Radiant energy – With charged particle beam deflection or focussing – With target means
Reexamination Certificate
2001-09-25
2003-10-21
Nguyen, Judy (Department: 2853)
Radiant energy
With charged particle beam deflection or focussing
With target means
C250S3960ML, C250S397000, C250S492300, C250S42300F
Reexamination Certificate
active
06635882
ABSTRACT:
The invention relates to a gantry system for adjusting and aligning an ion beam onto a target, according to the preamble of claim
1
.
A gantry system of that kind is known from U.S. Pat. No. 4,870,287. In the case of the known gantry system, the ion beam is supplied to the gantry system in the horizontally arranged gantry rotation axis and is firstly deflected from the gantry rotation axis by means of magnetic optics.
The ion beam is then guided parallel to the gantry rotation axis by means of magnetic optics and, from that direction parallel to the gantry rotation axis, is finally deflected into a radial direction with respect to the gantry rotation axis. The target is generally arranged at the point of intersection of the radially directed ion beam with the gantry rotation axis. That point of intersection is defined as the isocentre.
Consequently, on one full revolution of the gantry about the gantry rotation axis, the ion beam can be aligned onto the target in a plane perpendicular to the gantry rotation axis and adjusted to angles between 0 and 3600°.
Besides the gantry, the gantry system comprises a target carrier system having a rotatable target carrier. The carrier rotation axis of the target carrier is arranged in the isocentre in a vertical direction with respect to the gantry rotation axis. Consequently, the gantry system, which comprises at least one gantry and one target carrier system, can so adjust and align an ion beam that a target arranged in the isocentre can be irradiated from a freely determinable angle in space. In the of a gantry system of that kind, it is necessary for the final deflection magnet of the gantry to deflect the ion beam by 90°, which is why a gantry of that kind is also referred to as a 90° gantry.
In the case of the 90° gantry known from the publication U.S. Pat. No. 4,870,287, therefore, the ion beam is, on leaving the gantry in the direction of the gantry rotation axis, perpendicular to the gantry rotation axis. An angle &agr; of gantry rotation is defined between the plane in which the ion beam is guided through the gantry and the horizontal plane of the space in which the gantry rotation axis is located. A horizontal position of the gantry accordingly corresponds to either the angle &agr;=0 or the angle &agr;=180° when the gantry is in the horizontal plane and consequently the ion beam is guided in the gantry in that horizontal plane. The uppermost position of the gantry in the vertical direction accordingly corresponds to the angle &agr;=90° and the lowest position of the gantry has an angle of &agr;=270°.
A treatment angle &ggr; is defined between the horizontal plane of the space and the direction in which the ion beam enters a target volume. An effective treatment angle is defined between a frontal plane of a patient and the direction in which the ion beam enters a target volume. For a patient in a lying position, which is usual, the treatment angle and the effective treatment angle are identical.
In the 90° gantry system known from the publication U.S. Pat. No. 4,870,287, the target carrier is in the form of a table rotatable about a vertical axis and having a longitudinal axis and a transverse axis. An angle &bgr; of target carrier rotation is defined between the longitudinal axis of the target carrier table and the gantry rotation axis. By virtue of the rotatability of the target carrier about a vertical axis, the angle &bgr; can have values between 0° and 360°. For a prespecified treatment angle &ggr;, which is dependent upon the gantry rotation angle &agr;, it is furthermore possible for a specific entry channel for tumour irradiation to be selected by adjusting the angle , of carrier rotation. By virtue of the adjustability of the angle &bgr;, which is associated with the target carrier rotation, and the adjustability of the angle &agr;, which is associated with the gantry rotation, it is possible in a conventional system, wherein the ion beam is deflected by the final deflection magnet in a radial direction with respect to the gantry rotation axis, for the target volume fixed on the target carrier to be aligned for any entry channel for the purpose of tumour treatment.
The 90° gantry system known from the publication U.S. Pat. No. 4,870,287 has the disadvantage that the final deflection magnet of the gantry must deflect the ion beam through at least 90° in order to make possible all treatment angles &bgr; in a gantry system having a target carrier system. The large deflection angle of the final deflection magnet necessitates, depending upon the mass number of the ions to be deflected, a large radius or a high magnetic field strength. Associated with that is the disadvantage that, on the one hand, a gantry has hitherto been successfully constructed only for ions having the smallest mass number, that is to say for protons; for ions having a higher mass number of between 4 and 16 the final deflection magnet inflates the scale and mass of the gantry to such an extent, because of the heavy ions having a mass number higher than a proton, that a gantry system is no longer appropriate for clinical use.
In order to reduce the mass and volume of a gantry for ions that are heavier than protons, proposals exist for the use of super-conducting materials for the exciting coils of the deflection magnets. Although the masses to be rotated and the volume of the gantry would be reduced as a result, the costs for cooling the super-conducting materials would make the gantry system considerably more expensive, especially as 360° rotation is extremely problematic for a cooling system using liquid helium or liquid nitrogen for modern super-conducting materials.
A further proposal, presented in the Japanese publication Journal of the Japanese Society for Therapeutic Radiology and Oncology, vol. 9, suppl. 2, November 1997 as part of the Proceedings of the XXVII PTCOG Meeting by M. Pavlovic under the title “GSI Studies of a Gantry for Heavy Ion Cancer Therapy”, enables the mass and volume of the gantry to be reduced by changing the degree of deflection of the final deflection magnet from, formerly, 90° to 60°. That solution has the disadvantage that it is possible to achieve a treatment angle &ggr; of only from 0° to 60° by means of a so-called 60° gantry of that kind in conjunction with the conventional target carrier system. Consequently, it is no longer possible to achieve treatment angles &ggr; of between greater than 60° and 90° by means of a gantry system of that kind, which has a deflection angle of 60° for the final deflection magnet.
The problem of the invention is to provide, by means of a gantry having a reduced deflection angle of the final deflection magnet, a gantry system according to the preamble of claim
1
that does not require super-conducting materials for the magnetic optics and that, despite reducing the deflection angle of the final deflection magnet to below 90°, allows an ion beam to be adjusted and aligned onto a target from a freely determinable effective treatment angle. The problem of the invention is furthermore to provide a method for irradiating a target volume and adjusting and aligning an ion beam for treatment of a tumour using the gantry system according to the invention.
That problem is solved by the features of the subject matter of claims
1
and
60
.
For that purpose, the final deflection magnet so deflects the ion beam that it intersects the gantry rotation axis in the isocentre at an angle of between greater than or equal to 45° and less than 90°, so that the ion beam describes a surface of a cone on rotation of the gantry through a full revolution about the gantry rotation axis, and the target carrier system has a target carrier for two positions, which are perpendicular to one another in a vertical plane, the carrier rotation axis of which target carrier can be brought into the isocentre of the gantry system. Such a solution has the advantage that the target carrier has to be fixable only in two specific positions and, in both positions, which are perpendicular to one another
Pavlovic Marius
Schardt Dieter
Frommer Lawrence & Haug
Gesellschaft fuer Schwerionenforschung mbH
Nguyen Judy
Nguyen Lam
Santucci Ronald R.
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