An intraoperative multimodal probe for brain tumor surgery

489 Objectives: The removal of residual lesions is one of the key procedures in cancer staging to improve prognosis and quality of life of surgically treated patients. We are developing a novel intraoperative probe specifically dedicated to the localization brain tumor remnants after the bulk has been excised. The probe, built around clear and plastic scintillating fibers, was designed to detect β-emitting radiotracer and laser-induced fluorescence simultaneously to discriminate more specifically neoplastic from normal tissues. The probe was also built to be directly coupled to the excision tool in order to detect and remove lesions at onces. Methods: The first prototype of the beta probe consists of 8 detection elements held around the excision tool in a closed packed annular arrangement. This detection head is coupled to an fiber bundle that exports the scintillating light to a multi-channel photomultiplier connected to a 64-channel electronic ASIC. The γ ray background generated by the annihilation of β+ in tissue is eliminated by a real-time subtraction method. Results: The probe exhibits a β sensitivity of 140 cps/kBq and a γ ray rejection efficiency of 99.5 %. Its ability to detect residual lesions was evaluated with a brain phantom simulating the boundaries of the tumor. We showed that lesions as small as 5 mm can be detected for tumor-to-normal tissue uptake ratios of the fluorinated tracer greater than 3.5. Conclusions: Following these promising results, a second prototype based on two exchangeable heads composed of 12 and 28 detection elements was developed. Overall performances of this new probe will be presented. Preliminary evaluation of the surgical probe on a primate model will be also reported and discussed.