Evaluation of Prostate Cancer Detection with Ultrasound Real-Time Elastography: A Comparison with Step Section Pathological Analysis after Radical Prostatectomy

Abstract

Background

Conventional gray scale ultrasound has a low sensitivity and specificity for prostate cancer detection. Better imaging modalities are needed.

Objective

To determine sensitivity and specificity for prostate cancer detection with ultrasound-based real-time elastography (elastography) in patients scheduled for radical prostatectomy (RP).

Design, Setting, and Participants

Between July and October 2007, 109 patients with biopsy-proven localized prostate cancer (PCa) underwent elastography before RP. The investigator was blinded to clinical data.

Measurements

A EUB-6500HV ultrasound system with a V53W 7.5 MHz end-fire transrectal probe was used preoperatively. Areas found to be suspicious for PCa were recorded for left and right side of the apex, mid-gland, and base. These findings were correlated with the obtained whole-mount sections after RP.

Results and Limitations

Sensitivity and specificity for detecting PCa were 75.4% and 76.6%, respectively. A total of 439 suspicious areas in elastography were recorded, and 451 cancerous areas were found in the RP specimens. Positive predictive value, negative predictive value, and accuracy for elastography were 87.8%, 59%, and 76%, respectively. Nevertheless, there are limitations to our studies because we investigated specific patients scheduled for RP with apparent PCa. Whether elastography is practical as a diagnostic tool or can be used to target a biopsy and be at least as sensitive in tumor detection as extended biopsy schemes has yet to be determined.

Conclusion

Elastography can detect prostate cancer foci within the prostate with good accuracy and has potential to increase ultrasound-based PCa detection. Further studies need to be done to approve these data and to evaluate whether tumor detection can be increased by elastography-guided biopsies.

Introduction

The use of prostate-specific antigen (PSA) as a diagnostic and screening tool has led to a significant rise in the number of patients undergoing prostate biopsy. However the specificity of the PSA test is low [1], [2]. Furthermore, because of the intensive PSA testing, in recent years prostate tumors have become drastically reduced in size [3] and only a small portion of the prostate is sampled by biopsies. Hence repeat biopsies are often taken; these biopsies have a relatively poor negative predictive value (NPV) with a detection rate of less than 20% [4].

Conventional gray-scale ultrasound has a low sensitivity and specificity for prostate cancer (PCa) detection. It is useful to guide biopsies but insufficient as a screening tool. Thus, an improved imaging modality for PCa detection using targeted biopsies is needed.

Ultrasound-based real-time elastography imaging is a new technique that visualizes the differences in tissue strain produced by freehand compression [5]. Using elastography, the investigator is able to discriminate hard from soft tissue regions within the prostate. The phenomenon is based on the fact that the back-scattered ultrasound signals undergo displacement if the tissue is slightly compressed or decompressed (ie, approximately 2%). Stiffer tissues show less displacement than normal soft tissues (Fig. 1a). For visualization, stiffness values are marked in different colors and are shown in real-time images (Fig. 1b). Following the hypothesis that solid tumors differ in their consistency compared with the adjacent normal tissue, elastography has been investigated as a novel tool for detecting PCa. Promising results have been recently reported in small cohorts [6], [7], [8].

The goal of this study was to assess the value of elastography for localizing PCa in a selected, larger cohort of patients scheduled for radical prostatectomy (RP) by comparing results of the elastogram with PCa foci in whole-mount sections. In addition it was of interest to see whether elastography is feasible in daily routine.