Note: Descriptions are shown in the official language in which they were submitted.
CA 02565040 2006-10-20
APPARATUS AND METHOD FOR POSITIONING AND ORIENTATION OF
MEDICAL INSTRUMENTS.
FIELD OF THE INVENTION
This invention relates to an apparatus and mcthod for positioning, orientation
and
insertion of a medical instrument. More specifically this application relates
to an
apparatus that enables positioning, orientation and insertion of medical
instrument~ such
as needles or laser sources.
BACKGROUND
On average 2,944 Canadians will be diagnosed with cancer every week, of that
an
average of 1,354 Canadians will die of it every week. Based on the current
incidence
rates, 38% of Canadian women will develop cancer during their lifetimes, and a
staggering 44% of men.
One nzethod for treating certain cancers is to use internal or interstitial
radiation
therapy, or seed therapy, in which a radioactive implant is placed directly
into a
tumor. It involves surgical insertion of radiation source (radioactive seeds)
into the
treatment volume through tubular needles. Tubular needles loaded with
radioactive seeds
are inserted into the treatincnt volume, after which the radioactive seeds are
left in the
treatinent volunle, either permanently or for a specified amount of time.
This method is called brachytherapy. Bracllytherapy is used to treat various
types of
cancer throughout the human body, including the prostate, breast, cervix, and
lungs.
Docuinented brachytherapy procedure is perforined manually: thc surgeon
inserts
brachytllerapy needles into the cancerous tissue by hand, pushing them through
holes in
a specially prepared grid template (illustrated in Figure 1).
US patent 6, 398, 711 by Green et al. teaches the use of such a needle grid
template.
US patent 6, 540, 656 by Fontayne et al. discusses a targeting fixture again
making use
of a grid template. But this fixture can only provide 2-dimensional,
translatoiy
positioning of the instrument before insertion.
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Another instrument making use of the grid template is illustratcd in PCT
application
W098/56295 by Fanucci.
The main drawback of the manual procedure is that it is slow and not very
accurate. The
distance between two adjacent holes in the grid template limits achievable
accuracy of
needle tip placement. Further, as the holes in the grid template are long
(compared with
their diameter) and all parallel to each other, oblique trajectories of needle
insertion are
not achievable. To compensate for this, the surgeon would typically press the
needle by
hand from a side and/or rotate it during insertion. The surgeon does this
while
monitoring the actual position of the needle in a real-time image (typically
collected by
transrectal ultrasound imaging system) so the overall procedure is involved,
requires
extensive training, and takes time.
An emerging modality is the use of a robotic manipulator and a special end-
effector
called "iieedle driver" to perform the procedure (Figure 2). In robot-based
systems, the
robot is used to achieve quick and precise positioning and orientation of the
needle
driver (together with the brachytherapy needle that it holds). Once the
specified position
and orientation are achieved, the needle driver pushes the needle into the
cancerous
tissue. To increase the accuracy of the needle tip reaching the specified
point inside the
treatment volume, the needle may also be rotated along its axis during the
insertion. Both
the axial and rotary motion of the needle are driven by the needle driver.
Robot-based systems resolve somc of the problems associated with manual
brachytherapy such as the coarse spacing among the holes in a grid template
and they
allow for oblique insertion trajectories. However, they have some drawbacks of
their
own:
- The robot takes a lot of space, it gets into surgcon's way, and its presence
and motion can be intimidating to medical personnel involvcd in the
procedure.
- Integrating the robot with the rest of the brachytherapy systcm
(particularly
the ultrasound imaging system) is difficult as the robot is physically
detached
CA 02565040 2006-10-20
from the rest of the system. The intcgration requires precise mounting of the
robot as well as calibration of the complete system.
- The robot-based system is complex and the medical team needs extensive
training to learn how to use it.
- Typically the robot has a large working area which can be hazardous (for
example, it can hit the patient and/or surgeon if a large move is commanded
by accident). Therefore the size of the robot's workspace has to be
constrained by some safe means (typically by mechanical means).
The needs highlighted above are mostly for brachytherapy systems, but there
are other
medical instruments which require precise positioning and orientation. For
example the
proper positioning of a high-power laser source used for the treatment of
enlarged
prostate in a procedure termed benign prostate hyperplasia (BPH) is also
needed.
SUMMARY OF THE INVENTION
It is an object of the invention to offer an apparatus that provides precise
positioning and
orientation of a medical instrument.
It is anothel- object of the invention to achievc oblique trajectories for a
medical
instrument; making it possible to attain hard to reach places.
It is anothet- object of the invention to offer a less obtrusive apparatus,
leaving space for
the surgeon and medical staff to access the operating site.
It is another object of the invention to offer an apparatus which can be
integrated with
existing medical systems.
These and other objccts of the invention are accomplished by an apparatus for
the
positioning and orientating of a medical instrument, comprising a first
pentagonal
mechanism which offers two degrees offrcedom, and a second pcntagonal
mechanism
which offers three degrees of freedom of motion. The two are aligned along a
first axis
so as to pei7nit them to hold an instrument driving means.
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The instrument driving means is adapted to hold a medical instrument and
adapted to
permit said instrument to move along and rotate on its own axis. The
instrument driving
means offers another two degrees of freedom of motion. The apparatus is thus
provided
with a total of six degrees of freedom.
SHORT DESCRIPTION OF THE FIGURES
Figure 1(prior art) illustrates an embodiment of a brachytherapy method using
a manual
procedure
Figure 2(prior art) illustrates an embodiment of brachytherapy method using a
roboi
Figure 3 illustrates an embodiment of the apparatus for positioning and
orienting a
medical device
DETAILED DESCRIPTION OF THE INVENTION
This invention proposes the replacement of the serial-linkage robot with a
specially
designed parallel-kineinatics mechanism. The parallel-kinematics mechanism is
designed as a compact device that is easy to integrate with the rest of the
inedical
systems (for example, it can be pennanently integrated with the brachystepper
mcchanism used for support and positioning of the ultrasound imaging probe).
Furthermore, the size of its workspace is easily kept within desired limits by
the design
of its linkages, which significantly reduces hazards associated with the use
of actuated
dcvices in brachytherapy procedures.
An embodiment of this invention is illustrated in figure 3. It illustrates an
apparatus for
positioning and oricntating a medical instrument. The apparatus offers a total
of six
degrees of freedom which allow for the maneuverability and precision sought
after in
medical intcrvcntions.
Illustrated is a first and a second pentagonal mechanism (4 and 6
respectively) fixed to a
base (2). The first pcntagonal mechanism offers two degrees of freedom and the
second
pentagonal mechanism oiTers three degrees of fi-eedom of motion.
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The first pentagonal mechanism defines a first axis through it's center,
illustrated in
Figure 3 as the z axis. The first and the second pentagonal mechanisms are
aligned
along said first axis. (This is just to introduce axis z)
Attached to the first (4) and the second (6) pentagonal mechanism is an
instrument
driving means (8). The instrument driving means is adapted to hold a medical
instrument
and is adapted to permit the instrument to move along and rotate on its own
axis; the
instrument's axis is illustrated in figure 3 as the w axis.
The first pentagonal mechanism (4) consists of four bars assembled so as to
permit
movement of the pentagonal mechanism in two degrees of freedom.
It (4) is connected to the base (2) by two actuated joints (26 and 28). The
first bar (10) is
connected to the first actuated joint (26). The other end of the first bar
(10) is connected
to the second bar (12) by a passive revolute joint (34). The other end of the
second bar is
connected to the third bai- (14) by a second passive revolute joint (36). The
other end of
the third bar (14) is connected to the fourtli bar (16) by a third passive
revolute joint (38).
And finally the other end of the fourth bar is connected to the base by a
second actuated
joint (28).
The first (26) and the second (28) actuated joints can be driven by a first
(54) and a
second (56) driving means.
The second pentagonal mechanism (6) consists of four bars assembled so as to
permit
movement of the pentagonal mechanism in three degrees of freedom.
The second pentagonal mechanism (6) is connected to the base (2) by two
actuated joints
(30 and 32). The fifth bar (18) is connected to the third actuated joint (30).
The other end
of the fifth bar (18) is connected to the sixth bar (20) by a passive
universal joint (42).
The other end of the sixth bar (20) is connected to the seventh bar (22) by a
passive
revolute joint (40). The other end of the seventh bar (22) is connected to the
eighth bar
(24) by a second passive univetsal joint (44). And finally the other end of
the eighth bar
(24) is connected to the base (2) by a fourth actuated joint (32).
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The third (30) and the fourth (32) actuated joints can be driven by a third
(58) and a
fourth (60) driving means.
The shape of the bars that constitute the first and second pentagonal
mechanism can be
adjusted so as to suite requirements of any particular application. They can
be curved
("curved" is more suitable in geometrical sense) as illustrated in Figure 3,
but they could
also be straight, or any other shape to suite the requirements.
The instrument driving means (8) comprises an instrument holding means. The
instrument holding means is adapted to hold instruments such as needles,
lasers and
other suitable devices. The instrument illustrated in Figure 3 is a
brachytherapy needle
(70).
It comprises a first connection means to connect it to the first pentagonal
mechanism. In
one embodiment of the invention two revolute joints are used (46 and 48). In
another
embodiment the first connection means could be designcd as a suitably
positioned
universal joint.
It also comprises a second connection means to connect it to the second
pentagonal
mechanism so as to permit rotation in all directions. In one embodiment of the
invention
a spherical joint is uscd (50).
It also comprises an instt-ument moving means, which moves the instrument
holding
means along the instrument's axis, and an instrument rotating means, to permit
the
instrument to rotate on its axis (illustrated in figure 3 as w axis).
The instrument moving means (62) and the instrument rotating means (64) can be
driven
by a fifth (66) and a sixth drivitig mcans (68). The fiftll driving means will
cause the
instrumcnt to move along the w axis and the sixth driving means will cause the
instrumcnt to rotate on it.
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The first (54) and the second (56) driving means permit movement of the first
pentagonal mechanism so as to position the first connection means (46 and 48)
as
desired in a plane defined by a second axis and a third axis. Where the second
axis is
perpendicular to the first axis and the third axis is perpendicular to the
first and the
second axis; this plane is illustrated as the x y plane in figure 3; the
second axis is
illustrated as the x and the third axis is illustrated as they axis.
The third (30) and the fourth (32) driving means pennit movement of the second
pentagonal mechanism (6) so as to position the second connection means (50) as
desired
in the x-y plane. And the universal joints (42 and 44) permit movement in a
sagittal plane
defined by the third and first axis; illustrated in figure 3 as the y-z plane.
As a result, when the instrument driving means (8) is assembled with the first
and second
pentagonal mechanism (4 and 6), it has four degrees of freedom of motion: its
body can
be moved up-down in the y-z plane, left-right in the x y plane, rotated around
the axis of
the revolute joint (46), and rotated around the revolute joint (48).
The instrument driving means itself provides two degrees of freedom of motion
to the
instrument, relative to the instrument driving means' body. Thus, the
instrument has a
total of six degrees of freedom of motion in the x-v-z space, which is
necessaiy and
sufficient for achieving any desired position and orientation for it within
the workspace
of the apparatus.
The driving means can be connected to a computer (not illustrated) which would
control
their movement.
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