Kinetics of three lymphoscintigraphic agents in patients with cutaneous melanoma

Although lymphoscintigraphy is commonly used for the preoperative evaluation of patients with cutaneous melanoma and for intraoperative identification of sentinel lymph nodes, there is no consensus regarding the most useful radiopharmaceuticals or imaging times.

Fifty-one consecutive patients with clinical American Joint Committee on Cancer Stage I or II melanoma were assigned to one of three groups of 17 for lymphoscintigraphy with one of three radiopharmaceuticals: 99mTc-albumin colloid (AC), 99mTc-human serum albumin (HSA) or 99mTc-sulfur colloid (SC). Colloidal agents were filtered through 0.2 microm filters. After injecting 18.5-30 MBq (500-800 microCi) of the radiopharmaceutical, dynamic monitoring over injection sites and node basins was performed to identify draining lymphatic channels and sentinel nodes. In addition, static digital and analog images were acquired from the injection site and draining node basins immediately after injection and at 30 min (early) and 2 to 4 hr (delayed) after injection. Dynamic and static images were analyzed to determine transit times to the sentinel node, the number of nodes visualized in early and delayed images, the quality of lymph node and lymph channel visualization, the sentinel-to-nonsentinel uptake ratios and the washout rates from injection sites.

Early images with all three agents provided reliable identification of sentinel lymph nodes. Technetium-99m-HSA demonstrated faster washout rates from injection sites and better definition of lymph channels than either particulate agent, whereas particulate agents were retained longer in nodes and demonstrated more nodes in delayed images than in early images. All agents demonstrated lymph channels better in early images than in delayed images. In general, variations between patients exceeded differences between agents. Sentinel nodes could not be distinguished reliably from nonsentinel nodes in delayed images alone.

All three agents are acceptable for cutaneous lymphoscintigraphy, but reliable identification of sentinel nodes and their afferent lymph channels requires early imaging. Delayed imaging or localization alone is unreliable and may lead to incorrect identification of the sentinel node.