|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)
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.
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.
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.
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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