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1. FIELD OF THE INVENTION
The invention relates to a stereotactic-guided radiation therapy system, a
collimator useful in treating a patient with stereotactic-guided radiation
therapy, and a method of stereotactic-guided radiation therapy of a lesion
within a patient's body.
2. DESCRIPTION OF THE PRIOR ART
Dr. Lars Leksell in 1951 introduced radiosurgery, which used a Gamma Knife
to deliver a high dose of ionizing radiation delivered to a pre-selected,
stereotactically localized intracranial volume of normal or pathological
tissue. Although success has been achieved by this technique in treating
otherwise inaccessible abnormalities in the central nervous system,
investigators have been looking at other means of accomplishing the same
results. Although systems based on the beam characteristics of heavy
charged particles have been in use for a number of years, the greatest
amount of interest lies in applications involving linear accelerators, due
to the fact that the cost of acquiring either a Gamma Knife, or a heavy
particle system is significant, whereas many hospitals already possess
linear accelerators.
The principle behind linear accelerator-based systems is that by rigidly
fixating a patient to the accelerator rotatable couch so that the target,
or lesion inside the patient's skull lies at the isocenter of the
accelerator, the total radiation dose delivered to the tumor, lesion, or
target, can be distributed over a large treatment vector by either
simultaneously or independently rotating both the gantry of the linear
accelerator and the couch. The tumor receives a large dose of radiation,
while due to the steep dose dropoff, resulting from the large application
vector, normal brain tissue is spared.
Linear accelerator systems, depending upon the technique employed, use
either: a single plane of rotation of the isocentric mounted linear
accelerator to deliver the total dose of radiation; multiple, non-parallel
but converging arcs; or a dynamic mode of therapy where both the couch and
the gantry rotate simultaneously. In single-plane systems, because all of
the radiation is delivered in that single plane, conventional
two-dimensional planning systems can be used to determine isodose curves.
The dose fall-off outside the target volume in the plane of the treatment
are not sharp enough compared to the Gamma Knife to warrant usage of this
technique. Both of the other techniques, which distribute radiation over a
much greater arc than does the single-plane method, produce isodose curves
with drop-offs similar to that of the Gamma Knife. However, the treatment
planning for such approaches requires three-dimensional algorithms for
dose calculations. This necessity is based upon the fact that the
treatment radiation beam passes through different thicknesses of tissue as
it rotates around the head, or other portion of the patient's body. Thus
the amount of radiation the target receives depends upon the precise path
that the radiation beam follows.
In general, rotating arc protocols treat roughly spherical lesions centered
near the isocenter of the system with the isodose distributions
approximated by two-dimensional calculations dependent upon the depth of
the target, lesion, or tumor. In order to predict precisely the isodose
contours which will result from any given treatment protocol necessitates
the use of sophisticated planning systems which have the capability to
handle the three-dimensional calculations required on such applications;
however, such systems are both computer hardware and software intensive
and very expensive. The only time that such planning is not necessary is
in the theoretical case where the skull is a perfect sphere and the
target, or tumor, is at the exact center of that sphere. In this unique
case, the target receives the same dosage of radiation regardless of
radiation beam position, the isodose curves becoming standardized.
For stereotactic-guided radiation therapy, treatment plan verification is
computer labor-intensive because it is a three-dimensional problem. The
amount of radiation which any given area of the brain, or other portion of
the body, will receive from the treatment radiation beam is dependent upon
the amount of tissue through which the beam has to pass and is attenuated,
or dissipated, on its way to that particular area of the brain, or other
portion of the body. The computer must have stored the contour of the
scalp, the location of the target, or tumor, and the position of the beam
rotations. It then constructs a three-dimensional matrix, which sums the
radiation to every point in the brain, or other portion of the body,
receives from every position of the radiation beam for all the rotations
added together. Finally, it must display the results as conventional
isodose curves. If the dose distribution misses parts of the target, or if
vital tissue structure receives too much of a dose of radiation, either
the target location, the beam size, or the location of the rotations must
be changed and a new plan verification performed. Accordingly, such
process is expensive, time consuming, and requires sophisticated,
expensive computers to perform the necessary calculations.
Accordingly, prior to the development of the present invention, there have
been no stereotactic-guided radiation therapy systems, methods, and
collimators which: are simple and economical to manufacture and use; do
not require a sophisticated three-dimensional treatment planning system,
including expensive computer hardware and software; permits the use of a
hospital's existing linear accelerator without modification to the
accelerator head of the linear accelerator; and permit the use of
stereotactic-guided radiation therapy on lesions in other parts of the
body other than the skull.
Therefore, the art has sought stereotactic-guided radiation therapy
systems, methods and collimators, which: are simple and economical to
manufacture and use; do not require a sophisticated, expensive
three-dimensional treatment planning system, including expensive computer
and sophisticated software; permit the use of a hospital's existing linear
accelerator without modification of the accelerator head; and may be used
to treat targets, or tumors, in other areas of the patient's body, other
than the patient's skull.
SUMMARY OF THE INVENTION
In accordance with the invention, the foregoing advantages have been
achieved through the present system for stereotactic-guided radiation
therapy for treating a patient. The present invention includes: a
stereotactic fixation device; a linear accelerator having a rotatable
couch; and a collimator for focusing a beam of radiation from the linear
accelerator, including means for providing a variable length pathway for
the beam of radiation, the pathway having a material substantially
equivalent to tissue of the patient associated with the pathway, the beam
of radiation passing through the pathway prior to entering the patient.
Another feature of the present invention is that the tissue equivalent
material may be water.
Another feature of the present invention is that the variable length
pathway providing means may include a variable length, movable housing
which contains the tissue equivalent material. Another feature of the
present invention is that the variable length pathway providing means may
include a reservoir for the tissue equivalent material, and the variable
length, movable housing may be a variable length, movable piston, and the
piston contains the tissue equivalent material. An additional feature of
the present invention is that the housing may have a first end, adapted to
contact the patient, and means for controlling the movement of the
housing, whereby the first end of the housing maintains contact with the
patient. Another feature of the present invention is that the variable
length, movable housing may be a variable length movable piston, and the
piston contains the tissue equivalent material, the piston being a plastic
encased spring, which forms a variable length, movable bellows for
containing the tissue equivalent material.
In accordance with another aspect of the invention, the foregoing
advantages have been achieved through the present method of
stereotactic-guided radiation therapy of a lesion within a patient's body.
This aspect of the present invention includes the steps of: placing the
patient on a rotatable couch associated with a linear accelerator having a
collimator and a gantry; disposing the lesion of the patient at the
isocenter of the linear accelerator; focusing a beam of radiation toward
the lesion and through a variable length pathway associated with the
collimator, the pathway having a material substantially equivalent to the
tissue of the patient, the beam of radiation passing through the pathway
prior to entering the patient; moving the collimator with respect to the
patient while focusing the beam of radiation toward the lesion; and
varying the length of the variable length pathway while moving the
collimator, so that the beam of radiation passes through substantially the
same distance of tissue and tissue equivalent material while the
collimator is being moved.
A feature of the present invention is the step of utilizing water as the
tissue equivalent material. Another feature of the present invention is
the step of contacting the patient with a first end of the variable length
pathway and maintaining such contact while the collimator is being moved
by varying the length of the variable length pathway. An additional
feature of the present invention is the step of disposing a first end of
the variable length pathway a predetermined distance from the patient, and
maintaining the predetermined distance between the first end and the
patient while the collimator is moving by varying the length of the
variable length pathway.
In accordance with another aspect of the invention, the foregoing
advantages have been achieved through the present collimator useful in
treating a patient with stereotactic-guided radiation therapy. This aspect
of the present invention includes: means for focusing a beam of radiation;
and means for providing a variable length pathway for the beam of
radiation, the pathway having a material substantially equivalent to
tissue of the patient associated with the pathway, the beam of radiation
passing through the pathway prior to entering the patient. Another feature
of the present invention is that the tissue equivalent material may be
water. An additional feature of the present invention is that the variable
length pathway providing means may include a variable length, movable
housing which contains the tissue equivalent material.
A further feature of the present invention is that the variable length
pathway providing means may include a reservoir for the tissue equivalent
material. Another feature of the present invention is that the variable
length movable housing may be a variable length movable piston, and the
piston contains the tissue equivalent material. The piston may be a
plastic encased spring which forms a variable length, movable bellows for
containing the tissue equivalent material. A further feature of the
present invention is that housing may have a first end, adapted to contact
the patient, and means for controlling the movement of the housing,
whereby the first end of the housing maintains contact with the patient.
Another feature of the present invention is that the control means may be
a means for spring biasing the first end of the housing into contact with
the patient.
The system for stereotactic-guided radiation therapy, method of
stereotactic-guided radiation therapy, and collimator useful in treating a
patient with stereotactic-guided radiation therapy, when compared with
previously proposed prior art methods and apparatus, have the advantages
of: being simple and economical to manufacture and use; do not require a
sophisticated three-dimensional treatment planning system, including
sophisticated computer hardware and software; permit the use of a
hospital's existing linear accelerator, and do not require modification of
the accelerator head; and may be used to treat targets, or tumors, in
areas of other parts of the patient's body, other than the human skull.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a conventional linear accelerator including
a rotatable couch, collimator and gantry;
FIG. 2 is a top, schematic view of a patient's skull being treated with a
conventional linear accelerator;
FIG. 3 is a top, schematic view illustrating a patient's skull being
treated in accordance with the present invention;
FIGS. 4-10 are perspective views of a human patient having a tumor in his
skull being treated in accordance with the present invention;
FIGS. 11-13 are partial cross-sectional views of a collimator in accordance
with the present invention;
FIG. 14 is a partial cross-sectional view of a collimator taken along line
14--14 of FIG. 13;
FIG. 15 is a partial cross-sectional view of a collimator in accordance
with the present invention taken along lines 15--15 of FIG. 13;
FIGS. 16-17 and 20 are partial cross-sectional views of a collimator in
accordance with the present invention;
FIG. 18 is a partial cross-sectional view of a collimator in accordance
with the present invention, taken along line 18--18 of FIG. 17; and
FIG. 19 is a partial cross-sectional view of a collimator in accordance
with the present invention, taken along lines 19--19 of FIG. 17.
While the invention will be described in connection with the preferred
embodiment, it will be understood that it is not intended to limit the
invention to that embodiment. On the contrary, it is intended to cover all
alternatives, modifications, and equivalents, as may included within the
spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, a conventional linear accelerator 300 is shown as
including a gantry 301, turntable 302 which causes patient couch 303 to
rotate therewith, and a conventional collimator 304. The three axes of
rotation of the gantry 301, turntable and couch 302, 303, and collimator
304 are designated with the letters G, T, and C, respectively. As
illustrated in FIG. 1, the patient 305 is disposed upon the rotatable
couch 303 by use of a conventional stereotactic fixation device (not
shown) whereby the target, lesion, or tumor, 306 is disposed at the
isocenter 307 of the linear accelerator 300. The isocenter 307 is defined
as the point of intersection of the three axes of rotation, C, G, and T of
linear accelerator 300.
With reference to FIG. 2, the operation of linear accelerator 300 upon a
lesion, or tumor, 306 in the skull 308 of patient 305 is illustrated. As
collimator 304 is caused to rotate about the skull 308 of patient 305,
along the path shown by dotted lines 309, a beam of radiation 311, made up
of photons which generate gamma rays when they impinge on human tissue, is
focused and directed toward target 306. Collimator 304 is of conventional
construction and defines the size of the beam of radiation 311 exiting
from the conventional accelerator head 312 (FIG. 1) of linear accelerator
300. Conventional collimators 304 are either removeable, rigid tubes which
create either a square or circular beam of varying size, or contain
configurable leaflets so that an irregularly shaped beam can be produced.
The aperture size of collimator 304 are determined and selected in
accordance with the size of lesion 306 to be treated. Conventional
collimators are attached to the accelerator head 312 at a fixed distance
from the isocenter 307 of the linear accelerator 300. Since the distance D
from the end of the collimator 304 to the target 306 is a constant value,
and since the depth T of the target 306 with respect to the surface of the
skull 308 varies, as illustrated in FIG. 2, as accelerator head 312 (FIG.
1) and collimator 304 rotates, the amount of tissue which the beam of
radiation 311 passes through after it leaves the end of the collimator 304
on its way to the target 306, varies as well. It is this variance in the
depth of the tissue T passed through by the treatment beam of radiation
311 which necessitates the sophisticated treatment planning system
previously described.
With reference now to FIG. 3, the method of stereotactic-guided radiation
therapy and collimator 304' of the present invention will be described.
The same reference numerals will be used for the same components
previously described, and primed reference numerals will be used for
similar components to those previously described. The patient 305 of FIG.
3 is as illustrated in FIG. 1, placed upon the rotatable couch 303 of
linear accelerator 300, and the target, or lesion, 306 is disposed at the
isocenter 307 of the linear accelerator 300 as previously described.
Collimator 304' includes: a means for focusing 315 a beam of radiation
311, or a conventional collimator 304 previously described; and a means
for providing 316 a variable length pathway 317 for the beam of radiation
311. The pathway 317 has a material 318 substantially equivalent to tissue
of the patient 305 associated with the pathway 317, and the beam of
radiation 311 passes through the variable length pathway 317 prior to
entering the patient 305.
As illustrated in FIG. 3, the beam of radiation 311 is focused by
collimator 304' toward the lesion 306 and through the variable length
pathway 317 and through the tissue equivalent material 318 associated with
variable length pathway 317. Collimator 304' is moved with respect to the
patient 305 along path 309 while the beam of radiation 311 is focused
toward the lesion 306. As collimator 304' is moved along path 309, the
length L of the variable length pathway 317 is varied so that the beam of
radiation 311 passes through substantially the same distance T of tissue
of patient 305 and tissue equivalent material 318 while the collimator
304' is being moved with respect to the patient 305 along path 309.
As seen in FIG. 3, as collimator 304' is rotated about the skull 308 of
patient 305 with lesion 306 disposed at the isocenter of linear
accelerator 300, which is also the center of rotation of collimator 304',
the distance D from a fixed point 320 on collimator 304' remains constant.
As previously discussed, as collimator 304' rotates along path 309, the
depth or thickness T of tissue through which radiation beam 311 passes
varies, as previously described. As seen in FIG. 3, as collimator 304'
rotates about path 309, the length L of variable length pathway 317 also
varies. As collimator 304' rotates about path 309, the radiation beam 311
will always pass through substantially the same distance of tissue, or
tissue depth T, and tissue equivalent material 318 associated with
variable length pathway 317; the sum of the depth of tissue T and variable
length L of tissue equivalent material 318 being substantially equal to
the distance D between a fixed point 320 on collimator 304' and the
target, or tumor, 306 of patient 305. Thus, the effective tissue target
depth D remains the same, and regardless of the location of the target
306, the beam of radiation 311 will pass through that constant effective
tissue target depth D comprised of actual tissue target depth T and the
variable length L of tissue equivalent material 318. Thus, the amount of
radiation focused toward lesion 306 as collimator 304' rotates about a
skull 308 of patient 305 will always be a fixed constant determined by the
physical characteristics of the collimator 304'.
Since the effective tissue target depth D is always the same, the isodense
distribution around the target 306 becomes independent of the target
tissue depth T. Accordingly, the previously required computer hardware and
software intensive treatment planning, which utilizes a complicated
three-dimensional algorithm, of prior art systems is eliminated. For a
stereotactic-guided radiation therapy treatment consisting of a single
rotation of the collimator 304' the isodense distribution around the
target 306 will always be circular. For convergent or multiple arc
rotational treatments, the isodense distribution of the radiation around
the target 306 will be spherical, provided that enough treatment arcs are
used to deliver the total radiation dosage. Irregularly shaped lesions 306
may be treated in a conventional manner by overlapping spherical fields.
Stereotactic-guided radiation therapy treatment planning, in accordance
with the present invention, thus becomes dependent only upon: the size of
the target, or tumor 306, which determines the aperture size of the
conventional, rigid, beam defining collimator 304; the stereotactic
coordinates of the target 306 which are used in placing the patient 305 on
the rotatable couch 303 of linear accelerator 300 and disposing the
patient's lesion 306 at the isocenter 307 of the linear accelerator 300;
and the total planned radiation dosage and the stored characteristics of
the radiation beam and collimator 304 employed, both of which are used in
a conventional manner to adjust the unit settings on the linear
accelerator 300. Factors related to the surface contours of the scalp, or
skull 308, of patient 305 and the tissue target depth T, factors unique to
any individual patient 305, are eliminated. The characteristics for the
rigid collimator 304 will be predetermined and then becomes a constant for
a given size collimator 304.
With reference now to FIGS. 4-10, an example is shown of how a patient's
lesion, or tumor, 306 is disposed at the isocenter 307 of a linear
accelerator 300. As will be hereinafter described in further detail, it
should be noted that the method of stereotactic-guided radiation therapy,
collimator 304' and system for stereotactic-guided radiation therapy of
the present invention may be used not only for the treatment of lesions
disposed within the skull 308 of a patient 305, but may also be utilized
to treat lesions disposed in other parts of patient 305 wherever there is
a relatively constant tissue density, which generally are those areas
outside of the patient's thorax. Although when such other lesions, or
tumors, 306 are treated, more normal tissue may be exposed to radiation
when using a rotating collimator than in conventional stationary port
plans, the exposure is so small that the benefits in terms of the
steepness of the isodose curves are believed to far outweigh any potential
liabilities.
As seen in FIG. 4, patient 305 had a lesion or tumor 306 disposed within
his skull 308. With reference to FIGS. 5 and 6, a stereotactic fixation
device 330 is shown to include a positioning fixture 331 which is secured
to the patient's skull 308 in a suitable location with conventional bone
screws (not shown). Positioning fixture 331 also includes a ball socket
member 332 which is secured to the positioning fixture 331 prior to
computerized tomographic ("CT") scanning of the patient. Stereotactic
fixation device 330 may be any conventional stereotactic fixation device,
so long as stereotactic fixation device 330 does not present collimator
304' with any significant obstructions as it moves along paths 309 as will
be hereinafter described in greater detail. One such prior art
stereotactic fixation device 330 which may be utilized in practicing the
method of the present invention is that disclosed in U.S. Pat. No.
4,805,615, issued Feb. 21, 1989, to the inventor of the present invention,
which patent is incorporated herein by reference.
With reference to FIGS. 7 and 8, the patient 305 is placed upon the CT
imager table 333 of CT scanner 334, and the ball socket member 332 is
fixedly attached to imager table 333 via an attachment member, or
alignment rod, 335 and bracket 336. The ball socket member 332 allows the
ball of the ball socket member 332 to swivel until the attachment member,
or alignment rod, 335 can mate with the rod 337 attached to ball socket
member 332. Once the alignment rod 335 and ball rod 337 are mated, the
ball of ball socket member 332 is locked in place and the patient 305 is
imaged in the CT scanner 334 in a conventional manner, whereby the
stereotactic coordinates of the target, or lesion, 306 are determined.
With reference to FIGS. 9 and 10, the patient is then transferred to the
rotatable couch 303 of linear accelerator 300 where the ball rod 337 is
connected to an alignment rod, or attachment member, 335 and bracket 336
which are identical to those associated with the CT scanner 334, whereby
the geometric disposition of the patient with respect to rotatable couch
303 is a duplicate of the geometric relationship of the patient 305 with
respect to the imaging table 333. The ball of ball socket member 332 is
then brought to lie at the isocenter 307 of the linear accelerator 300 by
moving the rotatable couch 303 in a conventional manner. The target, or
lesion, 306 may then be brought to be disposed at the isocenter 307 of the
linear accelerator 300 by adjusting the position of the rotatable table
303 in accordance with the stereotactic coordinates of the tumor 306 which
were determined in the CT scanner 334. As seen in FIG. 10, with the tumor
306 being 300, collimator 304' , including the means for providing 316 a
variable length pathway 317 are rotated about patient 305 in the manner
previously described in connection with FIG. 3. It should be noted that
for treatment of lesions, or tumors, in other areas of the patient's body,
other than skull 308, the previously described steps would be followed,
with the exception that the positioning fixture 331 and ball socket member
332 of stereotactic fixation device 330 would not be disposed upon the
skull 308 of patient 305, but would be disposed upon another portion of
the patient's body, such as the sternum, as by an adhesive, whereby that
portion of the body wherein the tumor 306 is disposed may be scanned by
the CT scanner 334 in the manner previously described, the patient's
orientation on the imaging table 333 being duplicated upon the rotatable
couch 303 of linear accelerator 300, in the manner previously described.
With reference now to FIGS. 11-15, a collimator 304' in accordance with the
present invention, useful in treating a patient with stereotactic-guided
radiation therapy, includes means for focusing 315 a beam of radiation, or
a conventional rigid tube collimator 304; and means for providing 316 a
variable length pathway 317 for a beam of radiation, pathway 317 having a
tissue equivalent material 318 associated therewith. As previously
described, the tissue equivalent material 318 is preferably water, in that
water has approximately the same energy dissipation or attenuation,
properties as normal human tissue. As previously discussed, when a beam of
radiation passes through human tissue, its energy is dissipated or
attenuated. It should be noted that tissue equivalent material 318 could
be any other material having substantially similar density and energy
dissipation and attenuation characteristics as normal tissue.
Alternatively, materials with density, energy dissipation and attenuation
characteristics which vary linearly as a function of the thickness of the
material may be used, whereby knowing the density, energy dissipation and
attenuation characteristics of the material 318, it would be possible to
callibrate collimator 304' to provide a known quantity of radiation energy
to a lesion 306 (FIG. 3) dependent upon the thickness, or variable length
L of material 318 through which the beam of radiation 311 travels when
used in the method and apparatus previously described in connection with
FIG. 3.
Still with reference to FIGS. 11-15, variable length pathway providing
means 316 may include a variable length movable housing 340 which contains
the tissue equivalent material 318. The variable length pathway providing
means 316 may further include a reservoir 341 for the tissue equivalent
material 318, the tissue equivalent material 318 being contained in
reservoir 341 not having the beam of radiation pass therethrough.
Collimator 304' preferably includes a base member 342, or circular flange
343 which permits the collimator 304' to be fixedly secured to the
accelerator head 312 of linear accelerator 300 (FIG. 1). In the embodiment
of collimator 304' of FIGS. 11-15, the variable length, movable housing
340 may be afforded by a cylinder 345 which is matingly received by
another cylinder 346 in a fluid sealed relationship, the bottom of
cylinder 345 having an anular flange plate 347 being disposed in a sealing
relationship with respect to the interior of cylinder 346 and a central
tube 348. The upper end of cylinder 345 is sealed by an end plate member
349. End plate member 349 may include at least two or more guide cylinders
350 which cooperate with guide rods 351 to properly align the mating
cylinders 345, 346 of variable length, movable housing 340 as they move
with respect to one another as will be hereinafter described. It should be
noted that variable length, movable housing 340 could have any suitable
configuration, such as the cylindrical configuration illustrated in FIGS.
11-15; however, any other suitable cross-sectional configuration could be
utilized such as square, triangular, etc.
In the embodiment of collimator 304' illustrate in FIGS. 11-15, the mating
portions 345, 346 of variable length, movable housing 340 are sized so
that the volume of tissue equivalent material 318 contained between
cylinders 345, 346, as illustrated in FIG. 11 is equal to the sum of the
volume contained in cylinder 345 and the volume shown at the top of
cylinder 346 in FIG. 13, so that when the variable length, movable housing
340 is in its fully extended position shown in FIG. 13, the cavity within
cylinder 345 will be completely full of the tissue equivalent material, or
water, 318. It should be noted that the top of cylinder 346 has an anular
plate 352 secured thereto in a fluid tight relationship with the top of
cylinder 346 and the outer wall surface of cylinder 345. Further, the
lower end of cylinder 345 is in fluid communication with the interior of
cylinder 346, as by a plurality of openings 353 formed in the lower wall
surface of cylinder 345 above the anular sealing plate 347 of cylinder
345. Alignment rods 351 may have a plurality of bearings 355 disposed
thereon to cooperate with the interior of alignment tubes 350.
Variable length, movable housing 340 has at its first end 360 or end plate
349, a means for controlling 361 the movement of the housing 340. Control
means 361 may preferably be at least one sensor means 362, or conventional
proximity switch, which operates to control the operation of a motor (not
shown) which moves cylinder 345 upwardly or downwardly, to vary the length
of the variable length pathway 317. The sensor means 361, or switch 362
may preferably be a pressure sensitive switch. Collimator 304' in the
preferred embodiment of the method of stereotactic-guided radiation
therapy in accordance with the present invention, includes the step of
contacting the patient 305 (FIG. 3) with a first end 360, or end plate
349, of the variable length pathway 317, and maintaining such contact
while the collimator 304' is being moved by varying the length L of the
variable length pathway 317 or variable length, movable housing 340.
Accordingly, sensor means 361, or switch 362 operates to control the motor
(not shown), whereby the motor is operated to move the first end 360, or
end plate 349 of variable length pathway 317, or variable length, movable
housing 40, into contact with patient 305, as well as maintain such
contact while collimator 304' is being moved along path 309 (FIG. 3) as
previously described. Alternatively, the method of stereotactic-guided
radiation therapy of the present invention includes the step of disposing
the first end 360 of the variable length pathway 317 a predetermined
distance from the patient 305 and maintaining that predetermined distance
between the first end 360 and the patient 305 while the collimator 304' is
moved by varying the length L of the variable length pathway 317 or
variable length, movable housing 340. In that embodiment, sensor means
361, or switch 362, can be a location sensor switch or sonar type switch
which detects the location of the skull 308, or other portion of the body,
of patient 305 and controls the operation of the motor (not shown) to
maintain a predetermined fixed distance between the end 360 variable
length pathway 317, or variable length, movable housing 340 from the skull
308 or other portion of the body of patient 305.
With reference now to FIGS. 16-20, another embodiment 304" of collimator
304' is shown. For those components which are the same as those previously
described in connection with FIGS. 11-15, the same reference numerals will
be utilized, and for similar components primed reference numerals will be
utilized. Collimator 304" includes a means for providing 316 a variable
length pathway 317, wherein the variable length pathway providing means
316 includes a variable length, movable housing 340 having a first end
360, and contains the tissue equivalent material 318. A reservoir 341' for
the tissue equivalent material is also provided. In the embodiment of
collimator 304" of FIGS. 16 and 17, the variable length, movable housing
340 is a variable length, movable piston 380 which includes the tissue
equivalent material 318. As piston 380 extends upwardly from the position
shown in FIG. 16 to the fully extended position shown in FIG. 17, the
tissue equivalent material is drawn upwardly from reservoir 341' through
passageway 381 into the interior of piston 380, or variable length pathway
317. Variable length, movable housing 340 is provided with similar guide
rods 351' and guide tubes 350, the guide tubes 350' having bearings 355
disposed therein, for aligning the movable housing 340 as it moves
upwardly and downwardly.
Reservoir 341' may include a collapsible plastic enclosure 382, whereby
upon the outward extension of piston 380, the plastic bag, or enclosure,
382 of reservoir 341' collapses as illustrated in FIG. 17. Piston 380 may
preferably be formed of a spring 383 encased in a flexible plastic
enclosure 384 thus forming a variable length, movable bellows 385, which
permits the variable length, movable piston 380 to expand and contract as
illustrated in FIGS. 16 and 17, and to additionally draw the tissue
equivalent material 318 through passageway 381 in the manner previously
described as bellows 385 expands into the position shown in FIG. 17.
Collimator 304" may be provided with the same control means 361 as
previously described, or alternatively, spring 383 may provide a means for
spring biasing the first end 360 of the movable housing 340 into contact
with patient 305. Thus, the force exerted by spring 383 upon the end plate
349' of housing 340 serves to keep end plate 349' in contact with the
patient 305 as collimator 304" is moved about patient 305.
The embodiment 304"' of collimator 304' in FIG. 20 is identical to that
illustrated in connection with FIGS. 16-19, with exception that collimator
304"' is provided with a motor 400 which controls the operation and
movement of the variable length, movable housing 340. Collimator 304"' is
provided with control means 361 or switch 362 which is operatively
associated with motor 400, whereby motor 400 causes the movement of
movable housing 340, as by a gear 401 contacting a mating gear disposed
upon one of the guide rods 351", whereby movable housing 340, or piston
380 may be raised or lowered as illustrated in FIGS. 16 and 17.
It is to be understood that the invention is not to be limited to the exact
details of construction, operation, exact materials or embodiments shown
and described, as obvious modifications and equivalents will be apparent
to one skilled in the art; for example, other types of control means could
be used to control the varying of the length of the variable length
pathway. Accordingly, the invention is therefore to be limited only by the
scope of the appended claims.
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