An Alternative Radiopharmaceutical for Gastric/Small Bowel Emptying Due to Supply Chain Disruption

Introduction: Technetium Sulfur Colloid (Tc-99m Sulfur colloid) is an essential radiopharmaceutical used in various nuclear medicine studies. Technetium-99m Sulfur Colloid label eggs are commonly used in gastric/small bowel emptying studies. These studies are known to be very physiologic and comprehensive studies for gastric motility.1 A serial trial of this study can assist in determining if a specific treatment is effective.1 The disruption in the supply chain prompted us to evaluate other alternatives to replace Technetium-99m Sulfur Colloid in Gastric Studies. Our aim was to experiment with Technetium-99m Macroaggregated Albumin (Tc-99m MAA) as an alternative to Tc-99m SC. Tc-99m MAA in a previous study showed to be effective in maintaining structural integrity during the egg cooking process.2

Methods: This study mimicked the procedure of the Mayo Clinics' gastric and small bowel emptying study with two whole eggs prepared with a 1 mCi dose of Tc-99m SC or Tc-99m MAA. 10G of the egg sample was then weighed and assayed and then cut into small, pea-sized pieces. The eggs were then placed into a pH 3 solution at 37° C and agitated for 4 hours, this represented the Gastric phase.3 After the 4-hour duration, the solution was neutralized to a pH of 7.0.3 After neutralization, the eggs were then strained from the liquid solution using a metal strainer with hole sizes of approximately 1mm x 1mm. Both strained egg pieces and the remaining solution were assayed and weighed separately. The liquid solution was also tested using a Thin Layer Chromatography Test (ITLC) to assess the amount of free Tc-99m. The solution and egg pieces were recombined and Bile acid salts (8mg/ml) and Pancreatic enzymes (3mg/ml) were added to the mixture. The mixture was then slightly agitated and maintained at 37° C for 4 hours, this represented the Intestinal phase.3 Once more the remaining egg pieces were strained using the metal strainer and both the liquid and eggs were weighed and assayed separately. Finally, the resulting solution was tested using the same ITLC.

Results: Six trials each were performed for Tc-99m MAA and Tc-99m SC radiopharmaceuticals. During the experiment, portions of the egg had broken down and were able to pass through the strainer. The experiment accounted for particles that may have passed through the strainer. An ITLC of the liquid, that contained small egg pieces, was performed to determine the percentage of activity that remained in particle form within the residue liquid after being strained. The average activity bound to the large egg pieces in the gastric phase for Tc-99m SC eggs was 92.09% and 95.79% bound to the Tc-99m MAA. The radiopharm that was still in particle form found in the liquid was 92.10% for Tc-99m SC and 65.74% for Tc-99m MAA. As for the intestinal phase, the amount bound to the large egg pieces on average was 50.62% for Tc-99m SC and 57.64% for Tc-99m MAA. The radiopharm that was still in particle form in the liquid was 98.97% for Tc99m SC and 91.41% for Tc99m MAA. Overall, the average percent of activity that was bound to the eggs or in particle form after the gastric phase for Tc-99m SC was 99.37% and Tc-99m MAA was 98.53%. The average percentage of activity that was bound to the eggs or in particle form after the intestinal phase was 99.5% for Tc-99m SC and 96.38% for Tc-99m MAA.

Conclusions: The use of Tc-99m MAA as an alternative radiopharmaceutical for gastric and small bowel emptying studies is plausible. The data showed that the performance of the two radiopharmaceuticals was similar. Although there were more unbound free Tc-99m in the liquid of Tc-99m MAA in both gastric and intestinal phases it was negligible. The experiment elucidated that the sum activity within the egg, liquid, and ITLC of the liquid meant that the Tc99m MAA stayed bounded, or in particle form, during the intestinal phase. Although this data suggests positive results, there needs to be continued testing to solidify the usage of Tc-99m MAA as an alternative to Tc99m SC.