Analysis of Radiation Dose and Estimation of Secondary Cancer Incidence in Organs Exposed to Radiotherapy in Breast Cancer

Background: Radiotherapy plays an important role in the treatment of breast cancer by reducing local recurrence and improving survival. However, the side effects of radiotherapy on other organs are unavoidable. Objectives: In this study, we aimed to analyze the radiation to organs that are exposed to radiation during breast radiotherapy and to assess the cancer incidence in these organs at risk (OARs). Methods: This study examined the data of dose-volume curves of 40 patients with breast cancer treated with three-dimensional conformal radiotherapy (3D-CRT) in Imam Hossein Hospital to investigate the risk of secondary malignancy for lungs and breast using biological formulas and the concept of organ-equivalent dose (OED) and excess absolute risk (EAR). Results: The findings showed that the average dose received by the contralateral breast and contralateral lung was 0.4 grays (Gy) and 0.67 Gy, respectively, in patients with the supraclavicular field, and 0.43Gy and 0.3Gy, respectively, in patients without the supraclavicular field. For these two organs, V5 was 0 and 0.09 percent, respectively. For the lungs on the treatment side, the average dose and V20 were 18.2 Gy and 34.12 percent with the supraclavicular field, and 11.39 Gy and 19.89 percent without it. For left breast cancer cases, the mean dose and V20 for the heart were 7.58 Gy and 11.57 percent with the supraclavicular field, and 5.85 Gy and 7.59 percent without it. The average received dose of thyroid and esophagus in patients treated with the supraclavicular field was 16.33 and 5.32 Gy, respectively. The EAR for contralateral breast, the same side lung, and contralateral lung was 7.46, 229, and 8.89, respectively. Conclusions: Development of a secondary malignancy after radiotherapy is a notable issue in patients with breast cancer, and there is a need to measure the probability of its occurrence. Accurate radiotherapy treatment planning can probably reduce its incidence.