US3903421A

US3903421A - Device for irradiation with energy rich electrons

Info

Publication number: US3903421A
Application number: US473146A
Authority: US
Inventors: Riccardo G Benedetti
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-12-18
Filing date: 1974-06-23
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

A device for irradiation with energised electrons wherein the electrons are guided upon a specific irradiation field by means of a magnetic field, is particularly characterized by the provision of a deflection device and a magnetic focussing device located one behind the other in the direction of the electronic ray at the outlet window of the source of electrons.

Description

United States Patent Benedetti Sept. 2, 1975 [54] DEVICE FOR IRRADIATION WITH 2,824,969 2/1958 Milling 250/398 2,944,172 7/1960 Opitz 250/398 ENERGY RICH ELECTRONS Riccardo G. Benedetti, Erlangen, Germany Inventor:

Related US. Application Data Continuation of Ser. No. 316,354, Dec. 18, 1972.

US. Cl. 250/398; 250/492 Int. Cl. H01j 37/00 Field of Search 250/396, 398, 400, 492,

250/492 A, 493; 219/121 EB References Cited UNITED STATES PATENTS ]/1956 Robinson 250/400 Primary Examiner.lames W. Lawrence Assistant ExaminerC. E. Church Attorney, Agent, or Firm-V. Alexander Scher [57] ABSTRACT A device for irradiation with energised electrons wherein the electrons are guided upon a specific irradiation field by means of a magnetic field, is particularly characterized by the provision of a deflection device and a magnetic focussing device located one behind the other in the direction of the electronic ray at the outlet window of the source of electrons.

5 Claims, 3 Drawing Figures l I I \l DEVICE FOR IRRADIATION WITH ENERGY RICH ELECTRONS This application is a continuation of the co-pending Ser. No. 316,354 filed Dec. 18, 1972.

This invention relates to a device for irradiating with energised electrons, wherein the electrons are directed by a magnetic field to specific irradiation fields.

Known electronic accelerators used for producing an irradiating electronic ray emit as a rule a ray having a small cross-section. Electric deflecting means are used in order to be able to irradiatc larger surfaces with it. For that purpose the electronic ray was combined with so-called scattering 11 dies or scattering foils in order on the one hand to homogenize the cross-section of the ray and, on the other hand, to increase it.

In the deep therapy using energised electrons it is desired to place the location of the zone wherein 80% of the rays are still effective (80% isodose) as near as possible to the zone of the maximal depth of penetration of the electrons having a given energy. However, in known electronic outlet systems with divergent rays the reduction of the dose takes place with the 1:R rule, so that the deepness of the 80% isodose is reduced in addition to the loss of energy.

An object of the present invention is to improve these prior art devices. 3

Other objects will become apparent in the course of the following specification.

In the accomplishment of the objectives of the present invention it was found possible to magnify the cross-section of a ray bundle wherein the rays extend parallel or are convergent, so that the location of the 80% isodose is independent from the IR rule. This is accomplished by providing a deflection device and a magnetic focussing device located one behind the other in the direction of the electronic ray at the outlet window of the source of electrons.

An advantage of the present invention is that the parts used can be also applied to existing electronic accelerators. The effect of the present invention is based in that the ray of electrons on the one hand can have a large cross-section and yet can have parallel or convergent rays. On the other hand known processes for irradiating larger surfaces with electrons of high energy used means for increasing the irradiation field which produced a divergence of the rays.

The present invention can use as deflection devices all means which increase the cross-section of the ray bundle, for example, known scattering foils which are used in the medical ray technology, or also electromagnetic deflecting devices, such as a magnetic field. The focussing of the parallel or divergently extending rays resulting from the dispersing devices takes place by electromagnetic focussing devices provided at a distance from the dispersing device. These are quadruple lenses or deflecting fields which obey the Barber law and which have a focussing effect upon the electronic ray. It is also possible to use focussing toroid coils. Since the electronic ray receives a larger cross-section by the dispersing device the focussing lenses receive a correspondingly adapted crosssection.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing showing by way of example only, preferred embodiments of the inventive idea.

In the drawing:

FIG. 1 is a diagrammatic sectional view of a betatron combined with the subject matter of the present invention.

FIG. 2 is an enlarged diagrammatic cross-section of the outlet portion of the betatron provided with a scattering member and a focussing lens.

FIG. 3 is similar to FIG. 2 but shows an electromagnet used for scattering. 4

FIG. 1 shows a magnet 1 of a betatron having a tube 2 for accelerating the electrons in the known manner. The electrons leave through the electronic outlet window 3 and they can be directed to the irradiation field through an opening in a lead cover 4. An insert 5 located in the opening of the cover 4 contains the scattering and focussing elements of the present invention.

FIG. 2 shows the insert 5 on an enlarged scale. It includes in its framework shown by broken lines the scattering member 6 and the focussing coils 7 and 8. If the betatron of FIG. 1 produces 42 MeV electrons. the member 6, which is the scattering foil, has a'thickness of 1.5 mm., a diameter of 25 cm. and consists of Pb. The coils 7 and 8 are located relatively to the window 3 at a distance of 10 cm. after the member 6. The coils quadruples focussing the electron bundle have a passage opening of 30 cm. the two focussing coils 7 and 8 are shifted relatively to each other around the ray cone by 90 since each coil focusses only in one direction. Due to the nature of coils 7 and 8 there results a deviation of the ray bundle 9 by each coil as shown in FIG. 2 only for the plane of the drawings. There is a similar deviation out of the plane of the drawings.

The electronic ray bundle passing out of the window 3 and symbolically indicated in the drawing of FIG. 2 by the line 9, is scattered in the member 6, so that only a part of the electrons continues to move in the direction of the ray 9, while another part will move in the direction of the line 10 and in the direction of the line I 1. Thus there is a extension of the ray bundle in a diverging conical outlet angle extending between the lines 10 and 11. This divergent bundle is then brought together by the coils 7 and 8 to a converging ray cone which would lie between the

rays

12 and 13 shown by broken lines, if therewould not have been a deflection. Due to the deflection the cone is actually limited in the horizontal representation of the FIG. 2 by the

lines

12 and 13, so that the electrons instead of being limited in a diverging cone which is limited by outwardly extending lines 10 and 11, are acually limited by a converging cone being deflected out of the plane of the drawings. In a body of a patient for instance the limits of which are symbolized by the line 14, a concentric ray cone is thus produced wherein the isodose lies deeper by 50 than in prior art devices which are not provided with the member 5 of the present invention.

FIG. 3 shows a different embodiment of the present invention wherein the electronic ray bundle 17 passing out of the tube 15 through the window 16 is deviated by the coils l8, 18' of the lens belonging to the part 5 in directions extending between the

lines

19 and 20. The part 5' is a substitute for the part 5 in the ray outlet of the tube. Focussing

coils

21, 21 located behind the coils 18, 18' of the deviating lens in the direction of the rays, cause a focussing of the bundle 17. Then the direction of electrons penetrating into a body the outer surface of which is symbolized by the line 24, is concentrical focussed in the same manner as in the device of FIG. 2 so that the bundle will be limited by the lines 22 and 23. The

coils

18, 18 by which the deviation takes place have an opening of about cm. The focussing lens which consists of the

coils

21 and 21 and has an opening with a diameter of about 25 cm., causes a concentration of the directions of the divergently extending ray bundle and produces a deflection to convergent focussing. In both the

coils

18, 18 as well as in the

coils

21 and 21 takes place a deviation of the ray bundle within the plane of the drawings and a similar deviation out of the plane of the drawings. The deviations of the coils 18, 18' are contrary to those of the coils 21, 21'.

By changing the electrical power supply of the

coils

18, 18 the divergence of the

ray bundle

18, 20 and the diameter of the ry bundle 22, 23 may be changed. By changing the electrical power supply of the

coils

21, 21 in relation to the

coils

18, 18 the convergence of the ray bundle 22, 23 may be changed too.

I claim:

1. A device for irradiating areas with a convergent beam of high-energy electrons, comprising, in combination, an evacuated electron acceleration tube for creating a beam of high-energy electrons, the lastmentioned beam having a cross section smaller than the areas to be irradiated, said acceleration tube having an end portion with a vacuum-tight electronpermeable exit window through which the last-mentioned beam of accelerated electrons is emitted, a deflection device provided in the path of the accelerated electrons emerging said exit window, said deflection device being adapted to expand the last-mentioned beam of highenergy electrons to a divergent beam and an electromagnetic focussing device provided in the path of the accelerated electrons having passed the deflection device, said focussing device being spaced from said deflection device and having its solenoids leaving a free diameter of at least the diameter of said divergent beam passing its solenoids, and being adapted to make said divergent beam convergent for producing a convergent large diameter beam of electrons with an isodose at a particular object depth.

2. A device in accordance with claim 1, wherein said deflection device comprises a scattering foil expanding said beam.

3. A device in accordance with claim 1, wherein said deflection device comprises a magnetic field expanding the last-mentioned beam.

4. A device in accordance with claim 1, wherein said magnetic focussing device is adjustable in its depth of focus.

5. A device for irradiating areas with a beam of highenergy electrons emerging from a vacuum-tight electronpermeable exit window of an evacuated electron acceleration tube of an electron accelerator, said beam having a cross section smaller than the areas to be irradiated, comprising, in combination, a deflection device provided in the path of the accelerated electrons emerging said exit window, said deflection device being adapted to expand the last-mentioned beam of highenergy electrons to a divergent beam, and an electro magnetic focussing device provided in the path of the accelerated electrons having passed the deflection device, said focussing device being spaced from said deflection device and having solenoids leaving a free diameter of at least the diameter of said divergent beam passing its solenoids and being adapted to make said divergent beam convergent, for producing a convergent large diameter beam of electrons with an 80% isodose at a particular object depth.

Claims

1. A device for irradiating areas with a convergent beam of high-energy electrons, comprising, in combination, an evacuated electron acceleration tube for creating a beam of high-energy electrons, the last-mentioned beam having a cross section smaller than the areas to be irradiated, said acceleration tube having an end portion with a vacuum-tight electronpermeable exit window through which the last-mentioned beam of accelerated electrons is emitted, a deflection device provided in the path of the accelerated electrons emerging said exit window, said deflection device being adapted to expand the last-mentioned beam of highenergy electrons to a divergent beam and an electromagnetic focussing device provided in the path of the accelerated electrons having passed the deflection device, said focussing device being spaced from said deflection device and having its solenoids leaving a free diameter of at least the diameter of said divergent beam passing its solenoids, and being adapted to make said divergent beam convergent for producing a convergent large diameter beam of electrons with an 80% isodose at a particular object depth.

5. A device for irradiating areas with a beam of high-energy electrons emerging from a vacuum-tight electronpermeable exit window of an evacuated electron acceleration tube of an electron accelerator, said beam having a cross section smaller than the areas to be irradiated, comprising, in combination, a deflection device provided in the path of the accelerated electrons emerging said exit window, said deflection device being adapted to expand the last-mentioned beam of high-energy electrons to a divergent beam, and an electromagnetic focussing device provided in the path of the accelerated electrons having passed the deflection device, said focussing device being spaced from said deflection device and having solenoids leaving a free diameter of at least the diameter of said divergent beam passing its solenoids and being adapted to make said divergent beam convergent, for producing a convergent large diameter beam of electrons with an 80% isodose at a particular object depth.