Developing a coordinate-based strategy to support cognitive targeted prostate biopsies and correlative spatial-histopathological outcome analysis

Abstract

Lack of investment for magnetic resonance (MR) fusion systems is an obstacle to deliver targeted prostate biopsies within the prostate cancer diagnostic pathway. We developed a coordinate-based method to support cognitive targeted prostate biopsies and then performed an audit on cancer detection and the location of lesions. In each patient, the prostate is considered as two separate hemiprostates, and each hemiprostate is divided into 4 × 4 × 4 units. Each unit is therefore defined by a three-dimensional coordinate. We prospectively applied our coordinates approach to target 106 prostatic lesions in 93 men. Among 45 (of 106; 42.5%) lesions positive for cancer, 27 lesions (60.0%) harbored clinically significant disease. PSA density was significantly higher in patients with proven cancer (median: 0.264 ng ml^-2) when compared to the noncancer group (median: 0.145 ng ml^-2; P = 0.003, Wilcoxon rank-sum test). Lesions with Prostate Imaging-Reporting and Data System (PIRADS) score of 5 were found to have a cancer incidence of 65.2%, while PIRADS 4 and 3 lesions have a lower risk of cancer detection, as expected, at 37.3% and 31.3%, respectively. The probability of a lesion being cancerous in our series significantly decreases as we go from the "apex-to-base" dimension (odds ratio [OR]: 2.62, 95% confidence interval [CI]: 1.55-4.44, P = 0.00034). Our analysis also indicates that the probability of cancer decreases as the prostate volume increases (OR: 1.03, 95% CI: 1.01-1.05, P = 0.00327). Based on this feasibility study, the use of coordinates to guide cognitive targeted prostate biopsies warrants future validation study in additional centers.

Keywords: cognitive targeted prostate biopsies; coordinates; magnetic resonance imaging; prostate cancer.

Figure 1

Cross-sectional view of the three-dimensional coordinate system that is used to target lesions of interest. (a) Cartoon illustrates the coordinate system. (b) Images from transrectal ultrasound scan to highlight the coordinates in each of the three axes. The X-axis is oriented laterally, with +1 to +4 denoting lesions on the right-hand-side of the midline and −1 to −4 denoting lesions on the left-hand-side of the midline. The Y-axis is oriented longitudinally, with 1 denoting the apex of the gland and 4 denoting the base of the gland. The Z-axis is oriented such that 1 denotes the posterior region of the gland and 4 denotes the anterior region of the gland. Note that the scale of each axis varies depending on the size of the prostate. R: right; L: left.

Figure 2

Box and Whisker plot summarizing the analysis of PSA density between cancer and noncancer groups. PSA density is significantly greater in patients with targeted biopsy proven cancer (median: 0.264 ng ml⁻², IQR: 0.240), when compared to noncancer group (median: 0.140 ng ml⁻², IQR: 0.116; P = 0.003, Wilcoxon rank-sum test). In the Box and Whisker diagram, the middle band represents the median value, the upper and lower box represents the upper and lower quartiles, whiskers extend from the upper and lower quartiles by 1.5× the interquartile range, individual patients are also plotted as solid black points overlaid on the boxplots. PSA: prostate-specific antigen; IQR: interquartile range.

Figure 3

Marginal distribution of lesions for the (a) XY plane, (b) XZ plane, and (c) YZ plane, where we see that the more lesions cover the central area of the X and Y axes, and the higher area of the Z-axis. We also include marginal distributions for the proportion of lesions that are cancerous in the (d) XY plane, (e) XZ plane, and (f) YZ plane. Note that there appears to be a possible trend along the Y-axis, with lower values of Y possibly corresponding to a higher proportion of cancerous lesions. X: midline to lateral for right and left of the prostate; Y: apex to base of the prostate; Z: posterior to anterior of the prostate. Therefore, XY plane signifies the transverse plane, XZ plane refers to coronal (frontal) plane, and YZ plane represents sagittal. R: right; L: left.