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Description  |
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BACKGROUND OF THE INVENTION
The present invention refers to a convergent multibeam unit for radiation
and particularly to a combination of lineal accelerator with stereotaxic
means that contribute with substantial advantages to the devices used at
present for radiation of the cerebral structures.
Stereotaxy, which was initiated at beginning of this century with a Horsley
and Clark device used on animals for experimentation, made it possible to
locate different intracerebral structures with precision and to reach said
structures with stimulation and coagulation electrodes; it was developed
until 1947, when Spiegel and Wycis reported in the U.S.A. the first
concept of a stereotaxic device adapted for human use. Subsequently,
different reports were made from scientific societies of several European
countries.
In France, Prof. Jean Talairach was the pioneer of this discipline; his
contribution constitutes the most important neurosurgical work of that
country.
At present the possibility of observing the course of the encephalic
vessels in each individual case makes it possible to locate the cerebral
fissures and convolutions with precision, and consequently, effect
multiple biopsies. From an exact diagnosis and the consequent
histoprognosis an adequate therapy can be selected.
The possibilities of treatment would be:
(a) Surgical ablation (total or partial) if a situation and extent of
injury allows it,
(b) Radioactive interstitial implantation (with Iridium 192 or Iodine 125),
(c) External radiation with lineal accelerator due to its penetration and
minor effect on the skin compared, for example, with Cobalt 60,
(d) Radiation with Cobalt 60 with multiple fixed sources ("Gamma Unit"), to
which reference shall be made below and, finally;
(e) Radiation with the convergent multibeam unit of the invention in
stereotaxic condition.
Of the radiation methods in which we are interested, implantation is
effected on small glia tumors of low malignant degree and situated in the
nervous parenchyma.
Radiation through teletherapy with a lineal accelerator is used only on
extensive tumors, or in protocols of "implantation-teletherapy with lineal
accelerator" association, placing an important tumoricide dose on the
tumor itself and a smaller dose on the periphery of same to destroy the
tumor cells that are at a distance from the center of the injury and that
can be responsible for its reappearance.
The application of the convergent multibeam unit of the invention is based
on the necessity to apply a high dose in the center of the tumor, with a
rapid decrease of the dose on the edges and the possibility of protecting
the normal operational structures that have not been infiltrated by a
tumor, without applying too small a dose on the latter.
Numerous working trials have demonstrated that, as the volume of radiation
is increased, either through teletherapy or interstitial, the
possibilities of radionecrosis are consequently increased. This means the
death of the tumor in a significant of cases, but the complications to
which this leads also cause the death of the patient. Over and above a
volume of approximately 5.times.5.times.5 cm a radionecrosis is mortal
notwithstanding its surgical extirpation (which is sometimes possible),
due to complications of uncontrollable edema. Experience with biopsies and
necropsies corroborates this.
If at the same time the precision of the methodology permits examination of
the exact limits of the injury, the ideal would be to apply a therapy
that, without losing its efficiency, must be as circumscribed as possible,
reducing its diameter. This implies the necessity of a strict
localization, obtainable by means of estereotaxy and a minimum of the
complications based on the reduction of the diameter of the radiation
beams and the multiplication in number of the entries that allow to
obtain, within the perfectly admissible tolerances for each of them, the
concentration on the area, in this case the tumor, of the sum of said
radiations.
The focal concentration of numberless radiation beams of high energy (6 to
12 MV) centered on the injury obtain the desired end.
The smallest fields used in teletherapy for the axion are of 4.times.4 cm.
If, as stated above, radionecrosis is the inevitable result of radiation
on volumes of the order of 5.times.5.times.5 cm, the danger limits become
very narrow.
SUMMARY OF THE INVENTION
The convergent multibeam unit for lineal accelerator of the invention is
particularly applicable in small injuries, although those of medium size
diameter can be treated by more than one application separated in
different periods. A particular quality of those treatments is that they
can be effected in one only session, which substantially modifies the
classical concepts of radiotherapy.
In view that they also radiate small volumes, the dose can be increased,
which also causes very special changes in the tumor structure, such as the
transformation of solid tumors, or hypodense into radionecrotic hyperdense
tumors that, due to their small volume can be removed or that the
reduction of the volume improves the symptomatology.
This modification of the tumor structure also opens new ways in the
interpretation and treatment of tumors, whether glia tumors or acoustic
neurinoma in hypophysis adenoma and craniopharyngioma, among others.
On the other hand, vascular injuries, such as angiomas, aneurisms and even
cavernous-carotid fistula, have been treated with said concentrated
radiations in one session with the result of the progressive obliteration
of the defective afferent vessels or of aneurism collum, as the answer to
a vasculities by endotelities by radiation. This subject by itself is
sufficient to justify this technology that gives new solutions to complex
problems in vascular radiosurgery.
As a complement of the foregoing may be added the therapeutic radioinjuries
with the object to cause the exclusion of structures of pathological
performance within different operating cerebral circuits, that originates
the restructuring of same with the disappearance of clinical symptoms such
as certain Parkinson symptoms, obsessive neurosis and pains caused by
cancer.
With the object to obtain multiple entries for radiation, investigators of
the Karolinska Hospital in Sweden, after working at the University of
Upsala with different high energy radiation systems, arrived at a solution
that allowed them to use a high energy equipment within the hospital
premises. Thus, the group directed by Professor Lars Leksell designed
mechanically complex equipment using Cobalt 60 as the radiation source.
This device, known as "Gamma Unit", already mentioned above, has a head in
the shape of a spherical can at present with 200 sources of Co 60,
radially directed toward a center that can be given a high dose of
radiation. The periphery of said radiated volume receives a small dose of
radiation due to the multiplication of the entries.
This solution presents some difficulties, especially due to the complexity
of the apparatus, the high cost and restricted scope of application of
which makes its service possibility very limited. Added to the foregoing
is the natural decrease of the dose to half the initial energy in a period
of five years, that requires the replacement of the sources. Furthermore,
the energy of Co 60 varies from 1.17 to 1.33 MV, which is lower than that
obtained with a lineal accelerator that varies from 6 to 18 MV. On the
other hand, the fact of having fixed multiple entries confines the
possibility of its use and thus, enormously increases costs and in the
economic aspect restricts the possibilities of treatment.
Searching for an adequate solution of those problems, the conclusion was
arrived at that means should be found that are capable of radiating high
energy and which, having an ample scope of application, could be used in a
combination where the stereotaxic techniques could be used.
A lineal accelerator is a high energy radiation system that has other
applications besides those of neurosurgery as, among other purposes, it is
already used for radiotherapy treatment. Which means that, as a source of
radiation, its scope of application is very ample. The energy of the
photons of said accelerator varies from 6 to 18 MV that, as mentioned
above, is much higher than that of Cobalt 60.
The combination to obtain the multibeam unit of the invention thus obtains
a device that having higher radiation energy, allows a greater scope of
application. To the foregoing must also be added that the flow of photons
per sq. mm. is 1000 times higher than that of Cobalt 60. Besides, having a
variable multiplicity of entries within the innumerable possible entries
on a virtual spherical cap defined by the combined sweeping arches of the
lineal accelerator with the stereotaxic device, provides this method with
a higher flexibility.
Therefore, the multibeam unit of the invention was conceived based on a
stereo-tele-radiotherapy system that has the desired characteristics as
well as substantial advantages over the systems known at present.
The assembly includes:
Modification and adaptation of the stereotaxic system to transform it into
an arch system.
Adequate collimation system of 10 MV photons beam (that correspond to the
lineal accelerator selected in combination with said system) to obtain a
geometry with minimum penumbra.
System to hold the body of the patient, adaptable to all the positions of
the head that does not burden the supports of the stereotaxic system and
that maintains with same a common rotation axis.
In said device the approaching system by means of grates which is used with
stereotaxic frames has been eliminated in view that, although it is useful
for certain purposes, it does not have the particular characteristics
obtained with the invention in which as great a multiplicity of entries as
desired is obtained due to the fact that the scope of possibilities is
provided by means of continuous combined runs of the accelerator and the
stereotaxic frame and with same, the head of the patient.
The transformed stereotaxic frame has the characteristic that the center of
the injury in the brain that is fixed by the cranium to said frame becomes
the isocenter of an axis system that allows said frame to effect an
anterior-posterior angular displacement so as to allow the approach on all
its useful surface.
The frame can go up or down so that the center of the injury can be
situated on the rotation axis, being connected to the retention system by
means of slides. Said rotation axis, assembled on bushings arranged on
each side of the frame retention system, is aligned so that its central
axis can coincide with the center of the injury to be treated. As the
injury can be situated in the center line or be displaced to one side of
said center line, the system allows lateral displacements of up to 7 cm.
to both sides.
The device allows placing the injury in the isocenter of the system that
also coincides with the rotatory displacement isocenter of the lineal
accelerator with which same is combined.
The assembly maintains the coincidence of both isocenters for which purpose
the support of the stereotaxic frame has a rigid and non-deformable base
with columns that do not admit any kind of bending under the conditions to
which the unit is submitted and with a register system that allows the
above mentioned coincidence of both isocenters.
As the opening of the quadrangular collimation of the lineal accelerator is
prepared for areas the smallest of which generally used are of 3.times.3
cm., and it is desired to work with a beam in which the dose on the
periphery is 1% lower than that of the dose in the axis of the beam, and
in order that said reduction should occur within 5 mm from the axis of the
beam, it is necessary to add a supplementary collimation to the
accelerator, interposed in a stretch of 2.times.2 cm. of said accelerator.
The attached secondary collimator has a diameter of 5 cm. and a cylindrical
orifice with a diameter of 3, 5, 9 and 12 mm. and 15 cm. long. Its distal
end is situated at 12,5 cm. from the isocenter of the lineal accelerator.
The multiplication of the entries obtained with this unit which, as stated
above, constitutes one of its principal advantages, has the object to
obtain the maximum reduction of the radiation that must pass through the
normal structures to reach the area to be treated. A maximum of between 30
and 50 rads per entry has been imposed, said figure being lower than the
200 rads adopted as the maximum by Leksell in his above mentioned system
("Gamma Unit"), supplied with 200 sources of Co. 60.
The intercrossed radiation beams in the scope of the frontal bone due to
the rotation of the accelerator, and in the sagittal flat due to the
rotation of the stereotaxic assembly combined with the accelerator, said
rotations defining a virtual spherical cap, produce the effect of "crossed
fires" that determine a small volume within which radiation will be at the
maximum, the center of said volume being occupied by the area to be
radiated.
In the periphery of said volume and due to the above mentioned multiplicity
of entries, that can be selected from the 1225 possible entries if angular
displacements of 5.degree. are effected over a virtual spherical cap in
sweeping arches in the order of 175.degree. (if arches of 180.degree. are
taken, the radiation at the ends will be much higher than that foreseen);
or of the 28,900 possible entries if the angular displacements of the
lineal accelerator and the stereotaxic assembly are of 1.degree. at a time
on sweeping arches of 170.degree. ; radiation rapidly decreases to less
than 1% of the central dose, which allows an excellent tissular tolerance
and thus constitutes one of the most important advantages of the
invention.
One of the characteristics of the combination of the stereotaxic assembly
with the lineal accelerator is the support system of said assembly whose
base is unmovably associated with the base of the accelerator, and in
which the body of the patient does not mean a load on the supports of the
stereotaxic system. It must be taken into account that the unit, besides
fulfilling certain precision requirements, must also offer comfortable
conditions for a treatment that can last from half an hour to an hour and
a half per session.
As to each of the successive positions of the stereotaxic device on the
sagittal rotation axis corresponds a series of consecutive positions of
the lineal accelerator on the frontal bone, which define the virtual
spherical cap that covers the cranial cavity, the body of the patient must
accompany the different positions of the head in order to avoid pains or
contractures at the cervical area level which must act as compensator of
the movements of the head.
This objective was obtained by means of a particular concept of the
adaptation means for the patient under treatment, based on a seat with a
back, means to regulate the position and height, that is also displaceable
on curvilinear guides whose curve center coincides with the isocenter of
the system.
Other advantages and characteristics of the invention may be observed from
the specifications that for a better understanding and comprehension have
several figures attached, which represent the convergent multibeam unit
for radiation of the invention in one of its preferred embodiments, as a
non-restrictive example of its scope, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general perspective view of the convergent multibeam unit
assembly in which the component parts of same and their combination may be
observed.
FIG. 2 is an elevated side view that also shows the unit assembly.
FIG. 3 is a front elevated view and, finally,
FIG. 4 is a partial view showing details of the stereotaxic device which,
combined with a lineal accelerator, integrates the assembly.
DETAILED DESCRIPTION OF THE DRAWINGS
In the different figures the same reference numbers indicate equal or
corresponding parts, the different pieces and/or assemblies are indicated
with letters.
As may be observed from the drawings, the convergent multibeam unit for
radiation of the invention comprises a radiation means constituted by a
lineal accelerator a combined with a stereotaxic assembly mounted on a
base b, rigidly associated to the base of said lineal accelerator a,
obtaining a convergent radiation system, of multiple entries, that has the
characteristics and advantages mentioned above.
Said lineal accelerator a is angularly displaceable around an axis x and
has a radiation axis r, the intersection of which defines the isocenter of
said accelerator, said isocenter constituting the imaginary and fixed
point in space that, whatever is the angular position of the accelerator
around the above mentioned axis x, said axis x is intersected with the
radiation axis r.
The substantially rigid base of the stereotaxic assembly b is associated,
preferably beneath floor level, with the base of accelerator a, thus
constituting an assembly without any possibility of the relative
displacement of its components. On said base b, a set of rigid columns 1
are placed that form the supports of the stereotaxic frame m (FIG. 4).
Said frame m, supplied with towers 2 with means 3 for fixing to the cranium
of the patient, has pieces 4 on the opposite sides, with respect to which
it is longitudinally displaceable and fixed by means of bolts to the
desired position, that are also displaceable in the normal direction of
the former, in respective pieces 5 that have orifices for fixing to the
bar gudgeons 6 that define axis z of angular displacement of frame m. The
operation of said angular displacement is effected by means of a mechanism
with toothed sector 7 that connects with a band 8 operated with handle 9,
as shown in FIG. 4.
For placing said frame m, that is fixed to the cranium of the patient, same
has the possibility of movement pointed out with arrows in FIG. 4. The
lateral displacements of frame m are regulated by the axial displacement
of the bar gudgeons 6 into the top orifices of columns 1 which they pass
through.
The fixing into position of axis z must be sufficient to contain the
isocenter of the lineal accelerator, that is to say, the angular
displacement axis x of the lineal accelerator z of the stereotaxic frame m
and the radiation axis r are intersected in said isocenter that in the
operative condition of the unit, shall correspond to the position of the
area to be radiated.
The axial displacement of the bar gudgeons 6 at the top ends of columns 1
allow the lateral displacement of frame m and carry the area, that can be
to one side, to the isocenter of the system.
The base b of the stereotaxic assembly has a fixed strip formed by a set of
curvilinear rails 10 on which the base 11 is displaced along with a seat
12 that has a back 13.
Said seat 12, as well as the back 13, have position and height regulation
means. The base 11 has a reducing box 14, an operating handle 15 and said
box 14 is also connected to a rack rail placed on at least one of the
internal sides of one of the curvilinear rails 10, as shown in FIGS. 1 to
3.
The center of curvature of the above mentioned rails 10 coincides with the
position of axis z that contains the isocenter of the system, so that with
the angular displacement of frame m (with the patient's head) around said
axis z, the seat 12 and back 13 assembly that holds the patient is also
displaceable around said axis, accompanying the rotation of the above
mentioned frame m.
As may be observed from the foregoing description and drawings it is
possible to carry out multiple convergent entries on an area to be
radiated which, as stated above, is placed in the isocenter of the system,
with the combined movement of the arch of the lineal accelerator a on its
rotation axis x and the stereotaxic frame m around its axis z, both
rotations defining a virtual spherical cap that thus admits multiple
entries with the known advantages mentioned above.
As a variation of the invention, the possibility of the rotation frame m
around axis z can be replaced by the rotation of same--with the
patient--on a vertical axis and (FIGS. 2 and 3) therefore the virtual
spherical cap is defined by the angular displacement arch of frame m
around axis y and that of the lineal accelerator a around axis x.
On both sweeping arches the desired number of multiple radiation entries
may be selected, said radiation, as mentioned above, being concentrated on
the small volume around the isocenter of the system in which the area to
be radiated is placed.
Having thus particularly described and determined the nature of the
invention and the manner in which the same can be put into practice, we
hereby declare that the principal object of the same and the different
embodiments of same are defined, as regards its scope and claims of
exclusive property and right, in the claims that form an inseparable part
of the present specifications, which read as follows:
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