MR robot guided prostate biopsy: a pilot study

In 2005, prostaatcancer was with 8.800 new cases the most common form of cancer
in men in the Netherlands. Today, in regular clinical practice prostate
biopsies are performed under transrectal ultrasound (TRUS) guidance. Even
though the traditional ultrasound appearance of prostate cancer is a hypoechoic
lesion, other conditions such as prostatitis and prostatic intraepithelial
neoplasia may also present as hypoechoic lesions. Initial detection of prostate
cancer rates for extended schemes range between 22% and 44%.
Image guided biopsies towards tumor suspicious regions have been advocated to
improve tumor detection. MR imaging, with its higher tumor detection ability,
has been used to direct biopsies both under TRUS and MR guidance. Experience of
using MR guided biopsy devices at 1.5T, to biopsy tumor suspicious regions on
anatomical T2-weighted MR images, has been previously published. Robotics is a
new field in medicine due to stringent safety criteria. Robots are most often
used in minimally invasive procedures, such as cardiac, bladder, prostate, and
neurosurgery.
Robotic assistance for MR-guided interventions with the prostate has been
investigated at several institutions. Most robots have a manual positioning
system, which means that the patient has to be removed from the scanner in
order to correct the position. The department of Radiology of the Radboud
University Nijmegen Medical Centre (RUNMC) has conceptualized, tested (bench),
and manufactured a fully MR imaging- compatible robotic system designed to
perform MR imaging-guided transrectal needle intervention of the prostate. This
MR-compatible robotic device uses a pneumatic mechanism, which can be
controlled next to the MR console.

The purpose of our study is to prospectively establish in vivo in patients
proof of principle for the RUNMC MR imaging-compatible robotic system designed
for image-guided prostatic needle intervention.

Prospective, non-randomized, single centre pilot study. Twenty patients will be
included in this pilot study.

The robotic system consists of the robot and its controller unit. The
controller unit includes a computer, motion control elements, a series of
electropneumatic interfaces, and a software package. It is located outside the
MR imaging room and is connected to the robot by plastic hoses, which are 10 m
in length and carry air wires. The robot itself fits into a standard
closed-bore MR imager, and it is designed to interact with the patient within
the imager. To achieve full MR imaging compatibility, the entire robot is built
of nonmagnetic and dielectric materials, such as plastics and rubber.
Furthermore, a pneumatic actuator was specifically developed for this
application. The pneumatic motor achieves high precision in a safe and easily
controllable manner. Pressure waves are used to set the motors in motion. These
waves are created by a pneumatic distributor remotely located in the controller
unit and are transmitted to the robot through the plastic hoses. The motors use
solely pressured air but no electricity whatsoever. These features prevent the
robot from creating any interference with the electromagnetic environment
inherent to MR imaging technology. To meet standard safety requirements for the
use in medical applications, the robot's motors are designed for fail-safe
operation. Any form of malfunction leads to a lock and cannot result in
uncontrolled motion. The motors provide the robot with six degrees of freedom
to place and orient an end effector as desired. The end effector is easily
detachable from the robot and could be replaced with other end effectors (for
other percutaneous interventions) in the future. The needle guide is connected
to the robotic arm.

The device poses no risk for the patient. During manipulation of the biopsy
robot the mechanical construction will prevent any possible harm for the
patient. The pneumatic motor allows for easily controllable motion with
fail-safe operation. Furthermore, the needle guide has a fail-safe mechanism as
well. The biopsy itself will be performed by an experienced radiologist.

MR imaging may cause some discomfort, such as feelings of claustrophobia due to
loud sounds of the MR instrument during the study. Patients are screened for
prior claustrophobic symptoms using the same screening form described above to
search for metal device and foreign bodies. Earplugs are provided to all
patients in order to minimize the discomfort related to the loud noise.
When the biopsy is performed without anesthesia, 65% to 90% of men report mild
to severe pain. Patients receiving lidocaine anesthesia report a mean pain
score of 1.6 to 2.4 (0 to 10, 0 = no pain and 10 = worst pain). A topical
anesthetic gel will be applied as lubricant at the time of the prostate biopsy.