FR2764199A1 - Radiotherapy collimation procedure and apparatus - Google Patents

Abstract

Obtaining an isocentric radiation field from any type of particle accelerator delivering a beam of electrons, photons or protons for radiotherapeutic purposes uses a primary lead collimator attached to the accelerator by a rapid coupling to centre and regulate the beam emitted by a secondary collimator. The primary collimator is attached to the accelerator by a supporting adapter plate (3) and has a regulator (7) for the perpendicularity and/or x, y centering of the particle beam relative to the plate, and is equipped at its distal end with an additional interchangeable lead collimator shaped to fit the eye. The additional collimator is made up of a lead cylinder with an inner tunnel shaped to give the particle beam the required isocentre field for the therapy in question. The additional collimator is attached to the distal ene of a guide tube of a synthetic material such as polymethyl methacrylate (PMMA).

Description

COLLIMATION SYSTEM FOR EXTERNAL RADIOTHERAPY ESPECIALLY IN
AMD
The invention relates to a collimation system for obtaining a hyper reduced irradiation field, at a controlled distance from the isocenter of any type of particle accelerator delivering a beam of electrons, photons, or possibly protons, particularly intended for radiotherapy for specific treatments in stereotaxis such as for example the treatment of age-related macular degeneration (AMD). We know that age-related macular degeneration is the first cause of untreatable bilateral blindness in industrialized countries after the age of 50. Precursor lesions linked to aging, which are essentially alterations in the pigment epithelium, can progress and be complicated either by an atrophic form, but without therapeutic possibilities at present, or by an exudative hemorrhagic form with neovascularization in which certain clinical forms are accessible to laser photocoagulation.

 In reality, for every human being from the age of 65 and in some cases before, there is a risk of degeneration on the retina of the eyeball which manifests itself by a plaque visible on ophthalmological examination. It is a more or less circular zone of fibrosis whose effect is to cause a decrease in visual acuity and the visual field.

 The traditional treatment is fine surgery or laser which in common presents a significant risk due to the proximity of the optic nerve which can, if it is affected, create new complications and consequently a decrease in final visual acuity.

 Furthermore, laser treatment is not effective on all edematous forms, and the recurrence rate after laser treatment is more than 50% after three years; this treatment is, moreover, not indicated in the case of occult neovascularization and remains debatable in the retrofoveolar localization of the visible forms.

 A functional therapeutic alternative was therefore essential, and low-dose external radiotherapy falls within this framework.

 It has been known for a long time that radiotherapy is widely used in a certain number of non-cancerous conditions because of its two important properties: anti-inflammatory action and analgesic action.

Naturally, because of the risks linked to the action of radiation, radiotherapy for non-cancerous conditions is reserved for limited indications; in this case, applied to the
AMD, radiotherapy remains extremely dangerous, since the eye has intimate anatomical relationships with the brain and the areas to be treated are very close to the optic nerve, so that the location of an irradiation cannot tolerate any error because it would cause serious intracranial brain damage, even ophthalmic (reduced visual acuity, blindness). In addition, it is essential to clearly specify the dose delivered, due to the presence of the lens and other sensitive and fragile structures to avoid or reduce recurrent irradiation of the opposite eye and the brain.

 In this perspective, some teams of researchers already recommend using high energy radiation corresponding to doses of radiotherapy whose intensity of irradiation varies from 20 to 40 gray, delivered in one or more sessions. Very encouraging results have been observed by successfully using various energy sources, photons and electrons in particular, and soon, probably, protons. In all cases, the extent of the field of external radiotherapy in AMD must be as small as possible, between 1 and 3 centimeters in diameter, this field must also be at the center of the degeneration, while tilted by relative to the vertical axis.

One of the objects of the present invention is therefore to provide an apparatus which allows
- standardize the processing distances (for example 900 mm between the source and the output of the collimator)
- adapt collimation to any type of accelerator that is easy to handle.

 In accordance with the invention, a collimation system will therefore be described in order to be able to use external radiotherapy, in particular in AMD, by using any type of accelerator delivering high energy rays, and this, with maximum safety not only for the eye treated, but still for the brain and naturally to completely preserve the other eye.

 To this end, a method is first proposed for obtaining an irradiation field at the isocenter of any type of particle accelerator delivering a beam of electrons, photons, possibly protons, remarkable in that that from a quick adaptation interface to the type of accelerator used, pre-equipped with a primary collimation, one can perform with great precision a centering in x, y and an adjustment of perpendicularity with respect to the beam of a secondary or additional lead collimator whose shape is adapted to the ocular shape, mounted interchangeably at a fixed distance from the primary collimation in order to provide the isocentre with a field the shape and extent of which are strictly controlled with regard to the planned therapy.

 To implement this irradiation technique, it is then proposed, according to another object of the invention, several collimation plates depending on whether one wishes to use an electron accelerator or a photon accelerator.

According to a common characteristic of the collimation plates thus proposed, these comprise at least
- a primary lead collimator which is attached to a support plate naturally adapted to the type of accelerator used,
a system for adjusting the perpendicularity and / or the x, y centering of the beam with respect to the collimating stage, this system being provided at its distal part with a second lead collimator whose shape corresponds to the ocular shape, adapted to the characteristics of the energy used and correctly locked to ensure both safety of use and excellent interchangeability to obtain a field perfectly suited to the therapy envisaged.

Other characteristics and advantages will emerge more clearly from the description which follows of several alternative embodiments of collimation plates in accordance with the invention, given by way of nonlimiting examples, with reference to the drawing in which
FIG. 1 is a perspective view of a collimation plate intended for a particular type of electron accelerator,
FIG. 2 is a representation in sagital section of the collimation plate of FIG. 1,
FIG. 3 represents in perspective a collimation plate adaptable to a photon accelerator,
FIGS. 4 show in elevation and in view from below the additional collimator fitted to the collimation plate according to the previous figure,
FIG. 5 represents a sagital section of the collimating plate of FIG. 3 intended to equip an energy source of the photon type,
FIGS. 6 to 11 show the constituent parts of the system for adjusting the perpendicularity and the x, y centering of the beam with respect to the axis of the collimating plate whatever, moreover, the type of energy used,
FIG. 12 schematically represents the displacements x, y provided by the adjustment plate of FIG. 8 to the connecting piece shown in FIG. 10 so as to obtain a centering x, y of the beam,
- Figure 13 is a schematic representation of the adjustment of the perpendicularity of the beam relative to the axis of the plate.

 According to the invention, it is for the first time proposed to add to the collimator of a particle accelerator 1 or 1 ′ respectively delivering an electron beam or a photon beam, an additional collimation system making it possible to obtain the isocentre 2 of the accelerators 1,1 'an irradiation field the extent of which can be considerably reduced and the location extremely precise to limit all the side effects of the radiation.

 Whatever the energy used, in principle photons or electrons today, the general principle of operation of a collimation stage according to the invention therefore makes it possible to obtain on an area to be treated, for example the retina of the globe ocular in the treatment of age-related macular degeneration (AMD), a radiation field which it is absolutely necessary to control well and the intensity and frequency of the irradiations which can be done either in one session, or in several sessions successive, but still and perhaps above all the impact surface which must in principle be completely circumscribed to the area to be treated and the location of the impact which must in principle be at the center of macular degeneration while being inclined with respect to the vertical axis. So many extremely important parameters which have led to the production of collimation plates making it possible, on the one hand, to standardize the distances by predisposing the secondary collimators at a fixed distance from the collimator of the accelerator, and by proposing two series of adjustments allowing to obtain in a precise and stable manner irradiation fields of small diameter and of shape completely adapted to the shape of the eyeball for example.

 According to a first variant of the collimation plate provided for equipping an electron generator with reference to FIGS. 1 and 2, the collimation plate essentially comprises a support plate 3 conventionally coming to be superimposed on the collimator (not shown) of the accelerator 1 by means of two quick mounting handles 4, and for example four reference screws 5 which complete the mounting on the accelerator, in the same way as traditional accessories in radiotherapy.

 Once the support 3 is in place on the accelerator 1, there is, centered on the support plate 3, a first so-called primary collimator 6 which finally comes to be superimposed on the original collimator of the accelerator used.

 From this support plate 3, an adjustment system 7 is provided for the perpendicularity of the beam relative to the axis of the plate and its centering x, y; the adjustment system 7 will be widely described later.

 From the adjustment system 7, a tubular guide 8 made of synthetic material, for example polymethyl methacrylate (material known under the trademark ALTUGLAS), is provided to channel linearly and therefore control the electron beam over an advantageously fixed length which will be specified later. At the distal end of said tubular guide 8 there is a secondary collimator 9 made of lead, the shape of which is adapted to the ocular shape and the dimensions chosen to provide the isocentre 2 with an available field of sufficient width for the treatment of macular task. .

 The secondary collimator 9 is machined from a lead plate 10 mm thick sufficient for guiding the particles used at the outlet of the collimation stage.

 The collimator 9 which must be quickly interchangeable is mounted at the end of the tubular guide 8 by means of a support ring 10 normally made of Altuglas comprising on its distal face a recess 11 in which the collimator plate 9 is advantageously provided with 'A key allowing rigorous positioning in the plane of the recess 11, a tightening washer 12 hollowed out in its center comes ply the collimator 9 in its housing 11 to keep it there rigorously for example by means of four screws 13.

 Thus constituted, this first variant of the collimation plate, when it is adapted to an accelerator whose isocentric reference is 1,000 mm, is capable of delivering a beam at a fixed distance of 900 mm from the collimator of the accelerator 1 making it possible to rigorously position the area to be treated; it is also quite easy to modify the extent of the irradiation field by modifying the secondary collimator 9; for example for a field of diameter 20 at the isocentre, a collimator 9 made of lead will be taken, the cavity of which will have a diameter of 18 mm; for a field of 30 mm at the isocentre, the collimator cavity will be 27 mm; finally for a field of 40 mm at the isocentre, the cavity of the secondary collimator will be 36 mm; naturally, all of this remains linked to the cavity of the primary collimator, the diameter of which is in principle 21.8 mm. It goes without saying that all these dimensions are given only by way of example and that any other dimension could be validly retained without departing from the scope of the invention.

The complete system for adjusting the perpendicularity and the x, y centering of the collimation stage will now be described in detail with reference to FIGS. 6 to 13 of the drawings.
- The support plate 3 shown in Figure 6 is, as we said, arranged in line with the collimation of the accelerator 1 thanks to its handles 4 and to centering screws 5; on the distal surface of the support plate 3, a circular recess 14 is provided all around the central hole 15 allowing the passage of radiation at the outlet of the accelerator 1. In this recess 14 the primary collimator 6 is reported as shown in FIG. 7; the collimator 6, fixed by four screws 16, conventionally consists of a parallelepipedal piece of lead 12 mm thick. Of course, the shape of the central cavity 17 of the primary collimator 6 is chosen according to the shape of the field that is desired at the isocenter 2. The primary collimator 6 is by construction entirely included in the recess 14 of the support 3 to allow an adjustment plate 18 as shown in FIG. 8 to be superimposed without hindrance. The adjustment plate 18 of generally circular shape and having a passage for the particle beam in the center bears on the support 3 just above of the primary collimator 6 in accordance with the assembly shown in FIG. 9. The plate 18 is secured to the support 3 by three fixing screws 19 cooperating with three zones 20 of the support 3 extending radially inside the recess 14 to extend the distal support face of the plate 18; when these three screws 19 cooperate with threads 19 'provided on the three zones 20 of the plate 3 it is clear that the adjustment plate 18 can take in space practically all possible tilt positions in accordance with the diagrams of Figure 13. It suffices to change the inclination of this plate to play on one or the other of the three screws 19; this will subsequently allow the alignment of the tubular guide 8, and therefore of the secondary collimator 9, relative to the axis of the accelerator beam 1. Of course, the adjustment plate 18 itself comprises holes 19 "ensuring the free passage of the screws 19 as previously stated. Slightly offset and on the same diameter as the 19 "passages provided on the plate 18, three stop screws 21 cooperate with threaded holes emerging from the adjustment plate 18 in such a way that the three abutment screws 21 can, by screwing, come to bear against the regions 20 of the support 3. In this way and as shown schematically in FIG. 13, it is possible after adjusting the inclination in the space of the plate adjustment 18 relative to the support 3, corresponding to the adjustment of the perpendicularity of the beam, said adjustment plate 18 can be locked in its final position by locking the screws 21 on the zones 20 support 3.

 Now that the perpendicularity adjustment has been made, the beam must be centered x, y. To obtain this centering, the adjustment system 7 is completed by a last piece, called a connecting piece 22, shown in front view in FIG. 10. This piece 22 comprising, like the previous pieces, a central passage 23 for the particle beam , is attached concentrically on the adjustment plate 18 to which it is secured by four screws 24 cooperating with four threads 24 'provided on the plate 18 and four holes 24 "provided on the part 22; these four holes 24" have a diameter markedly greater than the diameter of the screws 24 so that the part 22 can move freely in x and in y around the screws 24, when the latter are not blocked on the plate 18. The linear displacements in x and in y of the connecting piece 22 are advantageously obtained by four vertical bosses 25 distributed towards the periphery of the adjustment plate 18, on its distal face according to a cardinal distribution, that is to say di re at 90 "from each other. The vertical bosses 25 have parallel faces 26 and 27 looking at each other in pairs and threaded in their center in radial directions to each receive a threaded rod 28 whose end, directed towards the center of the plate 18, can be moved over a few millimeters by the rotation of a drive wheel 29 secured to the other end of the threaded rod 28 in order to create, between two facing rods, a linear displacement in x then in y in the plane of the adjustment plate 18; the generally parallelepipedal part 22 has a square section and a thickness sufficient for the ends of the rods 28 to abut and create the desired centering x, y.

 Of course, and in accordance with the diagram shown in FIG. 12, it will suffice, after having obtained the correct centering x, y, to block the four fixing screws 24 in the threaded holes 24 ′ of the plate 18 to definitively keep this centering. According to a particular and interesting embodiment of the mechanism for centering x, y of the beam, with reference to the drawing in FIGS. 10 and 11, provision is made to add to the ends of two consecutive threaded rods 28, a stop 30, advantageously cylindrical, coming to cooperate with a mortise 30 'provided in correspondence on the side of the connecting piece 22 which can thus be linearly displaced by a single threaded rod and its control wheel, both in x and in y; indeed, the rotation of the threaded rod provided with its end stop 30 leads in one direction to an advance, and in the other a retreat of the part 22, the two threaded rods 28 not provided with the stops 30 then only serving as to block the device put in place by the two threaded rods thus equipped.

 Figure 11 shows in a bottom view a complete and mounted assembly.

 It remains to adapt the tubular guide 8 for the variant intended for electron accelerators in accordance with FIG. 2. For this purpose, a ring 31 made of the same material as the tubular guide 8 is fixed to the connecting piece 22 by four screws 32; the tubular guide 8 is then embedded just inside the ring 31, four lateral screws coming together to hold the ring and the tubular guide 8. Finally and incidentally, a cover 33 previously slid around the tubular guide 8 comes, a Once the tubular guide 8 mounted as just said, cover the entire adjustment system to protect it. This protective cover 33 is held in good position by means of a simple ring 34 screwed radially onto the tube guide 8 coming to counter-tighten said cover on the visible part of the mechanism of the adjustment system 7.

Finally, it suffices to carry out the adjustment operations independently of each other using the synoptic beam.
- Adjustment of the perpendicularity of the beam, the three screws 19 are loosened by about half a turn, then the three stop screws 21 also by a half-turn; the equipment is then suspended on the three screws 19 and one can act by screwing or unscrewing the same screws 19 until the tube guide 8 is rebalanced with the synoptic beam; once this adjustment which is necessarily very precise has been obtained, it suffices to tighten the stop screws 21 to permanently maintain this adjustment of perpendicularity,
- centering of the beam in x, y; in the same way we will proceed by loosening the four screws 24 allowing the part 22 to be slightly floating relative to the adjustment plate 18, then according to the variant, we will act on the threaded rods 28 by means of the knobs 29 to move in x and / or in y said connecting piece 22 and therefore the tubular guide 8, with respect to the synoptic beam; it is obvious that if the collimating plate comprises the most elaborate variant of adjustment, it suffices then to adjust the two knobs 29 until the desired centering and then to counterpress the connecting piece 22 by the two other threaded rods in order to 'A final blocking of said part 22.

 All of these adjustments being completed and normally carried out in the factory, it will suffice to reassemble the cover 33 and block it using the ring 34 as has been said. Such an assembly currently makes it possible to obtain an accuracy of the bombardment at the isocenter of less than 1 mm.

 In accordance with Figures 3,4,5, there will now be described a second variant of the collimation stage according to the invention allowing the use of a source delivering photon radiation to the isocenter of an accelerator 1 ' .

 The collimation stage adapted to the photon generator, as shown in perspective in FIG. 3 essentially comprises a rapid adaptation support 3 to the accelerator 1 ′, an adjustment system 7 of perpendicularity and of centering x, y of the beam with respect to the axis of the plate quite similar to the previous variant, finally an additional collimation 40 straight or focused, mounted on the distal part of a collimator holder 41 itself secured to the distal face 42 of the connecting piece 22 of the adjustment system 7, common to the two variants.

 Preferably, the additional collimator 40 respectively straight or focused, consists of a lead cylinder 43 axially comprising a tunnel 44 respectively cylindrical or frustoconical, normally arranged in the axis of the beam, so that it can through the reoriented tunnel 44 modify the trajectory of its particles so that at the output of said additional collimator 40, a field of particles of suitable width is obtained at isocentre 2.

 According to, for example, a particular embodiment of a collimation stage for a photon generator, the additional collimator 40 allowing external radiotherapy in AMD, consists of a lead cylinder 43 to avoid any emission of radioactivity, arranged inside a brass envelope for holding and fixing the collimator 40 to the collimation plate; to obtain at the isocentric reference 1.000, a correct available field, the output of the additional collimation 40, that is to say the distal end of the tunnel 44, will be approximately 688 mm from the collimator of the accelerator 1 ' . To have a good focusing of the particles inside the lead cylinder 43, a height of said cylinder 43 was retained of approximately 92 mm.

 As in the first variant adapted to the electron generator, it is essential to ensure perfect perpendicularity of the beam relative to the axis of the collimating plate as well as an x, y centering of the same beam.

Naturally, we will use a mechanism quite similar to that described above and that consequently, we will not detail here; the difference between the two variants is that the tubular guide 8 is replaced by the additional collimator 40 which is fixed on a collimator holder 41 on the distal face 42 of the connecting piece 22 as already said by means of three screws 46 (figure 3).

 The collimator holder 41 has a generally frustoconical hollow shape making it possible to receive in a very adjusted manner the head 47 of the brass casing 45 as shown in FIG. 4a. The head 47 is wider than the brass casing 45 so as to provide a hooking ring for a threaded ring 48 resting under the head 47 and maintaining in force the conical part of the head 47 in the hollow frustoconical part of the collimator holder 41.

 According to a more advantageous execution of the assembly, provision is made to have at the periphery of the projecting part of the head 47 of the additional collimator 40 bayonet coding systems 49 making it possible to mount the additional collimator 40 in the correct position on the distal part of the plate collimation.

 As before, the perpendicularity and centering adjustments are made in principle in the factory, but it is always possible to fine-tune these adjustments by removing the protective cover 33 and by playing on the various adjustments as detailed in the previous variant. . Here again, the additional collimators 40, as in the previous variant for the secondary collimator collars 9, are interchangeable very quickly, so that, overall, the collimation plates as they are proposed according to the invention are adaptable not only to all types of accelerators normally available on the market, but also to all eye forms with which the radiotherapist is confronted.

 As they have just been described, the two variants of collimation plates, in accordance with the invention, are naturally directly usable in external radiotherapy in age-related macular degeneration, but at present nothing opposes in principle that such plates are used by researchers, physicists or radiotherapists in the field of cataract treatment.

 It goes without saying that any modifications made to the system and devices described above which would consist in replacing such or such functional part by technical equivalents would not depart from the protective framework of the present invention.

Claims (10)

 1 - Method for obtaining an irradiation field at the isocenter of any particle accelerator delivering a beam of electrons, photons, possibly protons, intended for radiotherapy for the specific treatment in stereotaxis in particular age-related macular degeneration characterized in that, from an interface for rapid adaptation to the type of accelerator used, pre-equipped with primary lead collimation, it is possible to carry out with great precision a centering in x, y and an adjustment of perpendicularity with respect to the beam of a secondary or additional lead collimator, of a shape adapted to the ocular shape mounted interchangeably at a fixed distance from the primary collimation in order to provide the isocentre with a field whose form and extent are strictly controlled.  2 - collimation stage implementing the method according to claim 1 to obtain an irradiation field, at a fixed distance from the isocenter (2) of any type of accelerator (1 ') of particles delivering a beam of photons, intended for radiotherapy for the specific treatment in stereotaxis in particular of the macular degeneration related to the age characterized in that it comprises at least  - a primary lead collimator (6) which is integral with a support plate (3) adapted to the type of accelerator (1 '),  - a system for adjusting (7) the perpendicularity and / or the x, y centering of the beam relative to the axis of the collimating plate which carries in its distal part an additional collimator (40) of lead, of suitable shape to the ocular, interchangeable, straight or focused shape, with which locking means (47, 48) are advantageously associated with polarizing (49).  3 - collimating plate according to claim 2 characterized in that the additional collimator (40) respectively straight or focused consists of a lead cylinder (43) axially comprising a respectively cylindrical or frustoconical tunnel normally disposed in the beam axis , in such a way that through said tunnel (44) the trajectory of the particles is reoriented so that at the exit from said collimator (40) a field suitable for the envisaged therapy is obtained at said isocentre (2) ) being kept in good position in a brass envelope (45) perforated in its distal part so that the tunnel (44) emerges, and provided in its proximal part with a head (47) of frustoconical shape and wider than the 'envelope (45) to be precisely fitted under a collimator holder (41) secured to the adjustment system (7), to which it is locked, advantageously through a conventional bayonet keying system ettes (49) by means of a threaded ring (48).  4 - Collimation stage implementing the method according to claim 1 to obtain an irradiation field, at a fixed distance from the isocenter (2) of any type of accelerator (1) of particles delivering an electron beam, intended for radiotherapy for the specific treatment in stereotaxis in particular of the macular degeneration related to the age characterized in that it comprises at least  - a primary lead collimator (6) which is integral with a support plate (3) adapted to the type of accelerator (1),  - a system (7) for adjusting the perpendicularity and / or the x, y centering of the beam relative to the collimating plate which carries in its distal part a tubular guide (8) made of synthetic material, for example polymethyl methacrylate , secured to the adjustment system (7) in a known manner, equipped at its distal end with a secondary collimation (9) of lead, the shape of which is adapted to the ocular shape and the dimensions of which are chosen to provide the isocentre ( 2) an available field of desired dimensions.  5 - collimating plate according to claim 4 characterized in that the secondary collimator (9) is fixed to the distal end of the tube (8) in synthetic material by means such as rings and washers (10,12) in synthetic material and screws (13), and in that it includes keying pins allowing rigorous positioning in its housing (11).  6 - collimating plate according to any one of claims 4 or 5 characterized in that the length of the tubular guide (8) in synthetic material is provided so that the output of the secondary collimator (9) is 900mm for an isocentric reference 1000 mm and its section is sufficient to channel the beam between the two collimators (6,9).  7 - collimating plate according to any one of claims 2 to 6 characterized in that the support plate (3) is provided on one side with adequate means (4,5) to adapt to the collimator of the accelerator specific (1) and there is provided on the other side a recess (14) having a central passage 15 for the radiation beam, to completely embed the lead plate forming the primary collimator (6) and allow mounting, face against face , an adjustment plate (18), normally circular, also with a hole in the center to let the particle beam pass, secured to the support plate (3) by three fixing screws (19) providing the beam perpendicularity adjustment by screwing more or less each of them, the plate (18) being suspended on the three screw heads (19), each fixing screw (19) being associated with a stop screw (21) counterpressing the adjustment plate ( 18) and the support plate (3) at the end of setting.  8 - collimating plate according to any one of claims 2 to 5 characterized in that the support plate (3) is provided on one side with means (4,5) suitable for adapting to the collimator of the accelerator specific (1) and there is provided on the other side a recess (14) comprising a central passage (15) for the radiation beam, to completely embed the lead plate forming the primary collimator (6) and allow mounting, side on the opposite side, a normally circular adjustment plate (18), also with a hole in the center to allow the particle beam to pass, secured to the support plate (3) by fixing screws (19) and in that the adjustment plate (18) comprises on its distal face, distributed towards the periphery according to a cardinal distribution, four vertical bosses (25) with parallel faces (26,27) looking at each other in pairs, drilled and threaded in their center in radial directions to receive each a thread rod ée (28) whose end directed towards the center of the plate (18) can be moved over a few millimeters by the rotation of a drive wheel (29) integral with the other end in order to create between two rods (28 ) opposite, the linear displacement in x then in y in the plane of the plate (18) of a connecting piece (22) of advantageously square section, mounted floating on screws (24) fixing to the plate (18) that we block after the settings in x and y.  9 - collimation plate according to claim 7 characterized in that the adjustment plate (18) comprises on its distal face, distributed towards the periphery according to a cardinal distribution, four vertical bosses (25) with parallel faces (26,27) are looking two by two, drilled and threaded in their center in radial directions to each receive a threaded rod (28) whose end directed towards the center of the plate (18) can be moved over a few millimeters by the rotation of a wheel drive (29) integral with the other end in order to create, between two facing rods (28), the linear displacement in x then in y in the plane of the plate (18), of a connecting piece (22) advantageously square in section, floatingly mounted on fixing screws (24) to the plate (18) which are blocked after the adjustments in x and y.  10 - collimation plate according to any one of claims 8 or 9 characterized in that one or the other of the ends directed towards the center of the plate, of the two threaded rods (28) opposite is provided with an advantageously cylindrical stop (30) for cooperating with a mortise (30 ') provided in correspondence on the opposite side of the connecting piece (22) in order to be able to carry out the adjustment (x or y) by means of a single rod ( 28), the opposite rod then only locking the part (22) after the adjustment (x, y).  it - Apparatus for cataract radiotherapy characterized in that it incorporates a collimation plate according to any one of claims 2 to 10.