A Pilot Study of68Ga-PSMA11 PET/MRI and68Ga-RM2 PET/MRI for Biopsy Guidance in Patients with Suspected Prostate Cancer (2021)

1348 Introduction: Targeting of lesions seen on prostate multiparametric MRI (mpMRI) improves prostate cancer (PC) detection at biopsy. However, 20-65% of highly suspicious lesions on MRI (PI-RADS 4 or 5) prove to be false positives at biopsy. Here, we evaluated the potential utility of 68Ga-PSMA11 and 68Ga-RM2 PET/MRI for biopsy guidance in patients with suspected PC and prior negative biopsy or equivocal MRI. Methods: Nine men (mean±SD 59.8±4.6, range 54-68 years of age) with suspected PC were prospectively enrolled to undergo 68Ga-PSMA11 and 68Ga-RM2 PET/MRI, including prostate mpMRI. The prostate was contoured and divided into 12 segments (apex lateral, apex medial, base lateral, base medial, mid lateral, mid medial, left and right respectively) using PET/MRI data and MIM software (MIM Software Inc, Cleveland, OH, USA). Maximum standardized uptake values (SUVmax) of suspected PC lesions, as well as of background uptake in each segment was collected. Biopsies after PET/MRI included 1 core through each of the 12 segments and targeted sampling of any lesions seen on PET. PET/MRI results were then compared to the gold standard biopsy. Results: PSA at the time of PET/MRI was 12.27 ± 5.88 (range 6.7 - 25.46) ng/mL and PSA density was 0.22±0.11 (range 0.1 - 0.41) ng/mL2. The 9 patients had the scans within 7±2.8 days of each other. Prostate biopsy showed 6 PC lesions with Gleason score (GS) >7 in 4 patients, correlating to 6, 5 and 3 suspected PC lesions in 68Ga-PSMA11, 68Ga-RM2 PET/MRI and mpMRI, respectively. Three lesions in 3 participants were identified in all imaging modalities. Five lesions with GS 6 in 4 patients correlated to 5, 5, and 2 suspected lesions in 68Ga-PSMA11, 68Ga-RM2 PET/MRI and mpMRI. 68Ga-PSMA11 and 68Ga-RM2 PET/MRI showed more false positive (FP) lesions compared to mpMRI (15 and 17 vs. 2) leading to accuracy rates of 86.1%, 84.3% and 95.4% for 68Ga-PSMA11, 68Ga-RM2 PET/MRI and mpMRI, respectively. Sensitivity was high for PET/MRI with 100% for both 68Ga-PSMA11 and 68Ga-RM2 compared to 50% for mpMRI. Specificity was higher for mpMRI than PET/MRI (99% vs. 85.3%, 83.5% for 68Ga-PSMA11 and 68Ga-RM2 PET/MRI, respectively). Mean SUVmax for true positive (TP) were slightly higher than FP lesions in 68Ga-PSMA11 and 68Ga-RM2 PET/MRI, however not statistically significant (Mean SUVmax for TP [GS >7] vs. FP lesions 10.64±8.07 [range 4.97 - 22.46] vs. 6.44±4.64 [range 3.71 - 22.8], P=0.38, for 68Ga-PSMA11, and 19.24±17.8 [range 8.44 - 50.45] vs. 12.5±13 [range 5.37 - 44.09], P=0.47, for 68Ga-RM2; Mean SUVmax for TP [GS 6] vs. FP lesions in 68Ga-PSMA11 and 68Ga-RM2 PET/MRI were 8.37±6.42 [range 4.06 - 22.46] vs. 7.32±5.44 [range 3.97 - 22.8], P=0.72, and 17.72±17.17 [range 5.56 - 50.45] vs. 7.69±2.48 [range 5.14 - 12.68], P=0.12). 68Ga-PSMA11 and 68Ga-RM2 PET/MRI guided biopsy led to the finding of additional 3 PC (GS >7) lesions in 2 patients and 1 additional lesion with GS 6. Conclusions: Our preliminary results show that both 68Ga-PSMA11 and 68Ga-RM2 PET/MRI are not only feasible for biopsy guidance in suspected PC, but also identified additional cancers not seen on mpMRI. Table 1: Disease localization with 68Ga-PSMA11 and 68Ga-RM2 PET/MRI, and prostate mpMRI correlated with PET/MRI guided biopsy results (GS >7) as gold-standard. N=9 patients with a total of 108 prostate segments. Table 2: Comparison of SUVmax for true and false positive lesions in 68Ga-PSMA11 and 68Ga-RM2 PET/MRI, stratified by Gleason score.
 
Numerical factors are expressed as mean ± standard deviation (range).