# A Dosimetric Analysis of Reduction Cardiac Dose with Lead Shielding in Breast Cancer Radiotherapy
## 4 Discussion  
Radiotherapy may damage heart structures such as pericardium, myocardium and heart valves and cause injury-induced cardiovascular toxicity. Despite being a relatively common heart injury, acute pericarditis barely shows symptoms within one year of radiotherapy, as radiation-induced heart disease develops slowly and does not cause functional damage until after a few years. Similarly, radiation can damage lung structures, including \begin{table}
\begin{tabular}{l l c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Organ (Number)**}} & \multicolumn{2}{c}{**VMAT**} & \multicolumn{2}{c}{**VMAT-Pd 0.25 mm**} & \multicolumn{1}{c}{**Difference**} \\ \cline{3-5}  & \multicolumn{3}{c}{**Mean Dose (Gy)} & \multicolumn{1}{c}{**(\%)**} \\ \hline Thyroid & & & & \\  & Left (28) & 0.40 \(\pm\) 0.07 & 0.28 \(\pm\) 0.05 & \(-\)30.00\% \\  & Right (29) & 0.39 \(\pm\) 0.02 & 0.31 \(\pm\) 0.04 & \(-\)20.51\% \\ Heart & & & & \\  & Atrium (95) & 4.11 \(\pm\) 0.11 & 1.75 \(\pm\) 0.11 & \(-\)57.42\% \\  & Ventricle (108) & 4.31 \(\pm\) 0.09 & 1.88 \(\pm\) 0.08 & \(-\)56.38\% \\ Lung & & Left upper (97) & 11.10 \(\pm\) 0.14 & 4.68 \(\pm\) 0.13 & \(-\)57.83\% \\  & Right upper (102) & 2.44 \(\pm\) 0.04 & 1.92 \(\pm\) 0.07 & \(-\)21.31\% \\  & Left lower (100) & 1.02 \(\pm\) 0.09 & 1.01 \(\pm\) 0.05 & \(-\)0.98\% \\  & Right lower (106) & 0.81 \(\pm\) 0.12 & 0.78 \(\pm\) 0.08 & \(-\)3.70\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of the OAR doses of the VMAT plan before and after the lead shield of thickness 0.25 mm was applied to the surface of the phantom. alveoli, alveolar compartments, trachea, bronchi, and other pulmonary vessels, with one of the most common lung injuries being radiation pneumonitis. In most circumstances, the degree of lung injury is closely related to the irradiated volume as well as the radiation dose. In a study by [PERSON] et al. [22], a 3D-CRT breast radiotherapy plan with a total dose of 50 Gy was created on a 3D phantom. A total of 10 thermoluminescent dosimeters (TLDs) were then evenly distributed across the left lung of the phantom to measure doses and compare them to TPS calculations. The results indicated that the measured and the calculated average doses differed significantly, which is consistent with our results acquired with OSLDs. In a study by [PERSON] et al. [23] the authors investigated 10 patients with left breast cancer, they compared various techniques including standard tangential field-in-field (FinF), tangential IMRT, tangential VMAT, and continuous VMAT under a dose scheme of 50 Gy in five fractions. The study found that cVMAT had the lowest average heart dose, followed by tVMAT, IMRT, and FinF. The same study indicated that tVMAT was the most effective method to improve target homogeneity and reduce heart dose. On this basis, although cVMAT was more common in clinical practice, the authors included tVMAT as an option to treat future breast patients. Alternatively, [PERSON] et al. [24] published the outcome of 15 patients who underwent radiotherapy after left breast-conserving surgery in 2015. The dose scheme was 50 Gy in 25 fractions. The study indicated that the average heart dose of VMAT, Tomotherapy, and 3D-CRT was 9.24 \(\pm\) 2.12 Gy, 4.13 \(\pm\) 0.77 Gy, and 4.39 \(\pm\) 2.24 Gy, respectively, with VMAT having the highest average heart dose. Last, [PERSON] et al. [17] reviewed a total of 2168 women in Sweden and Denmark who received radiotherapy for breast cancer between 1958 and 2001. They found that their heart doses ranged between 0.03 and 27.72 Gy, and the average dose was 4.9 Gy. In addition, the results showed that the risk of heart disease increased by 7.4% with every 1 Gy of increase in heart dose. In this study, by applying lead shields, the heart dose was successfully reduced from 4.31 \(\pm\) 0.09 Gy to 1.88-2.18 Gy, thereby reducing the risk of associated heart diseases by 14.8%. The present study is limited to phantom experiments and cannot fully be adapted into clinical use.