Conventional ultrasound systems operate at 6-9 MHz and serve as standard of care for guiding 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 risk of prostatic carcinoma and enable real-time targeted biopsies.
The system (ExactVu™, Exact Imaging, Toronto, ON) is currently being used in a multi-site 2,000 patient randomized clinical trial. Cine loops of 400 biopsies from this trial were used to create the PRI-MUS™ protocol and risk scale. Validation was performed on an independent, pathology-blinded set of 100 cines. 3 of the 5 investigators performing this validation were familiar with micro-ultrasound but naïve to the PRI-MUS protocol and received only 1 hour of training.
Each increase in risk score demonstrated a 10.1% [95% CI 9.3 - 10.8%] increase in probability of clinically significant cancer. Risk score also increased with Gleason Sum and cancer length with slopes of 0.15 [0.09-0.21] and 0.58 [0.43-0.73], respectively. Sensitivity and specificity were 80% and 37% with area under the ROC curve of 60±2%. The protocol was more accurate in detection of high grade disease (GS >7), with a peak AUC of 74% (mean 66%).
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 protocol's improved performance in more significant disease is consistent with the field's focus on reducing insignificant diagnoses and detecting high risk disease early.