Radiant energy – Irradiation of objects or material
Reexamination Certificate
2002-12-04
2004-05-04
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Reexamination Certificate
active
06730921
ABSTRACT:
The invention relates to an ion beam system for irradiating tumour tissues and to a method of operating the system, in accordance with the preambles of the independent claims.
From U.S. Pat. No. 4,870,287 there is known a proton beam system for the selective production and transport of proton beams from a single proton source, via an accelerator, to a plurality of patient treatment stations, each of the treatment stations having a rotatable drum structure, hereinafter referred to as a gantry. In the known system, that gantry delivers the proton beam at various irradiation angles to a patient, who is arranged in a fixed position on a patient couch. A summary of gantry systems by Pedroni is known, from “Beam delivery” in Hadron Therapy in Oncology, Editors U. A. Maldi and B. Larson, Elsevier 1994, pages 434-452.
As long as such ion beam systems for irradiating tumour tissues operate with the lightest ion of the periodic system, namely the hydrogen ion or proton, the deflection magnets for a gantry and the masses of the latter are relatively small and manageable. However, when heavier ions such as the carbon ion, or others, are to be used, deflection magnets that are several times larger have to be used in order to direct the highly accelerated ions from the axis of a gantry to the periphery of the gantry and back to the gantry centre, where the patient is positioned. At the same time, correspondingly large masses have to be provided in the gantry as a counterweight to the deflection magnets, with the result that the rotating gantry structure, which has to be rotated and controlled with an accuracy of a few millimeters, weighs several hundred tonnes. As the ion mass number increases, so the gantry solution that has been favoured becomes heavier and less manageable and requires ever larger buildings for accommodating the treatment systems.
The aim of any beam therapy is to deposit as high a dose of radiation as possible in a narrowly circumscribed region—the tumour volume—and, as far as possible, to spare the surrounding healthy tissue. In customary X-ray therapy, because of the exponential decay of the photon dose with the depth of penetration in the conventional subcutaneous beam therapy of relatively deep-lying tumours, a high localised dose can be achieved only by directing the beam at the tumour volume from several directions in an intersecting irradiation technique. As a result, the involvement of healthy tissue in front of and behind the tumour volume is reduced. In clinical practice, two or three entry angles are usual and, with an inverse dose plan in the case of intensity-modulated therapy using photons, up to nine or ten entry channels, that is to say irradiation angle positions, are often planned. Such multi-field irradiations are feasible especially using the known gantry systems.
In a manner analogous to such photon beam therapy, a plurality of entry ports are also desirable in ion beam therapy although, as a result of the inverted dose profile of the ion beams, the dose in the entry channel is smaller than the dose in the region of the tumour volume. However, distribution of the unavoidable entry dose over a plurality of irradiation angles would, in the case of ion beam therapy too, signify a further clinical advantage. The known ion beam systems for proton beam treatment are therefore provided with irradiation application from all directions by means of appropriate gantry systems.
The gantry systems known from the Patent Specification U.S. Pat. No. 4,870,287 to that extent correspond to the gantry systems from photon and X-ray therapy. They first deflect the beam away from the patient axis and then bend it back at 90° to the patient. Variable irradiation angles are in that case achieved by means of the fact that the entire deflecting system is rotated through 360° along the beam direction with the aid of the gantry. The mechanical rotation serves the purpose, above all, of not having to vary the settings of the magnets and of having only to carry out mechanical rotation. However, that advantage of simple mechanical rotation without variation of the settings of the electromagnets holds only for as long as the gantry system uses a divergent ion beam for treatment. When a concentrated pencil-thin ion beam is produced, however, with an active scanning system being used for scanning the tumour volume, the magnetic field is no longer constant and unvarying, because the beam energy and, as a result, the magnetic constancy have to be utilised in accordance with the requisite energy steps having to be used for that pencil beam.
As a result, the main reason for a gantry having fixed magnet settings is no longer present, especially as, for the scanning system, the pencil beam already has to be deflected in an X and Y direction orthogonal to the central ion beam deflection region.
Furthermore, experience with the proton beam therapy system known from the Patent Specification U.S. Pat. No. 4 870 287 shows that, in the case of ion beam therapy of deep-lying tumours, not all the possible radiation-entry angles of a gantry are used with equal frequency. Rather, it has been found that there is a large range of seldom used irradiation angle zones because frequently occurring kinds of tumour necessitate frequently recurring restricted angle settings of the gantry. To that extent it has been found that conventional gantry systems do not constitute optimum solutions-for ion beam therapy because a large portion of the possible irradiation angles of a gantry remain little-used.
It is characteristic of the known and planned ion therapy systems that the particle beam is directed through the gantry system at a fixed angle and variation of the angle can be achieved only mechanically, by rotating the entire system. Because of the high energy of the particles—200 MeV for protons and approximately 400 MeV/U for carbon ions—and because of the large-area apertures necessary for scanning of the ion beams, deflection magnets having a high magnetic field strength and large-area apertures are necessary. That means that the electromagnets reach considerable dimensions and weight. A barrel-shaped gantry for carbon ions is accordingly designed for a radius of 7 m and a length of 15-20 m and a weight of 300-400 t, of which about 50 t alone is attributable to a concrete weight acting as a counterweight to the magnets. In the case of such considerable weights, the tolerances of the bearings and, as a result, the positional accuracy of the beam become increasingly important. In the case of the patient, however, the tolerance limits are in the millimeter range. In the case of the gantry systems constructed hitherto, such tolerance limits are difficult to meet.
In the construction of ion beam systems for hospitals, the construction of a plurality of gantry systems is a significant cost factor. The costs relate to the gantry itself, at more than 15 million DM per system, and to the construction of suitable operational rooms of more than 14 m in height and width and more than 20 m in length, which means an enclosed space of more than 4,000 m
3
. Such rooms have to be shielded by thick-walled concrete. In addition, the planned use of ion scanning methods still constitutes an as yet unsolved problem with regard to the necessary mechanical precision. For that reason, in the case of an ion scanning method, the requisite precision of 1 mm has to be checked, verified and corrected after each setting and for each new treatment.
The problem of the invention is to overcome the disadvantages of the prior art for an ion beam system and to provide irradiation systems that, after reducing costs and saving space, meet the requirements with, at the same time, increased precision.
The problem is solved by the features of the subject-matter of the independent claims. Preferred developments of the invention are shown by the features of the dependent claims.
The solution to the problem is based upon the fact that the patient is fixed in a lying posture on a patient couch and this horizontal position is not changed before or duri
Frommer & Lawrence & Haug LLP
Gesellschaft fuer Schwerionenforschung mbH
Lee John R.
Santucci Ronald R.
Smith II Johnnie L
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