# Feasibility of a Patient-Specific Bolus Using the Life-Casting Method for Radiation Therapy
## 4 Discussion
Their findings showed that the commercial boluses were associated with an improvement in the dosimetric results for the target, while reducing the radiation dose delivered to the lungs and heart [24]. When compared with the results of our study, a disparity in the observed trends for OAR sparing was noted. This can be attributed to the use of a phantom rather than human participants in our study, as well as to the smaller number of treatment plans employed. Furthermore, [PERSON] et al. reported improved OAR-sparing results, albeit with differences of less than \(1\) Gy across all outcomes. In our study, when a patient-specific bolus was used, there was an increase in the radiation dose delivered to the OARs. However, these differences were within the range of \(1\) Gy or \(1\%\). In addition, the established dose constraints were satisfied in all plans in which patient-specific boluses were employed. These limitations can be addressed by conducting phantom studies on diverse anatomical sites before clinical implementation. In the study by [PERSON] et al., a radiochromic film was used to evaluate the accuracy of the delivered dose for each bolus. Their results indicated that the 3D-printed bolus had more precise dose delivery and smaller measurement deviations. The bolus developed in our study exhibited a similar performance to those of boluses fabricated using 3D printing technology. [PERSON] et al. developed and assessed a device for simultaneous dose measurement and bolus effects using a PVA-GTA-MTB gel dosimeter. When comparing the EBT film and PVA-GTA-MTB gel dosimeters for dose assessment, [PERSON] et al. reported a relative difference of \(4.18\%\) in the lateral part of the breast [11]. In our study, when we compared the point dose from the TPS rather than from the EBT film, we observed a similar maximum difference of \(5.08\%\) for VMAT. One of the objectives of bolus development is to reduce the air gap between the skin and bolus. In our study, we quantified the air gap, whereas in the study by [PERSON] et al., no air gap quantification was performed. Moreover, in the study by [PERSON] et al., on examining the CT image, it appears that the air gap issue still persists. As radiation therapy often involves fractionated treatments, reproducibility is crucial for each treatment. Gel dosimetry is based on the principle that the density changes during radiation exposure, enabling the measurement of dose variations [12]. As a result, as the number of treatments increases, such variations accumulate, potentially leading to discrepancies in the initial treatment planning. The use of a new bolus for each treatment can also increase the cost-related concerns. [PERSON] et al. reported negligible toxicity in their study. However, if used on the skin, tests related to skin stability, such as skin sensitization and in vitro cytotoxicity, should be performed. Regarding EcoflexTM, this product has obtained skin safety certifications for all such tests [16]. Furthermore, EcoflexTM has a density of \(1.07\) g/cm\({}^{3}\), similar to that of water. In a study by [PERSON] et al. [16], when comparing the PDD values for 6 MV, the surface doses for water and Ecoflex were reported to be \(98.4\%\) and \(98.6\%\), respectively, whereas the D10 cm values were \(66.6\%\) and \(66.1\%\), respectively, indicating that they had similar values. These characteristics are highly beneficial for clinical applications. A limitation of our study was the difficulty in achieving a consistent thickness of the fabricated bolus. It was observed that certain parts of the bolus were thinner than desired (Figure 4). We believe that this problem can be addressed by devising a method to securely fasten the bolus material to the support structure, thereby ensuring a precise and uniform thickness. Nevertheless, the patient-specific bolus exhibited a reduced air gap and enhanced accuracy in dose delivery compared to the commercial bolus used in the present study.