Biodistribution of 111In-pentetreotide and dosimetric considerations with respect to somatostatin receptor expressing tumor burden.

The general features of the biodistribution of the labeled somatostatin analog 111In-pentetreotide are already known. We describe some details of 111In-pentetreotide accumulation in the thyroid gland, mammae, spleen and gastrointestinal tract with respect to endocrine parameters, kinetics and time of imaging. In addition, dose estimations were performed for liver, spleen and kidney in patients without neuroendocrine tumor load and in patients with large tumors positive for somatostatin receptors. The overall absorbed dose turned out to be within the range reported previously. However, in patients with extensive tumor burden the radiation dose in liver, spleen and kidney tended to be lower than in patients without such malignancy. The dependence of estimated organ doses on the presence of somatostatin receptor-expressing tumors will have to be considered if radiotherapy with suitable labeled somatostatin analogs becomes available.