Histopathology-validated lesion detection rates of clinically significant prostate cancer with mpMRI, [ 68 Ga]PSMA-11-PET and [ 11 C]Acetate-PET

Abstract

Objective: PET/CT and multiparametric MRI (mpMRI) are important diagnostic tools in clinically significant prostate cancer (csPC). The aim of this study was to compare csPC detection rates with [ 68 Ga]PSMA-11-PET (PSMA)-PET, [ 11 C]Acetate (ACE)-PET, and mpMRI with histopathology as reference, to identify the most suitable imaging modalities for subsequent hybrid imaging. An additional aim was to compare inter-reader variability to assess reproducibility.

Methods: During 2016-2019, all study participants were examined with PSMA-PET/mpMRI and ACE-PET/CT prior to radical prostatectomy. PSMA-PET, ACE-PET and mpMRI were evaluated separately by two observers, and were compared with histopathology-defined csPC. Statistical analyses included two-sided McNemar test and index of specific agreement.

Results: Fifty-five study participants were included, with 130 histopathological intraprostatic lesions >0.05 cc. Of these, 32% (42/130) were classified as csPC with ISUP grade ≥2 and volume >0.5 cc. PSMA-PET and mpMRI showed no difference in performance ( P = 0.48), with mean csPC detection rate of 70% (29.5/42) and 74% (31/42), respectively, while with ACE-PET the mean csPC detection rate was 37% (15.5/42). Interobserver agreement was higher with PSMA-PET compared to mpMRI [79% (26/33) vs 67% (24/38)]. Including all detected lesions from each pair of observers, the detection rate increased to 90% (38/42) with mpMRI, and 79% (33/42) with PSMA-PET.

Conclusion: PSMA-PET and mpMRI showed high csPC detection rates and superior performance compared to ACE-PET. The interobserver agreement indicates higher reproducibility with PSMA-PET. The combined result of all observers in both PSMA-PET and mpMRI showed the highest detection rate, suggesting an added value of a hybrid imaging approach.

Fig. 1

STARD diagram of study participant flow.

Fig. 2

Images from four study participants examined with ACE-PET/CT, PSMA-PET/sCT (both with PET intensity threshold SUV = 10) and mpMRI including a T2-weighted sequence, early dynamic contrast-enhancement, diffusion-weighted sequence (b = 1000 s/mm²), and apparent diffusion coefficient map. In our first example (case 1) all modalities (both observers), except for PSMA-PET, correctly identified the dominant intraprostatic lesion. In case 2, the dominant lesion was correctly identified by both PSMA-PET observers, while mpMRI and ACE-PET were read as negative. In case 3, both PSMA-PET observers, and one mpMRI observer detected the dominant lesion. Lastly, in case 4, all modalities were in agreement and all observers detected the lesion.

Fig. 3

Characteristics of lesions >0.05 cc identified in the histopathological examination (130 lesions). Each box represents the interquartile range with the median value marked with a black line. The black dots represent the individual data points in each ISUP grade. The >0.5 cc threshold is marked with a dashed line (n > 0.5 cc = 43).

Fig. 4

Mean observer detection rate of lesions with ISUP grade ≥2 calculated for each modality and with different lesions volume bins (upper graph), and the mean observer detection rate for each ISUP grade (lower graph).