Assessment of Radiation-Induced Secondary Cancer Risks In Breast Cancer Patients Treated with 3D Conformal Radiotherapy

Introduction: In the current study, radiation-induced secondary cancers risks (SCRs) have been evaluated in irradiated organs following three-dimensional conformal radiation therapy (3D-CRT) of breast cancer using the BEIR (Biological Effects of Ionizing Radiation) VII models. Material and Methods: Sixty patients with left-sided breast cancer were chosen for this study and who were treated with a total breast dose of 50 Gy in 2 Gy fractions. Differential dose volume histograms (dDVHs) were retrieved and values of mean organs dose were computed. SCRs to 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 BEIR VII committee of the U.S National Academy of Sciences.Average values of organ dose to 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. Results: From the BEIR VII models, ERR incidence was estimated to be 21.2, 5.0, 1.6 and 1.4 Gy-1 for the ipsilateral lung, thyroid, heart, and liver, respectively. EAR for cancer incidence was calculated as 105, 45.8, 15.8 and 4.35 Gy-1 for these same organs. Conclusion: The study showed SCRs quantitatively to various organs for patients with breast cancer who received 3D-CRT. We found that 3D-CRT treatment is associated with a relatively high SCR in the lung.