Deflection Analysis of Different Needle Designs for Prostate Biopsy and Focal Therapy

The biopsy needles currently used were designed for a transrectal biopsy and are known to experience significant deflection from the point of entry into the gland to the needle tip.

Five designs were selected for testing: 18-gauge Bard, 15-gauge lancet tip needle with 12° vet-point cannula, and trocar tip needle with 12°, 15°, and 20° vet-point cannulas. The 15-gauge needle was designed to take a variable specimen sample between 20 and 60 mm, whereas the Bard needle specimen bed was fixed at 20 mm. The needles were bench tested on a spring-loaded platform and fired into gelatin matrix with modulus of elasticity similar to human prostate.

The Bard device with lancet tip needle deflected an average of 0.9 mm (range 0.3-1.3 mm) and 1.9° (range 0.6°-2.8°). Increasing needle diameter from 18-gauge Bard to 15-gauge variable with the same lancet tip needle design resulted in an average deflection across the 3 test lengths of 0.9 mm (range 0-2.0 mm) and 0.9° (range 0°-2.0°) with no significant difference. On the contrary, the use of the 3-point trocar tip needles with 12°, 15°, and 20° vet-point cannulas demonstrated significant reduction in the extent of deflection in both millimeters and degrees. There was no deflection at the 2- and 4-cm shots for both spring loads and preloads for the 3 vet tip angles tested. At 6 cm, the 20° vet tip performed the best.

We proposed a mechanism that provides more accurate prostate sampling by combining a 3-point trocar tip on the needle with a 20° vet tip on the cutting cannula. Using the phantom, mimicking prostate gland tissue density, no deflection was revealed between 20- and 60-mm biopsy lengths, which should permit a straight sample in the majority of prostate glands and improve cancer localization for focal therapy planning.

Technology in cancer research & treatment. 2016 [Epub ahead of print]

Nelson N Stone, Vladimir Mouraviev, David Schechter, Josh Goetz, M Scott Lucia, E Erin Smith, E David Crawford

Department of Urology and Radiation Oncology, The Icahn School of Medicine at Mount Sinai, Mount Sinai, NY, USA ., Department of Urology, Bladder Health and Reconstructive Institute, Memorial Hospital Miramar, Miramar, FL, USA., Vention Medical, Boulder, CO, USA., Department of Pathology, University of Colorado Anschutz Medical Campus in Aurora, Aurora, CO, USA., Department of Urology, University of Colorado Anschutz Medical Campus in Aurora, Aurora, CO, USA.