M. C. Kreissl, T. Wendler, K. Herrmann, K. Scheidhauer Freehand SPECT: First experiences with a new method of 3D-SLN mapping in melanoma Proceedings of the International Sentinel Node Society Meeting, Yokohama, Japan, 2010 (bib)
	Objectives: Freehand SPECT (fhSPECT) was introduced lately as a 3D imaging modality capable of mapping sentinel lymph nodes (SLNs) in breast cancer. Due to its compact and flexible nature there is potential to introduce it to the OR for image-guided SLN biopsies (SLNBs). Here we present the first application of it for melanoma and Merkel cell carcinoma (MCC) patients in anatomies where a guided biopsy could increase safety and the overall output of SLNB. Methods: A fhSPECT system based on a gamma probe and a positioning system was used to scan 25 patients (aged 25-76, average 55.0) with confirmed malignant melanoma (n=23) and MCC (n=2). Patients had previously undergone indicated planar scintigraphy (2 min, 2 planes, peritumoral injection of 41-120 MBq Tc99m-nanocoll, average 75). fhSPECT acquisitions took 173-700s (average 374.0s). Images were reconstructed (MLEM 20i) in grids centered in the region of interest with resolution 5x5x5 mm3. Results: In all patients at least one SLN was mapped in planar scintigraphy and fhSPECT. Planar scintigraphy mapped 48 nodes, while fhSPECT mapped 47 nodes. fhSPECT could not resolve close 2 neighboring nodes in 5 pts, and missed completely 1 node in 1 pt. fhSPECT could resolve 1 further node in 1 pt and 2 further nodes in 2 pts. Sensitivity and positive predictive value of fhSPECT assuming planar scintigraphy as ground truth were 88% (42/48) and 89% (42/48) respectively. In all but 1 patient, fhSPECT images where considered essentially equivalent as planar scintigraphy. Conclusion: Freehand SPECT succeeded to map fairly SLNs in all analyzed anatomies in 23 of 25 pts. Neighboring SLNs not resolved by fhSPECT were not considered to play a major role, due to the fact that close nodes are resected anyhow in practice. This preliminary data supports the introduction of freehand SPECT in a pilot study setup for intraoperative localization of SLNs in melanoma & MCC towards image-guided SLNB.
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