FILTERED TECHNETIUM-99M-SULFUR COLLOID EVALUATED FOR LYMPHOSCINTIGRAPHY

Several Tc-99m-labeled radiopharmaceuticals have been developed for ly mphoscintigraphy of the extremities. In the United States, however, th ese agents are not widely used clinically. This study evaluates the us e of smaller particle sizes (< 0.1 mu m) of Tc-99m-sulfur colloid (Tc- 99m-SC) for lymphoscintigraphy. Methods: The Tc-99m-SC was prepared by kit, and the final preparation was filtered through a sterile 0.1-mu m filter. The radiochemical purity (RCP) of the filtered Tc-99m-SC was determined before administration. Nineteen patients with suspected ly mphedema were injected with 18.5 MBq (500 mu Ci) filtered Tc-99m-SC in tradermally in each foot, and whole-body images were obtained immediat ely and 1, 3, 6 and 24 hr later. Local views over the inguinal or axil lary lymph nodes were also obtained every 5 min for the first hour. Re sults: The average RCP value was 93.4% +/- 4.2% (n = 19), and the RCP difference pre-and postfiltration of the Tc-99m-SC preparation was -1. 7% +/- 1.4% (n = 40). Evaluation of the particle size with the polycar bonate filter showed that 89.9% +/- 4.5% (n = 28) of particles were le ss than 50 nm, and the particle size was further determined by electro n microscopy to be 38.0 +/- 3.3 nm (n = 202). The mean particle sizes of two peaks measured by laser light scattering techniques were 7.5 an d 53.9 nm (major peak). Clinical studies with filtered Tc-99m-SC demon strated similar lymphoscintigrams compared with those obtained with Tc -99m antimony sulfide colloid (Tc-99m-ATC). Filtered Tc-99m-SC Showed a faster transport rate to the inguinal lymph nodes and lower radiatio n dosimetry for liver, spleen and whole body compared with Tc-99m-ATC. Conclusion: Filtered Tc-99m-SC can be easily prepared and is readily available for routine clinical use in lymphoscintigraphic studies.