title: A pilot study of SPECT/CT-based mixed-reality navigation towards the sentinel node in patients with melanoma or Merkel cell carcinoma of a lower extremity.
abstract: OBJECTIVE
  To explore the feasibility of an intraoperative navigation technology based on preoperatively acquired single photon emission computed tomography combined with computed tomography (SPECT/CT) images during sentinel node (SN) biopsy in patients with melanoma or Merkel cell carcinoma.
  
  
  METHODS
  Patients with a melanoma (n=4) or Merkel cell carcinoma (n=1) of a lower extremity scheduled for wide re-excision of the primary lesion site and SN biopsy were studied. Following a Tc-nanocolloid injection and lymphoscintigraphy, SPECT/CT images were acquired with a reference target (ReTp) fixed on the leg or the iliac spine. Intraoperatively, a sterile ReTp was placed at the same site to enable SPECT/CT-based mixed-reality navigation of a gamma ray detection probe also containing a reference target (ReTgp).The accuracy of the navigation procedure was determined in the coronal plane (x, y-axis) by measuring the discrepancy between standard gamma probe-based SN localization and mixed-reality-based navigation to the SN. To determine the depth accuracy (z-axis), the depth estimation provided by the navigation system was compared to the skin surface-to-node distance measured in the computed tomography component of the SPECT/CT images.
  
  
  RESULTS
  In four of five patients, it was possible to navigate towards the preoperatively defined SN. The average navigational error was 8.0 mm in the sagittal direction and 8.5 mm in the coronal direction. Intraoperative sterile ReTp positioning and tissue movement during surgery exerted a distinct influence on the accuracy of navigation.
  
  
  CONCLUSIONS
  Intraoperative navigation during melanoma or Merkel cell carcinoma surgery is feasible and can provide the surgeon with an interactive 3D roadmap towards the SN or SNs in the groin. However, further technical optimization of the modality is required before this technology can become routine practice.
authors.affiliation: aInterventional Molecular Imaging Laboratory, Department of Radiology, Leiden University Medical Center, Leiden Departments of bUrology cNuclear Medicine dSurgery and Melanoma Center Amsterdam, and eHead and Neck Surgery and Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands fMelanoma Institute Australia, Sydney, New South Wales, Australia.
authors.forename: Nynke S
authors.initials: NS
authors.lastname: van den Berg
authors.forename: Thijs
authors.initials: T
authors.lastname: Engelen
authors.forename: Oscar R
authors.initials: OR
authors.lastname: Brouwer
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Mathéron
authors.forename: Renato A
authors.initials: RA
authors.lastname: Valdés-Olmos
authors.forename: Omgo E
authors.initials: OE
authors.lastname: Nieweg
authors.forename: Fijs W B
authors.initials: FW
authors.lastname: van Leeuwen
mesh_terms: D000328:Adult; D000368:Aged; D015266:Carcinoma, Merkel Cell / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D061705:Image-Guided Biopsy / Q000379:methods*; D035002:Lower Extremity / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008545:Melanoma / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D000071036:Sentinel Lymph Node / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D021701:Sentinel Lymph Node Biopsy / Q000379:methods*; D012878:Skin Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D014584:User-Computer Interface