Performance characterization and first clinical evaluation of a intra-operative compact gamma imager

The growing interest of cancer surgeons in intraoperative probes has led to the development of several prototypes of high resolution mini gamma cameras. The aim of this paper is to present a global characterization of the one that we developed and the corresponding first evaluation in a clinical context. The current prototype of POCI (peroperative compact imager) is a 24 mm diameter intensified position sensitive diode optically coupled to a scintillation crystal plate and a novel parallel hole tungsten collimator. In order to face the various clinical situations, two sets of collimator/scintillator imaging heads have been developed either for high spatial resolution or high efficiency purposes. Both of them have first been optimized for Tc-99m labeled tumor detection. Performances of POCI for these two head modules are presented using phantom studies. The results show spatial resolution values ranging between 1 and 1.9 mm (without significant distortion) and a corresponding detection efficiency ranging from 6.10(-3) up to 0.2 events/kBq/sec. Finally, first clinical evaluation of this new high-resolution compact camera concerned sentinel lymph node imaging which is included in melanoma and breast cancer staging protocols. Preliminary results already demonstrate that the performance characteristics of POCI are compatible with intra-operative imaging purposes and suggest how such mini-cameras can improve the success rate of tumor removal surgeries.