Note: Descriptions are shown in the official language in which they were submitted.
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COLLIMATORS
l D Oli Tl-IE INVl~Nl'ION
Tlle present invenfioll relates to radiosutgely genel-ally, and particulal-ly tocollimators used in stereotactic radios~n-~ery.
13ACKGROIJND Ol~ Tl IE INVENrrlON
Stereotactic ra~iosurgery invt)lves dose accu~ llatioll in a target volume by
irradiating the target fi-om a multilllicity of orientations witll rlnely collimated beams.
rI lle use of stel-eotactic r~(liosur~ety to ren(ler tiss~le necrotic is well established
an(l vario~ls systems are cul-l-elllly use(' s'or stereotactic ra(liosln~ely. The prior art recognizes the
need to conline ra(lialion as mucll as possil)le to tl-e tat~et volullle being treated. Generation of a
clesired dose l~attelll in an(l o~lt ortl-e tnl-L,et volulllc is Ille ol)jeclive of a treatnlent plall. Sucll a
plan takes into accoutlt linlitatiolls of tl~e l~artic~llal- ra(lios~ ical system used. System lypes
include a Gamllla Unit whicll utilizes a nlulfil~licity Or Cobalt-6() sources arl-al~ged on a spherical
surface, a linear accelerator (I,INAC) wl~ich ufili~es a proton bealll source nlounte(l on a rotating
gantry, and a stationary genel-alol- lor a cl-arge(J l)arlicles bealll. l'llese radioslll-gical systems, as
well as associated metllods, cllalaclcl-istics an(l l~erforlllallce al-e described in various publicafiolls,
e.g., Stereotactic Racliosul ~ery, Alexan(lel- E. el al.7 McGraw-l-lill, 19~)3, and Neul oslJI-L~ery
Clin s o~Nortll America, vol. ~, no. 1, L utlsfol(l l, D. (e(litor), W.13. S~l~ln(lers Co., Jan. 1992.
Treatlllellt ~!anllill~ capabililies inclu(le selectin~ a dose level to the tar~set,
choosing cnllinlatols for bealll s}la~in~ al1(1 a detern~inatioll of l-eam orientations fi-om whicll
ra{iialion is deposited in tlle target vol~ln-e. ln or~ler to re(lLIce tl~e (lose deposite(l in llealtlly tissue
outside the target vol~lme, it is generally desiral~le to spl-ea(l beam orientations over a wide range
and to employ collinlators wllicl~ conl;lle tlle ra(liatioll to t}le targel vol~nlle.
Pl-ior art stere(-)tactic radio.ciulgel-y systems incolpol-ate point soul-ces for
generatillg radiation l~ealns (a lloinl soln-ce is a ra(lialioll source wllicll is signilicantly smaller than
the tar~et). A collimator associated witll a }~oin~ sourGe pl~od~lces a divelging beam, i.e., the beasn
widtll increases witll inclease(l (lislance l'lonl the soulce. ~ucll a diverging collimator~ ortlle type
used in conjullcti~ witll a l lNAC or ~itll a (Janlllla Unit, is nla(le of a radiatioll inlpervious
material configured to define a divel-~,illg ra(liation patll.
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The collimators associated with prior art stereotactic radiosurgery systems
-incorporate clear (non-blocked) radiation paths. The intensity of a radiation beam produced by
such a clear path collimator, in any plane perpendicular to the beam axis, decreases monotonically
with radial distance from the axis. One of the consequences of such a beam profile is that prior
art stereotactic radiosurgery methods are restricted for treating targets smaller than about 50
millimeters in diameter. The apparent reason is the increased radiation to healthy tissue.
SUMMARY OF THE INVENTION
The present invention seeks to provide improved apparatus and techniques for
radiosurgery which represent a radical departure from the prior art.
The present invention includes a hollow path collimator, diverging or converging,
which is capable of producing a hollow radiation beam at the target, thus providing an ability to
irradiate mainly the target boundary. Causing tissue to be necrotic by irradiation mainly at the
target boundary may have adequate clinical results while reducing the radiation dosage to healthy
tissue. The prior art does not describe a collimator for stereotactic radiosurgery incorporating a
hollow radiation path.
The prior art does not describe a stereotactic radiosurgery system utili~in~ a
converging collimator, i.e., one with a converging radiation path. In the present invention, a
converging collimator may be used to produce a hollow radiation path.
The prior art does not describe a system ~Itili~ing an area source for generating
radiation beams for stereotactic radiosurgery. An area source or a large source is a radiation
source which is comparable in size or larger than the target. An area source, e.g., a Co-60 pack
used for conventional radiotherapy, could be much cheaper for stereotactic radiosurgery than a
LINAC or an array of 201 sources incorporated in the Gamma Unit.
In the present invention, a hollow radiation path collimator may be used to reduce
the penumbra associated with a radiation beam produced by an area source. Since a single hollow
radiation path reduces also the beam intensity (by blocking an internal portion of the beam), it
may be advantageous to incorporate several hollow radiation paths in a single collimator.
However, increasing the number of radiation paths may also increase the penumbra, suggesting
that a desirable compromise between increasing beam intensity and increasing penumbra be
reached. Such a compromise, for a given source and a given collimator material, may be obtained
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~y selecting optimally the number of hollow paths and the associated geometrical properties. The
prior art does not describe the use of an area source and a collimator incorporating one or more
hollow paths for stereotactic radiosurgery.
There is thus provided in accordance with a prerel~ed embodiment of the present
invention, a collimator for use in radiosurgery including material which is generally radiation
impervious and which is configured to define at least one at least partially hollow radiation path.
In accordance with a prerell ed embodiment of the present invention, the collimator
further includes a shield which is generally radiation impervious, the shield having formed therein
a beam passageway, and at least one beam blocker which is generally radiation impervious, the at
least one beam blocker being located in the beam passageway so as to form the at least one at
least partially hollow radiation path.
There is also provided in accordance with a p~ ed embodiment of the present
invention, a collimator for use in radiosurgery including material which is generally radiation
impervious and which is configured to define a converging radiation path.
There is also provided in accordance with a preferred embodiment of the present
invention, an irr~ ting device for use in radiosurgery including at least one source of radiation
arranged to irradiate a target, and at least one collimator disposed between the at least one source
of radiation and the target and including material which is generally radiation impervious and
which is configured to define at least one at least partially hollow radiation path.
In accordance with a preferred embodiment of the present invention, the at leastone collimator includes a shield which is generally radiation impervious, the shield having formed
therein a beam passageway, and at least one beam blocker which is generally radiation
impervious, the at least one beam blocker being located in the beam passageway so as to form the
at least one at least partially hollow radiation path.
There is also provided in accordance with a preferred embodiment of the present
invention, an irradiating device for use in radiosurgery including at least one source of radiation
arranged to irradiate a target, and at least one collimator disposed between the at least one source
of radiation and the target and including material which is generally radiation impervious and
which is configured to define at least one converging radiation path.
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- There is also provided in accordance with a preferred embodiment of the present
~invention, a method for radiosurgery including the steps of providing an irradiating device
including at least one source of radiation arranged to irradiate a target, and at least one collimator
disposed between the at least one source of radiation and the target and including material which
is generally radiation impervious and which is configured to define at least one at least partially
hollow radiation path, producing radiation beams with the irra~iatin3~ device, and directing the
radiation beams at a target volume from a multiplicity of orientations.
There is also provided in accordance with a pl~relled embodiment of the present
invention, a method for radiosurgery including the steps of providing an irradiating device
including at least one source of radiation arranged to irradiate a target, and at least one collimator
disposed between the at least one source of radiation and the target and including material which
is generally radiation impervious and which is configured to define at least one converging
radiation path, producing radiation beams with the irradiatinQ; device, and directing the radiation
beams at a target volume from a multiplicity of orientations.
There is also provided in accordance with a preferred embodiment of the present
invention, a method for radiosurgery including the steps of providing at least one radiation source,
collimating radiation from the at least one source to produce radiation beams which are at least
partially hollow at the location of a target, and directing the at least partially hollow radiation
beams at the target from a multiplicity of orientations to produce a radiation dose pattern having a
substantially higher dose level at the boundary of the target and a substantially lower dose level at
the interior of the target.
In accordance with a preferred embodiment of the present invention, the method
further includes the steps of collim~ting radiation from the at least one source to produce non-
hollow radiation beams at the location of the target, and directing the non-hollow radiation beams
at the target from a multiplicity of orientations to produce an additional radiation dose pattern
having a substantially higher dose level at the interior of the target and a substantially lower dose
level at the boundary of the target.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully from the
following detailed description, taken in conjunction with the drawings in which:
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Fig. 1 A is an illustration of a prior art radiation collimator;
Figs. lB, lC and lD illustrate three radiation collimators, constructed and
operative in accordance with three alternative preferred embodiments of the present invention;
and
Figs. 2A, 2B and 2C are illustrations of three di~lellt cross beam profile
configurations of radially symmetric beams in planes perpendicular to the corresponding beam
axis;
wherein Fig. 2A illustrates a non-hollow cross beam profile produced either by aprior art collimator according to Fig. lA, a collimator of the present invention according to Fig.
lC or a collimator of the present invention according to Fig. lD, at its focus;
Fig. 2B illustrates a hollow cross beam profile produced either by a collimator of
the present invention according to Fig. lB, or a collimator of the present invention according to
Fig. lD at a distance from its focus; and
Fig. 2C illustrates a superposition of a hollow beam profile and a non-hollow beam
profile.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is now made to Fig. lA, which illustrates a prior art radiation
collimator, and to Figs. lB, lC and lD which illustrate three alternative embodiments of
radiation collimators constructed and operative in accordance with a pre~ell~d embodiment of the
present invention. The radiation collimators of Figs. lA - lD are characterized in that they are
formed of material which is generally radiation impervious. The radiation collimator shown in Fig.
lA is configured to define a non-hollow and diverging radiation pathway. Radiation collimators
shown in Figs. lB and lD are configured to define an at least partially hollow radiation path. The
radiation collimator shown in Fig. lC is configured to define a non-hollow and converging
radiation pathway.
The hollow radiation path is useful for precise radiation treatment of targets in
accordance with a preferred embodiment of the present invention whereby it is desired to irradiate
the periphery of the target without substantially irr~ ting the center thereof~ or whereby it is
desired to irradiate a target using a large source of radiation. It is noted that throughout the
specification and claims, the terms large source of radiation and small source of radiation refer to
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~he relative size of the radiation source compared to the size of the irradiated target. A large
~ source of radiation is comparable in size or larger than the target, while a small source of radiation
is significantly smaller than the target.
Fig. lA illustrates a collimator assembly including an exterior shield 10 defining a
location 12 for a source of radiation, indicated by reference numeral 14. The exterior shield 10 is
formed with a bore 16 extending outwardly from location 12. Preferably a collim~ting unit 20 is
disposed in the bore 16.
In the embodiment of Fig. 1A, the collim~ting unit 20 defines an unblocked
diverging radiation beam pathway. It is noted that throughout the specification and claims the
terms blocked and unblocked refer to the presence or absence of a substantial central beam
obstruction, as distinct from the presence or absence of a material used for beam filtering.
- The embodirnent of Fig. lB is preferably generally identical to that of Fig. lA but,
unlike the prior art, includes a beam blocker 22, which is generally radiation impervious, disposed
within collim~tin~ unit 20. Blocker 22 may have any a~ ly shape, such as conical. The at least
partially hollow radiation pathway in the collimator defines a diverging hollow beam outside the
collimator.
Fig. lC illustrates a collimator assembly including an exterior shield 30 defining a
location 32 for a large source of radiation, indicated by reference numeral 34. The source 34 is
typically a pack of radioactive material, such as cobalt-60. The exterior shield 30 is formed with a
bore 36 extending outwardly from location 32. Preferably a collim~ting unit 40 is disposed in the
bore 36.
In the embodiment of Fig. 1C, the collim Iting unit 40 is configured to form a non-
hollow and converging radiation beam pathway. This pathway defines a non-hollow beam
converging towards the focal point and diverging away from the focal point outside the
collimator.
The embodiment of Fig. lD is identical to that of Fig. lC but also includes a beam
blocker 42, which is generally radiation impervious, disposed within collim~ting unit 40. Blocker
42 may have any arbitrary shape such as conical. The at least partially hollow and converging
radiation pathway in the collimator defines a beam outside the collimator which is converging and
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hollow near the collimator exit, non-hollow at the focus away from the collimator exit, and
diverging and hollow at a distance from the focus.
It is appreciated that any of the collimators of Figs. lA - lD may be used to form
an interchangeable collimator radiation generator. Any of the collimator elements may be simply
removed from the shield and another collimator element inserted in its place. Alternatively, the
collimator elements may be rigidly embedded in a movable shield, wherein a particular collimator
element may be selected by suitably moving the shield.
Reference is now made to Figs. 2A, 2B and 2C which illustrate three di~e~ t
cross beam profile configurations of radially symmetric beams in planes perpendicular to the
corresponding beam axis.
Fig. 2A illustrates a cross beam profile of a non-hollow beam produced either by a
prior art collimator according to Fig. lA, a collimator of the present invention according to Fig.
1C or a collimator of the present invention according to Fig. lD, at its focus. It is noted that the
beam profile is characterized by a relatively high level of radiation near the center of the target,
and the radiation level falls offrapidly at a certain distance from the center.
Fig. 2B illustrates a cross beam profile produced either by a collimator of the
present invention according to Fig. lB, or a collimator of the present invention according to Fig.
lD at a distance from its focus. It is noted that the beam profile is characterized by a relatively
negligible level of radiation near the center of the profile, and a relatively high level generally at
the periphery of the profile.
Fig. 2C illustrates a combined cross beam profile of a non-hollow beam and a
hollow beam. It is noted that the beam profile of Fig. 2C is disting~ hed from the profile of Fig.
2A, in that the beam profile of Fig. 2C has a generally sharper or steeper fall off than that of Fig.
2A, when the hollow beam is produced by a collimator according to Fig. lD. The steeper fall off
may be useful in protecting neighboring tissue from unwanted radiation.
It is appreciated that various features of the invention which are, for clarity,described in the contexts of separate embodiments may also be provided in combination in a
single embodiment. Conversely, various features of the invention which are, for brevity, described
in the context of a single embodiment may also be provided separately or in any suitable
subcombination.
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It will be appreciated by persons skilled in the art that the present invention is not
~ Iimited to what has been particularly shown and described hereinabove. Rather, the scope of the
present invention is defined only by the claims that follow:
