# A Dosimetric Analysis of Reduction Cardiac Dose with Lead Shielding in Breast Cancer Radiotherapy
## 3 Results
### Radiation Dose Difference after the Application of Lead Shields  
Comparison of the TPS calculated dose and the dose measured by OSLDs of different radiotherapy techniques indicated that sometimes the TPS could underestimate the OAR dose. Therefore, the actual measurements acquired with OSLDs were used to compare thyroid, heart, and lung doses following the application of lead shields. In terms of the dose distribution within the PTV, both the conformity and the homogeneity of the VMAT plan were superior to those of the IMRT plan. In addition, the average heart dose of the 3D-CRT plan, the IMRT plan, and the VMAT plan was 1.90 \(\pm\) 0.02 Gy, 3.79 \(\pm\) 0.04 Gy and 2.25 \(\pm\) 0.04 Gy, respectively, with IMRT having a higher heart dose than VMAT. Therefore, in this part of the study, the VMAT technique was utilized to identify the effect of lead shielding. Two different thickness of lead shields were deployed, namely 0.125 mm and 0.25 mm. The results are shown in Tables 6 and 7.  
Table 6 shows the results of using lead shields with a thickness of 0.125 mm, which were applied to the skin around the breast tumor area to protect critical organs. It was found that the absorbed doses of thyroids, heart, and lungs all decreased. After applying 0.125 mm of lead shields, the dose to the thyroid was reduced by 5.12-27.5%. In particular, for the left thyroid, the average dose before and after the application of the 0.125 mm lead shields was 0.40 \(\pm\) 0.07 Gy and 0.29 \(\pm\) 0.04 Gy, respectively, showing a significant dose reduction. Similarly, the heart dose reduced by 49.41-50.12% after 0.125 mm of lead shields were used. Before lead shields were applied, the average atrium and ventricle doses were 4.11 \(\pm\) 0.11 Gy and 4.31 \(\pm\) 0.09 Gy, respectively, and after lead shields were applied, these became 2.05 \(\pm\) 0.06 Gy and 2.18 \(\pm\) 0.09 Gy, respectively, the reduction of which was also significant. Last, the lung doses decreased by 1.23-45.22% with lead shields. More specifically, the left upper lung dose (No. 97) before and after the application of the lead shield of thickness 0.125 mm was 11.10 \(\pm\) 0.14 Gy and 6.08 \(\pm\) 0.09 Gy, respectively, again showing a significant dose reduction.  
Table 7 lists the results of using lead shields with a thickness of 0.25 mm to cover the skin around the breast tumor area to protect critical organs. It was found that the absorbed doses of thyroids, heart, and lungs all decreased. The dose to the thyroid was reduced by 20.51-30%. In particular, for the left thyroid, the average dose before and after the use of lead shields with a 0.25 mm thickness was 0.40 \(\pm\) 0.07 Gy and 0.28 \(\pm\) 0.05 Gy, respectively, showing a significant dose reduction. Similarly, the heart does were reduced by 56.38-57.42% when the lead shields were used. The average atrium and ventricle doses were 4.11 \(\pm\) 0.11 Gy and 4.31 \(\pm\) 0.09 Gy before the use of lead shields, while these doses become 1.75 \(\pm\) 0.11 Gy and 1.88 \(\pm\) 0.08 Gy with the use of lead shields. The lung doses were reduced by 0.98-57.83% with lead shields. The left upper lung dose (No. 97) before and after the application of the lead shield of thickness 0.25 mm was 11.10 \(\pm\) 0.14 Gy and 4.68 \(\pm\) 0.13 Gy, respectively. These results suggested that increasing the thickness of the lead shields could effectively reduce the OAR doses, thereby potentially minimizing the risk of normal tissue complications. The risk of heart disease was especially reduced (decreased by 7.4% for each reduction of 1 Gy; [PERSON] et al.) [19]. However, applying excessive thicknesses of lead shields in clinical practice can reduce treatment comfort, and therefore whether it is tolerable by the patient should be confirmed prior to treatment.