The survival outcome of patients suffering from gliomas is directly linked to the complete surgical resection of the tumour. To help the surgeons to delineate precisely the boundaries of the tumour, we developed an intraoperative positron probe with background noise rejection capability. The probe was designed to be directly coupled to the excision tool such that detection and removal of the radiolabelled tumours could be simultaneous. The device consists of two exchangeable detection heads composed of clear and plastic scintillating fibres. Each head is coupled to an optic fibre bundle that exports the scintillating light to a photodetection and processing electronic module placed outside the operative wound. The background rejection method is based on a real-time subtraction technique. The measured probe sensitivity for (18)F was 1.1 cps kBq(-1) ml(-1) for the small head and 3.4 cps kBq(-1) ml(-1) for the large head. The mean spatial resolution was 1.6 mm FWHM on the detector surface. The gamma-ray rejection efficiency measured by realistic brain phantom modelling of the surgical cavity was 99.4%. This phantom also demonstrated the ability of the probe to detect tumour discs as small as 5 mm in diameter (20 mg) for tumour-to-background ratios higher than 3:1 and with an acquisition time around 4 s at each scanning step. These results indicate that our detector could be a useful complement to existing techniques for the accurate excision of brain tumour tissue and more generally to improve the efficiency of radio-guided cancer surgery.

The precise delineation and excision of brain tumor extent allows to improve survival outcome and quality of life of surgically treated patients. In order to refine the resection of gliomas, we are developing a novel intraoperative probe specifically dedicated to the localization of residual tumor after the bulk has been excised. The probe, built around clear and plastic scintillating fibers, was designed to detect positrons emitted from radiolabeled brain tissue in order to discriminate more specifically neoplastic from normal tissues. The probe was also built to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor. We report here performances of the first radio-isotopic configuration of the intraoperative probe which consists of a detection head composed of eight detection elements held around the excision tool in a closed packed annular arrangement. This head is coupled to an optic fiber bundle that exports the scintillating light to a multi-channel photomultiplier tube. The ray background generated by the annihilation of + in tissues is eliminated by a real-time subtraction method. The detector exhibits a sensitivity of 139 cps/kBq and a ray rejection efficiency of 99.5%. The ability of the probe to detect residual lesions was evaluated with a realistic brain phantom representing the surgical cavity and the boundaries of the tumor. We showed that lesions as small as 5 mm in diameter can be detected for tumor to normal tissue uptake ratios of fluorinated tracers greater than 3.5. This ratio is achieved with radiopharmaceuticals like 18 F-FET or 18 F-choline. These promising results suggest that the features of our system are compatible with in situ localization of residual radiolabeled tumors.

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