Evaluation of the Efficacy of a Small CdTe γ-Camera for Sentinel Lymph Node Biopsy

Abstract

We previously reported the basic performance of a prototype small cadmium telluride (CdTe) g-camera (SSGC) intended for use in radioguided surgeries. In this study, we sought to confirm the favorable previous results and to extend the preliminary findings to examine the efficacy of the SSGC in an animal study and a clinical setting for sentinel lymph node biopsy. Methods: The prototype SSGC (1,024 pixels; field of view, 44.8 · 44.8 mm), equipped with a parallel-hole collimator, was used in both animal and clinical studies. 99m Tc-phytate (18.5 MBq) was injected into the tongues and legs of 6 rabbits. In the clinical study, 74 MBq of 99m Tc-phytate was injected into peritumoral regions in 8 patients with oral cancer. The detection of hot nodes by the SSGC was compared with that by a conventional scintillation g-camera (CGC). Results: The SSGC detected 29 hot nodes in images of 6 rabbits after injection. The number of hot nodes was the same as the number seen in CGC studies, but the CGC required a longer acquisition time to produce comparable images. There were no differences between the SSGC and the CGC in terms of activity ratios and hot node-to-background ratios. The biodistribution of 99m Tc-phytate in removed tissues was evaluated by contact radiography, and radioactivity was assayed with a g-well counter. The mean 6 SD radioactivity in specimens was 0.15% 6 0.15%, with a range of 0.01%-0.62%. In the clinical study, the SSGC detected 30 hot nodes with a 5-to 60-s acquisition time at 4 h after injection. The SSGC documented all hot nodes depicted by the CGC at 4 h after injection. Conclusion: The SSGC showed significant potential for the detection of sentinel lymph nodes in lymphoscintigraphy. The results of the studies suggested that the SSGC facilitates the exploration of hot nodes in sentinel lymph node biopsy.Key Words: lymphoscintigraphy; oncology; semiconductor g-camera; CdTe; handheld g-camera; sentinel lymph node biopsy; radioguided surgery; oral cancer Radi oguided surgery has been accomplished with the use of g-probes, primarily for sentinel lymph node biopsy.However, g-probes can provide only radioactivity counts and variable-pitch audio output based on the intensity of the detected radioactivity. Allowing the surgeon to see the spatial distribution of the increased radioactivity could result in more accurate delineation of the surgical field, thus facilitating the surgery. Therefore, we developed a prototype small semiconductor g-camera (SSGC) that provides images of radioactivities for surgical use (1).For radioguided surgery, the g-camera should be miniaturized or handheld to facilitate its application in the restricted space of a surgical field. A semiconductor detector containing cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe) has shown excellent performance and quality for imaging (2-7). The semiconductor detector is considered to be the most suitable for miniaturization because it does not require the relatively massive photomultiplier tube that characterizes a traditional scintil...

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