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Claims  |
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What we claim is:
1. A body-support frame for skeletal fixation and stereotactic
radiosurgery, comprising the following components:
(a) first, rigid means for supporting a patient in a horizontal position;
(b) second, rigid means, adjustably attached to said first means, for
immobilizing by skeletal fixation a portion of the body of the patient
targeted for stereotactic irradiation;
(c) third means for defining a reference plane along the main axis of said
first means; and
(d) fourth means, rigidly attached to said first means, for measuring the
coordinates of a region of interest with respect to the reference plane;
wherein said second, rigid means for immobilizing by skeletal fixation the
portion of the body of the patient targeted for stereotactic irradiation
comprises two braces straddling said first means and sufficiently large to
envelop the body of the patient, each of said braces lying in a plane
orthogonal to the longitudinal axis of and being adjustably connected to
said first means, so that the position of each brace can be shifted along
the longitudinal axis of said first means to lie outside the region of
interest in the patient;
wherein said second, rigid means further comprises at least one vise
slidably fastened to each of said braces, at least one swivel arm
adjustably connected to said vise through an upper swivel joint, and a
skeletal fixation clamp adjustably connected to said swivel arm through a
lower swivel joint, so that the fixation clamp can be oriented to reach
any point in the proximity of the brace across the width of the
body-support frame; and
wherein each of said two braces comprises two ends adjustably fastened to
said first rigid means by removably pins that are slotted through said
ends and into apposite receiving holes located at exact discrete intervals
along said first means.
2. A body-support frame for skeletal fixation and stereotactic
radiosurgery, comprising the following components:
(a) first, rigid means for supporting a patient in a horizontal position;
(b) second, rigid means, adjustably attached to said first means, for
immobilizing by skeletal fixation a portion of the body of the patient
targeted for stereotactic irradiation;
(c) third means for defining a vertical reference plane perpendicular to a
main axis of said first means, said third means being adjustable with
respect to the position of said second means and along the main axis of
the first means; and
(d) fourth means, rigidly attached to said first means, for measuring the
coordinates of a region of interest with respect to the reference plane.
3. The frame described in claim 2, wherein said first rigid means for
supporting a patient in a horizontal position consists of a horizontal
table comprising a flat horizontal platform, sufficiently long and wide to
receive the body of a human patient, and of two retaining side-walls
rigidly attached to the platform, so as to form a structure functionally
equivalent to a conventional stretcher.
4. The frame described in claim 3, wherein said retaining side-walls are
constructed in removable sections.
5. The frame described in claim 3, further comprising handles at each end
of said table to permit the transportation of the patient held in the
frame.
6. The frame described in claim 2, wherein the overall cross-sectional size
of the body-support frame is capable of being fitted with an area
corresponding to a circle approximately 28 inches in diameter.
7. The frame described in claim 2, wherein said second, rigid means for
immobilizing by skeletal fixation the portion of the body of the patient
targeted for stereotactic irradiation comprises two braces straddling said
first means and sufficiently large to envelop the body of the patient,
each of said braces lying in a plane orthogonal to the longitudinal axis
of and being adjustably connected to said first means, so that the
position of each brace can be shifted along the longitudinal axis of said
first means to lie outside the region of interest in the patient.
8. The frame described in claim 7, wherein each of said two braces
comprises two ends adjustably fastened to said first rigid means by
removable pins that are slotted through said ends and into apposite
receiving holes located at exact discrete intervals along said first
means.
9. The frame described in claim 8, wherein said braces are arcuated and
said second, rigid means for immobilizing by skeletal fixation the portion
of the body of the patient targeted for stereotactic irradiation further
comprises:
two vises having opposite sides mounted on each brace;
at least one tightening bolt connecting said opposite sides of each vise to
fasten the vise to the desired position along the brace;
a swivel rod rotatably mounted in a longitudinal bore between said two
opposite sides of each vise, wherein said rod has a first end and a second
end, and said first end contains a radial through-hole;
a swivel arm having a cross-section conforming with said radial
through-hole and being slidably connected therethrough to said swivel rod
in each vise;
a tightening knob screwably mounted on said second end of the rod of each
vise to lock the rod in position by providing a clamping action between
the knob and said swivel arm;
a double-swivel joint coupled to said swivel arm of each vise; and
a skeletal fixation clamp coupled to said double-swivel joint connected to
said swivel arm of each vise.
10. The frame described in claim 9, further comprising a tubular collar
inserted around said swivel rod of each vise as a spacer to adjust the
longitudinal position of the swivel arm.
11. The frame described in claim 9, wherein said skeletal fixation clamp
consists of:
a support housing having two side-arms connected to said double-swivel
joints coupled to the swivel arm of each vise, said support housing having
a removable top that is clamped to the housing by means of at least one
retaining screw and said support housing and removable top containing
facing semicircular recesses that define a cylindrical channel disposed
radially across the housing;
a clamp axle rotatably mounted in said channel; and
a skeletal fixation clamp rigidly attached to said clamp axle.
12. The frame described in claim 11, wherein said skeletal fixation clamp
consists of two facing jaws each having transverse guide-holes; a threaded
bolt passed through said transverse guide-holes in the jaws and screwably
connected to a threaded nut; and a spring around the bolt between the two
jaws of the clamp to urge the jaws to an open position.
13. The frame described in claim 12, wherein each of said jaws is
approximately 5 cm long, 1.5 cm wide and 3 to 5 mm thick.
14. The frame described in claim 11, further comprising friction bumps on
said jaws to increase their gripping ability.
15. The frame described in claim 11, wherein said skeletal fixation clamp
consists of a cancellous screw mounted in said cylindrical channel of said
support housing.
16. The frame described in claim 11, wherein said double-swivel joint
consists of two facing blocks, each containing opposite hemispherical
recesses wherein conforming spheres are rotatably housed, and a locking
screw that fastens said two blocks together and provides tightening means
around said spheres.
17. The frame described in claim 2, wherein said third means for defining a
vertical reference plane perpendicular to a main axis of said first means
consists of:
a bracket adjustably fastened to said second means;
a flat panel slidably mounted on said bracket perpendicularly to the main
axis of the body-support frame;
a plurality of longitudinal support holes in said flat panel;
at least three calibration rods slidably held in said longitudinal support
holes in parallel to the main axis of the body-support frame; and
a radiographically discernible target attached to each of said calibration
rods.
18. The frame described in claim 17, wherein said calibration rods are made
of phenolic material and each radiographically discernible target consists
of a painted lucite ball approximately 1.3 cm in diameter containing a
concentric steel ball about 4 mm in diameter; and wherein each lucite ball
contains a fine circumferential calibration line perpendicular to the main
axis of the rod.
19. The frame described in claim 2, wherein said fourth means for measuring
the coordinates of a region of interest with respect to the reference
plane consists of three measurement scales affixed to said first means in
positions corresponding to a selected system of coordinates.
20. The frame described in claim 19, wherein said selected system of
coordinates is the orthogonal x,y,z coordinate system.
21. The frame described in claim 2, further comprising an N-shaped
reference sight slideably positioned on horizontal supporting tracks on
said first means for radiographic confirmation of the exact position of
scanner images taken along the longitudinal axis of the body-support
frame.
22. The frame described in claim 21, wherein said N-shaped reference sight
consists of three straight segments of aluminum, wherein two segments
corresponding to the parallel legs of the N-shaped sight are placed
precisely in parallel to the main axis of the body-support frame and the
slanted segment is disposed across the width of the frame in variable x-y
coordinates.
23. The frame described in claim 22, wherein said N-shaped reference sight
is attached to a rigid support panel slidably mounted on supporting
longitudinal tracks, so that the sight can be moved along the main axis of
the frame to a position underlying the region of interest in the body of a
patient lying in said first means, and so that the sight is visible in
radiographic images produced in scanning the region.
24. The frame described in claim 2, further comprising a radiographic
target capable of being positioned in close proximity to the region of
interest for stereotactic radiosurgery.
25. The frame described in claim 24, wherein said radiographic target
consists of:
a bracket adjustably fastened to said second means;
a flat panel slidably mounted on said bracket perpendicularly to the main
axis of the body-support frame;
a longitudinal support hole in said flat panel;
a positioning rod slidably held in said longitudinal support hole in
parallel to the main axis of the body-support frame; and
a radiographically discernible target attached to said positioning rod.
26. The frame described in claim 25, wherein said positioning rod is made
of phenolic material and said radiographically discernible target consists
of a painted lucite ball approximately 1.3 cm in diameter containing a
concentric steel ball about 4 mm in diameter; and wherein each lucite ball
contains a fine circumferential calibration line perpendicular to the main
axis of the rod.
27. A body-support frame for skeletal fixation and stereotactic
radiosurgery, comprising the following components:
(a) a horizontal table comprising a flat horizontal platform, sufficiently
long and wide to receive the body of a human patient, and two removable,
multiple-section retaining side-walls rigidly attached to the platform, so
as to form a structure functionally equivalent to a conventional
stretcher;
(b) handles at each end of said table to permit the transportation of the
patient held in the frame;
(c) two braces straddling said horizontal table and sufficiently large to
envelop the body of the patient, each of said braces lying in a plane
orthogonal to the longitudinal axis of said platform and being adjustably
connected to said side-walls, so that the position of each brace can be
shifted along the longitudinal axis of said platform to lie outside the
region of interest in the patient;
(d) at least one vise slidably fastened to each of said braces, at least
one swivel arm adjustably connected to said vise through an upper swivel
joint, and a skeletal fixation clamp adjustably connected to said swivel
arm through a lower swivel joint, so that the fixation clamp can be
oriented to reach any point in the proximity of the brace across the width
of the body-support frame;
(e) a bracket adjustably fastened to said brace;
(f) a flat panel slidably mounted on said bracket perpendicularly to the
main axis of the body-support frame;
(g) a plurality of longitudinal support holes in said flat panel;
(h) at least three calibration rods slidably held in said longitudinal
support holes in parallel to the main axis of the body-support frame;
(i) a radiographically discernible target attached to each of said
calibration rods;
(j) a positioning rod slidably held in one of said longitudinal support
holes in parallel to the main axis of the body-support frame;
(k) a radiographically discernible target attached to said positioning rod;
(l) three measurement scales affixed to said horizontal table in positions
corresponding to an orthogonal x,y,z coordinate system; and
(m) an N-shaped reference sight slidably positioned horizontally on said
platform for radiographic confirmation of the exact position of scanner
images taken along the longitudinal axis of the body-support frame. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related in general to the fields of stereotactic
radiosurgery and radiation therapy. In particular, the invention provides
a new method and apparatus for producing a precise set of coordinates of
the portion of a patient's body affected by a tumor with reference to a
fixed frame wherein the patient is immobilized, so that the required
dosage of radiation can be accurately delivered to the prescribed target
volume with substantial sparing of surrounding normal tissues.
2. Description of the Related Art
The main object of radiotherapy is to deliver the prescribed dose of
radiation to a tumor in a patient while minimizing the damage to
surrounding, healthy, tissue. Since very-high-dose radiation (in the order
of several thousand rads or cGy, typically generated by a linear
accelerator) is normally used to destroy tumors in radiotherapy, the high
dose is also destructive to the normal tissue surrounding the tumor.
Therefore, it is essential that the delivery of radiation be limited
precisely to the prescribed target volume (i.e., the tumor plus adequate
margins). This is normally accomplished by placing appropriately
constructed shielding blocks in the path of the radiation beam. Thus, the
goal is to accurately identify the malignancy within the body of the
patient and to target the prescribed dosage of radiation to the desired
region in the immobilized patient.
To that end, the ideal procedure requires the identification of the exact
anatomical location of the tumor and the corresponding accurate
positioning of the radiation field during treatment. This could be easily
achieved if it were possible to locate and treat the tumor at the same
time. In practice, though, this is not possible because the equipment used
to identify the tumor (x-ray machine, computed tomography equipment, or
any of the other scanning machines currently in use) is separate from the
equipment used for the therapeutic irradiation of the patient, requiring
the movement and repositioning of the patient from one piece of equipment
to the other.
As illustrated in schematic form in FIG. 1, a conventional treatment unit
10 consists of a linear accelerator (linac) head 2 mounted on a gantry 4
so that its high-energy emissions R irradiate a patient P lying on a table
6 directly below, typically through shielding blocks 8 attached to the
head. A bracket 12 supporting a detector 14 may be mounted on the opposite
side of the head within the field of radiation in order to take
radiographs of the patient being treated. The gantry 4 is movable around a
pivot 16 to permit the rotation of the head (and of the detector) around
the patient to afford different views of the area to be treated ("multiple
fields" treatment).
The normal procedure involves the use of a diagnostic simulator, which is a
diagnostic x-ray machine with the same physical characteristics of the
radiation therapy machine (schematically also represented by FIG. 1, where
a diagnostic x-ray head replaces the linac head 2), so that the field of
view of the low-energy x rays emitted in the simulator is the same as that
of the high-energy radiation emitted in the radiation therapy machine.
Prior to treatment, the patient is radiographed using the simulator and an
image of the target area is obtained with low-energy radiation, which
yields good image quality. The exact target volume is then delineated on
the radiograph by a physician and matching shielding blocks are
constructed to limit the field of view of the irradiating machine to the
region so delineated.
A different approach has been used in the field of cranial radiosurgery,
which requires very precise high-intensity radiation delivered in a single
session. Rather than irradiating the target through shielding blocks,
which provide only a coarse alignment of the tumor area with the field of
emission, cranial radiosurgery relies on a highly focussed stereotactic
radiation beam pointed precisely toward the center of the tumor. In order
to be able to direct the radiation with sufficient accuracy, a cranial
frame consisting of a rigid ring is affixed to the skull of a patient
below the tumor area by means of at least four pressure pins evenly
distributed around the ring. The pins compress the bone to the point of
becoming rigidly affixed to the skull, thus providing a fixed frame of
reference for delineating the position of the malignancy. With the use of
scanning equipment, such as a CT scanner, the exact location of the tumor
can thus be mapped in terms of three-dimensional coordinates in relation
to the ring of the cranial frame. Once these exact coordinates are known,
the patient is moved to the linac machine where the cranial frame is lined
up with a special cranial support calibrated to the machine's own
reference system and the frame is positioned so that the stereotactic
radiation beam is focussed on the center of the tumor. Thus, as the
linac's gantry rotates around head of the patient for multiple-fields
treatment, the tumor is subjected to the cumulative amount of radiation
emitted during the radiation session, while the areas surrounding the
tumor receive only the radiation emitted while the path of the beam passed
through them.
This technique requires precise measurements and targeting of the radiation
beam, but it is indispensable for the treatment of cranial tumors, where
even a slight misalignment of the radiation beam may cause severe damage
to surrounding vital tissue. Therefore, it would be very desirable to have
an apparatus that permitted the use of a similar technique for
extracranial applications. The present application is directed at the
development of a device that enables the use of this technique for
stereotactic localization and radiation therapy of extracranial targets.
BRIEF SUMMARY OF THE INVENTION
One objective of this invention is the development of an apparatus that
permits the immobilization of a patient's body for conducting stereotactic
localization of a target tumor during the scanning procedure.
Another objective is an apparatus that can also be used as a reference
frame for targeting the radiation beam and for conducting radiosurgery of
extracranial targets in a linear accelerator after the scanning procedure.
A further goal of the invention is an apparatus that permits the focussing
of the radiation beam on the target tumor with a degree of precision that
is acceptable within the tolerances allowed for high-dose radiosurgery.
Still another objective of the invention is an apparatus that can be used
as an accessory to existing radiation-therapy diagnostic and treatment
units.
A final objective of this invention is the realization of the above
mentioned goals in an economical and commercially viable manner. This is
done by utilizing components and methods of manufacture that are either
already available in the open market or can be developed at competitive
prices.
According to these and other objectives, the present invention consists of
a body-support frame comprising a horizontal table having two adjustable
braces that can be moved along the main axis of the table for straddling a
patient lying within the frame. Each brace is equipped with a swiveled
clamp attached to an adjustable system of bracket-arms for the skeletal
fixation and immobilization of the patient craniad and caudad to the area
of interest. The frame contains orthogonal scales for orthogonal
localization and measurements of the area of interest with reference to a
chosen set of coordinates within the table. The frame also contains three
adjustable radiographic calibration targets that are used for selectively
setting a plane of reference in the proximity of the area of interest, so
that the plane may be used for lining up the frame with radiographic
imaging and radiation treatment apparatus. An additional, adjustable
radiographic target may be provided for fine calibration of the position
of the reference coordinates by permitting its placement as near as
possible to the area of interest externally to the body of the patient.
The apparatus is used to determine the exact coordinates of the area of
interest with reference to the chosen reference point while the body of
the patient is immobilized. These coordinates are then translated to an
exact position in the radiation therapy apparatus for subsequent
stereotactic radiosurgery.
Various other purposes and advantages of the invention will become clear
from its description in the specification that follows and from the novel
features particularly pointed out in the appended claims. Therefore, to
the accomplishment of the objectives described above, this invention
consists of the features hereinafter illustrated in the drawings, fully
described in the detailed description of the preferred embodiment and
particularly pointed out in the claims. However, such drawings and
description disclose but one of the various ways in which the invention
may be practiced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational schematic representation of a typical radiation
therapy unit.
FIG. 2 is a perspective view of a body-support frame for the skeletal
fixation of a patient according to the present invention.
FIG. 3 is a top view of the table illustrating an N-shaped reference sight
mounted within the retaining side-walls of the invention.
FIG. 4 is a front elevational view of the table illustrating the removable
portions of the side-walls and the x- and z-coordinate scales mounted on
the frame of the invention.
FIG. 5 is an elevational side view of the preferred embodiment of the brace
of the invention, illustrating the vise, arm and clamp of the skeletal
fixation mechanism attached to each side of the brace.
FIG. 6 is an elevational front view of the preferred embodiment of the
vise, arm and clamp of the invention, as seen from the left side of FIG.
5.
FIG. 7 is an isolated elevational view of the double-swivel joint used to
connect the straight arm with the clamp frame of the invention.
FIG. 8a is an elevational view of the fixation clamp frame of the
invention.
FIG. 8b is an elevational view of a cancellous screw mounted on the
fixation clamp frame of the invention.
FIG. 9 is a view of the fixation clamp shown in FIG. 8 as seen from the
right side of that figure.
FIG. 10 is an isolated elevational view of the calibration frame mounted on
at least one brace of the invention.
FIG. 11 is an isolated view of the calibration frame shown in FIG. 10, not
including the brace of the invention, as seen from the left side of that
figure.
FIG. 12 is a perspective view of the preferred embodiment of the invention
containing a patient immobilized within the body-support frame as it would
appear during use.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
This invention is directed at developing an apparatus for the skeletal
fixation of a patient to a rigid frame to permit the stereotactic
localization and radiation therapy of extracranial targets, such as
targets in the thoracic cavity, abdominal cavity, upper and lower
extremities, and paraspinal regions. The device of the invention also
permits the determination of an orthogonal set of coordinates for the
target and the translation of these coordinates from computerized
tomography or equivalent scans to the linear accelerator.
Referring to the drawings, wherein like parts are identified with like
symbols and numerals throughout this specification, FIG. 1 illustrates in
schematic elevational representation a typical linear accelerator (linac)
radiation therapy unit. Although the present invention can be used in
equivalent fashion with other radiation therapy equipment, the linac
machine will be referred to consistently herein for illustration. The
critical feature of any radiation unit that is relevant for this
disclosure is a calibration system that permits the positioning of a
chosen target exactly within the focal point of the radiation beam.
FIGS. 2-4 illustrate the body-support frame 200 of the invention,
comprising a horizontal table 20 for supporting the body of a patient and
at least two braces 50 straddled across the table. The table 20 consists
of a flat horizontal platform 22 sufficiently long and wide to receive the
body of a human patient lying on it, either in supine or prone position,
and of two retaining side-walls 24 rigidly attached to the platform or
integral thereto, so as to form a structure functionally equivalent to a
conventional stretcher or gurney. As in the case of stretchers, sets of
handles 44 are provided at both sides of the platform 22 to permit the
transportation of the patient held on the table. Differently from
conventional stretchers, though, the table 20 must be constructed with
rigid material in order to minimize physical deformations caused by
mechanical and thermal stresses that would alter the coordinates of a
chosen target in the body of the patient held immobilized on the table.
The overall cross-sectional size of the table 20, including the braces 50,
must not exceed the space available for positioning the frame in the
scanning machine. In the case of a typical CAT scanner, the bore of the
machine is round and approximately 28 inches in diameter. Accordingly, the
geometry of the side-walls 24 and of the braces 50 may be selected with a
conforming shape in order to maximize space utilization, as shown in the
figures.
Three measurement scales are affixed to the table 20 in positions
corresponding to a chosen system of coordinates. The scales shown in the
figures correspond to an orthogonal x,y,z coordinate system, but any
system that allows the exact determination of the location of a point with
respect to a reference point on the frame 200 can be used in equivalent
manner, as would be obvious to those skilled in the art. Thus, an x-axis
scale 26 is affixed rigidly to each side-wall 24 in parallel to the
longitudinal axis of the table 20; a y-axis scale 28 is affixed rigidly to
the side-walls 24 perpendicularly to the longitudinal axis of the table
20; and a z-axis scale 30 is similarly affixed rigidly to the table (or,
equivalently, to any other part of the structure capable of supporting the
scale) perpendicularly to the plane containing the platform 22. Obviously,
these scales provide the means for setting the origin of an orthogonal
coordinate system that can be used to establish the corresponding
coordinates of an identified target, such as a tumor in a patient,
positioned within the table 20. Once these coordinates are measured, so
long as the target does not move with respect to the table, the position
of the target can be reestablished simply by measuring its coordinates
from the origin of the orthogonal system. Thus, if the position of a tumor
in the body of a patient immobilized within the frame 200 is identified,
that position can be measured and expressed in terms of coordinates
relative to the orthogonal system provided by the measurement scales 26,
28 and 30.
As will become more apparent from the description given below of the
operation of the apparatus of the invention, an N-shaped reference sight
32 is provided on the surface of the platform 22 for radiographic
confirmation of the exact position of scanner images taken along the
longitudinal axis of the table 20. Referring to the top view of the table
seen in FIG. 3, the sight 32 consists of three straight segments of
material, such as aluminum, that is visible in radiographic scanning
images without producing significant artifacts. The two segments 34
corresponding to the parallel legs of the N-shaped sight are placed
precisely in parallel to the main (longitudinal) axis of the platform 22,
preferably near the interior face of the retaining side-walls 24, so that
the slanted segment 36 is disposed across the width of the platform in
variable x-y coordinates. The sight 32 is attached to a rigid support
panel 40, such as a rectangular sheet of plexiglass, that is slidably
mounted on supporting longitudinal tracks 41 within the retaining
side-walls 24 on the top surface of the platform 22. Thus, the sight can
be moved along the x-axis of the table 20 to a position underlying the
region of interest in the body of a patient lying on the table (such as
the position of a tumor), so as to be visible in radiographic images
produced in scanning the tumor region.
FIG. 5 shows the detailed geometry of the preferred embodiment of each
brace 50 straddling the table of the invention. Each brace consists of a
rigid span of solid material sufficiently large to envelop the body of a
patient lying in the frame 200. Each brace lies in a plane orthogonal to
the longitudinal axis of the table 20 and is adjustably connected to the
retaining side-walls 24 so that the position of the brace can be shifted
along the x coordinate of the table to lie outside the region of interest
in the patient. That is, each brace is moved along the side-walls 24 of
the table to a position that permits the fixation of the patient as
closely as possible to the region of interest, but that is outside the
area that will be evaluated radiographically. Accordingly, the two braces
are positioned to straddle the body of the patient craniad and caudad to
the area of interest. Since after skeletal fixation a patient is expected
to spend many hours in an immobilized position on the table, the side
walls 24 may be constructed in removable sections, as illustrated in FIGS.
2-4; that permits the removal of those sections that are not being used to
support the braces 50, thus giving the patient some freedom of limb
movement.
As seen particularly in FIGS. 2, 3 and 4, each end 52 of a brace 50 is
adjustably fastened to the corresponding side-wall 24 by means of
removable pins or bolts 54 that are slotted or screwed through the brace
and into apposite receiving holes 42 located at exact discrete intervals
along the side-walls 24. Thus, the location of each brace can be adjusted
along the x coordinate in discrete steps corresponding to the distance
between two adjacent holes 42. As will be explained below, finer
adjustments for the position of the apparatus supported by each brace are
possible by means of swivel joints and spacers built into the brace
itself. This apparatus, which is common to each brace 50, consists
generally of a skeletal fixation mechanism 70 for immobilizing a patient
lying on the table. At least one of the braces also comprises a
radiographic calibration device 140 that is used for selectively setting a
plane of reference in the proximity of the area of interest. Finally, at
least one of the braces is also equipped with an adjustable radiographic
target 160 for fine calibration of the position of the reference
coordinate system.
The skeletal fixation mechanism 70 mounted on each brace comprises at least
one vise 72 slidably fastened to the brace 50, so that its position may be
adjusted along the span of the brace. One end of a swivel arm 74 is
adjustably connected to the vise 72 by means of an upper swivel joint,
while the other end of the arm is connected to a skeletal fixation clamp
76 by means of another, lower swivel joint. Thus, by virtue of the freedom
of movement of the vise 72 along the brace 50, of the swivel arm 74 around
the upper swivel joint, and of the fixation clamp 76 around the lower
swivel joint, the fixation clamp 76 can be oriented to reach any point in
the proximity of the brace across the width of platform 22. It is a
critical feature of this invention that all movable parts (such as the
vise, swivel joints, and clamp) be capable of being rigidly and immovably
fixed once a position is chosen for the clamp, as required for a given
procedure. Obviously, any mechanical system consisting of fixable, hinged
levers that permit the accurate and rigid placement of the fixation clamp
76 over a patient lying under the support brace 50 would be equivalently
suitable to practice the invention.
In the preferred embodiment illustrated in the drawings, each brace 50
consists of an arcuated portion spanning over the table 20 with two ends
removably attached to the side-walls 24 by means of pins 54. Two vises 72
having opposite sides are slidably mounted on the arcuated portion of the
brace 50, so that the position of each can be adjusted to anywhere along
the span of the brace. Each vise comprises tightening bolts 78 (at least
one) to fasten the vise to the desired position along the brace and, as
illustrated in the front view of FIG. 6, a swivel rod 80 rotatably mounted
in a longitudinal bore 82 between the two sides of the vise. One end of
the rod 80 contains a radial through-hole 84 for receiving in slidable
connection a straight swivel arm 74 having a conforming cross-section.
Although not critical to the functioning of the invention, as will become
apparent from the description given below, a compression screw 88 may be
provided on the swivel rod 80 for locking the arm 74 in place after it has
been slided to the desired position in the through-hole 84. The other end
of the rod 80 contains a tightening knob 90, screwably mounted on the rod,
which is used to lock the rod in position by providing a clamping action
between the knob and the arm 74 across the vise. A tubular collar 92 may
be inserted around the swivel rod 80 as a spacer to adjust the
longitudinal position of the arm 74. Obviously, collars with different
lengths may be used along the rod 80 on either side of the vise to provide
the desired spacing for fine adjustments of the position of the arm 74.
The lower end of each arm 74 is coupled to the skeletal fixation clamp 76
by means of a double-swivel joint 94. In the preferred mode, this joint
consists of two facing blocks 96, each containing opposite hemispherical
recesses 98 wherein conforming spheres 100 built into the lower end of
each arm 74 and in the frame 104 of the clamp are housed, as illustrated
in FIGS. 5, 7 and 8a. This configuration obviously permits the rotation of
each sphere within the cavity in which it is housed, providing a high
degree of freedom in the motion of the clamp. A locking screw 102 that
fastens the two blocks 96 together also provides the means for tightening
the blocks around the spheres 100 and fixing the clamp 76 in the desired
position.
FIGS. 8a and 9 show the construction and functional components of the
skeletal fixation clamp 76 of the invention. The clamp frame 104 consists
of a support housing 106 having two side-arms 108, each comprising a
swivel sphere 100 connected to the double-swivel joint 94 at each side of
the clamp. The support housing 106 has a removable top 110 that is clamped
to the housing by means of retaining screws 112. The main body of the
support housing and the removable top contain facing semicircular recesses
that define a cylindrical channel 114 disposed radially across the
housing, wherein a clamp axle 116 is rotatably mounted to support the
clamp 76. As the retaining screws 112 are tightened, the axle 116 is
locked in place with respect to the housing, thus also fixing the position
of the clamp in relation to the housing.
As better illustrated in FIG. 9, the clamp 76 is rigidly attached to clamp
axle 116, so that the clamp's position is fixed when the axle is tightened
to the housing 106. As would be obvious to those skilled in the art,
different mechanical arrangements could be used to support the fixation
clamp 76, the critical feature being that it be capable of
multidirectional pivotal adjustment and rigid fixation with respect to the
pair of straight swivel arms 74 connecting it to the brace. The clamp 76
consists of two facing jaws 118 that are pulled together by a
normally-open spring-loaded compression bolt mechanism 120 that permits a
user to adjustably compress, grip and firmly hold a selected part of the
anatomy of a patient. In the preferred mode of practicing this invention,
the mechanism 120 consists of a threaded bolt 122 passed from one side of
the clamp through transverse guide-holes in the jaws 118 and screwably
connected to a threaded nut 124 on the other side of the clamp. A spring
126 around the bolt 122 between the two jaws of the clamp ensures that the
jaws remain open within the adjustment provided by the compression bolt
mechanism. The geometry of the jaws is chosen to conform to the shape of
the anatomical part for which they are intended. The shape and size
illustrated in the figures (approximately 5 cm long, 1.5 cm wide and 3 to
5 mm thick) have been designed specifically for spinous process
attachment, but it has been found to be suitable as well for clamping
other skeletal parts. Friction bumps 128 are added on the contact surface
of the jaws to increase their gripping of the bone.
The skeletal fixation mechanism of the invention can also be used without
the clamp 76, utilizing a cancellous screw instead. As illustrated in FIG.
8b, a cancellous screw 115 of the type normally used for cancellous
fixation by orthopedic surgeons can replace the clamp axle 116 in the
cylindrical channel 114 of the clamp frame 104. Thus, the screw provides
fixation by being driven directly into the bone.
Note that each of the two braces 50 must be equipped with a skeletal
fixation mechanism 70 in order to provide the ability to grip two fixation
points on the skeleton of a patient. Thus, by choosing a bone in the
vicinity of the region of interest (such as the spinal column for the
treatment of a chordoma, for instance), the bone can be clamped by the two
fixation clamps and immobilized for radiographic imaging and for
stereotactic treatment. For example, an incision is made through the
tissue above the spinal column and each fixation clamp is positioned
around the spinous process of a selected vertebra. The clamps are then
closed to firmly grip and immobilize the bone. The patient is now ready
for radiographic scanning to locate the precise coordinates of the tumor
in relation to the reference system on the table 20. Then, these
coordinates can be used to precisely position the table in the linear
accelerator machine to focus the radiation beam on the desired region in
the body of the patient (corresponding, of course, to the region
delineated by the coordinates produced by radiographic scanning).
In order to complete the procedure just described, it is also necessary to
have a reference system that permits the exact positioning of the table 20
within the calibration system of the radiographic and linac apparatus. For
that purpose, the body-support frame 200 also comprises at least one
radiographic calibration device 140 mounted on one brace 50, as
illustrated in FIGS. 10 and 11. Although not critical, greater flexibility
is achieved if each brace includes a calibration device because the more
convenient one can then be used, as determined by the position of the
table in the | | |
