Patent Number: 
Section: description

FIG. 1 shows the basic design of a radiation device in which the collimator 1 in accordance with the invention can be used. The collimator 1 is disposed on a collimator block 19 which is mounted to a gantry 41. The gantry 41 contains the radiation source 3. The radiation can be produced e.g. by a linear accelerator 43. The gantry 41 can be rotated about a horizontal axis of rotation 44, wherein the rays 2 are directed towards a radiation object 20, e.g. a tumor. The radiation object 20 is located in the isocenter of the rays 2, and the radiation source 3 as well as the collimator 1 circle around the patient 46 through rotation of the gantry 41. The treatment table 42 can also simultaneously rotate about a rotational axis 45 to further change irradiation of rays 2 onto the treatment object 20 within the patient 46. Of course, further adjustments are feasible. The intent is that the object to be treated 20 experiences maximum radiation dose by changing the different radiation directions while, however, protecting surrounding tissue to the greatest extent possible by only exposing it to the rays 2 for short periods of time. Furthermore, certain regions of the body must often be completely avoided such as e.g. the spinal cord or organs, wherein the irradiation directions must be chosen accordingly. The rays 2 are formed by the collimator opening 18 such that they impinge on the radiation object 20 in correspondence with its shape to protect the surrounding tissue. The profile of the tumor is detected e.g. through computer tomography recordings. This data is processed to generate a collimator opening 18 corresponding to this shape and can optionally irradiate different portions of the irradiation object 20 with different intensities. The shape and intensity are calculated and adjusted for each irradiation direction. FIG. 2 shows a collimator opening 18 of a multi-leaf collimator. The invention concerns such a collimator 1 having the above-mentioned improvements which are also shown and explained in the subsequent figures. In accordance with the invention, the collimator leaves 4 and 4xe2x80x2 can produce a collimator opening 18 which corresponds to the shape of the object to be treated 20 without producing a half shadow 47. This will be further explained below. FIG. 2 shows the principle of a collimator 1 designed as a multi-leaf collimator which reproduces the shape of a tumor in a collimator opening 18 using collimator leaves 4, 4xe2x80x2. Advantageous embodiments of the invention thereby provide that the collimator leaves 4 and 4xe2x80x2 can be pushed beyond the central line 17 of the maximum possible collimator opening 18. This is required e.g. if the radiation object 20 has a U- or similar shape which can be reproduced only if the collimator leaves 4 and 4xe2x80x2 extend beyond the central line 17. Moreover, the collimator leaves 4 and 4 can be closed, as shown at the left and right sides. The collimator leaves on these sides do not abut at the central line 17 but are staggered to reduce leakage radiation in this region. FIG. 3a shows the principle of half shadow 47 production in some collimators of prior art. The collimator leaves 4 and 4 therein have straight front edges 5 and 5xe2x80x2. If rays 2 from a substantially point-like radiation source 3 pass through the collimator opening 18, part of these rays 2 must pass through the entire material thickness and another part of the rays does not contact the material. In the intermediate region, the rays penetrate only part of the material of the collimator leaves 4, 4xe2x80x2 and are partly absorbed to produce half shadows 47. The further the collimator leaves 4 and 4xe2x80x2 are moved apart by the adjustment 48, the larger this half shadow 47. Due to this half shadow 47, the surroundings of this radiation object 20 are also irradiated with attenuated intensities 2, in addition to the irradiation object 20. This causes unnecessary damage to the surrounding tissue of the patient 46. With rounded front edges 5, 5xe2x80x2 or with collimator leaves 4, 4xe2x80x2 which are disposed on top of one another in steps, such half shadows can be reduced, however, not eliminated. FIG. 3b shows the principle of avoiding half shadows 47 in the inventive collimator 1. The inventive collimator leaves 4 and 4xe2x80x2 are designed such that their front edges 5 and 5xe2x80x2 are always oriented in parallel to the rays 2, despite their linear displacement to thereby ensure that a ray 2 either completely passes through the collimator opening 18 and hits the radiation object 20 or is absorbed by the entire material thickness of the collimator leaves 4 and 4xe2x80x2. The front edges 5 and 5xe2x80x2 are aligned according to the adjustment 48 of the collimator leaves 4 and 4xe2x80x2 thereby ensuring that a half shadow 47 is prevented for all widths of the collimator opening 18. FIG. 3c shows partial prevention of a half shadow by designing the collimator leaves 4 and 4xe2x80x2 in an asymmetrical trapezoidal shape 13. The viewing direction of the collimator 1 is rotated through 90xc2x0 with respect to the representations of FIGS. 3a and 3b and directed onto the front edges 5, 5xe2x80x2. The design shown prevents the side surfaces 14 of the collimator leaves 4, 4xe2x80x2 and the lateral borders 16 from producing half shadows 47. The collimator leaves 4 and 4xe2x80x2 thereby have an asymmetrical trapezoidal shape 13 such that the two side surfaces 14 of each collimator leaf 4, 4xe2x80x2 extend parallel to the rays 2. The inner surfaces 15 of the lateral borders 16 also have a corresponding alignment and are adjacent to the side surfaces 14 of the outer collimator leaves 4 and 4xe2x80x2, without leaving gaps. In FIG. 3c the two outer collimator leaves 4 and 4xe2x80x2 are shown in cross section, since they are closed. The other collimator leaves 4, 4xe2x80x2 are opened to a greater or lesser degree to thereby form the collimator opening 18. A corresponding design of the collimator leaves 4, 4xe2x80x2 was disclosed in prior art, but had the functional problems discussed above. Only the inventive design of the collimator leaves 4 and 4xe2x80x2 permits guaranteed trouble-free function despite the asymmetrical trapezoidal shapes 13 without having to accept large tolerances or introduce a further set of collimator leaves, displaced by 90xc2x0, in the optical path 2. In this fashion, both the functions shown in FIG. 3b and FIG. 3c can be provided by the same set of collimator leaves 4 and 4xe2x80x2. This is a considerable advantage over prior art. FIG. 4 shows the principle of an inventive embodiment of the collimator 1. The collimator leaves 4 and 4xe2x80x2 comprise rear parts 6 and 6xe2x80x2 and front parts 7 and 7xe2x80x2. The latter are formed as semi-circular bodies 8 and 8xe2x80x2 and are disposed in corresponding recesses 9 and 9xe2x80x2 of the rear parts 6 and 6xe2x80x2 of the collimator leaves 4 and 4xe2x80x2. Such mounting can e.g. be effected when the front parts 7 and 7xe2x80x2 have a groove 56 about their semi-circular shape into which the rear parts 6 and 6xe2x80x2 engage with corresponding graduation in the region of the corresponding recesses 9 and 9xe2x80x2 such that full material thickness is maintained. Retaining pins 49 are provided within corresponding slots 50 for securely mounting the front parts 7 and 7xe2x80x2. The length of the slots 50 defines the adjustment region. When the collimator leaves 4 and 4xe2x80x2 are displaced in accordance with the arrows 48, the front parts 7 and 7xe2x80x2 are simultaneously turned about an imaginary axis of rotation 36 such that the front edges 5 and 5xe2x80x2 are always aligned parallel to the rays 2. This means that the front edges 5 and 5xe2x80x2 are perpendicular in the region of the central line 17 of the possible collimator opening 18 and, when displaced from this central line 17, are oriented in the one or the other direction such that they point towards the radiation source 3. To guarantee these adjustments, the front ends 12 of the rear parts 6 and 6xe2x80x2 must be set back correspondingly such that the front edges 5 and 5xe2x80x2 are located in the region of these front ends 12 only when maximum adjustment has been reached. The height 12 of the rear parts 6 and 6xe2x80x2 is preferably as large as the diameter 11 of the semi-circular bodies 8 and 8xe2x80x2, thereby ensuring constant material thickness. This embodiment has the further advantage that the front parts 7 and 7xe2x80x2 always have the same height as the rear parts 6 and 6xe2x80x2. FIG. 4 also shows a transmission for the collimator leaves 4 and 4xe2x80x2 which ensures that the front edges 5 and 5xe2x80x2 are correctly aligned for each position of the collimator leaves 4 and 4xe2x80x2. This can be effected through forced mechanical coupling defined by a driving toothed wheel 23 which engages a collimator toothed rack 21 as well as a front edge toothed rack 22, wherein these toothed racks 21 and 22 have different subdivisions 52, 53 or 54 (see FIGS. 5a and b) to achieve the different required adjusting motions. It must thereby be guaranteed that the different subdivisions 52,53 or 54 lie within the tolerance limits of the gearing of the driving toothed wheel 23 to prevent jamming. The arrow 51 shows the direction of rotation of the driving toothed wheels 23 and the arrows 48 show the adjustment of the collimator leaves 4 and 4xe2x80x2 caused by this driving direction. The collimator leaf 4 of FIG. 4 assumes the maximum opening position 64 and the collimator leaf 4 assumes the maximum over-travel 63. The latter represents maximum traverse of the central line 17. This over-travel permits the collimator opening 18 to reproduce a tumor 20 of any shape, up to the size of the maximum collimator opening 18. The arrangement of the drives in FIG. 4 at the lower end of the collimator leaves 4 and 4 is merely an example. It is also possible to dispose these drives 23,21,22 in the upper region or alternately at the bottom of a collimator leaf 4 or 4xe2x80x2 and at the top of the neighboring collimator leaf 4 or 4xe2x80x2 to thereby obtain more space for the drives. In the embodiment of FIG. 4, the teeth of the collimator toothed rack 21 are milled into a longitudinal edge 37 (see FIG. 7) of a rear part 6 or 6xe2x80x2. The front edge toothed rack 22 is disposed within a central groove 66 of this milled collimator toothed rack 21 (FIG. 8) and is pivotally connected to the front part 7,7xe2x80x2 via a pivot 57 to effect adjustment. Since the collimator toothed rack 21 and the front edge toothed rack 22 have different divisions 52,53,54, the driving toothed wheel 23 provides different advances. The advance difference can be defined by the subdivision differences. The different tooth subdivisions 52,53,54 are shown in FIGS. 5a and 5b. FIG. 5a shows the subdivisions 52,54 of collimator toothed rack 21 and front edge toothed rack 22 when they are disposed above the collimator leaves 4 and 4xe2x80x2. In this case, the subdivision 52 of the collimator toothed rack 21 is larger than the subdivision 54 of the front edge toothed rack 22 which produces a larger advance of the collimator toothed rack 21 compared to that of the front edge toothed rack 22. If the rear part 6, 6xe2x80x2 is moved in the direction of the double arrow 48, its displacement is somewhat larger than that of an upwardly disposed front edge toothed rack 22 to turn the front part 7,7xe2x80x2 such that the front edge 5, 5xe2x80x2 extends parallel to the rays 2. This alignment is ensured in all positions, even when the central line 17 is crossed. In FIG. 5b, the subdivision 52 of the collimator toothed rack 21 is smaller than the subdivision 53 of the front edge toothed rack 22 when it is disposed below the collimator leaves 4 and 4xe2x80x2. The function is the same as described above with the difference that, in this arrangement, the advance of the front edge toothed rack 22 must be larger than that of the collimator toothed rack 21 for corresponding alignment of the front edges 5 and 5xe2x80x2. Of course, other arrangements are also possible. The toothed racks 21 and 22 can also be disposed on rear extensions of the collimator leaves 4 or 4 and it is also possible to provide a separate driving toothed wheel 23 to guarantee allocation of the advances for the two toothed racks 21 and 22 via a no-load toothed wheel 24. FIG. 6 shows coupling of a front part 7 or 7xe2x80x2 to a rear part 6 or 6xe2x80x2 of a collimator leaf 4 or 4xe2x80x2 and shows how the front edge toothed rack 22 is guided in a groove 66 which was milled in the center of the collimator toothed rack 21. Both gearings are therefore at the same height and a single toothed wheel 23 or 24 can engage both gearings. Since the collimator toothed rack 21 is directly milled in a longitudinal edge 37 of a rear part 6 or 6xe2x80x2, this adjustment will be transferred directly onto this rear part 6 or 6xe2x80x2. To adjust the front parts 7 and 7xe2x80x2, the front edge toothed rack 22 is pivotally mounted 57 to the front part 7 or 7xe2x80x2 for transmitting the adjustment motion. FIG. 7 shows displaced arrangement of the rear parts 6 or 6xe2x80x2 of the collimator leaves 4 or 4xe2x80x2. This displaced arrangement serves to accommodate guidance means 38 via grooves 26 and 39. Such grooves 26, 39 can be milled into either the side surfaces 14 or into the longitudinal edges 37. FIG. 8 shows the arrangement of such guidance means 38 as well as disposition of a driving toothed wheel 23, a toothed wheel 24, the collimator toothed rack 21, and the front edge toothed rack 22. A first guidance 38 is defined by a groove 39 milled into the longitudinal edge 37 of the rear part 6 or 6xe2x80x2 in which a guiding element 40 of the collimator block 19 runs. A further guidance 38 has a guiding groove 26 located in the side surface 14 of a rear part 6 or 6xe2x80x2. A guiding element 25 of the collimator block 19 also engages in this guiding groove 26. The guiding groove 26 is disposed at the end of the rear part 6 or 6xe2x80x2 where the collimator toothed rack 21 is located. The collimator toothed rack 21 is milled into a longitudinal edge 37 of the rear part 6 or 6xe2x80x2. The central region of this collimator toothed rack 21 is provided with a groove 66 in which the front edge toothed rack 22 is disposed such that a toothed wheel 24 or 23 engages in said gearing and also in the gearing of the collimator toothed rack 21. Different advances are achieved due to the different subdivisions, as described above. FIGS. 9a and 9b show a second embodiment of the invention which differs from the first embodiment in that a driving toothed rack 55 and a driving toothed gear 23 are located in the front region of the rear part 6 or 6xe2x80x2 and the collimator toothed rack 21 and the front edge toothed rack 22 are disposed in the rear region. A non-loaded toothed wheel 24 engages both toothed racks 21 and 22 to transmit the differing advance to the front edge toothed rack 22. In the present embodiment, the driving toothed wheel 23 is disposed in a collimator block 19 or in a collimator block half which can be displaced with respect to a base frame 58. The further toothed wheel 24 is connected to the base frame 58 via a bearing 59. In this arrangement, the front edges 5 and 5xe2x80x2, once correctly adjusted, remain aligned and parallel to the rays 2 even when the entire collimator block 19 is displaced with respect to the radiation source 3 or if two collimator block halves are moved apart to enlarge the collimator opening. This is shown in FIGS. 9a and 9b. The collimator block 19 of FIG. 9a is in a first position with respect to the center line 17 and, in FIG. 9b, in a second position displaced in the direction of the arrow 60. This displacement produced a change in the angle xcex12 of the front part 7 or 7xe2x80x2 via the mechanics shown, such that the front edges 5 or 5xe2x80x2 also extend parallel to the rays 2 in the new position. The figure shows that the front edge 5 or 5xe2x80x2 in FIG. 9b has a larger distance from the center line 17 than in FIG. 9a, and the angle xcex11 was increased to xcex12 through displacement. The driving toothed rack 55 in the front region can thereby be identical to the gearing of the collimator toothed rack 21 or have a different subdivision or tooth size. In any event, the front edge toothed rack 22 must not have any teeth in this region and lies in the groove 66 at a depth which permits the driving toothed wheel 23 to run in the driving toothed rack 55 and the front edge toothed rack 22 to be freely displaced in this region. FIGS. 10a and 10b show a third embodiment wherein the adjusting motion of the front parts 7 and 7xe2x80x2 is effected through a linkage. In this embodiment as well, the rear parts 6 or 6xe2x80x2 are provided with a driving toothed rack 55 for adjusting the rear part 6 or 6xe2x80x2 via a driving toothed wheel 23. A connecting link guide 27 is joined by a rigid connection 61 to the driving toothed wheel 23 for producing adjustment of the front part 7 or 7xe2x80x2. A slider 28 runs in this connecting link guide 27 which is mounted to a cable drive 29. One end 30 of this cable drive 29 is mounted above the imaginary axis of rotation 36 at the front part 7 or 7xe2x80x2 and the other end 31 below said imaginary axis of rotation 36. FIGS. 10a and 10b show the possible adjustment range. FIG. 10a shows the position of the maximum over-travel 63 and FIG. 10b shows the maximum opening 64. The adjustment displacement 48 is transferred via the driving toothed wheel 23 to the rear part 6 or 6xe2x80x2 and the slider 28 is displaced by the connecting link guide 27 in the direction of the arrow 65. FIG. 11 shows a fourth embodiment which differs from the third embodiment in that the slider 28 is located at the end of a two-armed lever 32. The lever 32 pivots on the rear part 6 or 6xe2x80x2 via a rotation axle 33. The front end 35 of the two-armed lever 32 pivots on the front part 7 or 7xe2x80x2, i.e. in the rear region, removed from the imaginary axis of rotation 36. In this embodiment, the two-armed lever 32 is pivoted by the connecting link guide 27 thereby effecting the adjustment leading to the corresponding alignment of the front edges 5 or 5xe2x80x2 of the collimator leaves 4 or 4xe2x80x2. A certain recess must be provided in the rear parts 6 or 6xe2x80x2 for accommodating the two-armed lever 32. FIG. 11 shows the maximum over-travel 63 on one side and the maximum opening 64 on the other side. FIG. 12 shows a further embodiment which is a variation of FIGS. 10a and b. It differs in that the connecting link guides 27 are connected to the base frame 58 and the driving toothed wheels 23 are connected to the collimator block 19 or collimator block halves. In this fashion, the collimator opening 18 can also be enlarged. The connecting link guides 27 must have a length which corresponds to the entire adjustment distance, i.e. the adjustment distance of the collimator leaves 4,4xe2x80x2 and the adjustment distance of the collimator block halves. The embodiment of FIG. 11 can be modified accordingly. The embodiments shown are, of course, only exemplary. Further embodiments are feasible in particular with respect to the forced coupling, and also with respect to the drives and design of the two parts of the collimator leaves. 1 collimator 2 rays 3 radiation source 4,4xe2x80x2 collimator leaves 5,5xe2x80x2 front edges of the collimator leaves 6,6xe2x80x2 rear part of the collimator leaves 7,7xe2x80x2 front part of the collimator leaves 8,8xe2x80x2 semi-circular body 9,9xe2x80x2 corresponding recesses 10 height of the rear part 11 diameter of the semi-circular body 12 front ends of the rear part 13 asymmetrical trapezoidal shape 14 side surfaces of the collimator leaves 15 inner surfaces of the lateral borders 16 lateral borders of the possible collimator opening 17 central line of the possible collimator opening 18 collimator opening 19 collimator block 20 radiation object (tumor) 21 collimator toothed rack 22 front edge toothed rack 23 driving toothed wheel 24 toothed wheel 25 guiding element 26 guiding groove 27 connecting link guide 28 slider 29 cable control 30 end of the cable control 31 other end of the cable control 32 two-armed lever 33 rotation axle of the two-armed lever 34 rear end of the two-armed lever 35 front end of the two-armed lever 36 imaginary axis of rotation 37 longitudinal edge of the rear part 38 guidance 39 groove 40 guiding element 41 gantry 42 treatment table 43 linear accelerator 44 horizontal axis of rotation of gantry 45 axis of rotation of treatment table 46 patient 47 half shadow 48 arrow: adjusting motion of the collimator leaves 49 retaining pin 50 slot 51 arrow: direction of rotation of the driving toothed wheel 52 subdivision of the collimator toothed rack 53 subdivision of a front edge toothed rack disposed below a collimator 54 subdivision of a front edge toothed rack disposed above a collimator 55 driving toothed rack 56 groove for guiding the front part in a rear part 57 pivoting of the front edge toothed rack to the front part 58 base frame 59 pivoting of the further toothed wheel 60 arrow: displacement of the collimator block 61 fixed connection: connecting link guidexe2x80x94driving toothed wheel 62 deflecting rollers 63 maximum over-travel of a collimator leaf 64 maximum opening of a collimator leaf 65 arrow: adjustment of the slider 28 66 groove