Transport and retention of colloidal tracers in regional lymphoscintigraphy in melanoma: Influence on lymphatic mapping and sentinel node biopsy

Sentinel node (SN) biopsy is a staging technique used to select patients for regional lymphadenectomy in melanoma. We compared the two most widely used radioactive tracers, ^99mTc-colloidal albumin (^99m)Tc-CA) and ^99mTc-sulphur colloid ((^99m)Tc-SC), with respect to scintigraphy, success rate in gamma probe guided biopsy and absolute uptake in the SN. Scintigraphy was performed in six volunteers after simultaneous injection of the respective tracers in each leg. Comparison of uptake of both tracers showed a higher uptake on the ^99mTc-CA side. The scintigraphic count ratio of SNs labelled with ^99mTc-SC compared with ^99mTc-CA was 1 to 9-28. Next, 20 patients with biopsy-proven melanoma were randomized for injection of ^99mTC-CA or ^99mTc-SC followed by SN biopsy. Within 20 min after the injection, focal uptake was seen in all cases of the ^99mTc-CA group but in only seven of the 10 patients in the ^99mTc-SC group (P < 0.05). Focal accumulations were seen in all patients of both groups after 2 h. Spill to non-SNs was seen in five of the (99m)Tc-CA patients and three of the ^99mTc-SC patients. In all patients the SNs could be retrieved under the guidance of a gamma probe and blue dye. The uptake in the SN was significantly higher (P < 0.001) after the injection of ^99mTcCA (0.92 ± 0.40%) compared with ^99mTc-SC (0.34 ± 0.34%). When dynamic scintigraphy is performed, ^99mTc-CA is preferable. SN uptake of ^99mTc-SC is less than that of ^99mTC-CA but this does not adversely affect the surgical procedure.