MOSFET探测器再生方法研究及其在CT剂量检测中的应用

There is direct evidence from epidemiologic studies that the radiation exposures corresponding to a common CT study result in an increased risk of cancer. As a result, it has become a top priority to understand how much radiation dose medical imaging delivers to the patient during diagnostic CT examinations. Supported by National Natural Science Foundation of China Grant 30900324, we have developed an in vivo dosimetry system including a linear MOSFET-array dosimeter, which may provide a feasible way to carry out online CT dose measurement for each individual patient. However, the short lifetime of the MOSFET dosimeter hampered its large-scale application in clinical practice. Thus a frequently asked question is if there is a method to prolong the dose measurement range of the MOSFET dosimeter. The main purpose of this study is to investigate the MOSFET reusability, which can extend the use of a MOS sensor to a virtually unlimited dose range, in order to improve its benefit-cost ratio by using current annealing techniques. To optimize the annealing process for reusability of the same detector, the associated parameters such as bias voltage, current density and annealing time are explored. Also, the current MOSFET design will be optimized to enhance its sensitivity for low dose measurement in diagnostic CT examinations. Our research outcome will help developing reasonable strategies to minimize unnecessary exposures associated with common CT studies.

现有流行病学研究结果已经证明了CT辐射的潜在致癌性，因此如何监控CT受检者所受辐射照射是关系到生命健康的一个重要问题。在09年国自然基金资助下我们成功试制了一种适用于高能辐射剂量检测的微型MOSFET探测器。但是目前此类探测器尚存在使用寿命短、对低剂量测量灵敏度偏低的固有缺陷，阻碍了其在诊断CT中的应用。本研究拟在前期工作的基础上进一步探讨MOSFET探测器"再生"的方法，通过对再生条件和再生参数的筛选形成一种实用技术，使达到使用寿命的MOSFET探测器阈值电压恢复到辐照前的状态，实现其可重复使用性，从而克服探测器使用寿命短的瓶颈。同时通过改进栅极偏置电路设计，提高现有微型MOSFET探测器的灵敏度，使其适用于低剂量CT辐射测量，解决CT检查缺乏辐射监测工具的现状。本研究有望为临床CT扫描中个体化辐射剂量测试与评价提供一种可靠的技术手段，填补我国在这一研究领域的空白。

为了合理开展CT诊疗，降低CT辐射的潜在致癌性，有必要对CT受检者所受辐照剂量开展个体化监测。但是现有适于人体辐射剂量测定的仪器如MOSFET探测器存在使用寿命短、成本高的缺陷。针对这一问题，本课题组在前期研究的基础上，提出了运用电流退火技术无损再生MOSFET探测器的方法。研究中通过退火电路将一定强度电流按一定频率经探测器引脚直接施加在MOSFET芯片源极（S）和漏极（D）上，在探测器Si基底座近SiO2灵敏体积处产生局部高温，诱发电子隧穿等效应中和交界处累积的正电荷，从而使MOSFET探测器阈值电压恢复到辐照前的状态。结果显示使用电流退火技术可以使单P型MOSFET探测器阈值电压恢复95%以上，并且该技术不会损伤探测器，再生后MOSFET探测器各项性能变化<1.6%。再生MOSFET探测器在CT辐射场中灵敏度>12 mV/cGy，可以满足低剂量条件下高精度测量所需灵敏度要求。目前该探测器已成功应用于临床部分胸部肿瘤患者CBCT扫描的监测中。研究共发表SCI论文4篇，中文核心期刊论文2篇。研究成果有望为临床CT扫描中个体化辐射剂量测试与评价提供一种可靠的技术手段，填补我国在这一研究领域的空白。