# Development of Inclined Applicators for Flattened Beam Intraoperative Radiotherapy
## 4 Discussion  
The study's novelty is the development of an inclined applicator for IORT that improved treatment performance and reduced unnecessary doses to normal tissues. The applicator directed the IORT beam at 45\({}^{\circ}\) and shielded it in other directions while forming a flattened beam for a uniform tumor dose delivery. To ensure safe and effective beam delivery for IORT, quality assurance was necessary, and this study performed the leakage, beam profile, PDD, and output measurements to \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{5}{c}{**Uniformity**} \\ \hline  & **Surface** & **2 mm Depth** & **5 mm Depth** & **15 mm Depth** \\ \hline
0\({}^{\circ}\) FF & 1.23 & 1.28 & 1.30 & 1.22 \\
**Flat appl.**\({}^{\star}\) & 1.31 & - & 1.13 & - \\
0\({}^{\circ}\) FF & 1.29 & 1.32 & 1.27 & 1.25 \\
**Surface appl.**\({}^{\star}\) & 1.28 & - & 1.47 & - \\ \hline \hline \end{tabular} \({}^{\star}\)[PERSON] et al., 2014 [22]. Abbreviations: FF, flattening filter; FFF, flattening filter-free.  
\end{table} 
Table 1: Measured uniformity of the developed applicators at surface and depths of 2, 5, and 15 mm. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Type of Applicator**} \\ \cline{2-5}  & **0\({}^{\circ}\) Flattening** & **45\({}^{\circ}\) Flattening** & **0\({}^{\circ}\) FFF** & **45\({}^{\circ}\) FFF** & **w/o Filter** \\  & **Filter** & **Filter** & & & \\ \hline
**Dose (cGy)** & 51.0 & 48.5 & 52.9 & 54.8 & 113.7 \\ \hline \hline \end{tabular} Abbreviations: FFF, flattening filter-free.  
\end{table} 
Table 2: The output of the developed applicator. Figure 7: Calibration curve of the developed applicator obtained from RIT software. verify the dose distribution of each applicator prior to clinical use. Figure 6 shows the shielding's effectiveness, as the dose was not measured beyond 1 mm. Any dose appearing in the upper region of the horizontal leakage measurement can be explained with artifacts from bending or cutting the film surface during film cutting, as shown in Figure 3c [24]. The developed applicator showed an almost equal or better performance in terms of uniformity compared to flat and surface applicators measured by [PERSON] et al. [22]. The developed IORT applicator demonstrated similar or superior performance to existing flat and surface applicators. To optimize treatment for the tumor bed, both the 0\({}^{\circ}\) and 45\({}^{\circ}\) applicators were designed to deliver a flat dose distribution at a depth of 5 mm, which is where the tumor bed exhibited the most uniform dose distribution. This was a significant improvement over the surface applicator, which was optimized for treatment but did not achieve the same level of uniformity [25]. Our output measurements showed that applying the flat collimator or FFF collimator resulted in a slight difference in output for the 0\({}^{\circ}\) and 45\({}^{\circ}\) applicators. This is because the intensity of the X-ray decreases when the flattening filter is used. The small output difference between the 0\({}^{\circ}\) and 45\({}^{\circ}\) applicators allows for flexibility in adjusting the angle during the procedure and lowering the air gap between the applicator and the surrounding cavity. The difference in dose by approximately two times with and without the collimator can be explained by the decrease in dose due to the corresponding area, as the spherical applicator was shielded during development. The developed applicator was clinically employed at Gangnam Severance Hospital on four patients after conducting dose evaluations (Figure 8). Patient 1 presented a 2.86 cm lymph node metastasis on the posterior aspect of the left internal iliac vessel after undergoing low anterior resection for rectal adenocarcinoma (Figure 8a). Patient 2 displayed a 1.9 cm metastasis at the left lateral edge of the mesorectal fascia following low anterior resection for rectal adenocarcinoma (Figure 8b).