Crypt Cell Dosimetry for 99 Tc m -Sestamibi in a New Small Intestinal Dosimetry Model

The aim of the study was to calculate the absorbed dose to the crypt cells in the small intestine from ⁹⁹Tc^m-sestamibi excreted through the intestinal tract. The absorbed dose was calculated taking into consideration the biodistribution of the radiopharmaceutical in the small intestinal wall and its contents, based on data gathered in rats. Absorbed dose calculations were performed using a new intestinal model in which S values for crypt cells are given both for the intestinal wall and for the intestinal contents as source organs. A maximum of 6% of the injected activity was found to be located in the intestinal wall at 30 minutes after injection and 13% in the intestinal contents at 2 h, resulting in an absorbed dose of 8.9 μGy/MBq to the crypt cells. Assuming the activity to be located only in the wall, we calculate an absorbed dose to the crypt cells 2.5 times higher than if all the activity is assumed to be present in the intestinal contents. Using the new intestinal dosimetry model, together with detailed biokinetic data for the radiopharmaceutical from animal studies, it is possible to calculate the absorbed dose to the crypt cells, which is not possible when using external imaging.