Tc-99m-MIP-1404-SPECT/CT for Patients with Metastatic Prostate Cancer: Inter- and Intraobserver Variability in Treatment-related Longitudinal Tracer Uptake Assessments of PSMA-positive Lesions

Ziel/Aim Tc-99m-MIP-1404 is a single-photon emission computed tomography (SPECT)-suitable PSMA ligand for detection of prostate cancer. In patients with metastatic prostate cancer, there is no data as yet on inter- and intraobserver variability when assessing PSMA-positive lesions for longitudinal changes of tracer uptake.

Methodik/Methods Tc-99m-MIP-1404 SPECT/CT scans of 22 patients with metastatic prostate cancer were analyzed, and each subject was imaged at two separate points in time, before and after treatment. Three independent observers visually assessed a total of 96 PSMA-positive metastases (bone 69, lymph node 22, viscera 3) or local recurrences (n=2) for longitudinal changes in tracer uptake on planar scintigraphy and SPECT/CT. All lesions were categorized as regressive, stable, or progressive based on visual findings and on SUV_peak values of quantitative SPECT/CT (progressive, >30 % SUV_peak increase; regressive, <30 % SUV_peak decrease; or stable, all others).

Ergebnisse/Results Quantitative analysis of PSMA-positive lesions yielded significantly higher interobserver agreement (90.6 %, 95 % CI: 0.83-0.96) than visual assessments by either SPECT/CT (76.0 %, 95 % CI: 0.66-0.84) or planar scintigraphy (56.3 %, 95 % CI: 0.46-0.66). Intermethod comparison of aggregated results yielded significantly higher agreement between quantitative and visual SPECT/CT (85.1 %, 95 % CI: 0.80-0.89), as opposed to quantitative SPECT/CT and planar scintigraphy (53.1 %, 95 % CI: 0.47-0.59) or visual SPECT/CT and planar scintigraphy (54.9 %, 95 % CI: 0.49-0.61). In visual and quantitative analysis of 96 PSMA-positive lesions, number of discrepancies ranged from 9 (9.4 %) for quantitative SPECT/CT to 42 (43.8 %) for planar scintigraphy. Intraobserver agreement was near-perfect for all methods, whether SPECT/CT (visual, all κ=0.94-0.97; quantitative κ=0.94-0.98) or planar scintigraphy (all κ=0.90-0.94).

Schlussfolgerungen/Conclusions Quantitative evaluation of longitudinal change in tracer uptake by PSMA-positive lesions measured via SPECT/CT is superior to visual interpretation of images by planar scintigraphy or SPECT/CT.