Development of a Solid-State Imaging Probe for Radio-Guided Surgery

This thesis describes the development and the characterisation of a novel CMOS digital imaging sensor for the detection of ionizing radiation and its prototypal implementation in a handheld instrument (beta probe) providing, in real time, high resolution images of a radiation field containing localized b - sources. One of the possible applications of the beta probe is radioguided surgery (RGS) where a radioisotope is administered to the patient and a scan of the surgery field is performed along a safety margin around the resection. In the first chapter a short review is given of the state-of-the-art of RGS and of other complementary imaging techniques employed as advanced diagnostic tools. The second chapter describes the working principle of the new sensor, a pixelated doublelayered CMOS device allowing in-pixel coincidence between pairs of vertically integrated pixels. The characterization of the first sensor prototype and the results obtained with laboratory tests and with a dedicated particle beam test are also reported, together with a description of the second version of the sensor and of the first prototypes of the beta probe, which were developed by the ASAP collaboration, within the framework of the R&D activities supervised by the Scientific Commission 5 of INFN (Istituto Nazionale di Fisica Nucleare). The following chapter describes a thorough simulation which was implemented in GEANT4 to study the expected performance of the probe under different conditions in a realistic scenario of RGS, mimicking the spatial distribution and activity of a set of discrete sources, and taking into account tissue absorption. Chapter four describes a set of measurements that were carried out in our laboratory where the probe was tested using a radioactive source and the dark count rate was measured under a number of different conditions. Finally, some preliminary conclusions are drawn on the detector performance and on the expected improvements with more advanced versions of the sensor and probe. Also, the limitations to the application of this technique in RGS, mainly driven by the maximum dose that can be administered to the patient, are discussed.