Internal Landmarks of the prostate in transrectal ultrasound as basis for long-term monitoring and targeted biopsy : an observational study

To monitor prostatic tissue changes (Trend Monitoring) and perform authentic targeted biopsy, it is essential to reliably identify the same region of interest (ROI) of the prostate and hit targets in their true anatomical locations over time. Transrectal ultrasound (TRUS) identifiable morphologic structures including calcifications, cysts or anatomical fix-points are utilized as natural anchor points (Internal Landmarks) to facilitate exact imaging correlation, and this technique is termed as “Internal Fusion”. This study analyses the feasibility and accuracy of Internal Landmarks. From January 2017 to May 2018, 164 patients with at least one prior series of 5-mm spaced TRUS images analyzed by artificial intelligence algorithm and stored as computed tomographic online data set (AI-US-CT) were included. Operators collected new TRUS images in one-to-one correlation with each prostate cross-section of the previous examinations based on Internal Landmarks and targeted biopsies were taken if with indication. Overall, 1846 Internal Landmarks were utilized as anchor points during Trend Monitoring, including prostatic calcifications (1128, 62%), cysts (524, 28%), seminal colliculus (133, 7%) and others (61, 3%). Basing on re-locating of Internal Landmarks, accurate correlations were attained in 1021 out of 1090 TRUS slices (94%), after years, despite volume changes. The longest Trend Monitoring with exact image correlation had so far reached 9 years and 5 months. Internal Landmarks are of vital importance to exact image correlation in long-term monitoring of the prostate. Trend Monitoring by ANNA/C-TRUS could possibly offer a new opportunity not only in continuous observation of prostatic natural change or disease progression by imaging as a complement to longitudinal PSA, but also to perform per-lesion-based active surveillance or focal therapy. In case of PCa suspicion, Internal Fusion helps targeted biopsies in high accuracy with less biopsy cores.