## 4 Discussion  
In this study, we evaluated the fundamental characteristics of a CZT detector and conducted validation tests to assess its potential for SRS and SBRT applications. The results indicate that the CZT detector satisfies the various requirements for utilization with therapeutic X-ray beams. The elements constituting the CZT detector exhibit high atomic numbers (Z), providing excellent radiation absorption characteristics. Additionally, the detector's large carrier mobility-lifetime product is conducive to high-energy radiation measurements. In the dose linearity test, the CZT detector exhibited nearly perfect linearity across a dose range from 0 to 1000 cGy, including the low-dose region. The single-crystal CZT exhibited excellent linearity, as shown in Figure 2, with very small error bars. This characteristic suggests that the CZT detector can provide reliable values under various treatment conditions, especially in SRS and SBRT, where the dose distribution is concentrated in specific regions and rapid dose fall-off is required outside the target area. In the dose rate dependence experiment, the signal generated by the CZT detector exhibited minimal variations with changes in the dose rate. Dose rate dependence issues--particularly over-response with increasing dose rate caused by electron-hole recombination in semiconductor junction structures--are typically observed in diode-type detectors. In such cases, dose rate correction factors are required to monitor and adjust for dose rate variations continuously. However, this dose rate-dependent over-response is not exhibited by the fabricated CZT detector, which generates signals by collecting electron-hole pairs under an applied bias. Thus, this detector does not require extensive dose rate correction processes. The energy dependence analysis reveals that the intensity of the signal obtained from the CZT detector decreases slightly with the increase in beam energy. The gradual decrease in signal with increasing energy indicates a reduction in absorption efficiency at higher energy regions, despite the high-Z characteristics of CZT. This dependency is a common issue in solid-state detectors, requiring calibration based on the energy range used. However, within the primary energy range (6 and 10 MV) used in this study, the intensity difference is only about 1%. Although the detector is composed of high-Z materials, the observed energy dependence could be attributed to the Z-effect, where interactions with higher-energy photons are less probable in high-Z materials. The angular dependence deviation, particularly near 60\({}^{\circ}\) and 120\({}^{\circ}\), could be attributed to the detector's asymmetric structure in the upper and lower regions. This phenomenon is typically observed in fixed detector structures and can be corrected in clinical practice by compensating the results or by positioning the detector perpendicular to the beam path. Although the SSD dependence results of the CZT detector differ from those of the ionization chamber, they follow the inverse square law and can be corrected in practice. Reproducibility and depth dependence experiments yielded favorable results. The CZT detector maintained consistent performance with minimal changes when subjected to beam exposure over a period of more than 1 month. The depth dependence results were consistent with those of the ionization chamber at both 6 and 10 MV. This consistent performance could be attributed to the characteristics of the detector, which uses a single material rather than a junction or hybrid structure. The field size dependence results were consistent with those obtained using the ionization chamber, which is crucial for small-field measurements. Guidelines for SRS and SBRT measurements discuss the challenges of small-field dosimetry and the necessity for high detector densities and large sample treatment volumes [36].