DIAGNOSTIC ACCURACY OF 68Ga-PSMA PET/MRI AND MULTIPARAMETRIC MRI IN DETECTING INDEX TUMOR IN RADICAL PROSTATECTOMY SPECIMEN

ABSTRACT Objective To evaluate the diagnostic accuracy of the 68Gallium (68Ga) - prostate specific membrane antigen (PSMA) positron emission tomography/magnetic resonance imaging (PET/MRI) and multiparametric MRI (mpMRI) by region-based comparison of index tumour localisations using histopathological tumour maps of patients who underwent radical prostatectomy due to clinically significant prostate cancer. Patients and Methods The study included 64 patients who underwent radical prostatectomy after primary staging with mpMRI and 68Ga-PSMA PET/MRI. Diagnostic analysis was performed by dividing the prostate into four anatomic regions as left/right anterior and left/right posterior. The extension of the lesions in mpMRI and the pathological uptake in 68Ga-PSMA PET/MRI were matched separately for each region with the extension of the index tumour into each region. Results The sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, and the accuracy of mpMRI and 68Ga-PSMA PET/MRI are shown as 55.7%, 91.8%, 80.6%, 77.2%, 78.1% and 60.8%, 94.3%, 86.8% 79.8%, 83.5%, respectively. 68Ga-PSMA PET/MRI has higher sensitivity and specificity compared with mpMRI. However, no statistically significant difference was found (p = 0.464). Combined imaging had significantly higher diagnostic accuracy compared with mpMRI and 68Ga-PSMA PET/MRI (change in AUC: 0.084 and 0.046, p < 0.001 and p = 0.028, respectively), while no statistically significant difference was found between mpMRI and 68Ga-PSMA PET/MRI (change in AUC: 0.038, p = 0.246). Conclusion 68Ga-PSMA PET/MRI had higher clinical diagnostic accuracy in prostate cancer compared with mpMRI. Diagnostic accuracy was significantly increased in the combined use of both imaging modalities.

Lack of Anatomical Concordance between Preablation and Postablation CT Images: A Risk Factor Related to Ablation Site Recurrence

Objective. Variation in the position of the liver between preablation and postablation CT images hampers assessment of treatment of colorectal liver metastasis (CRLM). The aim of this study was to test the hypothesis that discordant preablation and postablation imaging is associated with more ablation site recurrences (ASRs).Methods. Patients with CRLM were included. Index-tumor size, location, number, RFA approachs and ablative margins were obtained on CT scans. Preablation and postablation CT images were assigned a “Similarity of Positioning Score” (SiPS). A suitable cutoff was determined. Images were classified as identical (SiPS-id) or nonidentical (SiPS-diff). ASR was identified prospectively on follow-up imaging.Results. Forty-seven patients with 97 tumors underwent 64 RFA procedures (39 patients/63 tumors open RFA, 25 patients/34 tumours CT-targeted RFA, 12 patients underwent >1 RFA). Images of 52 (54%) ablation sites were classified as SiPS-id, 45 (46%) as SiPS-diff. Index-tumor size, tumor location and number, concomitant partial hepatectomy, and RFA approach did not influence the SiPS. ASR developed in 11/47 (23%) patients and 20/97 (21%) tumours. ASR occurred less frequently after open RFA than after CT targeted RFA (P<0.001). ASR was associated with larger index-tumour size (18.9 versus 12.8 mm,P=0.011). Cox proportional hazard model confirmed SiPS-diff, index-tumour size >20 mm and CT-targeted RFA as independent risk factors for ASR.Conclusion. Variation in anatomical concordance between preablation and postablation images, index-tumor size, and a CT-targeted approach are risk factors for ASR in CRLM.