# Feasibility of a Patient-Specific Bolus Using the Life-Casting Method for Radiation Therapy
## 4 Discussion  
In this study, we developed a patient-specific bolus by using the LC method and compared it with a commercial bolus. When comparing the dosimetric results of the 3 DCRT and VMAT treatment plans, it was observed that using the patient-specific bolus resulted in better target coverage than using the commercial bolus. However, the doses delivered to the lung and heart were higher for both types of treatment plans when patient-specific boluses were used. Nevertheless, all the plans in this study satisfied the set dose constraints. We observed a reduction in the air gap when using a patient-specific bolus, which led to an improvement in the accuracy of the dose delivery. In particular, the commercial bolus exhibited a poorer accuracy of dose delivery in areas with a large air gap than the patient-specific bolus developed in this study. This may be attributed to the challenge of using the commercial bolus in inter-fraction setup variations. In contrast, the position of the patient-specific bolus can be consistently reproduced, even in the presence of an air gap, which can reduce the inter-fraction setup variations. This can be inferred from the lower standard deviation observed in the measured values when a patient-specific bolus was used for the three measurements. Furthermore, inaccuracies in the dose delivery were more pronounced in the VMAT plan, which is inherently more complex than the 3D-CRT plan. In the study by [PERSON] et al., 3D printing technology was employed to fabricate 3D custom boluses, which were then compared with the commercial boluses. [PERSON] et al. reported that during treatment, patients showed a reduced air gap volume of 46.1 cm\({}^{3}\) when using a 3D-printed custom bolus compared to the air gap volume of 169 cm\({}^{3}\) exhibited by a standard bolus [14]. These findings demonstrate a substantial reduction of 72.72% in the total air gap when utilizing the 3D-printed custom bolus compared to the standard bolus. Our study results demonstrated a 77.62% reduction in the air gap when utilizing the patient-specific bolus developed in this study compared to the commercially available bolus. This finding indicates that the bolus developed in this study exhibits a performance similar to that of a bolus fabricated using 3D printing technology. [PERSON] et al. also reported the in-vivo dosimetry results, according to which the mean absolute difference between the expected and received doses was 5.69 \(\pm\) 4.56% (with a maximum of 15.1%) for the standard bolus and 1.91 \(\pm\) 1.31% (with a maximum of 3.51%) for the custom bolus. In addition, another study reported that areas with larger air gaps corresponded to larger differences in the dose [14]. This finding is consistent with the results of our study and confirms that the bolus developed in our study exhibits a performance similar to that of the bolus fabricated using 3D printing technology. Furthermore, we observed certain advantages over the 3D printing technology in terms of the fabrication of the bolus. [PERSON] et al. revealed that designing the boluses for the patient and the phantom took approximately 1 h each. Additionally, the printing of the bolus holds for the phantom and patient required approximately 2 days and 6 days, respectively. In our study, the entire process, including mold and bolus fabrication, took less than 1 day to complete. Furthermore, our study benefits from the absence of a 3D printer, which eliminates the cost and space constraints. Moreover, creating a bolus mold using a 3D printer requires a patient's CT scan; after fabrication, applying the bolus necessitates another CT scan, resulting in a total of two CT scans. This results in unnecessary radiation exposure. The method employed in the present study has the advantage of avoiding unnecessary radiation exposure. [PERSON] et al. conducted a study on six patients who underwent post-total mastectomy radiation treatment. The 3D-printed boluses were fabricated, clinically applied, and compared with the commercial boluses [24].