# A Dosimetric Analysis of Reduction Cardiac Dose with Lead Shielding in Breast Cancer Radiotherapy
## 3 Results  
### PTV Dose Evaluation  
This study utilized three plan techniques, of which IMRT and VMAT belonged to inverse planning. According to the results from the Pinnacle 9.8 TPS, among the three plan types, only the target volume receiving 90% prescribed dose of the 3D-CRT plan was lower than 80%. The PTV D\({}_{\text{mean}}\) of the 3D-CRT, IMRT, and VMAT plans was 49.16 \(\pm\) 0.05 Gy, 50.78 \(\pm\) 0.06 Gy, and 51.24 \(\pm\) 0.10 Gy, respectively. Alternatively, the V47-5 Gy of the 3D-CRT, IMRT, and VMAT plans was 90.88 \(\pm\) 0.53%, 90.74 \(\pm\) 0.17%, and 97.87 \(\pm\) 0.06%, respectively. The VMAT plan had the best V95% PTV coverage. The CI of the 3D-CRT, IMRT, and VMAT plans was 0.70 \(\pm\) 0.01, 0.81 \(\pm\) 0.02, and 0.89 \(\pm\) 0.02, respectively, with VMAT ranking the top. Similarly, the VMAT plan had the best HI of 0.10 \(\pm\) 0.01, followed by the IMRT plan with an HI of 0.13 \(\pm\) 0.01 and the 3D-CRT plan with an HI of 0.18 \(\pm\) 0.02.  
The average heart dose and the V5 Gy, V15 Gy and V30 Gy of the three plan types calculated by the TPS are listed in Table 1. The average heart dose of the 3D-CRT, IMRT, and VMAT plans was 1.90 \(\pm\) 0.02 Gy, 3.79 \(\pm\) 0.04 Gy, and 2.25 \(\pm\) 0.04 Gy, respectively. The IMRT plan had the highest heart dose because of restricted beam angles.  
The V5 Gy of the 3D-CRT, IMRT, and VMAT plans was 16.16 \(\pm\) 0.23%, 28.17 \(\pm\) 0.34% and 26.18 \(\pm\) 0.17%, respectively. The low-dose spillage volume of the 3D-CRT plan was the smallest, whereas that of the VMAT plan was relatively large. Alternatively, the V15 Gy of the 3D-CRT, IMRT, and VMAT plans was 4.08 \(\pm\) 0.06 Gy, 7.09 \(\pm\) 0.09 Gy and 6.18 \(\pm\) 0.14 Gy, respectively, with the 3D-CRT plan showing the smallest volume and the IMRT plan showing the largest volume. Last, the V20 Gy of the 3D-CRT, IMRT, and VMAT plans was 0.32 \(\pm\) 0.02 Gy, 0.52 \(\pm\) 0.01 Gy and 0.40 \(\pm\) 0.01 Gy, respectively, and again the 3D-CRT plan had the smallest volume, while the IMRT plan had the largest volume.  
\begin{table}
\begin{tabular}{l l c c c c c} \hline \hline  & & **3D-CRT** & ** IMRT** & **VMAT** & **3D-CRT** & **3D-CRT** & ** IMRT** \\  & & & & **vs. IMRT** & **vs. VMAT** & **vs. VMAT** \\ \cline{3-8}  & & \multicolumn{3}{c}{**Mean Dose \(\pm\) SD (Gy)**} & \multicolumn{3}{c}{_p-Value_} \\ \hline PTV & & & & & & \\  & D\({}_{\text{mean}}\) (Gy) & 49.16 \(\pm\) 0.05 & 50.78 \(\pm\) 0.06 & 51.24 \(\pm\) 0.10 & 0.0007 * & 0.0008 * & 0.0022 * \\  & V\({}_{\text{47.5 Gy}}\) (\%) & 90.88 \(\pm\) 0.53 & 90.74 \(\pm\) 0.17 & 97.87 \(\pm\) 0.06 & 0.3722 & 0.0009 * & 0.0001 * \\  & D\({}_{\text{25}}\) (Gy) & 52.81 \(\pm\) 0.09 & 53.76 \(\pm\) 0.06 & 52.56 \(\pm\) 0.11 & 0.0003 * & 0.0754 & 0.0032 * \\  & D\({}_{\text{98\%}}\) (Gy) & 43.70 \(\pm\) 0.58 & 48.26 \(\pm\) 0.15 & 49.79 \(\pm\) 0.12 & 0.0026 * & 0.0021 * & 0.0031 * \\  & CI & 0.70 \(\pm\) 0.01 & 0.81 \(\pm\) 0.02 & 0.89 \(\pm\) 0.02 & 0.0120 * & 0.0014 * & 0.0286 * \\  & HI & 0.18 \(\pm\) 0.02 & 0.13 \(\pm\) 0.01 & 0.10 \(\pm\) 0.01 & 0.0068 * & 0.0026 * & 0.0099 * \\ Heart & & & & & & & \\  & D\({}_{\text{mean}}\) (Gy) & 1.90 \(\pm\) 0.02 & 3.79 \(\pm\) 0.04 & 2.25 \(\pm\) 0.04 & 0.0001 * & 0.0034 * & 0.0001 * \\  & V\({}_{\text{5 Gy}}\) (\%) & 16.16 \(\pm\) 0.23 & 28.17 \(\pm\) 0.34 & 26.18 \(\pm\) 0.17 & 0.0003 * & 0.0001 * & 0.0087 * \\  & V\({}_{\text{15 Gy}}\) (\%) & 4.08 \(\pm\) 0.06 & 7.09 \(\pm\) 0.09 & 6.18 \(\pm\) 0.14 & 0.0001 * & 0.0002 * & 0.0005 * \\  & V\({}_{\text{30 Gy}}\) (\%) & 0.32 \(\pm\) 0.02 & 0.52 \(\pm\) 0.01 & 0.40 \(\pm\) 0.01 & 0.0036 * & 0.0029 * & 0.0046 * \\ \hline \hline \end{tabular}  
* PTV: Planning target volume; Dx (Gy): a volume received greater than x Gy; CI: conformity index; HI: Homogeneity Index; Vx (%): x% of the prescribed dose volume;
* _p-value_ < 0.05 was considered statistically significant.  
\end{table}
Table 1: Comparison of PTV and heart dose-volume histogram (DVH) parameters in three different treatment plans.