Background: In head/neck melanomas, near-the-injection-site sentinel nodes (NIS-SNs) may be missed on planar lymphoscintigraphy and/or SPECT/CT. The aim of the present study is to establish the performance of a portable gamma camera (PGC) to detect NIS-SNs in a simulation phantom set-up, and subsequently in head/neck melanoma patients scheduled for a SN procedure.
Methods: Five plastic Eppendorf tubes filled with technetium-99m-albumin nanocolloid were used to simulate 4 radiotracer deposit sites, as traditionally injected in melanoma patients, and 1 NIS-SN. A PGC was used with 2 pinhole collimators (2.5 and 4.0 mm). Image acquisition time was 1 minute with the camera positioned at various distances (range 1.5-15.5 cm). Results were compared with conventional lymphoscintigraphy and SPECT/CT acquired with a dual-head gamma camera as well with a gamma probe. Additionally, the same PGC setting was used in a case series of 3 patients with head/neck melanomas.
Results: The simulated NIS-SN was differentiated from the injection site at a distance of 3 mm with the 2.5-mm pinhole and at 5 mm with the 4-mm pinhole when the PGC was positioned at 1.5 cm distance. Planar lymphoscintigraphy, SPECT/CT, and the gamma probe depicted the NIS-SN separated from the injection site at distances of 7, 10, and 22 mm, respectively. In all 3 patients, 6 NIS-SNs were depicted with the PGC.
Conclusion: A high-resolution PGC, positioned close to the skin, is able to detect SNs at distances of at least 3 mm from the injection site. A further clinical evaluation of this device to establish its added value in reducing false-negative procedures and potential recurrences is necessary.