Surgical tissue characterization based on radiotracer uptake has become much more common in recent years, particularly due to the advent of the sentinel lymph node biopsy technique. Radiolabeled pharmaceuticals are used with hand-held gamma-sensitive probes, which are capable of localizing small tumors and lymph nodes that are first identified via scintigraphy. The radiation safety of such radioguided procedures, which typically employ 99mTc, has been well established. Now, with the emergence of 18F-fluorodeoxyglucose (18FDG) as a widely used tracer for PET imaging of cancer patients, there is increasing interest in the possibility of utilizing 18FDG for intraoperative tumor detection. First, though, the exposure to operating room personnel must be shown to be at a safe level. Due to the short half-life of 18F, the exposure rate will vary significantly with the start time post-injection as well as the duration of the procedure. The aim of this investigation is to determine empirically an exposure rate equation that can be integrated to estimate the exposure to a surgeon and assistants, from patients injected with 18FDG, over an arbitrarily chosen time interval. The study was conducted by measuring the radiation exposure rate from hospital in-patients receiving 18FDG-PET scans at various times from one to seven hours post injection; the empirical equation was determined from the plot of exposure rate vs. time for all patients. The resulting effective dose equivalent for the surgeon for typical values of injected activity, delay time and procedure duration was approximately 60 microSv.

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We have developed a working prototype of a beta camera based on solid state photomultipliers (SSPMs), to demonstrate proof of concept. The SSPM, essentially an array of avalanche photodiodes operating in Geiger mode, produces a gain equal to or better than that of a photomultiplier tube, while operating at low bias voltage. The beta camera consists of a sheet of red-emitting plastic scintillator coupled to a 4 x 4 array of SSPMs. The signals are multiplexed through a 4-channel readout board and digitized by a custom data acquisition program; the image is constructed via simple Anger logic. We have obtained a positron energy spectrum and initial images from the camera, as well as linearity data and spatial resolution measurements.

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