Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2001-12-11
2002-11-05
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S398000, C315S501000, C315S507000
Reexamination Certificate
active
06476403
ABSTRACT:
The present invention relates to a gantry with an ion-optical system according to the preamble of claim
1
.
Such an ion-optical system for a gantry encloses a first bending magnet with a bending angle as known from U.S. Pat. No. 4,870,287 of 90° for bending a proton beam off an axis of rotation of said gantry. Further a second bending magnet with a bending angle identical to the bending angle of the first bending magnet bends said ion beam parallel to said axis of said gantry. Finally, a third bending magnet with a bending angle of 90° according to the above mentioned prior art bends said ion beam toward an intersection of said ion beam with said axis of rotation of said gantry. This intersection is called isocentre.
From U.S. Pat. No. 4,870,287 is further known, that between the first and the second bending magnet two quadrupole magnets are positioned. Also between the second and the third bending magnets two other quadrupole magnets are positioned. The disadvantage of such a gantry is, however, that if a non-symmetric ion beam is introduced to the gantry input from a fixed transfer line the beam transport within such a gantry having only four quadrupoles becomes dependent on the angle of gantry rotation, wherein the non-symmetric beam is ment as a beam having different emittances in vertical and horizontal planes.
Theoretical studies of medical synchrotrons as well as the measurements at existing facilities have shown that the slowly extracted beams do have the above mentioned different emittances in horizontal and vertical planes. This complicates the matching of the fixed transfer line to the rotating gantry. The input beam parameters in the horizontal and vertical planes of the gantry become a function of the angle of gantry rotation and this dependence, unless special precautions are applied, is transformed also to the beam parameters of the gantry exit.
To overcome these disadvantages a special matching section, called a “rotator” comprising additionally to the quadrupole magnets within the gantry a plurality of other quadrupole magnets was proposed by M. Benedikt and C. Carli, “Matching to gantries for medical synchrotrons”, Particle Accelerator Conference PAC '97, Vancouver 1997. The rotator is positioned upstream the gantry within the fixed transfer line.
The rotator provides a universal method allowing to match the rotating gantries to the fixed transfer lines without applying any specific ion-optical constraints upon the gantries. On the other hand, it occupies about 10 m of extra length of the transfer line, which is a disadvantage for design of extremely compact medical accelerator complexes fitting to the hospitals.
In addition the entire rotator has to be rotated synchronously with the gantry, which requires an extra equipment for extremely precise mechanical rotation.
Therefore it is the object of the present invention to save space and costs and to avoid such a rotator so that a gantry rotation independent transport of non-symmetric ion beams is possible. Thus, the ion-optical settings should make the beam parameters at the gantry exit independent from the angle of gantry rotation even if the beam enters the gantry with different emittance in horizontal and vertical planes.
This object is achieved by the subject matter of independent claim
1
. Features of preferred embodiments are enclosed in dependent claims, depending on claim
1
.
Therefore the gantry with an ion-optical system further comprises:
a horizontal scanner magnet positioned upstream said third bending magnet for horizontal scanning of said ion beam in a plane perpendicular to the beam direction;
a vertical scanning magnet positioned upstream said third bending magnet for vertical scanning of said ion beam in a plane perpendicular to the beam direction,
at least six quadrupole magnets with adjustable excitation positioned downstream the said first bending magnet and upstream said scanner magnets, wherein the quadrupole magnets provide:
a fully achromatic beam transport from the gantry entrance to the isocentre;
a control of the size of said ion beam in the isocentre according to a pre-defined beam-size pattern; and
the size of said ion beam in the isocentre and the spot-shape of said ion beam in the isocentre which is independent from the angle of gantry rotation, wherein the gantry can be rotated to any angle between 0° and 360° with respect to a fixed beam transfer line connecting an accelerator with the gantry and wherein said ion beam coming from said fixed beam transfer line and entering said gantry has different emittances in the horizontal and vertical planes of said fixed beam transfer line.
It is a well-known fact that beams of ions (typically 1≦Z≦8) have favourable physical and biological properties for their use in cancer-therapy. The most appropriate beam delivery technique, in particular for ions heavier than protons, is a so-called active beam scannig comprising an energy variation from the accelerator and lateral intensity-controlled raster scanning according to the characterising portion of claim
1
. In contrast to a passive beam delivery the active scanning systems aim to deliver a narrow pencil-like beam with a variable spot size to the patient and to scan it over the treatment area.
Forming and preservation of the pencil-like beam by the beam transport system is of crucial importance in this case for the ion-optical system of the gantry. The dose-to-target conformity can further be optimised if the beam can enter the patient from any direction. This task is performed by said gantry which is rotated around the horizontal axis with respect to the room, coordinate system. The combination of the pencil-beam scanning with a rotating gantry brings about special additional ion-optical problems.
The beam is described at the exit of the transfer line, at the entrance of the gantry, and at the gantry isocentre by its sigma-matrices &sgr;(0), &sgr;(1), and &sgr;(2), respectively, where the sigma-matrices have, in general, a form:
σ
(
i
)
=
σ
(
i
)
11
σ
(
i
)
12
σ
(
i
)
13
σ
(
i
)
14
σ
(
i
)
21
σ
(
i
)
22
σ
(
i
)
23
σ
(
i
)
24
σ
(
i
)
31
σ
(
i
)
32
σ
(
i
)
33
σ
(
i
)
34
σ
(
i
)
41
σ
(
i
)
42
σ
(
i
)
43
σ
(
i
)
44
(
1
)
where i=0, 1, 2 and the individual matrix-terms have their usual meaning. The sigma-matrix is a real positive definite, and symmetric matrix. The square roots of the diagonal terms of the sigma-matrix are a measure of the beam size in x, x′, y and y′ coordinates, where [x, x′, y, y′] is a four-dimensional phase space in which the beam occupies a volume inside a four-dimensional ellipsoid characterised by the sigma-matrix. The off-diagonal terms determine the orientation of the ellipsoid in the phase space. At the exit of the transfer line, a so-called uncoupled beam is expected, i.e. there is no correlation between the two transverse phase spaces [x, x′] and [y, y′]. In such a case, the elements of the sigma-matrix coupling the horizontal and vertical phase vanish. Taking into account these properties, the sigma-matrix of the beam at the exit of the transfer line can be written in a simplified form:
σ
(
0
)
=
σ
(
0
)
11
σ
(
0
)
12
0
0
σ
(
0
)
12
σ
(
0
)
22
0
0
0
0
σ
(
0
)
33
σ
(
0
)
34
0
0
σ
(
0
)
34
σ
(
0
)
44
(
2
)
If the gantry is rotated with respect to the fixed transfer line by an angle &agr;, the sigma-matrix of the beam at the gantry entrance, &sgr;(1), will be given by the transformation:
&s
Dolinskii Alexeiy
Franczak Bernhard
Pavlovic Marius
Frommer & Lawrence & Haug LLP
Gesellschaft fuer Schwerionenforschung mbH
Lee John R.
Santucci Ronald R.
Vanore David A.
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