The biodistribution of 111In-pentetreotide was assessed in patients with gastroenteropancreatic (GEP) neuroendocrine tumors or lymphoma and in control patients and analyzed as a function of scanning time, presence or absence of tumor uptake, tumor type and previous octreotide treatment.
Methods: Patients underwent imaging 4 and 24 hr after injection of approximately 200 MBq 111In-pentetreotide. The frequency of organ visualization was assessed on planar views. Total organ and tumor uptake (% injected dose [ID]) was determined using the geometric mean method and regional tissue uptake (% ID/100 ml) by semiquantitative SPECT.
Results: Liver, spleen, kidneys and urinary bladder were visualized in all patients. Thyroid, bowel and pituitary were more often visualized at 24 hr than at 4 hr. Activity in the gallbladder, breast, ureters and ascites was only occasionally observed. Total liver, spleen and thyroid uptake was stable over time, whereas kidney activity decreased slightly. At 24 hr, regional uptake was threefold lower in the liver than in the spleen or kidneys and was similar in the three groups. In patients with long-term octreotide therapy, a positive correlation was found between the duration of octreotide therapy and liver or spleen uptake. Total and regional tumor uptake showed high intraindividual and interindividual variations. Total tumor activity was stable over 24 hr in patients with GEP and decreased in those with lymphoma. The mean regional tumor uptake was 10-fold lower in patients with lymphoma than in those with GEP. Cold octreotide injected 24 hr after tracer administration did not result in any displacement of organ and tumor activity.
Conclusion: Organ uptake seems not to be influenced by the presence of 111In-pentetreotide-positive lesions or by tumor type. Tumor uptake is highly variable among patients and clearly lower in patients with lymphoma than in those with GEP. The widespread of uptake values in tumors indicates that radiotherapy using radiolabeled somatostatin analogs may not be applicable to all patients with 111In-pentetreotide-positive tumors.