Measured Human Dosimetry of 68Ga-DOTATATE

For more than a decade, PET emitter–labeled high-affinity somatostatin receptor analogs have been used for imaging, predominately outside the United States. The improved spatial and contrast resolution of PET imaging results in improvements in the quality of information used by care-givers, leading to better patient care decisions for those with somatostatin receptor–expressing tumors. These synthetic somatostatin analogs can also be labeled with β-emitting radionuclides, resulting in directed radiotherapy (peptide receptor radionuclide therapy [PRRT]) to these tumors, with several trials demonstrating improved outcomes in patients who are not candidates for attempted surgical cure and who demonstrate poor response to conventional medical treatments (1,2). Several somatostatin analog peptides have been used for PET-based imaging of somatostatin receptor–expressing tumors. These are typically DOTA-conjugated peptides allowing chelation with PET-emitting metal ions (such as 68Ga or 64Cu (3)) for diagnosing, staging, and assessing treatment response or allowing chelation with 177Lu (4), 90Y (5), or a combination of each (6) for PRRT. The imaging-based radiopharmaceuticals have been used to estimate tumor dosimetry before the administration of PRRT, an important function because significant radiation-induced toxicity can occur with the unsealed radiotherapeutic compounds (7). Diagnostic scans permitting a rough estimate of uptake in the tumor and normal vital organs (8) are especially important for patients receiving multiple PRRTs because of the resulting transient and sometimes permanent deterioration of renal and hematopoietic function that can result (9,10). Diagnostic scans also allow the detection of patients with tumors that have become poorly differentiated or anaplastic, with loss of somatostatin receptor expression, thereby identifying patients who are unlikely to benefit from PRRT. The use of 68Ga-DOTATATE PET/CT scans after PRRT is also predictive of response, with a decrease in uptake in the tumor-to-spleen ratio after PRRT, compared with baseline, identifying patients with prolonged time to progression. This decrease in the tumor-to-spleen uptake ratio also correlated with improvement in clinical symptoms, compared with patients with no change or increase in the tumor-to-spleen uptake ratio (11). A variety of synthetic somatostatin analog peptides, including DOTATOC, DOTATATE, and DOTANOC, have been described in numerous published articles. Detailed measured human dosimetry has been reported in the peer-reviewed literature for 68Ga-DOTATOC (12) and 68Ga-DOTANOC (13) but not for 68Ga-DOTATATE. Accordingly, we report our results for the imaging of 6 subjects with 68Ga-DOTATATE using multiple time points.