PSMA PET/CT imaging seems to be a valuable imaging modality for evaluation of primary prostate cancer and it seems to have potential for the detection of lymph node and bone metastases. Early images 5 min p.i. can help to better distinguish between urinary bladder (before tracer accumulation occurs) and tumour lesions.
Aim
In this study, we aimed to measure interobserver and intraobserver agreement in Ga-68–prostate-specific membrane antigen (PSMA) PET/computed tomography (CT) image interpretation. In addition, the limitations of these criteria and levels of personal confidence reported by the readers when reporting the findings were determined. The effects of interpersonal differences on clinical decisions were also investigated.
Methods
PSMA PET images from 133 cases were reported independently by four different readers at different times according to the molecular imaging TNM (miTNM) and PSMA-reporting and data system (RADS) templates.
Results
There was substantial interobserver agreement for overall positivity, miT, miN and miM staging (Fleiss’ κ = 0.65, 0.625, 0.731, and 0.779). Substantial agreement levels were observed in reporting of seminal vesicle invasion, the number of lymph node stations with metastasis, total number of intraprostatic areas containing tumors, and lymph node metastasis staging (Fleiss’ κ = 0.622 and 0.779). The highest variation was seen in the reporting of intraprostatic distribution: In International Society of Urological Pathology (ISUP) grade group 1, moderate agreement was observed, and it was seen that the agreement level for the T staging increased with an increasing ISUP group in the staging group (Fleiss’ κ = 0.531 vs. 0.655). There was near-perfect interobserver agreement in the reporting of five-point PSMA-RADS scoring [intraclass correlation coefficient (ICC) κ = 0.904; 95% CI, 0.865–0.934]. Disagreement according to miTNM staging had a major effect on clinical management in only 9% (n = 12) of the patients.
Conclusion
PSMA PET has a lower interobserver variability and higher reproducibility than other imaging methods used for imaging of prostate cancer do, including CT, MRI, and bone scintigraphy. The miTNM template provides a reporting format that is highly reproducible and has a high level of agreement among readers, but the prostatic template needs development. In contrast, the PSMA-RADS system leads to slightly increased interobserver reporting differences and reduces personal confidence, but at the same time, it still exhibits almost-perfect agreement in terms of scoring.
PET/CT with Ga-PSMA is a valuable tool for assessing recurrence of PCa with a high sensitivity in patients who have PSA levels between 0.2 and 5 ng/ml. In addition, this study suggests that PSMA PET/CT can be used in patients with very low (<0.2 ng/ml) but increasing PSA levels, which, in many cases, may influence further clinical management.
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