Magnetic resonance imaging-transectal ultrasound image-fusion biopsies accurately characterize the index tumor: correlation with step-sectioned radical prostatectomy specimens in 135 patients

Abstract

Background: Prostate biopsies targeted by elastic fusion of magnetic resonance (MR) and three-dimensional (3D) transrectal ultrasound (TRUS) images may allow accurate identification of the index tumor (IT), defined as the lesion with the highest Gleason score or the largest volume or extraprostatic extension.

Objective: To determine the accuracy of MR-TRUS image-fusion biopsy in characterizing ITs, as confirmed by correlation with step-sectioned radical prostatectomy (RP) specimens.

Design, setting, and participants: Retrospective analysis of 135 consecutive patients who sequentially underwent pre-biopsy MR, MR-TRUS image-fusion biopsy, and robotic RP at two centers between January 2010 and September 2013.

Intervention: Image-guided biopsies of MR-suspected IT lesions were performed with tracking via real-time 3D TRUS. The largest geographically distinct cancer focus (IT lesion) was independently registered on step-sectioned RP specimens.

Outcome measurements and statistical analysis: A validated schema comprising 27 regions of interest was used to identify the IT center location on MR images and in RP specimens, as well as the location of the midpoint of the biopsy trajectory, and variables were correlated.

Results and limitations: The concordance between IT location on biopsy and RP specimens was 95% (128/135). The coefficient for correlation between IT volume on MRI and histology was r=0.663 (p<0.001). The maximum cancer core length on biopsy was weakly correlated with RP tumor volume (r=0.466, p<0.001). The concordance of primary Gleason pattern between targeted biopsy and RP specimens was 90% (115/128; κ=0.76). The study limitations include retrospective evaluation of a selected patient population, which limits the generalizability of the results.

Conclusion: Use of MR-TRUS image fusion to guide prostate biopsies reliably identified the location and primary Gleason pattern of the IT lesion in >90% of patients, but showed limited ability to predict cancer volume, as confirmed by step-sectioned RP specimens.

Patient summary: Biopsies targeted using magnetic resonance images combined with real-time three-dimensional transrectal ultrasound allowed us to reliably identify the spatial location of the most important tumor in prostate cancer and characterize its aggressiveness.

Keywords: Biopsy; Cancer volume; Gleason score; Image fusion; Index tumor; Location; Magnetic resonance imaging; Prostate cancer; Radical prostatectomy; Ultrasound.