⁶⁴Cu-DOTATATE PET/CT for Imaging Patients with Known or Suspected Somatostatin Receptor–Positive Neuroendocrine Tumors: Results of the First U.S. Prospective, Reader-Masked Clinical Trial

Dose-Ranging Study Design

Twelve patients with NETs were recruited into 3 ⁶⁴Cu-DOTATATE dose groups (111 MBq [3.0 mCi], 148 MBq [4.0 mCi], and 185 MBq [5.0 mCi] ± 10%) with 4 patients per group. Patient demographics and characteristics are shown in Table 1. PET/CT images were acquired at 60 ± 15 min after injection and with a 5-min acquisition time per bed position. Image quality was evaluated by 3 experienced readers masked to dose information. Image quality was assessed using the following scoring system: 0, inadequate (grainy images with poor delineation of lesions); 1, questionable (clear images, but lesion delineation is suboptimal and small lesions [1 cm] are hard to assess); and 2, acceptable (clear images; large and small lesion delineation is possible). Cohort scores were calculated by adding together the average image subject scores in each dosing group. Consistent with the as-low-as-reasonably-achievable (ALARA) principle, the lowest dose level with a cohort score of at least 7 was deemed the lowest ⁶⁴Cu-DOTATATE dose that provides diagnostic-quality PET/CT images. The study was approved by the Biomedical Research Alliance of New York Institutional Review Board, and all subjects gave written informed consent.

Phase III Study Design

The pivotal phase III study (NCT03673943) was an open-label, single-dose, single-arm, single-center, prospective design that evaluated the sensitivity and specificity of ⁶⁴Cu-DOTATATE PET/CT imaging in patients with known or suspected NETs against an independent reader’s SOT for each subject; readers were masked to the SOT. Patient demographics and characteristics are shown in Table 1. To obtain at least a 90% chance of showing more than 0.70 sensitivity and more than 0.60 specificity, 63 subjects were required. After a preestablished 2:1 (NET-positive/NET-negative) ratio, 42 SOT-positive patients and 21 SOT-negative healthy volunteers were recruited under a U.S. Food and Drug Administration–approved Investigational New Drug application. Of note, the 4 patients at the optimal ⁶⁴Cu-DOTATATE dose (148 MBq [4.0 mCi]) in the dose-ranging study were eligible and subsequently enrolled in the phase III study. NET positivity by the SOT was determined using MRI, CT, ¹⁸F-FDG PET/CT, bone scintigraphy, ¹¹¹In-DTPA-octreotide scans, or ⁶⁸Ga-DOTATATE PET/CT. This prospective study was performed in accordance with the Helsinki Declaration and followed the International Conference on Harmonisation Good Clinical Practice guidelines. The study was also approved by the Biomedical Research Alliance of New York Institutional Review Board, and all subjects gave written informed consent.

Synthesis and Radiolabeling of ⁶⁴Cu-DOTATATE

⁶⁴CuCl₂ was produced at the cyclotron facility at Washington University in St Louis, Missouri, and DOTATATE peptide was manufactured by ABX GmbH. ⁶⁴Cu-DOTATATE drug was prepared by RadioMedix, Inc., according to current good-manufacturing-practice guidelines. Briefly, ⁶⁴CuCl₂ (5,550–9,250 MBq) was added to sodium acetate buffer containing DOTATATE (0.4 mg) and gentisic acid (4.0 mg). The reaction mixture was incubated for 10 min at 95°C and then passed through a Sep-Pak C18 cartridge (Waters). The cartridge-retained product was eluted with 1 mL of ethanol into a vial containing sodium ascorbate solution (50 mg/mL). The contents of the vial were filtered through a 0.22-μm filter. The final ⁶⁴Cu-DOTATATE drug underwent standard radiopharmaceutical quality control. The radiochemical purity of ⁶⁴Cu-DOTATATE was more than 95% (high-performance liquid chromatography), and the average specific activity was 29.6 MBq/μg.

Image Acquisition

All subjects had a PET/CT scan performed on a Biograph Horizon 16-slice scanner (Siemens Healthineers). PET/CT scans were undertaken on average 63 min (median, 60 min; range, 39–97 min) after a single intravenous dose of 148 MBq ± 10% (range, 132–163 MBq) of ⁶⁴Cu-DOTATATE. PET scans (from vertex of skull to mid thigh) were obtained in 3-dimensional mode, with an acquisition time of 5 min per bed position over an approximately 30-min total scan time. A non–contrast-enhanced CT scan was performed using the CT exposure factors of 140 kVp and 80 mA in 0.5 s. PET/CT images were reconstructed using CT for attenuation correction and ordered-subsets expectation maximization with 2 iterations and 24 subsets.

Image Analysis and Data Interpretation

PET/CT images acquired at the clinical site were transferred to an independent medical-imaging-research contract organization that masked all clinical, imaging, and laboratory information. Thereafter, the contract organization randomized the images to 3 experienced, independent, board-certified nuclear medicine physicians who had been trained previously by the contract organization to detect abnormal images associated with SSTRs. Readers 1, 2, and 3 had 37, 5, and 8 y of experience in nuclear medicine, respectively, and all had read hundreds of ⁶⁸Ga-based SSTR PET/CT scans. On assessment, each physician reader categorized subjects as disease or no disease based only on ⁶⁴Cu-DOTATATE tumor uptake. Subjects categorized as disease were further subcategorized as localized or metastatic, as appropriate. Ten percent of the images (7 cases) were randomly selected for assessment of interreader variability by reintroducing the images to the independent readers for a second masked read no earlier than 4 wk after the primary read.

In parallel, an independent oncologist established the SOT for each subject using available scan reports from composite conventional imaging modalities and pathology studies; ⁶⁴Cu-DOTATATE scans were not used to establish the SOT. The SOT oncologist used the collective information to categorize each patient as disease or no disease and as localized or metastatic, as appropriate.

Safety Assessments

Safety was determined primarily through investigator-assessed treatment-emergent adverse events. An adverse event was considered treatment-emergent if the start date and time were on or after the start date and time of ⁶⁴Cu-DOTATATE injection. Adverse events observed by the investigator or obtained during nonleading telephone interviews 24 and 48 h after injection were recorded using the MedDRA, version 19.1, coding system from the International Council for Harmonisation. In addition, observed or patient-reported immediate adverse events were assessed within 1 h before and 2 h after ⁶⁴Cu-DOTATATE administration. The severity of adverse events was assessed independently by investigators and graded using the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0, in which grades 1, 2, 3, 4, and 5 indicate a mild adverse event, a moderate adverse event, a severe or medically significant but not life-threatening adverse event, a life-threatening adverse event, and death related to an adverse event, respectively.

Vital signs were recorded within 30 min before and up to 1 h after administration of ⁶⁴Cu-DOTATATE. Blood samples for clinical laboratory tests and hematology were collected within 30 min before and within 2 h after ⁶⁴Cu-DOTATATE administration. All subjects also underwent continuous electrocardiogram recording at least 15 min before ⁶⁴Cu-DOTATATE administration, with continuation for at least 30 min after administration. In addition, a 12-lead static electrocardiogram was performed within 60 min before and after ⁶⁴Cu-DOTATATE administration. All electrocardiogram data were collected, analyzed, and reviewed by an independent physician to determine normal versus abnormal and whether the abnormality was clinically significant.

For 8 subjects of child-bearing potential, a urine pregnancy test was performed before imaging to rule out pregnancy.

Statistical Analysis

Confidence limits for all binomial parameters, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, were calculated using the Wilson score with continuity correction (the score method). The level of significance for each hypothesis test was a 1-sided α-value of 0.025. Point estimates of sensitivity and specificity were calculated along with 2-sided 95% confidence intervals using the score method. Sensitivity and specificity were calculated on an individual-reader basis. In addition, a majority-read statistical analysis was performed, taking into account the most favored category of reading for each subject from the 3 readers, as it was a consensus reading. Success on the primary endpoints could be declared if 2 of the 3 independent readers achieved a sensitivity and a specificity exceeding preestablished thresholds.

Analysis of NPV, PPV, and accuracy was computed using the majority read (i.e., the majority ⁶⁴Cu-DOTATATE diagnosis from the 3 readers) and using reader reports. Point estimates of the majority read and individual-reader NPV, PPV, and accuracy were calculated along with 95% confidence intervals using the score method. Sensitivity and specificity were determined relative to the SOT. The statistical analysis plan included a testable hypothesis for the coprimary endpoints (i.e., sensitivity and specificity). Thus, P values were calculated for sensitivity and specificity and not for PPV, NPV, or accuracy. P values of less than 0.05 were considered statistically significant.

For the inter- and intrareader agreement analysis of each reader pair (readers 1 and 2, readers 1 and 3, and readers 2 and 3), a Cohen κ along with a 95% confidence interval on the Cohen κ were computed. A 95% confidence interval for κ was also computed (12). A Fleiss generalized κ and associated 95% confidence interval were used to assess overall agreement among the 3 readers (12).

The data analyses were conducted using SAS Software, version 9.4 or higher (IBM).