Published in:
01-10-2007 | Original Article
Prospective comparison of two gamma probes for intraoperative detection of 18F-FDG: in vitro assessment and clinical evaluation in differentiated thyroid cancer patients with iodine-negative recurrence
Published in: European Journal of Nuclear Medicine and Molecular Imaging | Issue 10/2007
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Purpose
This study was aimed at evaluating the spatial resolution and sensitivity of two hand-held gamma probes. Radioguided surgery was tested in seven patients with iodine-negative differentiated thyroid cancer (DTC) recurrence using 18F-FDG PET.
Methods
Two gamma probes were evaluated: Clerad’s GammaSup with a collimated CsI(Tl) scintillator and Novelec’s Modelo2 with a BGO scintillator. Five measurement tests were performed following the NEMA guidelines (NU3-2004). Radioguided surgery was performed in patients with recurrent DTC and abnormal 18F-FDG uptake on preoperative 18F-FDG PET images. Patients were injected with rTSH 2 days before surgery. A mean activity of 211 MBq of 18F-FDG was injected 60 min before surgery. In vivo and ex vivo counts were recorded for suspected tumours and normal tissue.
Results
Spatial resolution was higher with the CsI(Tl) than with the BGO detector: 20.2–40.6 mm vs 20.6–55.3 mm from 0 to 20 mm depth. Sensitivity in air and water and through side shielding was higher for BGO but the signal-to-noise ratio was 88 and 22 with the BGO compared to 131 and 76 with the CsI(Tl) at 10 and 30 mm depth. Median in vivo SNR (tumour/non-tumour ratio) was 1.8 with both the BGO and the CsI(Tl) detector, while ex vivo ratios of 2.3 and 2.1, respectively, were obtained. Radioguided surgery allowed detection of all of the tumours identified by 18F-FDG PET images.
Conclusion
This study demonstrated the feasibility of high-energy photon detection with a conventional scintillator equipped with a collimator. The CsI(TI) probe detected more true events from background than did the BGO detector during surgery.