Intraoperative imaging guidance for sentinel node biopsy in melanoma using a mobile gamma camera

Abstract

Objective: To evaluate the sensitivity and clinical utility of intraoperative mobile gamma camera (MGC) imaging in sentinel lymph node biopsy (SLNB) in melanoma.

Background: The false-negative rate for SLNB for melanoma is approximately 17%, for which failure to identify the sentinel lymph node (SLN) is a major cause. Intraoperative imaging may aid in detection of SLN near the primary site, in ambiguous locations, and after excision of each SLN. The present pilot study reports outcomes with a prototype MGC designed for rapid intraoperative image acquisition. We hypothesized that intraoperative use of the MGC would be feasible and that sensitivity would be at least 90%.

Methods: From April to September 2008, 20 patients underwent Tc99 sulfur colloid lymphoscintigraphy, and SLNB was performed with use of a conventional fixed gamma camera (FGC), and gamma probe followed by intraoperative MGC imaging. Sensitivity was calculated for each detection method. Intraoperative logistical challenges were scored. Cases in which MGC provided clinical benefit were recorded.

Results: Sensitivity for detecting SLN basins was 97% for the FGC and 90% for the MGC. A total of 46 SLN were identified: 32 (70%) were identified as distinct hot spots by preoperative FGC imaging, 31 (67%) by preoperative MGC imaging, and 43 (93%) by MGC imaging pre- or intraoperatively. The gamma probe identified 44 (96%) independent of MGC imaging. The MGC provided defined clinical benefit as an addition to standard practice in 5 (25%) of 20 patients. Mean score for MGC logistic feasibility was 2 on a scale of 1-9 (1 = best).

Conclusions: Intraoperative MGC imaging provides additional information when standard techniques fail or are ambiguous. Sensitivity is 90% and can be increased. This pilot study has identified ways to improve the usefulness of an MGC for intraoperative imaging, which holds promise for reducing false negatives of SLNB for melanoma.

FIGURE 1

Sample MGC Imaging sequence in a participant with a left upper extremity melanoma that drained to the left axilla. All images were obtained over 60 seconds. A, Anterior MGC image of the participant’s left axilla before incision for SLNB. B, Ex vivo image of SLN#1. C, Anterior image of left axilla after removal of SLN 1.

FIGURE 2

A, Average scoring by investigator for 20 study participants of logistical challenges for use of MGC imaging in pilot study. Logistics were graded on a scale of 1 to 9, with 1 being “outstanding” and 9 being “prevented completion of the study.” B, Analysis of logistical challenges comparing participants injected with radio-labeled colloid the day before surgery versus participants injected the day of surgery demonstrates that logistical challenges were less for same-day participants, although this difference was not statistically significant (P = 0.23).

FIGURE 3

In participant 12, the handheld gamma probe identified an apparent residual node whose activity was 13% of that of the hottest node. MGC camera imaging revealed that what appeared to be a single hot spot (A) was in fact 3 separate spots (B) that individually did not meet the activity criteria for sentinel nodes.

FIGURE 4

An atypical location for an SLN, adjacent to injection site in the left upper arm of the patient. This hot spot was identified in the FGC (A) but questioned by the nuclear medicine team. It was not found with initial evaluation with the handheld probe. There was a suggestion of the hot spot on the first MGC image (B) and with rotation of the camera around the arm (C) the hot spot was clearly seen. The node was removed and was hot.