Assessing Cancer Risk on Novel 29 MHz Micro-Ultrasound Images of the Prostate: Creation of the Micro-Ultrasound Protocol for Prostate Risk Identification

Purpose: Conventional ultrasound systems operate at 6 to 9 MHz and serve as the standard of care to guide prostate biopsies. We present a protocol using a novel high resolution (29 MHz) transrectal prostate micro-ultrasound system. This protocol includes a scoring system to assess the risk of prostatic carcinoma and enable real-time targeted biopsies. Materials and Methods: The ExactVu (TM) system is currently being used in a multisite, 2,000-patient, randomized clinical trial. Cine loops of 400 biopsies from this trial were used to create the PRI-MUS (TM) (prostate risk identification using micro-ultrasound) protocol and risk scale. Validation was performed in an independent, pathology blinded set of 100 cines. Three of the 5 investigators performing this validation were familiar with micro-ultrasound but naive to the PRI-MUS protocol and they received only 1 hour of training. Results: Each increase in risk score demonstrated a 10.1% increase (95% CI 9.3-10.8) in the probability of clinically significant cancer. The risk score also increased with Gleason sum and cancer length with a slope of 0.15 (95% CI 0.09-0.21) and 0.58 (95% CI 0.43-0.73), respectively. Sensitivity and specificity were 80% and 37%, respectively, and the mean +/- SD ROC AUC was 60% +/- 2%. The protocol was more accurate for detecting high grade disease (Gleason sum greater than 7) with a peak AUC of 74% (mean 66%). Conclusions: The new resolution of the micro-ultrasound platform paired with the PRI-MUS protocol shows promise for real-time visualization of suspicious lesions and targeting of biopsies. The improved performance of the protocol in more significant disease is consistent with the focus of the field on decreasing insignificant diagnoses and detecting high risk disease early.