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

Abstract

Objective: 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. Methods: 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. Results: 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. Conclusion: 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.

End‐user evaluation of software‐generated intervention planning environment for transrectal magnetic resonance‐guided prostate biopsies

“…While inserting the needle in the tissue, deflection of the needle cannot be avoided but can be reduced by following certain approaches 30 . Stone et al achieved no deflection in 2–6 cm of biopsy tissue length on a phantom by using a 3‐point trocar tip on the needle with a 20° vet tip on the cutting cannula 31 . Another potential approach, though demonstrated in transperineal prostate interventions, involves a robot controlling the pose of the needle guide, and the needle is continuously sensed 32,33 and steered 34 while being inserted to minimize the deflection.…”

Prostate Cancer Diagnosis: Biopsy Approaches

“…Biopsy core length improves quality of tissue and sensitivity for diagnosis with suggestion that 12 mm is the minimum length required, whereas needle diameter does not appear to improve prostate cancer detection rates (66)(67)(68)(69)(70)(71). Most biopsy guns are designed to obtain standard core lengths of 20 mm, some devices have been designed to take longer cores, though longer needles have an increased risk of deflection and therefore potentially lower sampling accuracy (72,73).…”