 for the ipsilateral lung, thyroid, heart, and liver, respectively. In addition, excess absolute risks for cancer incidence were calculated as 105, 45.8, 15.8, and 4.35 Gy-1 for these organs, respectively.
In this survey, SCRs were quantitatively measured for various organs of breast cancer patients who received 3D-CRT. We observed that 3D-CRT treatment was associated with a relatively high SCR in the lung.