US3882314A

US3882314A - Device for X-ray treatment

Info

Publication number: US3882314A
Application number: US440706A
Authority: US
Inventors: Riccardo Benedetti; Rudolf Meyer; Franz Petersilka; Rudolf Schittenhelm; Leonhard Taumann; Wolf-Eberhard Schiegl
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1973-02-09
Filing date: 1974-02-08
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06

Abstract

A device for X-ray treatment comprising an electronic accelerator, an anticathode exposed to the accelerated electrons for producing X-rays, an adjustable collimator for the X-rays, and at least one member for equalizing the density of the X-rays passing the collimator. The invention is particularly characterized by the provision of two ray detectors for increasing the operational safety of the irradiating device, the ray detectors being connected to supervising devices and being located in the part of the X-ray cone which is not influenced by the screen. The first detector is located centrally to the X-ray cone passing the collimator and in the ray direction behind the equalizing member, while the second detector is located to the side of the central ray of said X-ray cone.

Description

United States Patent 191 Benedetti et al.

[451 May 6,1975

[ DEVICE FOR X-RAY TREATMENT [75] Inventors: Riccardo Benedetti; Rudolf Meyer;

Franz Petersilka; Rudolf Schittenhelm; Leonhard Taumann, all of Erlangen; Wolf-Eberhard Schiegl, Weisendorf, all of Germany [7 3] Assignee: Siemens Aktiengesellschaft, Munich,

Germany 22 Filed: Feb. 8, 1974 21 Appl. No.: 440,706

[30] Foreign Application Priority Data Feb. 10, 1973 Gennany 23065198 [52] US. Cl 250/505; 250/510 [51] Int. Cl. G031) 41/16 [58] Field of Search 250/505, 510, 511, 512, 250/513, 514

[56] References Cited UNITED STATES PATENTS 3,278,747 10/1966 Ohmart 250/359 'IIIIIIIIIA 2g 33 31,

Edholm 250/510 Williams 250/505 [57] ABSTRACT A device for X-ray treatment comprising an electronic accelerator, an anticathode exposed to the accelerated electrons for producing X-rays, an adjustable collimator for the X-rays, and at least one member for equalizing the density of the X-rays passing the collimator. The invention is particularly characterized by the provision of two ray detectors for increasing the operational safety of the irradiating device, the ray detectors being connected to supervising devices and being located in the part of the X-ray cone which is not influenced by the screen. The first detector is located centrally to the X-ray cone passing the collimator and in the ray direction behind the equalizing member, while the second detector is located to the side of the central ray of said X-ray cone.

4 Claims, 5 Drawing Figures PATENTEB MAY 6 I975 SHEET 10F 2 nu m LIIIG- ---Q Fig.1.

DEVICE FOR X-RAY TREATMENT This invention relates to a device for X-ray treatment having an electronic accelerator, an anticathode exposed to electrons for producing X-rays, an adjustable collimator, and at least one equalizing member which can be shifted into the X-ray cone.

Such irradiating devices are known wherein are used an electronic accelerator and an anticathode consisting of heavy metal and located in the path of the accelerated electrons. If, in such an irradiating device, a dose rate of the X-rays is measured interdependent upon the space angle, then a maximum is measured substantially in the direction of the electron beam striking the anticathode. This part of the X-rays is used for X-ray treatment and is collimated with an adjustable collimator to the desired field size.

In distances and field sizes which are customary in human medicine, the diminution of applied ray dose within the field being X-rayed, with the increased distance from the central ray of the X-ray beam, was found to be disturbing. It is known to provide uniform dose outputs throughout the entire cross section of the X-ray beam by providing an equalizing member having the shape of a cone with a rounded tip within the X-ray cone; its own absorption is diminished with an increased distance from the central rounded tip to its sides traverse to the ray direction to the same extent as the dose output in this part of the X-ray cone. Due to the different weakenings of X-rays passing through the equalizing member in the direction parallel to its axis of symmetry, a corresponding centering of the equalizing member can provide behind it an X-ray cone which will always have the same dose output throughout its cross-section. In this procedure, the dose output in the center of the X-ray cone is reduced to values which otherwise would exist only on the edges of the cone. Therefore, in the case of small field sizes to be illuminated, equalizing members of smaller diameter are used, which do not reduce the dose output too much. It can happen in these irradiating devices that greatly excessive ray doses will be applied if the balancing member, by mistake, was not shifted into the X-ray cone, or was shifted relatively to the central ray.

An object of the present invention is to provide an irradiating device for medical X-ray treatment of the described type wherein incorrect and excessive irradiations are avoided, and wherein the introduction and proper centering of the equalizing body in the X-ray cone are controlled.

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

In the accomplishment of the objectives of the present invention, it was found desirable to increase the operational safety of the irradiation device by the provision of two ray detectors connected to supervising devices and located in the part of the X-ray cone which is not influenced by the X-ray collimator. The first of these detectors is located centrally to the central ray and in the ray direction behind the corresponding equalizing member. The second detector is located to the side of the central ray.

Such an arrangement of ray detectors makes it possible to determine the applied ray dose with the first ray detector located in the central ray of the X-ray cone passing the collimator. Then the second ray detector located to the side of the central ray will determine a ray dose in the case of a properly set equalizing memher which has a specific positive ratio to the ray dose determined by the first ray detector. Deviations from this ratio indicate a wrong centering of the balancing member relatively to the central ray.

According to a further advantageous development of the present invention, the two ray detectors can be arranged in ray direction in front of the X-ray collimator and behind the corresponding equalizing member. This makes it safe that a change in the opening of the X-ray collimator will have no effect upon the ratio of measured values of the two ray detectors. Thus, the supervision of the correct position of the equalizing member is also possible with an X-ray collimator which is opened only by a slit, or which is even closed.

The operational safety can be further increased when, according to an advantageous construction of the present invention, the first ray detector located centrally to the central ray is shaped as a round disk and is surrounded by the second ray detector, shaped as a ring. In that case, deviations of the equalizing member relatively to the central ray can be determined with the same precision independently from the direction of this deviation due to the concentrical arrangement of the second ray detector.

According to a further development of the present invention, a constructively particularly simple structure is provided when the two detectors are fixed to the same equalizing member. Then the equalizing member is used to provide the build-up effect by generating secondary electrons necessary for an adequate X-ray sensibility of the ray detectors. This has the further advantage that the otherwise necessary metal plate need not be used.

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

In the drawings:

FIG. 1 shows in section an irradiating device having two separate ray detectors.

FIG. 2 is a perspective view of the operational desk of the irradiating device.

FIG. 3 is a diagrammatic sectional view of a different irradiating device wherein the two ray detectors are fixed.

FIG. 4 shows the two ray detectors of FIG. 3 in view from the side of the X-ray collimator.

FIG. 5 is a sectional view showing the arrangement of the two ray detectors in an irradiating device having a linear electron accelerator.

FIG. 1 shows in section a betatron 1. An accelerating tube 4 is shown between the poles 2 of an electromagnet 3. A theoretical path 5 is shown by broken lines within the accelerating tube 4, upon which the electrons are held and accelerated by the magnetic field. The accelerated electrons are deviated upon an anticathode 6, made of heavymetal, by a not shown deviating device known in prior art. X-rays produced in the anticathode leave through the window 7 of the accelerating tube 4 and can proceed into the open through the opening 8 of an adjustable X-ray collimator 9 to be used for irradiating an object. To diminish stray rays, the accelerating tube 4 is provided with a rayprotecting screen 10. A socalled equalizing member 11 is pushed into the X-ray cone 12 in front of the X-ray collimator 9 in ray direction, which provides for a uniform close output in the cross-section of the outgoing X-ray cone. This equalizing member 11 and a second equalizing member 13, provided for a smaller field to be irradiated, are fixed upon a swingably mounted lever 14 with two arms, and can be swung selectively into the X-ray cone 12. A first small pill-like ray detector 16 is provided in the central ray 15 of an X-ray cone emerging from the X-ray collimator 9. A second ray detector 17 is located on the side of the central ray in a section of the X-ray cone, which is not influenced by the X-ray collimator.

FIG. 2 shows a control panel 18 for the betatron of FIG. 1, wherein the irradiating parameters can be set. Among others, the control panel carries

switches

19, 20 for preliminary setting of the opening of the X-ray collimator 9, as well as separate indicating instruments 21, 22 for the ray dose measured by the two ray detectors 16, 17 (FIG. 1). Above the two indicating instruments is shown an alarm device 23 with optical and

acoustical signal givers

24, 25. A switching-off automat 26 is provided upon the panel 18 close to the alarm device 23. The automat 26 switches off the betratron automatically when a maximal preset ray dose has been reached in one of the two ray detectors.

Electrons accelerated upon the theoretical path are guided against the anticathode 6 in a manner not shown herein. In the anticathode, X-rays are produced by the braking of electrons. These X-rays, due to the rayprotecting screen 10, can leave only through the opening 8 of the adjustable X-ray collimator 9. The intensity of X-rays emitted by the anticathode 6 has a maximum in the direction of the electron ray striking the anticathode. The X-ray collimator 9 is centered to this maximum of the dose output. The central ray of the X-ray cone leaving the X-ray collimator thus coincides with this maximum.

To avoid that during irradiation of larger surfaces, those surface parts of the area being irradiated, which are located in a distance from the central ray of the X-ray cone, would receive a reduced X-ray dose, namely, to make possible uniform irradiation of larger areas, so-called equalizing members 11, 13 are shifted into the X-ray cone 12. These cone-shaped equalizing members have into their center a greater X-ray absorption than at their edges. Their shape is adapted to the distribution of the dose output over the corresponding angular areas of the X-ray cone of the respective accelerator in such manner that the X-ray cone 12 passing the equalizing member and leaving the X-ray collimator has the same dose outputs per space angle unit within the maximal opening angle given by the diameter of the equalizing member. It follows that a precise centering of the equalizing members 11, 13 to the central ray 15 is absolutely necessary. The equalizing members 11 must equalize the X-ray intensity in the larger opening angles of the X-ray cone, and therefore, they must weaken the intensity of the X-rays in the center of the cone 15 corresponding to the lower X-ray intensity on the sides of the cone. Therefore, the intensity of the X-ray cone behind such a larger equalizing member 1 1 is weaker than behind a smaller equalizing member 13, which must equalize only a smaller opening angle of the X-ray cone. Therefore, in order not to produce a too large intensity loss for smaller opening angles, an equalizing member with a smaller diameter is swung into the X-ray cone when a corresponding small collimator opening has been preselected.

When an equalizing member has been set correctly, namely, centrally to the central ray 15 of the X-ray cone, the dose outputs measured by the two

ray detectors

16, 17 must be related to each other in a predetermined ratio which is specific for each of the equalizing members 11, 13. A differential amplifier, which is not shown herein, is connected to the two ray detectors l6, l7 and to the alarm device 23; for that purpose, it is correspondingly switched over when the corresponding equalizing member is swung. Thus, the alarm device 23 is actuated only when the ratio of the measured ray dose deviates from the value which had been given to the respective equalizing members 11, 13. After the maximum ray dose given by the doctor has been reached, the illuminating device is switched off by the known automatic switching member 26 through the first ray detector located in the central ray. If no equalizing member has been shifted into the X-ray cone, if a wrong equalizing member has been shifted, or if the equalizing member has been shifted incompletely, then the ray detector 16 located in the central ray 15 of the X-ray cone receives a larger ray dose per time unit in relation to the ray detector 17 located to the side of the central ray. Consequently, the irradiating device will be timely switched off due to the above operational disturbances by the ray detector 16, which lies in the central ray l5. Independently thereof, the differential amplifier will release, in that case, the alarm device 23. Thus, there is no danger at all for the patient.

In the embodiment shown in FIG. 1, the X-ray collimator 9 must remain open at least to such an extent that the ray detector 16, located in the central ray 15, remains completely exposed to X-rays. However, this is not necessary in the embodiment of FIGS. 3 and 4, showing a different improved arrangement of the ray detectors. As in the embodiment of FIG. 1, in the embodiment of FIGS. 3 and 4, different equalizing members 27 (only one of which is shown), depending upon selected ray parameters, can be shifted into the X-ray cone 28 between the window 29 of the accelerating tube 30 and the opening 31 of the X-ray collimator 32. However, according to FIG. 3, the two

ray detectors

33, 34 are fixed directly to the corresponding equalizing member 27, which is different from the embodiment of FIG. 1. Thus, according to FIG. 3, the two ray detectors are located both in the ray direction in front of the X-ray collimator 32. FIG. 4 shows the two

ray detectors

33, 34 of FIG. 3 in view from the X-ray collimator 32. It is apparent that the first ray detector 33, arranged in the central ray 36, has the shape of a circular disk and is enclosed by the second ring-shaped ray detector 34, located to the side of the central ray. The first and the second ray detectors have equal surfaces directed to the anticathode 37, and are equally sensitive to X-rays.

According to the embodiment of FIG. 3, when the equalizing member 27 is correctly positioned, the two

ray detectors

33, 34 will also be correctly positioned. Due to the equal surfaces of both ray detectors, they will always deliver equally large measuring signals, and their corresponding indicating instruments 21, 22 upon the control panel 18 will always have equal deflections. This greatly facilitates the control. Thus, the measuring signals of the two

ray detectors

33, 34 can be transmitted without any switching through a fixedly set differential amplifier to the alarm device 23 (FIG. 2). If, in such an arrangement of the ray detectors, the equalizing member is placed excentrically to the central ray 36 as the result of an error, then this takes place also to the two ray detectors fixed to the equalizing member. In such a case, the central ray of the X-ray cone having a stronger intensity will pass through the less strongly absorbing edge portions of the equalizing member, and

will produce a comparatively larger measuring signal in l the second ring-shaped ray detector 34. The measuring signal of the first ray detector located centrally to the equalizing member 27 will be weaker due to the greater absorption of the balancing member in that region and due to the lower intensity of the X-rays passing through it to the side of the central ray 36. These two influences are superposed and result in a very great sensitiveness of the device shown in FIG. 3.

The above statements pertaining to FIG. 3 are equally applicable to the embodiment shown in FIG. 5. FIG. 5 differs from FIG. 3 substantially only by the use of a linear accelerator 38 instead of a betatron 1. FIG. 5 shows, in partially broken-off representation, such a linear accelerator 38. The accelerating tube 39 of the linear accelerator is closed by a thin but vacuumtight outgoing window 40 for the accelerated electrons. Two of the accelerating

electrodes

41, 42 of the accelerating tube are shown in front of the window in ray direction. The accelerating tube is surrounded by a ray-protecting casing 43, which is provided with a break 44 for the ray passage opposite the outgoing window 40 of the accelerating tube 39 of the linear accelerator 38. A so-called target 45 is located in ray direction directly behind the outgoing window; it is swingably mounted in the electronic ray leaving the accelerating tube open upon an axle 47 fixed in the ray-protecting casing 43 and extending parallel to the symmetry axis 46 of the accelerating tube 39. In case of a linear accelerator 38, the axis of symmetry 46 of the accelerating tube 39 coincides with the central ray 48 of the X-ray cone 49. An equalizing member 50, having the shape of a truncated cone, is located in ray direction and directly behind the break 44; it is swingable at the ray-protecting casing 43 about an axle 51 extending parallel to the symmetry axis 46 of the accelerating tube 39. Two

concentrical ray detectors

52, 53 are located symmetrically to the ray direction upon the side of the equalizing member 50, which is away from the target 45. An adjustable collimator 54 is located in the ray direction behind the equalizing member.

In the described embodiments, it is also possible to connect additionally the automatic switch-off device 23 to the outlet of the differential amplifier. In that case, the irradiating device would be switched off automatically directly after having been switched on if the equalizing member was incorrectly pushed in.

What is claimed is:

l. A device for X-ray treatment, comprising an electronic accelerator, an anticathode exposed to the accelerated electrons for producing X-rays, an adjustable collimator for X-rays, at least one member for equalizing the density of the X-rays in the cone of X-rays passing the collimator adapted to be shifted into the X-ray cone, supervising devices for the correct positioning of said member, and two ray detectors connected to said supervising devices in the part of the X-ray cone which is not influenced by said collimator for increasing operational safety, the first one of say ray detectors being located centrally to the central ray of the X-ray cone passing the collimator behind said equalizing member, the second of said ray detectors being located to the side of said central ray, wherein, in the ray direction the two ray detectors are located in front of said collimator and said equalizing member, wherein said first ray detector, located centrally to the central ray of the X-ray cone, has the shape of a circular disk, and wherein the second ray detector surrounds annularly the first ray detector, the two ray detectors being fixed to said equalizing member, and wherein the two ray detectors are equally sensitive toward X-rays and have equal surfaces directed to the X-ray source, said supervising devices comprising an alarm device and a differential amplifier connected to the two ray detectors and to said alarm device.

2. A device for X-ray treatment according to claim 1, said supervising device comprising separate rayindicating instruments connected to each of said ray detectors.

3. A device for X-ray treatment according to claim 1, said supervising device comprising an automatic switching-off device connected to the two ray detectors for switching off said accelerator when a maximum preset X-ray dosage has been reached in one of said two ray detectors.

4. A device for X-ray treatment according to claim 1, comprising an automatic switching-off device connected to said alarm device for switching off said accelerator.

Claims

1. A device for X-ray treatment, comprising an electronic accelerator, an anticathode exposed to the accelerated electrons for producing X-rays, an adjustable collimator for X-rays, at least one member for equalizing the density of the X-rays in the cone of X-rays passing the collimator adapted to be shifted into the X-ray cone, supervising devices for the correct positioning of said member, and two ray detectors connected to said supervising devices in the part of the X-ray cone which is not influenced by said collimator for increasing operational safety, the first one of say ray detectors being located centrally to the central ray of the X-ray cone passing the collimator behind said equalizing member, the second of said ray detectors being located to the side of said central ray, wherein, in the ray direction the two ray detectors are located in front of said collimator and said equalizing member, wherein said first ray detector, located centrally to the central ray of the X-ray cone, has the shape of a circular disk, and wherein the second ray detector surrounds annularly the first ray detector, the two ray detectors being fixed to said equalizing member, and wherein the two ray detectors are equally sensitive toward X-rays and have equal surfaces directed to the X-ray source, said supervising devices comprising an alarm device and a differential amplifier connected to the two ray detectors and to said alarm device.

2. A device for X-ray treatment according to claim 1, said supervising device comprising separate ray-indicating instrumenTs connected to each of said ray detectors.