Noninvasive Real-Time Prostate Tracking Using a Transperineal Ultrasound: A Clinical Trial Comparison to RF Transponders With Visual Confirmation

Abstract

Interfraction image guidance in the management of prostate cancer reduces uncertainty and has become standard of care. More recently, real-time fiducial/transponder tracking to further reduce uncertainty from intrafraction target motion has become available, but these techniques require an invasive procedure. A noninvasive transperineal ultrasound system using rigid structure registration (4DTPUS) has been developed to account for interfraction, as well as intrafraction motion. This technique has potential advantages over historic ultrasound-based interfraction adjustments. The 4DTPUS is less affected by user variability, abdominal pressure, approach, anatomy, bowel gas, and bladder filling. As older ultrasound techniques were transabdominal, they were not amenable to real-time tracking. Our objective was to validate the 4DTPUS accuracy of tracking using visual confirmation and a comparison of tracking to RF transponders. Seven patients were accrued to an IRB approved prospective clinical study where RF transponders were implanted and patients treated per institutional standard of care for biopsy proven prostate cancer. The 4DTPUS data was collected during each radiation treatment fraction for direct comparison of 3D motion of the prostate. In addition, visual tracking of the prostate by 4DTPUS was reviewed by 3 attending physicians who independently rated each ultrasound series on a score of 1-5 with 1 being the best. There was high concordance between 4DTPUS and RF transponder tracking of the prostate. Twenty-eight fractions were usable for the comparative analysis at the time of this report with a total of 188 minutes. The root mean square difference and standard deviation of the tracking for the 2 systems was 0.2 +/- 0.55 mm in the sup/inf, 0.1 +/- 0.4 mm in the left/right and 0.1 +/- 0.8 mm in the ant/post dimensions. The number of fractions that were analyzable was limited due to artifact in the ultrasound images caused by the RF transponder system. The 4DTPUS was visually reviewed for 364 minutes of patient treatment over 62 fractions. The average visual correlation was scored as 1.21. The majority of these fractions included some artifact from the transponders that did affect the 4DTPUS image quality. A fraction was only excluded if complete data for transponders and/or 4DTPUS was unavailable or if synchronization of the data could not be performed. A novel 4D transperineal ultrasound system accurately and reproducibly tracked prostate motion in patients. Visual confirmation of prostate tracking was excellent. Transperineal ultrasound tracking of the prostate offers a noninvasive alternative to currently available marker-based systems.