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Chair for Computer Aided Medical Procedures & Augmented Reality
Lehrstuhl für Informatikanwendungen in der Medizin & Augmented Reality

T. Wendler, K. Herrmann, A. Schnelzer, T. Lasser, J. Traub, O. Kutter, A. Ehlerding, K. Scheidhauer, T. Schuster, M. Kiechle, M. Schwaiger, N. Navab, S. I. Ziegler, A. K. Buck
First Demonstration of 3D Lymphatic Mapping using freehand SPECT
Proceedings of the International Conference on Sentinel Node Biopsy and Radioguided Head & Neck Surgery (SNB), Copenhagen, Denmark, May 2010 (bib)

Aims
Freehand SPECT (fhSPECT) is a novel 3D tomographic imaging modality based on data acquisition with a hand-held detector that is moved freely, in contrast to conventional, fixed gamma camera systems. In this pilot study, the feasibility of fhSPECT for 3D lymphatic mapping in the simple setup of breast cancer was evaluated.
Methods: A total of 85 patients (pts) (age, 29–88 years) with an initial diagnosis of invasive breast cancer prospectively underwent sentinel lymph node (SLN) biopsy. Preoperative lymphatic mapping (35–87 MBq 99mTc-Nanocoll) included SPECT/CT (Siemens Symbia T6) and fhSPECT. Initially, the fhSPECT approach was assessed in a pilot study consisting of 50 pts. The quality of each fhSPECT acquisition was ranked as good, intermediate, or poor. In another series comprising a further 35 pts (validation study), a guidance system for the acquisition was implemented based on the results of the pilot study, ensuring acquisitions with good quality. For 3D tomographic image reconstruction, ad hoc models and iterative reconstruction algorithms were used. For adequate comparison, SPECT/CT and fhSPECT were registered within the same coordinate system.
Results: In the pilot study, fhSPECT enabled mapping of 24/83 SLNs. Using SPECT/CT as reference, the accuracy of fhSPECT was 77.8% (7/9 nodes) in scans with good quality, while for intermediate and poor quality scans, the accuracy was reduced to 34.3% and 12.8%, respectively. In the validation study, quality feedback improved the results significantly and fhSPECT showed a sensitivity of 83.3% (35/42 nodes). False negative findings were related to insufficient scanning time, insufficient coverage of the axillary region, close proximity of the SLN to the injection site, and low tracer uptake in the SLNs.
Conclusions: In this preliminary study in a simple setup, we demonstrated that 3D localization of SLNs is feasible using fhSPECT technology. Prerequisites for acquisition of a good scan quality, most likely allowing precise SLN mapping, have been defined. This approach has high potential to allow further standardization of SLN dissection in particular in the case of head and neck malignancies where it can help the surgeon plan the incision and visualize the depths of the SLNs in situs towards image-guided biopsy.
Acknowledgements: This research was partly funded by DFG’s SFB 824.
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