Shima Mahmoudi - Department of Medical Physics and Medical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Nasim Kavousi - Department of Medical Physic, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
Mohssen Hassani - Department of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Mahbod Esfahani - Department of Medical Physics and Medical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Hassan Ali Nedaie - ۱. Department of Medical Physics and Medical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. ۴. Radiation Oncology Research Center, Cancer Institute ,Tehran University of Medical Sciences, Tehran, Iran

Introduction: In this survey, radiation-induced secondary cancer risks (SCRs) have been assessed in irradiated organs following three-dimensional conformal radiation therapy (۳D-CRT) of breast cancer using the Biological Effects of Ionizing Radiation (BEIR) VII models. Material and Methods: Sixty patients with left-sided breast cancer, who were treated with a total breast dose of ۵۰ Gy in ۲ 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. Results: The mean organ dose values of these ۶۰ patients were ۶.۸, ۱۵.۹, ۳.۷, ۴.۵, and ۱.۵ Gy in the thyroid, ipsilateral lung, contralateral breast, heart, and liver, respectively. Based on the BEIR VII models, ERR was estimated to be ۲۱.۲, ۵.۰, ۱.۶, and ۱.۴ Gy-۱ for the ipsilateral lung, thyroid, heart, and liver, respectively. In addition, excess absolute risks for cancer incidence were calculated as ۱۰۵, ۴۵.۸, ۱۵.۸, and ۴.۳۵ Gy-۱ for these organs, respectively. Conclusion: In this survey, SCRs were quantitatively measured for various organs of breast cancer patients who received ۳D-CRT. We observed that ۳D-CRT treatment was associated with a relatively high SCR in the lung.

Radiotherapy, Secondary cancer risk, Breast Cancer