Shear wave elastography for detection of prostate cancer: a preliminary study

Abstract

Objective: To assess the diagnostic value of shear wave elastography (SWE) for prostate cancer detection.

Materials and methods: In this retrospective study, 87 patients with the suspicion of prostate cancer (prostate-specific antigen > 4 ng/mL and abnormal digital rectal examination) underwent a protocol-based systematic 12-core biopsy followed by targeted biopsy at hypoechoic areas on grey-scale ultrasound. Prior to biopsy, SWE was performed by placing two circular 5 mm-sized regions of interest (ROIs) along the estimated biopsy tract in each sector and one ROI for hypoechoic lesions. SWE parameters, S (mean stiffness) and R (mean stiffness ratio), were calculated and compared regarding different histopathologic tissues and their accuracy for diagnosing prostate cancer was analyzed. SWE parameters were correlated with Gleason score and were compared between indolent (< 8) and aggressive (≥ 8) tissues in prostate cancer patients.

Results: Prostate cancer was detected in 7.5% of 1058 cores in 29.9% of 87 patients. Seven (43.8%) of 16 hypoechoic lesions were confirmed as prostate cancer. SWE parameters were significantly different among the histopathologic entities (p < 0.001). Prostate cancer was stiffer than benign tissues (p ≤ 0.003). Sensitivity, specificity and receiver operating characteristic curve area for diagnosing cancer were 43%, 80.8%, and 0.599, respectively, for a cutoff of S > 43.9 kPa and 60.8%, 66.4%, and 0.653, respectively, for R > 3. Both, S and R showed a significant correlation with Gleason score (r ≥ 0.296, p ≤ 0.008) and were significantly different between indolent and aggressive prostate cancer (p ≤ 0.006).

Conclusion: Shear wave elastographic parameters are significantly different between prostate cancer and benign prostate tissue and correlate with Gleason score.

Keywords: Gleason score; Prostate cancer; Shear wave elastography; Ultrasonography; Young modulus.

Fig. 1

Distribution of 12 sectors for systematic 12-core biopsy and acquisition of shear wave elastographic (SWE) parameters. A. Twelve systematic cores consisting of paramedian (1-6) and lateral (7-12) cores from base, mid-level and apex at each side of prostate gland. Image on lower right is representative axial slice at mid-level of prostate gland which is demonstrated as with line traversing schematic drawing of prostate on left. B, C. SWE images acquired in 57-year-old man demonstrate total of four 5-mm-sized regions of interest (ROI), two each at paramedian and lateral sectors, placed along estimated path of core biopsy at left (B) and right (C) prostate glands. Left upper paramedian ROI demonstrates higher stiffness (red color) than surrounding prostate tissue (blue color) in left lateral and right areas. Quantitative SWE parameters of this sector were 52.9 kPa and 6.4 for S and R, respectively. Upon 12-core biopsy, this area was confirmed as prostate cancer with Gleason score of 7.

Fig. 2

80-year-old man with prostate cancer in focal lesion with hypoechogenicity and elevated stiffness on shear wave elastography. A. After acquisition of shear wave elastographic images, region of interest was placed at and around focal lesion with hypoechogenicity compared with surrounding prostate gland. After three region of interest measurements, mean S and R were 191.2 kPa and 11.2, respectively. B. Dotted line shows needle guide for real-time biopsy targeted at focal lesion which was confirmed as prostate cancer with Gleason score of 7 at pathology.

Fig. 3

Shear wave elastographic parameters according to histopathology. Shear wave elastographic parameters were significantly different between prostate cancer and benign prostatic tissue. Mean S and R values were 54.6 kPa and 6.0 for prostate cancer, and 33.4 kPa and 3.1 for benign prostate tissues (p < 0.001 and p = 0.003 for S and R) respectively. Mean stiffness (S) = mean value of Young' modulus measured from two regions of interest placed along estimated path for core biopsy for each of 12 sectors. Mean stiffness ratio (R) = ratio of S of sector to that of lowest S of patient.

Fig. 4

Receiver operating characteristic curve analyses in differentiation of benign and malignant prostate tissue using shear wave elastography parameters. Prostate cancer could be predicted with sensitivity and specificity of 43.0% (95% confidence interval [CI], 31.9-54.7%) and 80.8% (95% CI, 78.2-83.2%) using cutoff value of S > 43.9 kPa (area under the curve [AUC] = 0.599; 95% CI, 0.569-0.629) and those of 60.8% (95% CI, 49.1-71.6) and 66.4% (95% CI, 63.3-69.4) with cutoff value of R > 3 (AUC = 0.653, 95% CI, 0.624-0.682). Mean stiffness (S) = mean value of Young' modulus measured from two regions of interest placed along estimated path for core biopsy for each of 12 sectors. Mean stiffness ratio (R) = ratio of S of sector to that of lowest S of patient.

Fig. 5

80-year-old man with prostate cancer in focal lesion in peripheral zone with elevated stiffness on shear wave elastography but negative findings on grey-scale ultrasound. Focal lesion in peripheral zone at left lateral base demonstrated with persistent elevated stiffness but without abnormal finding on grey-scale ultrasound. S and R were calculated to be 29.2 kPa and 2.6. It was confirmed as prostate cancer on histopathology.