DEVELOPMENT OF QUALITY CONTROL SYSTEM FOR DIAGNOSTIC X-RAY UNITS TO AIM REDUCTION OF PATIENT DOSE

本研究的目的是利用高分辨率肖特基Cd Te探测器(TOYO MEDEC RAMTEC 413A)测量诊断X射线能谱，并利用上升时间分辨(RTD)电路对初级X射线能谱进行校正，以确定Cd Te探测器对测量光谱进行校正的最佳响应函数。由于测量的光谱受镉镉探测器响应的影响而失真，不能反映真实的光子光谱，因此采用了剥离校正方法。用蒙特卡罗模拟方法计算了光子相互作用(K逃逸、相干散射和康普顿散射)和由于空穴捕获和使用RTD电路而导致的不完全电荷收集，确定了探测器的响应函数。该模拟使用了各种重要因素(平均路径长度。空穴的λ_h和不完全电荷收集的权重因子W_q)，以寻找最佳响应函数。用不同的响应函数修正后的光子谱与高纯Ge(HP-Ge)探测器(普林斯顿伽马-TECH NIGP1013345)测量的修正后的光子谱进行了比较，并比较了由修正后的光谱计算的铝衰减曲线和用HP-Ge探测器测量的铝衰减曲线。确定了最佳的响应函数，由该响应函数校正的光谱计算的衰减曲线与HP-Ge探测器测得的衰减曲线在衰减率0.03和半值层5.0%的最大误差范围内一致。

The purpose of this study is to measure diagnostic x-ray spectra using a high resolution Schottky CdTe detector (TOYO MEDIC RAMTEC 413A) and to determine the best response function of CdTe detector for correcting the measured spectra with using a rise time discrimination (RTD) circuit to primary x-ray spectra. Since the measured spectra were distorted by the response of CdTe detector and did not present the true photon spectra, the correction by the stripping procedure was applied. The response function of CdTe detector has been determined by using Monte Carlo simula-tion method for calculating the photon interaction (K-escape, coherent scattering and Compton scattering) and incomplete charge collection by trapping of hole and use of RTD circuit. This simulation performed with various important factors (mean path length. λ_h of hole and weight factor W_q of incomplete charge collection) for finding the best response function. The photon spectra corrected with those various response functions were compared with the corrected photon spectra measured using a high purity Ge (HP-Ge) detector (PRINCETON GAMMA-TECH NIGP1013345), and the Al-attenuation curves calculated from corrected spectra and measured using the HP-Ge detector were compared. The best-fitted response function was determined, and the attenuation curves calculated from the spectra corrected with this response function were agreed with that measured using the HP-Ge detector within maximum error 0.03 of the attenuation rate and 5.0 % of the half value layer.