FR2811472A1 - Radiographic therapy convergent X ray beam having circular crown anode/rotating cathode and arm section with filament electrons focussing deflector/anode face beam sweep converging - Google Patents

Abstract

The convergent X ray beam unit has a sealed chamber (1) with a good vacuum, with two high voltage electrodes. The anode (2) is a circular crown, whilst the cathode is a rotor (3). There is an arm section (4) carrying a heated filament (5) producing electrons and an electrostatic deflector (6) focussing the electron beams (7) on the internal anode face. During the electron beam sweep the beam formation is convergent.

Description

-1 - *; d2811472 The present invention relates to an apparatus for producing

  X-rays, or X-ray tube, making it possible to obtain X-rays in the form of a convergent beam,

  which gives it particularly interesting applications in radiotherapy.

  The technical field of the invention is that of the construction of X-ray tubes. Since the discovery of X-rays by Roentgen in 1895, the technique for manufacturing X-ray generating tubes has changed very little. It can be summarized as follows: in an enclosure where there is a very high vacuum are arranged two electrodes subjected to a high potential difference (several tens of kilovolts). The cathode emits and concentrates a beam of electrons on the anode which attracts the electrons with all the more force as the potential difference is high. At the point of impact of these electrons on the anode occurs the emission of an electromagnetic wave with a wavelength close to the angstrom: 10 -7 nmmn (X-rays) whose direction is a function of l angle made by the anode with respect to the incident electron beam. But the density of the electronic current causes a significant release of heat at the point of impact on the anode, this heating being proportional to the density of the electron beam and to the kinetic speed of these. The anode must therefore be made of a conductive but very refractory material (tungsten, carbon, etc.) so as not to be quickly destroyed. The use of a rotary anode in X-ray tubes of

  strong power allows to dissipate more quickly the heat produced.

  But in the current state of the art of manufacturing X-ray tubes, and whatever the variants used, the X-ray beam is emitted from the point of impact of the electrons on the anode. From this point of impact (focus) emerges a

  X-ray beam which is always divergent.

  While it is interesting for diagnostic radiology applications to obtain an X-ray with a conical configuration, emanating from a focal point as small as possible, it is not the same with regard to radiotherapy. Indeed, a beam of X-rays emanating from a focal point located at the top of a cone will irradiate more the superficial tissues than the tumor located in depth. It is the opposite which is desirable, and the use of a convergent X-ray makes it possible to have a maximum concentration of X-radiation at the level of the tumor

  destroy, while preserving surrounding tissue.

  However, to date there is no X-ray tube capable of directly producing a convergent beam of X-rays. On the other hand, it is impossible to focus X-rays because they can neither be reflected by mirrors, nor refracted

  by lenses, even electronic ones.

  The aim of the present invention is to propose the production of a device capable of generating X-radiation which can be concentrated in a very small region, which being placed in coincidence with the tumor to be destroyed, this latter will receive a maximum of radiation. , while the density of the X-ray will go quickly

  decreasing on both sides of the tumor.

  The device according to the invention which makes it possible to obtain a convergent X-ray beam, comprises a sealed enclosure where there is a very high vacuum in which are placed two electrodes between which a high potential difference is applied (from a few tens to a few hundred kilovolts). One of the electrodes (the anode) consists of a fixed circular crown and the other electrode (the cathode) is rotating, its axis of rotation coinciding with the axis of revolution of the anode. The cathode is provided with an arm, perpendicular to its axis of rotation, which is itself provided at its end with an electron-producing heating element.

  and electrostatic deflectors ensuring the concentration of the electron beam.

  During its rotation, the electron emitting arm projects these on the internal face of the anode which attracts them violently. The succession of the points of impact of the electrons on the anode, which constitute as many focal points of X-rays, determines on the internal face of the anode a circle producing X-rays. The beam of X-rays emitted from this circular hearth can have a configuration either cylindrical, or divergent, or convergent, according to the slope, or conicity, more or less accentuated of the face of the anode which undergoes the electronic bombardment. In the case of a converging beam, the angle given to the anode also determines the distance at which the point of convergence is situated in relation to the anode. It is obvious that each of the points of the anode bombarded by the electron beam emits not only a main ray, but also a sheaf of divergent secondary rays which are of no use in the context of the invention . Consequently, the device according to the invention also comprises a diaphragm situated inside or outside the enclosure, said diaphragm

  for selecting the main X-rays from the anodic emitting circle.

  After passing through the diaphragm, the X-ray beam assumes the form of a conical envelope which transforms, at the point of convergence, into a small volume of highly concentrated X-rays with maximum destructive activity. After passing this convergence zone, the X-ray beam becomes

  diverge and quickly lose its intensity.

  Other characteristics and advantages of the invention will become apparent from

  reading of the description which follows and of the attached drawings, in which:

  - Figure 1 shows in section a device according to the invention according to

a first embodiment.

  - Figure 2 shows in section a device according to the invention according to

a second embodiment.

  - Figure 3 shows in half-section a variant of the invention allowing

  accelerated cooling of the anode.

  - Figure 4 shows in half-section a variant of the invention allowing

  improved cooling of the anode.

  - Figure 5 shows how the use of the device according to the invention

  allows to destroy malignant tumors located in depth.

  With reference to these drawings, the various devices according to the invention comprise a sealed enclosure (1) which can have the shape of a bulb, a tube or a balloon or have a toric configuration, in which a very high vacuum prevails. Inside this enclosure are arranged two electrodes between which a very high potential difference is applied. The anode (2) consisting of a circular crown having YY 'for axis of revolution is fixed. It can be cooled by convection, or accelerated by the circulation of a coolant. In another embodiment the anode can be an integral part of the wall of the enclosure (1) and its cooling can be improved by fins located outside the enclosure. The cathode consists of a rotor (3) which has at its periphery one or more electron-producing elements (4), each of which consists of a heating filament (5) and electrostatic deflectors ( 6) intended to focus the electron beam (7) on the anode (2). The rotating assembly which constitutes the cathode, and which projects one or more electron beams onto the anode, is rotated through the wall of the enclosure (1) by an external inductor (11). The supply current of the filament (s) (5) is transmitted to the rotating assembly by a collector (12). The electron beam (s) (7) determine on the anode (2), during the rotation of the cathode, a circular track (9) which becomes the focal point of emission of an X-ray beam (8). The greater or lesser convergence of said beam, and therefore the greater or lesser distance from point O relative to the plane of the anode (2) are a function of the angle a which characterizes the slope, or conicity, of the anode. In the particular embodiment of the invention which is illustrated in FIG. 2, it is possible to imagine that for a very precise angle each point of impact of the electrons on the anode (2) determines a main X-ray which remains in the same plane as the emissive circle (9), the point of convergence O also being in this same plane. In this very specific case, and subject to building an enclosure of sufficient dimensions, it is possible to introduce the patient inside and position it so that the part to be irradiated is placed in coincidence with the point of convergence O It is also possible to design, from an embodiment of the invention similar to that described above, a system allowing the realization of densitometric sections. It suffices in fact to have, opposite to the X-ray produced by each point of impact of the electrons on the anode (2), a detector collecting the data relating to the density variations of the tissues traversed by the radiation rotating in the plane of the emissive circle (9) and transmit these

  information to the computer responsible for reconstructing the sections.

  In all the embodiments of the invention it is essential to provide a diaphragm (10) inside or outside the enclosure (1), and sometimes several of these diaphragms, in order to clearly delimit the beam of X-rays (8) in

  relation to the intended use.

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Claims (8)

  1. An apparatus for producing X-rays with a convergent beam characterized by a sealed enclosure (1) where a very high vacuum prevails, in which are placed two electrodes subjected to a potential difference of several tens of kilovolts, the anode (2) being consisting of a fixed circular crown having YY 'for axis of revolution and the cathode consisting of a rotor (3) whose axis coincides with YY', and an arm (4) perpendicular to YY ', said arm (4) carrying a filament (5) heated electronically to produce electrons, and electrostatic deflectors (6) which focus the electron beam (7) on the internal face of the anode (2), such that the succession of points of impact of the electrons on the internal face of the anode (2) during the circular scanning of the electron beam (7) generates an emission of X-rays (8) having the circle (9) for origin and a point of convergence O located on the axis YY '. 2. X-ray producing apparatus with a convergent beam characterized by a sealed enclosure (1) in the general shape of a torus, where a very high vacuum prevails, in which two electrodes are placed, subjected to a potential difference of several tens of kilovolts, 'anode (2) consisting of a fixed circular crown having YY' for axis of revolution, and the cathode consisting of a rotor (3) in the form of circular crown having YY 'for axis of rotation and an arm (4) oriented towards the anode, said arm (4) carrying a filament (5) electrically heated to produce electrons, and electrostatic deflectors (6) which focus the electron beam (7) on the so-called active face of the anode (2), so that the succession of points of impact of the electrons on the anode (2) during the circular scanning of the electron beam (7) generates an emission of X-rays ( 8) having the circle (9) for   origin and a point of convergence O located on the axis YY '.   3. X-ray converging beam producing apparatus according to claim 1 -6 or claim 2, characterized in that the internal face (or active) of the anode (2) has a slope, or taper, of a more or less important angle ct, intended to direct the X-ray beam (8) towards a point of convergence O located at a   greater or lesser distance from the emitting circle (9) on the axis YY '.   4. X-ray converging beam producing apparatus according to claims 2   and 3, characterized in that the angle ca of the active face of the anode (2) is calculated in order to produce an X-ray beam (8) of which all the rays coming from the emissive circle (9) are contained in the plane passing through the circle (9), as well as the point of convergence O.   5. A convergent beam X-ray producing apparatus according to claims 1   or 2 and claims 3 or 4, characterized in that it comprises a cathode   rotary (3) provided with several arms (4) arranged in a star with n branches in order to   produce multiple electron beams (7) simultaneously.   6. A convergent beam X-ray producing apparatus according to any one   claims 1 to 5, characterized in that the anode (2) forming part   integral with the enclosure (1) is provided with cooling fins.   7. A convergent beam X-ray producing apparatus according to any one   claims 1 to 5, characterized in that the anode (2), whether or not part   of the enclosure (1) is cooled by a coolant.   8. A convergent beam X-ray producing apparatus according to claims 1   or 2 and any one of claims 3 to 7, characterized in that a   diaphragm (10) is arranged, either inside or outside the enclosure (1) in order to delimit in a precise manner, and as required, the contours of the X-ray beam (8).