Development of an active radiation detector for clinical applications

The growing frequency of diagnostic and therapeutic medical procedures based on minimally invasive techniques of interventional radiology, has raised concerns about the occupational radiation doses to medical professionals. Radiation doses heavily depend, among others factors, on the complexity of the procedure and the operator's technique and experience. The very close proximity of medical operators to the incident beam increases significantly the risk for radiation-induced health effects such as malignancies, cataract development and radiation dermatitis. Monitoring the occupational radiation exposure during such procedures, has resulted in the reduction of radiation exposure and long-term dose-dependent health risks. Several types of active and passive radiation detectors have been used by medical professionals to monitor the radiation exposure during occupational ionizing radiation-based procedures. For most personal dosimeters, passive systems are used. Such systems usually accumulate radiation doses over an occupational period of one month. At the end of this period, the accumulated dose is being monitored. This requires the involvement of an accredited dosimetry service and special radiation readers, a practise that does not allow real-time monitoring of the accumulated dose. Although electronic personal dosimeters do offer real-time monitoring capabilities, the size of those devices implies usage limitations. In this study, the first step towards a small x-ray radiation detector is made, to incorporate the benefits of conventional passive dosimeters with the real-time capabilities of electronic personal dosimeters. Hence, an investigation of two independent material systems is presented; a) a system based on AlGaN/GaN high electron mobility transistor (HEMT) and b) a hybrid device consisting of a synthetic thin film diamond layer and a piezoelectric lithium niobate (LiNbO${}_3$) surface acoustic wave (SAW) delay line. It was found that both material systems provide the capability of real time monitoring in the medical diagnostic dose-rate regime. The first system showed a rapid signal increase, and a similar signal decrease after the radiation was switched of. Moreover, a linear sensor response with dose rate was observed between about 20 to 50 μGy/s. However, it turned out that the signal increase was only in the order of several tens to hundred pA which is difficult to be used in practical environments. In contrast, the second system shows a much more pronounced signal increase under exposure to ionizing radiation. Dependence on dose rate was rather linear with a tendency to saturate at higher dose rates of more than 800 μGy/s. The system was tested under typical medical radiation fields (C-arm and CT-scanner) and turned out to be useful. The SAW detection principle offers the unique possibility for wireless remote powering and sensing, features that increase the practicability of such radiation sensor in clinical practice. This study can anticipate promising applications of the developed prototypes as radiation detectors in radiation fields where lightweight, compact devices and modification flexibility matters in medical applications.