# A Dosimetric Analysis of Reduction Cardiac Dose with Lead Shielding in Breast Cancer Radiotherapy
## 1 Introduction
The larger the irradiated heart volume, or higher the radiation dose, the higher the mortality of heart disease. Radiation-induced heart complications are likely to occur when the heart dose exceeds 40-50 Gy. Clinically, the pericardial disease may have typical symptoms or sudden onset symptoms. Early symptoms of acute pericarditis include chest pain, fever, dyspnea, pericardial friction sounds, abnormal ECG, etc., which are common during radiotherapy. Continued radiotherapy can lead to delayed pericarditis within 4 months to several years after the procedure, which can develop into constrictive pericarditis and severe heart failure due to fibrosis [16]. [PERSON] et al. conducted a study on the incidence of coronary artery disease in 2168 female cancer patients who received radiotherapy between 1958 and 2001. Their research found that the average heart dose was 4.9 Gy, and the incidence of heart disease increased linearly at a rate of 7.4% per 1 Gy of heart dose increase. In addition, they indicated that the exposure of the heart to ionizing radiation during breast radiotherapy would increase the incidence of ischemic heart disease at a rate that was proportional to the average heart dose. Consequently, the disease, which could not appear until after years of the exposure, could last over two decades. Women with heart risk factors were more likely to develop complications [17]. After collecting the data of patients who received breast radiotherapy between 2001 and 2013, [PERSON] et al. reported that the average heart dose of patients undergoing conventional tangential radiotherapy fields was lower than that of patients undergoing IMRT. The average heart dose of the former and the latter was 1.3 Gy and 5.6 Gy, respectively. They also found that patients whose tumor was at the left side had a higher risk of heart disease than those in whom the tumor was at the right side. In addition, the risk of heart disease was substantially lifted if patients with left breast cancer received radiotherapy and anthracycline chemotherapy simultaneously [18]. In the study by [PERSON] et al. that recruited 647 patients who underwent radiotherapy, it was found that the average heart dose was 4.4 Gy, whereas the incidence of heart disease 10 years after the procedure was 1.3% (95% CI: 1.15-1.46; \(p<0.001\)). Their results indicated that when the dose of the entire heart increased by 1 Gy, the incidence of heart disease increased by 0.04% [19]. The accuracy of optically stimulated luminescence dosimeter (OSLD) has been proven to be within 5% of the actual dose. Relevant research has shown that it possesses both superior dose reproducibility and good accuracy within a certain energy range. Therefore, OSLD was adopted in this study as the dose measurement tool [20; 21]. The purpose of this study was to perform a dosimetric comparison of 3D-CRT, IMRT, and VMAT on left breast cancer patients who underwent breast-conserving surgery. More importantly, the dose reduction to organs at risk (particularly to the heart dose) was evaluated using lead shields covered surrounding the left breast.