Development and characterization of sensitive, energy-independent solid-state photon dosemeters with high spatial and temporal resolution. Applications in clinical radiology and radiation protection

Abstract: AbstractModern medicine and health care rely on a variety of diagnostic and therapeutic equipment and methods that involve ionizing radiation. To guarantee quality and the safety of patients and staff, advanced radiation detectors and dosemeters are needed that have low energy and operate with directional independence for X-ray and γ-ray photons. Similar instruments are also of great importance for measurements used in radiation protection and safety outside of hospitals and the health care sector and for nuclear and radiological emergencies. In this thesis, new sensors, detectors, and dosemeters based on silicon were designed, manufactured, characterized, and tested. The aim was to develop dosemeters with signals that are as independent as possible of the energy and direction of the incoming X-ray and γ-ray photons. Starting with a 350 µm silicon wafer, a sensor was constructed with electrical contacts on one side only. A flex card was adapted with anisotropic conductive adhesive (ACA) and mounted to the sensor. Since all components have low X-ray attenuation, the disturbance of the radiation field by the detector is minimal from all directions. Another important component is the metal filter encapsulating the silicon detector. Made of stainless steel, this encompassing filter compensates for the energy and directional variation of sensitivity of the silicon detector. The filter was designed using a series of Monte Carlo calculations. The hole pattern was selected so that the signal (proportional to the absorbed dose) was independent of the X-ray source position (in 4π). Due to the small structures, additive manufacturing (AM) in the form of metal 3D printing was needed to fabricate the filter. The functionality of the 4π dosemeter was verified by simulation to meet the quality criterion that the energy dependence is less than 5% for the IEC beam qualities RQR and RQT in the range 65–145 kV. The best way to microfabricate the sensor, sensor holder, flex card, and energy filter was evaluated and a method to control its mounting accuracy is proposed. The application of silicon detectors in radiology (CT, CBCT, and planar radiography) was tested, and a specific dosemeter construction also was tested for eye lens dosimetry and for emergency situations. To broaden the use of silicon detectors in future medical imaging and dosimetry applications, an overview of silicon photomultipliers (SiPM) for this area is included and a learning and training program targeted to graduate students is described.