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Claims  |
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What is claimed is:
1. Stereotactic radiosurgery apparatus comprising:
a gantry supported for rotation about a gantry axis, the gantry having a
radiation-emitting head for movement in an arc in a radiation plane about
a center point corresponding to an intersection of the gantry axis and the
radiation plane, said gantry axis being normal to said radiation plane;
a collimator disposed to focus radiation from said radiation-emitting head
on said center point; and
collimator linking means for linking movement of said collimator to said
radiation-emitting head for automatic rotation of said collimator in said
radiation plane and about said gantry axis upon rotation of said gantry,
and wherein said collimator linking means allows movement of said
collimator relative to said radiation emitting head, said collimator
linking means includes a linking member connected to said collimator, said
linking member allowing said collimator to track rotation of said gantry
with no or minimal transfer of positioning inaccuracies from said gantry
to said collimator.
2. The stereotactic radiosurgery apparatus of claim 1 further comprising
patient support means to support a patient for treatment by said
radiation-emitting head.
3. The stereotactic radiosurgery apparatus of claim 1 wherein said
collimator linking means is a mechanical connection between said
collimator and said radiation-emitting head automatically moving said
collimator with said gantry and allowing said collimator to move relative
to said gantry to minimize incorporation of positioning inaccuracies from
said gantry to said collimator.
4. The stereotactic radiosurgery apparatus of claim 3 further comprising a
first support member, a collimator bearing means, a second support member
rotatably mounted to said first support member by way of said collimator
bearing means, and wherein said collimator is fixed to said second support
member and said first support member is anchored independent of said
gantry.
5. The stereotactic radiosurgery apparatus of claim 4 wherein said
collimator linking means is a gimbal mounted to said radiation-emitting
head.
6. The stereotactic radiosurgery apparatus of claim 5 wherein said gimbal
comprises an outer member mounted to said radiation-emitting head, an
intermediate member pivotably connected to the outer member, and said
linking member, said linking member being an inner member pivotably
connected to said intermediate member, said inner member serving as a slip
collar and having said collimator extending therethrough.
7. The stereotactic radiosurgery apparatus of claim 6 wherein each of said
outer members, intermediate member and inner member is a ring.
8. The stereotactic radiosurgery apparatus of claim 4 further comprising:
patient support means to support a patient for treatment by said
radiation-emitting head, said patient support means including a treatment
table for supporting the bulk of a patient and a stereotactic floorstand
for supporting a portion of the patient subject to radiation from said
radiation-emitting head, said treatment table and said stereotactic
floorstand both rotatable about a patient axis in said radiation plane,
said stereotactic floorstand operable to rotate said patient by way of a
floorstand bearing means, said floorstand bearing means mounted for
precise rotation of said floorstand with minimal or no incorporation of
any positional inaccuracies from said treatment table.
9. The stereotactic radiosurgery apparatus of claim 8 further comprising
floorstand linking means for linking movement of said stereotactic
floorstand to said treatment table for automatic rotation of said
stereotactic floorstand about said patient axis upon rotation of said
treatment table about said patient axis.
10. The stereotactic radiosurgery apparatus of claim 9 wherein said
floorstand linking means is a mechanical connection between said
stereotactic floorstand and said treatment table.
11. The stereotactic radiosurgery apparatus of claim 10 wherein said
floorstand linking means includes at least one arm fixed relative to said
treatment table and extending to said stereotactic floorstand to rotate
said stereotactic floorstand with said treatment table, while also
allowing movement of said treatment table relative to said stereotactic
floorstand.
12. The stereotactic radiosurgery apparatus of claim 1 further comprising:
patient support means to support a patient for treatment by said
radiation-emitting head, said patient support means including a treatment
table for supporting the bulk of a patient and a stereotactic floorstand
for supporting a portion of the patient subject to radiation from said
radiation-emitting head, said treatment table and said stereotactic
floorstand both rotatable about a patient axis in said radiation plane,
said stereotactic floorstand operable to rotate said patient by way of a
floorstand bearing means, said floorstand bearing means mounted for
precise rotation of said floorstand with minimal or no incorporation of
any positional inaccuracies from said treatment table.
13. The stereotactic radiosurgery apparatus of claim 12 further comprising
floorstand linking means for linking movement of said stereotactic
floorstand to said treatment table for automatic rotation of said
stereotactic floorstand about said patient axis upon rotation of said
treatment table about said patient axis.
14. Stereotactic radiosurgery apparatus comprising:
a gantry supported for rotation about a gantry axis, the gantry having a
radiation-emitting head for movement in an arc in a radiation plane about
a center point corresponding to an intersection of the gantry axis and the
radiation plane, said gantry axis being normal to said radiation plane; a
collimator disposed to focus radiation from said radiation-emitting head
on said center point; and patient support means to support a patient for
treatment by said radiation-emitting head, said patient support means
including a treatment table for supporting the bulk of a patient and a
stereotactic floorstand for supporting a portion of the patient subject to
radiation from said radiation-emitting head, said treatment table and said
stereotactic floorstand both rotatable about a common patient axis in said
radiation plane, said stereotactic floorstand operable to rotate said
patient by way of a floorstand bearing means, said floorstand bearing
means mounted to allow precise rotation of said floorstand with minimal or
no incorporation of any positional inaccuracies from said treatment table
and to allow movement of said floorstand relative to said treatment table,
and wherein said stereotactic floorstand is anchored independently of said
treatment table.
15. The stereotactic radiosurgery apparatus of claim 14 further comprising
floorstand linking means for linking movement of said stereotactic
floorstand to said treatment table for automatic rotation of said
stereotactic floorstand about said patient axis upon rotation of said
treatment table about said patient axis.
16. The stereotactic radiosurgery apparatus of claim 15 wherein said
floorstand linking means is a mechanical connection between said
stereotactic floorstand and said treatment table.
17. The stereotactic radiosurgery apparatus of claim 16 wherein said
floorstand linking means includes at least one arm fixed relative to said
treatment table and extending to said stereotactic floorstand to rotate
said stereotactic floorstand with said treatment table, while also
allowing movement of said treatment table relative to said stereotactic
floorstand.
18. The stereotactic radiosurgery apparatus of claim 15 further comprising:
collimator linking means for linking movement of said collimator to said
radiation-emitting head for automatic rotation of gantry axis upon
rotation of said gantry, said linking means allowing said collimator to
track rotation of said gantry with no or minimal transfer of positioning
inaccuracies from said gantry to said collimator.
19. The stereotactic radiosurgery apparatus of claim 18 wherein said
collimator linking means is a mechanical connection between said
collimator and said radiation-emitting head automatically moving said
collimator with said gantry and allowing said collimator to move relative
to said gantry to minimize incorporation of positioning inaccuracies from
said gantry to said collimator. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates generally to a radiosurgery system employing
multiple beams of radiation focused onto a stereotactically localized
target, and more particularly to stereotactic radiosurgery apparatus
affording greatly improved mechanical accuracy in the focusing of
radiation from a moving linear accelerator with respect to a moving
stereotactic frame.
In 1951, Dr. Lars Leksell coined the term "radiosurgery", to describe the
concept of focusing multiple beams of external radiation on a
stereotactically localized intracranial target. After experimentation with
standard X-ray treatment devices, proton beam, and linear accelerators, he
and his collaborators developed a device which is called the GAMMA KNIFE
(currently marketed by the Electra Corporation, Stockholm, Sweden). The
device consists of a hemispheric array, currently containing 201 Cobalt-60
sources. The radiation from each of these sources is collimated and
mechanically fixed, with great accuracy, on a focal point at the center of
the hemisphere. When a patient has a suitable lesion for treatment
(usually an intracranial arteriovenous malformation), it may be precisely
localized with another device called a stereotactic frame. Using the
stereotactic apparatus, the intracranial target is positioned at the focal
point of the GAMMA KNIFE. Since each of the 201 radiation pathways is
through a different area of the brain, the amount of radiation to normal
brain tissue is minimal. At the focal point, however, a very sizable dose
is delivered which can, in certain cases, lead to obliteration of the
lesion. This radiosurgical treatment is, in some instances, a much safer
treatment option than conventional surgical methods.
Four GAMMA KNIFE devices are currently being used worldwide for
stereotactic radiosurgery (Stockholm, Sweden; Buenas Aires, Argentina;
Sheffield, England; Pittsburgh, U.S.A.), and have been used to treat
approximately 1500 patients. The results of treatment, as well as many
technical issues, have been discussed in multiple publications. Several
factors, however, have impeded the widespread usage of this device. First,
the device costs about $2.2 Million Dollars, U.S. Second, the Nuclear
Regulatory Commission has ruled that this device cannot be shipped loaded
in the U.S.A. Consequently, loading must be done on site, necessitating
the construction of a portable hot cell. Third, the half life of Cobalt-60
is 5.2 years, which requires reloading the machine, at great expense,
every 5-10 years. Fourth, the dosimetry system currently marketed with the
device is relatively crude, especially when utilized with more modern
imaging modalities such as CT scan and MRI scan.
An alternative method for radiosurgery involves irradiation of intracranial
targets with particle beams (i.e., proton or helium). In this instance,
one does not rely solely on multiple cross-fired beams of radiation. A
physical property of particle beams, called the "Bragg-peak effect",
allows one to deliver the majority of the energy of a small number of
beams (approximately 12) to a precisely predetermined depth. Multiple
publications regarding particle irradiation of intracranial lesions
(especially pituitary tumors and arteriovenous malformations) have
appeared in the literature. The results have not generally been as good as
those obtained with the GAMMA KNIFE. This may, however, be solely a
consequence of patient selection criteria. Particle beam devices require
the availability of a cyclotron. Only a few such high energy physics
research facilities exist in the world.
A third current radiosurgical method uses a linear accelerator (LINAC) as
the radiation source. As mentioned above, Leksell rejected the LINAC as
mechanically inaccurate. More recently, groups from Europe have reported
their methods for radiosurgery with LINAC devices. In the U.S.,
researchers at the Peter Bent Brigham Hospital in Boston have developed a
prototype LINAC system using highly sophisticated computer techniques to
optimize dosimetry. Thus far, approximately 12 patients have been treated
with good results. This LINAC system, however, suffers from certain
mechanical inaccuracies which have limited its use. In addition, the
computer dosimetry system employed is very time consuming, rendering the
treatment program inefficient.
Currently, there is great interest in radiosurgery. Although the GAMMA
KNIFE represents the "gold standard", its great expense and requirement
for frequent replenishment of radiation sources have discouraged most
potential users. The proton beam devices are never likely to be widely
available because of the requirement for high-energy particle beam source
(cyclotron). The linear accelerator offers an attractive alternative to
such devices. However, a major disadvantage of known linear accelerator
based systems is their mechanical inaccuracy.
It is desirable to provide stereotactic radiosurgery apparatus employing
linear accelerators which overcomes the disadvantages of known systems,
and it is to end that the present invention is directed.
SUMMARY OF THE INVENTION
The present invention affords stereotactic radiosurgery apparatus
particularly adapted for use with the LINAC which comprises a guiding
structure having three bearing systems for eliminating mechanical
inaccuracies occasioned by the relative movement between a LINAC gantry
and a stereotactic floorstand. The three bearing systems of the guiding
structure include one which guides the radiation collimator, one which
allows rotation of the stereotactic floorstand, and one which allows the
gantry to drive the collimator and couples the collimator of the LINAC to
the stereotactic localizing device. The collimator itself is mechanically
uncoupled from the LINAC housing. As the LINAC arcs through space, the
mechanical bearing system ensures that "sag" in the LINAC does not result
in angular deviation of the collimated beam from the target point. These
bearing systems, therefore, greatly improve the mechanical accuracy of the
LINAC, eliminating the major previous disadvantage of this radiosurgical
method.
The invention may be employed with a dosimetry system being developed at
the University of Florida which incorporates improvements in computer
hardware and software that allow very rapid but highly accurate dosimetry
computations. The hardware utilized includes the SUN 3/280 system, with a
fast rate array processor and DIGIKON digitizing board. This configuration
allows greater than 4 MIPS and 12 MEGAFLOPS. Such improvements in software
design and hardware will allow dosimetry calculations in approximately one
tenth of the time currently required by the Boston system, while greatly
exceeding the sophistication currently obtained with the GAMMA KNIFE
system. Thus, the time efficiency of the treatment process will be greatly
improved.
The invention overcomes a major previous disadvantage of LINAC based
systems, mechanical inaccuracy. It also offers improved dosimetry and
quality control procedures. The price of LINAC based radiosurgical systems
in an order of magnitude less than GAMMA KNIFE and, therefore, very
attractive economically.
An additional advantage of LINAC based systems is its potential
applicability to lesions elsewhere in the body (GAMMA KNIFE is currently
limited by design to the head). The inventive concept of mechanically
coupled LINAC systems and stereotactic localization is also useful for
radiation therapy of may different types of lesions throughout the body.
Briefly, in one aspect, the invention provides radiosurgery apparatus
comprising a gantry supported for rotation about a horizontal axis, the
gantry carrying a radiation-emitting head for movement in an arc in a
substantially vertical plane about a center point corresponding to an
intersection of the horizontal axis and the vertical plane; a fixed
mounting plate; a stand supported on the mounting plate by first bearing
means for rotation of the stand about a vertical axis located in said
vertical plane, the vertical axis intersecting said center point; a first
support member connected to the mounting plate; a second support member
rotatably connected to the first support member by second bearing means
for rotation about said horizontal axis, the second support member having
an arm adapted to be positioned adjacent said head; a collimator connected
to the arm for focusing radiation at said center point; and gimbal means
carried by the head for coupling the collimator to the head such that upon
rotation of the gantry about the horizontal axis the collimator swings in
another arc in said vertical plane while maintaining a predetermined
distance between the collimator and said center point so as to compensate
for deviations in the movement of the head with respect to the center
point.
The present invention may alternately be described as stereotactic
radiosurgery apparatus comprising a gantry supported for rotation about a
gantry axis, the gantry having a radiation-emitting head for movement in a
radiation plane about a center point corresponding to an intersection of
the gantry axis and the radiation plane. The gantry axis is normal to the
radiation plane. A collimator is disposed to focus radiation from the
radiation-emitting head on the center point. A collimator linking means
links movement of the collimator to the head for automatic rotation of the
collimator in the radiation plane and about the gantry axis upon rotation
of the gantry, the collimator linking means allowing the collimator to
track rotation of the gantry with no or minimal transfer of positioning
inaccuracies from the gantry to the collimator. A patient support means
supports a patient for treatment. The collimator linking means is a
mechanical connection between the collimator and the head automatically
moving the collimator with the gantry and allowing the collimator to move
relative to the gantry to minimize incorporation of positioning
inaccuracies from the gantry to the collimator. A first support member, a
collimator bearing means, and a second support member rotatably mounted to
the first support member by way of the collimator bearing means are used.
The collimator is fixed to the second support member and the first support
member is anchored independently of the gantry (i.e., the first support
member is not anchored to the floor or ground or other fixed base by way
of the gantry). The collimator linking means is a gimbal mounted to the
head. The gimbal comprises an outer member mounted to the head, and
intermediate member pivotably connected to the outer member, and an inner
member pivotably connected to the intermediate member. The inner member
serves as a slip collar having the collimator extending therethrough. Each
of the outer member, intermediate member, and inner member is a ring. The
patient support means includes a treatment table for supporting the bulk
of a patient and a stereotactic floorstand for supporting a portion of the
patient subject to radiation from the radiation-emitting head. The
treatment table and the stereotactic floorstand are both rotatable about a
patient axis in the radiation plane. The stereotactic floorstand is
operable to rotate the portion of the patient by way of a floorstand
bearing means, the floorstand bearing means mounted to allow precise
rotation of the floorstand with minimal or no incorporation of any
positional inaccuracies from the treatment table. The floorstand linking
means links movement of the stereotactic floorstand to the treatment table
for automatic rotation of the stereotactic floorstand about the patient
axis upon rotation of the treatment table about the patient axis. The
floorstand linking means is a mechanical connection between the
stereotactic floorstand and the treatment table. The floorstand linking
means includes at least one arm fixed relative to the treatment table and
extending to the stereotactic floorstand to rotate the stereotactic
floorstand with the treatment table, while also allowing movement of the
treatment table relative to the stereotactic floorstand.
The invention may alternately be described as a stereotactic radiosurgery
apparatus comprising: a gantry supported for rotation about a gantry axis,
the gantry having a radiation-emitting head for movement in an arc in a
radiation plane about a center point corresponding to an intersection of
the gantry axis and the radiation plane, the gantry axis being normal to
the radiation plane. A collimator is disposed to focus radiation from the
radiation-emitting head onto the center point. A patient support means to
support a patient for treatment by the head includes a treatment table for
supporting the bulk of the patient and a stereotactic floorstand for
supporting a portion of the patient subject to radiation from the head.
The treatment table and stereotactic floorstand are both rotatable about
the patient axis in the radiation plane. The stereotactic floorstand is
operable to rotate the portion of the patient by way of a floorstand
bearing means. The floorstand bearing means is mounted to allow precise
rotation of the floorstand with minimal or no incorporation of any
positional inaccuracies from the treatment table. The stereotactic
floorstand is anchored independently of the treatment table (i.e., the
stereotactic floorstand is fixed to a base or floor and is not fixed to
the treatment table).
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features of the present invention will be more readily
understood when the following description is considered in conjunction
with the accompanying drawings wherein like parts have the same number
throughout and in which:
FIGS. 1 and 2 are a side elevation view and an end elevation view,
respectively, of conventional linear accelerator apparatus which may be
employed for stereotactic radiosurgery, the figures illustrating possible
misalignments of a radiation-emitting head of the apparatus;
FIGS. 3 and 4 are a side elevation view and a top view, respectively, of
stereotactic radiosurgery apparatus embodying the invention;
FIG. 3A is a side exploded view of a linking arrangement for linking a
collimator to a radiation-emitting head;
FIG. 4A is a top view showing parts of a floorstand support arrangement:
FIG. 4B shows a side exploded view with some parts in cross-section of
parts of FIG. 4A;
FIGS. 5 and 6 are a side elevation view and a top view, respectively, of
guiding structure in accordance with the invention;
FIG. 5A is a top exploded view of parts from FIG. 5;
FIG. 7 is a perspective view illustrating conceptually a preferred form of
a main arcing bearing in accordance with the invention;
FIG. 8 is a perspective view illustrating conceptually a preferred form of
a gimbal bearing in accordance with the invention;
FIG. 9 shows an alternate arrangement for supporting a collimator;
FIG. 10 shows an alternate arrangement for supporting a floorstand;
FIG. 11 shows a further alternative arrangement for supporting both the
collimator and a floorstand by way of a common support;
FIG. 12 shows a side view of an arrangement for linking rotation of a
floorstand to rotation of a treatment table;
FIG. 13 shows a cross-section view of the connection between the floorstand
and treatment table of FIG. 12; and
FIG. 14 shows a side view of an alternate arrangement for linking a
floorstand to a table.
DETAILED DESCRIPTION
The invention is particularly well adapted for compensating for
misalignments due to mechanical inaccuracies of a moving linear
accelerator head in order to maintain precise focusing of the radiation at
a predetermined point, and will be described in that context. As will
become evident, however, this is illustrative of only one utility of the
invention.
FIGS. 1 and 2 illustrate a conventional LINAC device which comprises a
fixed base 10 and an L-shaped gantry 12 which is rotatable with respect to
the base about a horizontal axis 14. The gantry carries a
radiation-emitting head 16, and rotation of the gantry causes the head to
sweep through an arc R located in a substantially vertical plane which is
perpendicular to the horizontal axis. The dotted lines in the figures
indicate potential misalignments caused by mechanical inaccuracies or sag
of the gantry in any of the directions indicated in the FIGS. as A, B or
z. These misalignments result in misfocusing of the radiation from the
head 16 and are intolerable in radiosurgery, for the reasons noted
hereinafter.
In order to best understand the invention, the three principle components
of a stereotactic radiosurgery procedure will first be explained. These
components are localization, dose computation and optimization, and
execution of treatment. The ultimate accuracy of the procedure is
dependent on each of these components.
The first component in the procedure involves the localization of the
tumor. This is accomplished by one of two means. Currently, the method of
choice is through stereotactic angiography. The procedure begins with the
stereotactic ring being fitted to the patient. An angiographic localizing
device is then attached to the ring. This device is known and consists of
four sets of fiducial alignment markers. Two sets of these markers project
onto each of two orthogonal angiographic x-rays. By location of the
fiducial points and the target on each x-ray, the precise, x, y, z
coordinates of the target (to an accuracy of 1 mm) relative to the
stereotactic ring can be derived. While this part of the procedure allows
the coordinates of the target relative to the localization ring to the
determined, more anatomical information is needed for dosimetric analysis.
The next step replaces the angiographic localizing device with another
localizer specially designed for localization in computer tomography. This
is the standard BRW CT Localizer. The patient is aligned in the CT gantry
and contiguous 5 mm slices, beginning at the level of the localization
ring and advancing superiorly past the top of the patient's skull, are
obtained. If the target volume can be identified in the computerized
tomography image, then the x, y, z coordinates of the target volume are
again calculated. (This can provide a double check of the x, y, z
coordinates relative to the stereotactic ring.) If not, then the target
obtained from the angiographic procedure can then be superimposed onto the
CT scan data.
With the digitally encoded data from the CT scan and the two angiographic
films, the data may be then transferred to a dosimetry computer system.
The CT scan provides three dimensional anatomical information of the
patient allowing a solid patient model to be constructed. The coordinates
of the target volume from the angiogram and the CT scan data are then
merged.
Computation and Dose Optimization: In order for the high single fractions
of radiation to be delivered to the target volume, a technique to
concentrate the radiation at the target while spreading out the radiation
to lesser concentrations throughout the normal tissues must be utilized.
Moving the radiation source through multiple arcs achieves this objective.
It is important for the radiotherapist and neurosurgeon to be able to
examine the consequence of each portion of the arc. The computer system
which computes the dosimetry must have the ability to display each arc
segment. In the routine stereotactic procedure, it is anticipated that
four arcs, three at 100 degrees and one at 240 degrees, will be utilized.
The computer must allow the CT scan to be reformatted in each of these arc
planes (relative to the patient's skull) so that each individual arc's
dose distribution can be examined. If any particular arc results in an
extensive dose to a critical structure, the therapist can alter the arc
parameters to avoid the anatomical area of concern. The first version of
the dosimetry system under development will allow dose optimization
through operator control. For subsequent versions, the operator will
identify the target region and the areas where dose should be minimized.
The computer will then, through use of an optimization algorithm, design
the treatment which best concentrates the radiation over the tumor volume
while minimizing the dose to normal tissues. The spacing between arcs, the
size of the collimator, and the variation in arc length and weight will be
parameters used in the optimization.
The method necessary for dose computation and optimization using a CT scan
is complicated by the high resolution necessary in the procedure. The .
stereotactic targets can be identified to plus and minus a millimeter. The
treatment portals can range anywhere from 1 to 3 cm in diameter. The
spatial coordinates of the computational grid, in the area of the target,
must be in the 1 mm range. However, there is little need for 1 mm accuracy
outside a 5 cm radius of the target itself. A 0.5 grid is adequate in this
region. By working with both the 1 mm and 5 mm grids, the number of
computation points at which a dose must be evaluated for the complex arcs
can be vastly reduced.
Once the acceptable treatment scheme has been derived, the coordinates of
the isocenter (focal point of the radiation), the collimator size, and the
arc parameters are then transferred to the operator of the linear
accelerator.
FIGS. 3 and 4 illustrate the stereotactic treatment setup. As shown, a
patient is placed on a treatment table 20 which is supported by a member
22 on a rotating plate 24 posi | | |
