In the example shown (figure 1), the cutaneous melanoma was excised from the midportion of the patient’s back. This is considered a watershed area—that is to say, the lymphatic drainage may go to either axilla or groin. Accordingly, a preoperative scintigram is required to demonstrate which lymphatic basin receives the lymphatic drainage from the tumor site. The most common areas are the axillary and inguinal regions for extremity or truncal lesions and cervical or supraclavicular regions for head and neck primaries. Other sites include deep iliac, hypogastric, and obturator regions and the popliteal or epitrochlear regions for legs and arms, respectively. Finally, ectopic sites are also possible.
The skin must be cleared of any active infections, as must the excision site for the melanoma. Preparation, inspection, and monitoring of the radionuclide solution must be coordinated with the nuclear medicine staff.
A few hours before operation, the patient is injected with a radionuclide solution intradermally about the perimeter of the surgical site, using sterile technique. This may be done by the radiologist or the surgeon. The commercially available human serum albumin or sulfur colloid solution tagged with technetium 99m is filtered and sterilized. Four syringes of approximately 100 μC Tc 99m filtered sulfur colloid and 0.1 mL of normal saline each are prepared, for a total dose of about 400 μC. The area for injection is prepared with an antiseptic solution. Disposable paper drapes are widely placed and the physician is gloved. Extensive shielding for radioactivity is not required, but the site and supplies are monitored with a radiation survey meter. The gloved physician injects the radionuclide in an intradermal pattern about the incision (figure 2). The area is washed and all the disposable items are surveyed and disposed of in a radiologically safe manner.
The lymphatic drainage area or basin is noted on a large or whole-body scintigram; a hand-held gamma detector is used to identify the hottest area. This spot is marked with indelible ink as a temporary tattoo and the patient is transported to the operating room.