US3322950A

US3322950A - Linear accelerator radiotherapy device and associated beam defining structure

Info

Publication number: US3322950A
Application number: US394391A
Authority: US
Inventors: John S Bailey; Haimson Jacob
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1964-09-01
Filing date: 1964-09-01
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30

Description

y 1957 J. s. BAILEY ETAL 3,322,950

LINEAR ACCELERATOR RADIOTHERAPY DEVICE AND ASSOCIATED BEAM DEFINING STRUCTURE Original Filed Nov. 25, 1962 :5 Sheets-Sheet 1 J I I INVENTORS JACOB HAIM SON JOH s. BAILEY BY lg TORNEY y 30, 1957 J. s. BAlLEY ETAL 3,322,950

LINEAR ACCELERATOR RADIOTHERAPY DEVICE AND ASSOCIATED BEAM DEFINING STRUCTURE Original Filed Nov. 23, 1962 3 Sheets-Sheet 2 lllHll Illlllll llll II II II Hll IHII 1| 1| ll II I] I'llllllllllll I 03 INVENTORS JACOB HAIMSON JO 8. BAILEY 67 BY z gjfi TORNEY y 1967 J. s. BAILEY ETAL 3,322,950

LINEAR ACCELERATOR RADIOTHERAPY DEVICE AND ASSOCIATED BEAM DEFINING STRUCTURE Original Filed Nov. 23, 1962 3 Sheets-Sheet 5 IIIIII INVENTORS JACOB HAIMSON JOHN S. BAILEY BY W TORN EY United States Patent C) 3,322,950 LINEAR ACCELERATOR RADIGTHERAPY DE- VICE APJD ASSGCIATED BEAM DEFlWiNG STRUCTURE John S. Bailey, Sunnyvale, and Jacob Hairnson, Palo Alto, alif., assignors to Varian Associates, Palo Alto, Caliii, a. corporation of California Continuation of application Ser. No. 239,567, Nov. 23, 1962. This appiication Sept. 1, 1964, Ser. No. 394,391 31 Claims. (Cl. 250-105) The present invention relates in general to a novel X-ray beam or electron beam or other charged particle beam defining diaphragm system and peripheral equipment for high energy X-ray therapy, diagnostic radiography, electron therapy and other irradiation techniques. This application is a continuation application of U.S. Ser. No. 239,567 by John S. Bailey et al., filed Nov. 23, 1962 now abandoned and assigned to the same assignee as the present invention.

Modern methods of treating cancer and other related diseases demand high intensity levels of radiation for deep X-ray therapy applications. Therefore high energy devices in the range of, by way of example, 4 to 8 mev., are presently employed to obtain the desired intensity and quality of radiation. In X-ray therapy it is very advantageous to be able to obtain high energy outputs while simultaneously being capable of achieving a high degree of mobility of the beam defining apparatus, thereby avoiding having to manipulate the patient to suit the radiation source.

There are certain optimum distance relationships with regard to the X-ray target, exit portal of the beam defining apparatus, point of skin entry of the X-ray, etc., which should be maintained in order to achieve maximum clinical benefits from a high energy radiotherapy device.

When utilizing linear accelerator radiotherapy machines having outputs in the range of 4 to 8 mev., by way of example, many advantages are derived by maintaining a distance of from 20-30 cm. between the exit portal of the beam defining diaphragm system and the nearest skin entry port while simultaneously maintaining at least a 100 cm. distance between the X-ray source and the axis of rotation of the accelerator. A 20-30 cm. distance between the exit portal of the beam defining diaphragm system and the nearest skin entry port can be achieved by maintaining at least a 40 cm. distance between the accelerator axis of rotation and the exit portal of the beam defining diaphragm system.

Since it is desirable in radiotherapy treatment utilizing high energy X-rays, etc. to minimize skin dosage and integral dose to all parts of the patient except that portion which is to be irradiated, as for example, a deep seated tumor, multiple port and are therapy techniques as well as patient rotation techniques are necessarily employed.

When utilizing multiple port, patient rotation, or arc therapy techniques, it is highly desirable that the height of the axis of rotation of the linear accelerator above the floor of the treatment room should be maintained at a convenient minimum level since quite obviously patient set-up procedures are greatly facilitated thereby. An optimum maximum distance between the floor of the treatment room and the axis of rotation of the linear accelerator would be around 117 cm. (46").

Considering then the design constraints of (l) 100 cm. distance between the axis of rotation of the linear accelerator and the X-ray source, (2) the 40 cm. distance between the axis of rotation of the linear accelerator and the nearest point or exit portal of the beam defining diaphragm system, and (3) the maximum distance between the axis of rotation of the linear accelerator and the floor of the treatment room, around 117 cm., it is seen that severe restrictions are imposed on the designer of the machine.

3,322,950 Patented May 30, 1967 A machine configuration such as that shown in copending US' patent application Ser. No. 46,432, by Robert T. Avery, filed on Aug. 1, 1960 now abandoned in favor of continuation U.S. patent application Ser. No. 411,170 filed Sept. 14, 1964 and assigned to the same assignee as the present invention, enables the designer to meet the above mentioned design limitations.

The maintenance of a 40 cm. distance between the axis of rotation of the linear accelerator and the nearest art of the collimating system enables skin to collimater distances of the order of 30 cm. to be routinely obtained. As a consequence, the skin dose contributions from recoil and scattered electrons emanating from the beam defining system and due to the high energy X-rays, are considerably reduced. Typically, with the X-ray beam from a 6 mev. machine, extrapolation ionization chamber measurements indicated a skin dose of only 18% of the maximum, which occurred at a depth 16 mm. beyond the surface with a 10x10 cm. field at cm. F.S.D. Furthermore, ample room is provided within which operators may manipulate auxiliary equipment, such as a shadow tray with external filtration and shield blocks, etc., during patient set-up procedures.

The larger the focal skin distance F.S.D. (the distance between the X-ray target and the point of skin entry of the X-ray beam), the more favorable the depth dose characteristics (plots of tissue depth beneath the skin vs. rads per min.) will be, since the rate of reduction of X-ray intensity vs. penetration depth is reduced with increasing F.S.D. as can be expected from considerations of the inverse square law. Thus, a minimum fall-off in dose over a given penetration depth would be achieved with an infinite F.S.D. However, considering the above mentioned design constraints, the instant invention still provides a sufiiciently large F.S.D. even when treating a deeply situated tumor placed at a distance of 100 cm. from the X-ray target which in the present invention is the axis of rotation of the linear accelerator such that the fall-off in dose is held at an absolute minimum for the aforementioned design restrictions. Additional factors which infiuence the rate of reduction of intensity with depth of penetration are beam energy, field size and nature of absorbing medium. Typically, the X-ray beam from a 6 mev. machine has a depth dose characteristic such that with a 10x10 cm. field at 100 cm. F.S.D. 67.5% and 38.5% of the maximum ionization occurs at 10 cm. and 20 cm. depths, respectively.

Additionally, high energy radiotherapy machines must minimize the intensity and extent of the penumbral portion of the X-ray field by preventing oblique transmission through the edges of the beam defining diaphragm blocks or jaws. This has been accomplished in the present invention by providing a novel method of movement for upper and lower pairs of beam defining jaws whereby the jaws can move in arcs of a circle subtended by the target while simultaneously providing means to enable the entire beam defining diaphragm system, including wedge filter facility, motors and gearing apparatus for electrically driving both sets of jaws, optical system including range finder and other attachments, to be rotated 360 about the center line of the X-ray beam.

The ability to rotate the X-ray beam defining jaws and wedge filter facility through 360 about the X-ray beam enables, by way of example, angularly located tumors wherein portions of the tumor are displaced diflerent distances from the exit portal of the beam defining jaws to be treated with equal intensity radiation over all portions of the tumor within the field of the X-ray beam, regardless of the angular orientation of the tumor with respect to the plane of the exit portal of the beam defining apparatus. Conversely, this ability to rotate the X-ray beam defining jaws and wedge filter enables multi-port therapy techniques to administer a uniformly intense dose of radiation to an irregularly shaped volume.

The novel beam defining diaphragm system of the present invention results in a radiotherapy linear accelerator which is capable of 360 arc therapy, as well as multiport, patient rotation and electron therapy while utilizing a minimal amount of space for the design under consideration and additionally providing optimum patient set-up conditions. The radiotherapy linear accelerator of the present invention can, for example, fit into a room having a height of 8' or less.

It is considered highly desirable in radiotherapy applications of high energy devices, such as the instant invention, to provide an extremely low leakage intensity such as fl th of the flattened central axis intensity by utilizing heavy metal blocks of approximately threetenth value layers in thickness, for example, 12.5 cm. of lead and tungsten in the direction of primary transmission of the X-ray beam. One-tenth value layer is the thickness of a specified absorbing material which, when introduced into the path of an X-ray beam, reduces the dose rate to of its original intensity. Two-tenth values reduce the dose to A of its original value and three-tenth value layers reduce the rate to etc. The present invention utilizes stepped tungsten face plates mounted on lead blocks which together form jaws for providing extremely sharp cut-off in intensity at the edges of the X-ray field while simultaneously minimizing oblique transmission of energy therethrough and defining the beam field.

The utilization of novel guiding arced grooves within which the beam defining jaws of the present invention move in has eliminated the necessity for a complex, awkward and expensive link system for ensuring that the jaws open and close by moving on arcs of a circle subtending the target, which is located in the fixed portion of the X-ray head, while simultaneously permitting both pairs of jaws and peripheral equipment to rotate 360 around the central axis of the X-ray beam.

A novel flatness monitoring device which comprises two radiation detectors diametrically opposed on opposite sides of the beam is utilized whereby any deviation in intensity in the beam which could be caused by mal-tuning of the accelerator, for example, can be readily detected and quickly corrected. This monitoring capability is extremely useful as it is of vital importance in radiotherapy to be assured of beam flatness, the uniformity of the intensity level of the beam in a plane normal to the beam, so as to insure uniformity of irradiation of a patient throughout the period of treatment, for example, or to be able to select the proper wedge filter for a given application and to again constantly monitor the beam to insure proper radiation dosage.

Previous techniques required interruption of the treatment of the patient since generally either monitors were inserted into the main beam field itself or the beam was scanned by some external device. In either case, patient treatment was interrupted. The present invention provides novel beam flatness monitoring means for a radiotherapy machine which constantly indicates beam flatnes while treatment is under progress regardless of the type of therapy being employed. This invention has been particularly useful and time saving in checking beam flatness during rotation of the accelerator under such conditions where the application of an externally located device is extremely diflicult.

The present invention further employs an optical field simulator and optical range finder system integrated with the novel beam defining apparatus described herein which enables the operator to quickly locate the desired BSD.

The present invention further provides a novel method of locating the required electrical cables between the rotating mounting plate for the jaw assembly and the mounting plate to which it is attached whereby slip-rings or other relatively movable junctions are obviated, thus achieving a substantial saving in time and cost of construction.

It is therefore, a principal object of the present invention to provide a novel X-ray beam defining diaphragm system together with peripheral equipment for a high energy radiotherapy linear accelerator having a high degree of mobility as well as an extremely compact construction whereby optimum clinical results are achieved.

A feature of the invention lies in providing a novel beam defining system in a radiotherapy linear accelerator capable of rotating 360 around a cantilevered patient support assembly and of providing multiple port therapy, arc therapy, patient rotation therapy and electron therapy wherein the horizontal axis of rotation of the linear accelerator is maintained at an absolute minimum height above the floor level while simultaneously maintaining a cm. distance between the axis of rotation of the linear accelerator and the X-ray target and a 40 cm. free space distance between the nearest part (exit portal) of the beam defining system and the horizontal axis of rotation of the linear accelerator and additionally providing for 360 rotation of the beam defining system about the central axis of the emergent X-ray or electron beam.

Another feature of the present invention is to provide novel beam defining jaws which are capable of minimizing the intensity and extent of the penumbral portion (at the edges) of the X-ray field by preventing oblique transmission through the edges of the beam defining jaws by arranging the jaws so that they move on arcs of a circle subtended by the target while simultaneously providing for 360 rotation of the entire beam defining system, including wedge filter facility, electric drive motors for both sets of jaws, optical range finder system and other peripheral equipment, about the center line of the X-ray beam.

Another feature of the present invention is to employ novel beam defining diaphragms (jaws) which utilize a novel means to move about arcs of a circle subtending the X-ray target, or other source of energy, to provide a continuously variable field size from zero up to 27 x 30 cm. at 100 cm. F.S.D.

Still another feature of the instant invention lies in the novel construction of the jaws themselves which provides an extremely low leakage intensity outside of the primary cone of approximately 1/1000 of the flattened central axis intensity of the X-ray beam.

Another feature of the instant invention lies in the utilization of an optical field simulator and range finder system mounted on the rotatable beam defining diaphragm system.

An additional feature of the present invention lies in a novel method of mounting electrical cables between the rotatable head portion containing the beam defining diaphragm system and the beam bending end portion of the linear accelerator.

Still another feature of the present invention lies in the provision of a novel flatness monitoring device which includes a pair of radiation detectors diametrically opposed and positioned within the beam defining rotatable head system such that a continuous read-out of beam flatness may be obtained even while treatment is in progress.

These and other features and advantages of the present invention will be more apparent after a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevation view partially broken away of a radiotherapy linear accelerator employing the novel beam defining rotatable head system of the instant invention as used in a typical treatment set-up, and illustrating the maintenance of a large free air space between the X-ray head and the patient irrespective of anterior .or posterior field applications. The latter is accomplished without detrimental skin build-up effect by having the patient supported with a thin mylar panel;

FIG. 2 is a view partially broken away in section of the X-ray beam defining rotatable head section and end portion of the linear accelerator delinated by oval line 22 of FIG. 1;

FIG. 3 is a cross-sectional view of the rotatable beam defining head taken along line 33 of FIG. 2;

FIG. 4 is a plan view of the pattern presented by the optical simulator and range finder system taken along line 4-4 of FIG. 3;

FIG. 5 is a sectional view of the rotatable head and beam defining pairs of jaws taken along line 5-5 of FIG. 3;

FIG. 6 is a fragmentary sectional view of part of the optical simulator system taken along line 6-6 of FIG. 3 rotated 180;

FIG. 7 is a cross-sectional view of one of the flatness monitoring radiation detectors positioned in a slot in one of the lower jaws taken along line 77 of FIG. 3, and

FIG. 8 is a sectional view of the upper jaw support and stabilizing means taken along line 88 of FIG. 3.

Referring in more detail to FIG. 1, there is shown a side view of a radiotherapy linear accelerator 1, having a main accelerator section 15, and electron gun 2 and colinear termination such as shown and described in copending US. patent application Ser. No. 120,597, by Jacob Haimson, filed on June 29, 1961 now Patent Number 3,264,515 and assigned to the same assignee as the present invention, beam bending end section 3, rotatable beam defining head 4 and counterweighted modulator portion 5. The main accelerator section 15 is designed to rotate 360 about horizontal axis 6, which is located, by way of example, approximately 117 cm. above the floor level or, to assume any fixed radial position about horizontal axis 6 for therapy treatment of a patient as shown. The rotatable beam defining head 4 is designed to rotate 360 about central beam axis 12 and can easily be moved into any desired position with respect to the patient such as the positions shown.

A special treatment couch 8 with detachable wheel assemblies is provided which is clamped or otherwise suitable attached to float table 10 which is supported by post 11 which is arranged for dual speed vertical movement and which in turn is mounted on a rotatable floor level platform 13 designed for circular movement about the central beam axis 12. Couch 8 has a thin mylar or other suitable supporting material 9 attached thereto whereby the patient can be irradiated from a posterior position as shown without danger of ionization build-up and severe skin reactions. The float table 10 is provided with a means for translational movement of the patient in the horizontal plane.

It is readily seen that the spatial relationships between the accelerator horizontal rotational axis 6, the central axis 12, of the X-ray beam and the vertical rotational axis 12 of the patient support assembly result in the intersection of the above three axes at a fixed point, the isocenter 7.

The above indicated relationships facilitate patient setup procedures and provide a radiotherapy linear accelerator system which is capable of multiple port, patient rotation and are therapy treatments in a manner which is extremely advantageous from a clinical standpoint as well as from time, space, and monetary considerations.

In FIG. 2 there is depicted a partially broken away view of the beam defining rotatable head 4 and beam bending target section of the end portion 3 of linear accelerator 15. A linear accelerator for providing a high energy horizontally directed beam of electrons is generally shown at 15. The beam of electrons represented by the broken lines 31 is bent through 90 and can either impinge on a target assembly 16 to produce X-rays or be bent in such a manner as to by-pass the target and emerge through a window along the axis of the existing collimating system for electron therapy, radiobiology and other radiation applications. The 90 beam deflection techniques described in the aforementioned copending US. application of Robert T. Avery may be employed herein.

A heavy metal primary collimator 17 with a vacuum window 111 located at the top thereof as shown is used to obtain the desired X-ray beam configuration. Ionization chambers and a flattening filter, generally shown at 19 and normally used with the X-ray beam to measure dose rate and for integrating total dose and to obtain uniform intensity of the beam across a plane normal to the beam path, may be horizontally retracted, and is electrically interlocked, to facilitate extraction of the electron beam.

Retraction apparatus for retracting and inserting the ionization chambers and beam flattener is shown generally at 21. A fixed mounting plate 23 is securely attached by brazing, bolting or the like to flange member 22 and serves to support the rotatable head portion 4 depending therefrom.

Turning specifically now to the particular details of the novel rotatable head portion 4 as shown best in FIGS. 2, 3, 5 and 8, a cone-like member 4' surrounds the beam defining diaphragm system housed therein. A rotatable head support plate 24 is mounted in movable relationship to fixed mounting plate 23 by means of bearing assembly 28 which comprises inner and outer annular bearing retainer members 26, 25, respectively, which are securely fastened to

plates

24 and 23, respectively, by means of screws as shown or in any other suitable manner. Within the hollow ring bearing member 28, as defined by outwardly extending flanged portions of members 25 and 26 together with accompanying off-set portions of

plates

24 and 23 as shown, are spaced ball bearings 27 subjected to shearing forces exerted by head 4 relative to plate 23 upon which the entire head 4 supported from plate 24 Will rotate. Provision is made for easy insertion of any desired wedge filter assembly 71 which may be slid into place with a minimum of effort, and actuate a switch and warning light system.

Depending from plate 24 and suitably bolted or otherwise secured thereto are two spaced

support plates

46 and 46 upon which upper diaphragms or jaws 53 and 53' are supported from in a unique manner to be described in more detail hereinafter. Integral outwardly extending

arm portions

50, 50' and 51, 51' depend from spaced support plates, 46, 46', respectively. Bolted to arm

portions

50, 51 and 50, 51' respectively, are

support plates

60, 66, each having an inwardly directed curved groove portion 63, 63', respectively, cut therein as best seen in FIG. 3. Each groove is curved so as to form an arc of a circle subtending by the target 16. Support plates 60, 60' each have an additional inwardly directed groove 65, 65', respectively, cut therein. Supported within curved groove portions 63, 63' are rollers 62, 62' which are attached to the sides of lower jaw members 67, 67'. Each jaw can have as many rollers as needed to adequately support the jaw within the curved grooves of the support plates.

Grooves

65, 65 are not curved as are grooves 63, 63 but are cut within

support plates

60, 60 so as to lie in a plane normal to the central axis of the beam.

Positioned within groove 65 are upper and lower

elongated rack members

66 and 68 which are securely mounted within groove 65 and maintained therein by toothed pinion member 64 which is attached to and driven by shaft 69 which is secured to and driven by drive gear 56 centrally located in bearing assembly 70 which is in turn driven by drive chain 57 which is controlled by gearing assembly 54 and motor assembly 74.

Counterbalance racks 66', 68', pinion 64', rotatable shaft 69' and bearing assembly 70' are provided to support the other side portion of

jaw members

67, 67. No drive mechanism is attached to these parts which function strictly as counterbalancing elements for jaws 67, 67'.

A dial 53 is placed on the drive gear 56 and suitable graduations are made thereon to indicate the degree to which the lower jaws are opened or closed. A direct reading dial indication of beam field size at cm. from the target is desirable and may de advantageously employed. A similar dial 36 is placed on the drive gear 27 for the upper jaws 53, 53' which are driven by drive chain 35 which in turn is driven by motor 33.

The jaws are controlled to provide the desired field size by push buttons 110 located on the X-ray head. The electrical connections to the

motors

74 and 33 as well as the optical field simulator and optical range finding system and flatness monitoring device are brought out through the head through a novel cable mounting arrangement which acts in much the same manner as a wound watch spring. Cable space 29 is provided between relatively

rotatable support plates

23, 24, as best seen in FIG. 3, by cutting suitably dimensioned annular slots within

plate member

23, 24 outwardly from the bearing assembly as shown in FIG. 3 or alternatively inwardly from the bearing assembly. A suitable length of cable 35; is wound within cable space 29 and the ends brought out through suitable apertures through

plates

23 and 24 to the beam bending end portion 3 of linear accelerator 2 and to the rotatable head 4. As the head is rotated the cable turns 30 will wind in and out like a clock spring. It is desirable to have a cable space of about 125% greater width than the cable diameter to allow suitable freedom for the cable to wind and unwind. Means for preventing relative rotation between

plates

23 and 24 of greater than about 370 are provided, thereby eliminating any possibility of snapping the electrical cable.

It is readily seen that an extremely simple method of providing electrical connections between the rotatable head and the end portion of the accelerator is thus provided which completely eliminates any need for slip ring connections, or other complex electrical junctions.

Lower jaw members

67, 67 are stabilized and .prevented from movement normal to their direction of travel within grooves 63, 63' by stabilizing

rollers

55, 55 positioned within slots located within the jaw members 67, 67' along the top edges thereof. These stabilizing rollers bear against the inner faces of the support plates 60, 60' for the lower jaws as shown and prevent any side swaying or lateral movement of the jaws as the jaws are being moved within the grooves, thereby maintaining parallelism between the upper inwardly directed jaw edges 61, 61 of the lower pair of jaws as well as parallelism between the lower inwardly directed jaw edges 59, 59 of the lower pair of jaws. This stabilizing feature permits very accurate control of the beam field size and assures that integral doses of radiation will not be presented to tissue which is not to be irradiated.

The above mentioned rollers are better seen in connection with their counterparts mounted within

upper jaws

53, 53 wherein in FIG. 3 and FIG. 8 the rollers for the upper jaws are more clearly shown. Each upper jaw as shown is provided with a pair of stabilizing rollers 52, 52' on each upper side edge of the jaw. As can be seen in FIG. 3, the outwardly positioned stabilizing rollers are located in slots within the jaws.

Drive pinion 64 for lower jaws 67, 67' functions exactly as upper jaw drive pinion 40. Since the upper and lower jaw assemblies including the drive techniques are similar a complete description of one alone or utilizing parts of each for clarity should be adequate to explain their functions.

As best seen in FIGS. 2, 3, and 8, elongated upper and

lower racks

42, 43 and counterbalance racks 42', 43' together with toothed pinions 4d, 40' provide the moving force for the upper jaws. Each rack has a slotted U-shaped guide member attached at the end thereof by any suitable means or integral therewith as best seen in FIG. 3 wherein counterbalance racks 42', 43 and their associated slotted

U-shaped guide members

78, 79 are clearly shown. Mounted on each of the four jaws on each side face thereof are screws with eccentrics thereon, such as 98 and 99 as showns in FIGS. 3 and 8. The eccentrics are utilized to compensate for any dimensional inaccuracies between the parts used in the beam defining system to thus provide a quick method of assuring proper jaw alignment in a closed position. The upper jaws 53, 53' are supported by rollers 44 which move in arced

grooves

49, 49 in similar fashion to lower

jaws

67, 67.

In operation, the drive motors 33 and '74 controlled by arr operator can provide, for example, a continuous adjustment of the beam field size from zero to 27x30 cm. at a 100 cm. distance from the target. The jaws move easily within the aforementioned grooves as the drive racks are actuated causing the slotted U-shaped members to bear upon the aforementioned eccentrics mounted on screws attached to the jaws, thereby moving the jaws within the arced grooves. Both upper and lower sets of jaws are similarly controlled and the faces of the jaws will always be radially aligned with respect to the target and thus provide a very sharply defined beam field pattern with a minimum of scattering and oblique transmission, thus resulting in a minimum entrance skin dose and a very low penumbra.

Each jaw of the upper and lower sets of jaws has a stepped tungsten face, such as 76 as seen in FIGS. 3 and 5. The use of a stepped tungsten face on the massive lead jaws provides an extremely low leakage intensity of approximately of the flattened central axis intensity. Suitable dimensions for the jaws are 12.5 cm. in depth which will provide approximately three-tenth value layers in thickness in the direction of primary transmission of the beam with a 48 mev. range of operation. The provision of the stepped tungsten faces prevents any leakage radiation between the interface of the lead and tungsten. Only two steps are shown; however, it is to be understood that any number may be employed. The tungsten face plates are employed since tungsten is a much better absorber of X-rays within the 48 rnev. range of operation of the linear accelerator. It is, course, understood that all dimensions and operating ranges are given by way of example only.

The optical simulator system of the present invention includes, as best seen in FIGS. 3, 4, 5 and 6, a prefocused lamp assembly 84, having a lamp 34-, optical mount 97 having a reticle therein, with a suitable dimensional aperture zoom lens 92, reflecting mirror assembly mirror 85, light beam channel 96 and additional reflecting mirror 73 positioned within the path of the X-ray beam. The reticle contains cross-hairs which will project a dark cross-hair image 93 within a circular light pattern as shown in FIG. 4, which pattern defines the X-ray beam pattern. Zoom lens $2 has an adjustable focal length. As can be readily seen in FIG. 6, the light beam from lamp 34 is reflected twice from mirrors 85' and '73. The optical simulator system shown in FIG. 6 is adjusted by changing the focal length of the zoom lens to provide the desired light beam pattern to illuminate the skin area being irradiated by the X-ray beam. Provision is also made for easy adjustment of mirror 85 by means of adjustable retaining screws. The reticle may be provided with a graduated scale so that in addition to the cross-hair projection, a scale is provided on an axis of the crosshair projection as shown in FIG. 4. The scale may be graduated in cm. with the cm. graduation located at the intersection of the horizontal and vertical lines of cross-hair image as shown in FIG. 4. A second optical system consists of optical range finder assembly 87 which includes lamp bracket 88 afiixed to support plate 60. Mounted on bracket 88 is a conventional lamp 89 having straight filament and a lens mounted within lens bracket 90. The angular orientation of the axis of the light image 91 projected from the lens is set with respect to the central beam axis such that the bright oblong shaped image 91 cast by the straight filament lamp as seen in FIGS. 3 and 4 will coincide with the intersection of the cross-hairs of the reticle image at a 100 cm. distance when the P.S.D. is at 100 cm. or 85 cm. F.S.D. or any other desired BSD. Rectangular broken lines $5 indicate the X-ray beam field size at the 100 cm. F.S.D. in relation to the optical field when the jaws are opened to their greatest field size. It is seen that only round corners are present in otherwise identical optical and X-ray field sizes. Thus, as is readily apparent a novel optical range finding system is provided which eliminates the use of a mechanical front pointer in determining F.S.D. which results in speeding up patient set-up time considerably. Provisions are made for easy adjustment of the angular orientation of the axis of the light image projected from the lens with respect to the central X-ray beam axis so that any desired F.S.D. may be utilized. A captive nut and set screw 1% bearing on the bracket as shown may be used for adjustment purposes.

Lower jaw members 67, 67' are each provided with a centrally located slot 81 as shown in FIGS. 3 and 7 at the upper face thereof. Each slot extends across the entire width of the lead jaw and is of a depth and width sufficient to position a flatness monitoring indicator device 82 therein. Each slot terminates at the tungsten face plate which is not slotted. The slots 81 are diametrically opposite each other and the flatness monitoring devices 82 positioned therein will present an accurate indication of the intensity of the X-ray beam on opposed sides of the beam, without superimposing shadows within the applied X'ray field.

Each flatness monitoring device may consist, by way of example, of a cadmium sulfide photocell 101 embedded in epoxy resin, positioned within a light opaque conductive housing 102' as shown in FIG. 7 with a two conductor shielded cable 103 brought out the open end of the housing to function as electrical leads for the flatness monitoring device. The open end of the housing is preferably filled with epoxy. Thus, photocell 191 is completely opaque to any light rays but is sensitive to X-rays. Since the photocells are positioned on opposite sides of the beam, any diiference in intensity on either side of the beam can be detected. The leads from cable 103 for each monitoring device are brought out through the novel spring wound cable 30 and the difference signal generated between the two monitoring devices is amplified and arranged to provide continuous readout at a control console located outside the treatment room. It is of vital importance in radiotherapy applications to maintain uniformity of intensity of the beam during treatment, and the above novel flatness monitoring device allows continuous checking of the beam flatness performance while treat ment is in progress, thus assuring a proper dosage to the patient without costly and time consuming interruption of treatment.

Since many changes could be made in the above construction and many apparently widely difierent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A radiotherapy linear accelerator comprising, means for producing and directing a charged particle beam along a first axis, means for bending said charged particle beam substantially 90 from said first axis to thereby define a second axis, means for producing an X-ray beam directed along said second axis, rotatable means for defining said X-ray beam to a predetermined field about said second axis, said rotatable beam defining means being rotatably mounted for rotation about said second axis, said means for producing said X-ray beam being disposed on said second axis at a position which is axially removed along said second axis from said rotatable beam defining means.

2. Collimator apparatus for defining a beam of ionizing radiation including a beam defining system adapted and arranged to define a beam of ionizing radiation about a central axis comprising, two pairs of heavy metal jaws mounted for movement in 90 space rotated planes to define a beam field cross-section transverse to said central axis along which said beam of ionizing radiation is di rected, said pairs of heavy metal jaws being axially dis placed from each other along said central axis, each of said pairs of heavy metal jaws being supported for movement toward and away from said central axis by being adjustably supported in a pair of arcuate grooves located on opposite sides of each pair of jaws, said grooves being defined inwall portions disposed on each side of both of said pairs of jaws, a pair of facing rack bars connected to each pair of jaws, each of said pair of rack jaws being disposed in additional grooves in said wall portions and having a common pinion disposed therebetween and engaging each of said rack bars in a given pair.

3. Radiotherapy linear accelerator apparatus comprising, first means for rotatably supporting linear accelerator means, said first means positioned around and defining a first axis and capable of 360 rotation about said first axis, said linear accelerator means defining a second axis spaced from said first axis and rotatably supported by said first means, said linear accelerator means adapted and arranged for 360 rotation about said first axis and for accelerating a beam of charged particles along the second axis, means for deflecting said beam substantially from said second axis, and rotatable head means including beam defining diaphragm means operatively connected to said means for deflecting said beam, and capable of being rotated 360 about the central axis defined by said 90 deflected beam.

4. The apparatus as defined by claim 3 wherein said means for deflecting said beam includes X-ray target means positioned within the path of said 90 deflected beam for converting said charged particle beam into an X-ray beam.

5. The apparatus of claim 3 wherein said beam defining diaphragm means comprises a pair of metal jaws positioned about said beam axis, each of said jaws adapted and arranged to move in arced grooves located in support plates positioned within said rotatable head means.

6. The apparatus of claim 3 wherein said beam defining diaphragm means comprises a first pair and a second pair of metal jaws positioned about said central beam axis, each of said jaws of each of said first pair and said second pair of jaws adapted and arranged to move in arced grooves located in support plates positioned within said rotatable head means.

7. The apparatus as defined in claim 6 wherein, said first pair of jaws is longitudinally displaced along said central beam axis from said second pair of jaws and said first pair of jaws is space rotated substantially 90 about said central beam axis with respect to said second pair of jaws.

8. The apparatus of claim 4, wherein said beam defining diaphragm means comprises a first pair and a second pair of heavy metal jaws positioned about said central beam axis, each of said first pair and said second pair of jaws adapted and arranged to move in paths defining arcs of a circle subtending said X-ray target.

9. The apparatus as defined in claim 8, wherein said first pair of jaws is longitudinally displaced along said central beam axis from said second pair of jaws and said first pair of jaws is space rotated substantially 90 about said central beam axis with respect to said second pair of jaws, and wherein said paths defining arcs of a circle subtending said X-ray target comprise arced grooves located in support plates positioned within said rotatable head means.

10. A beam defining system comprising, X-ray source means for producing an X-ray beam about a central beam axis, primary collimator means surrounding said central beam axis, a first mounting plate for said X-ray source means and said primary collimator means, said first mounting plate having an aperture therein whereby said X-ray beam may pass through said aperture, a second mounting plate aflixed to said first mounting plate and capable of rotation with respect thereto, said second mounting plate having an aperture therein whereby said X-ray beam may pass through said aperture, first and second supporting plates affixed to said second mounting plates, said first and second supporting plates lying in first and second fixed spaced parallel planes, said first and second spaced parallel planes being normal to the plane of said second mounting plate and equally spaced from said central beam axis, third and fourth supporting plates affixed to said first and second supporting plates, said third and fourth supporting plates lying in third and fourth spaced parallel planes, said third and fourth spaced parallel planes being normal to each of said first and second spaced parallel planes and equally spaced from said central beam axis, each of said supporting plates having an arced groove therein, located on the face of each supporting plate directed toward said central beam axis, each of said arced grooves forming an arc of a circle subtending the X-ray source means, a first pair of beam defining heavy metal jaws, each of said jaws of said first pair supported in the arced grooves of said first and said second supporting plates and adapted and arranged to move in said grooves, and a second pair of beam defining heavy metal jaws, each of said jaws of said second pair supported in the arced grooves of said third and said fourth supporting plates and adapted and arranged to move in said grooves.

11. The system of claim .10 wherein said second mounting plate is affixed to said first mounting plate and capable of rotation with respect thereto, by means of a pair of space annular inner and outer bearing retainer members, said inner bearing retainer member being affixed to one of said mounting plates and said outer bearing retainer member being affixed to the other of said mounting plates, said bearing retainer members being spaced from each other to thereby define a bearing space therebetween, and a series of ball bearings are positioned within said bearing space and serve to rotatably afiix said first and said second mounting plates to each other.

12. The system of claim 10 wherein each of said beam defining heavy metal jaws of one of said pairs of jaws has a radiation detector positioned thereon.

13. The system of claim 10 wherein, optical field simulator means and optical range finder means are attached thereto, said optical field simulator means being adapted and arranged to provide a light image corresponding in size to that of the beam field and in substantial registry with the beam field, and said optical range finder means being adapted and arranged to provide an optical focal skin distance reference.

14. The system of claim 10 wherein an annular enclosed ring-like space is provided between said first and said second mounting plates, a wound electrical cable is positioned within said annular ring-like space, one end of said cable extending through an aperture in said first mounting plate, and the other end of said cable extending through an aperture in said second mounting plate.

15. A beam defining diaphragm system comprising, a mounting plate defining a first plane, first and second supporting plates afiixed to said mounting plate and defining first spaced parallel planes normal to the plane of said mounting plate, third and fourth supporting plates afiixed to said first and second supporting plates, said third and fourth supporting plates defining third and fourth spaced parallel planes, said third and fourth parallel planes being normal to said first and second spaced parallel planes as well as being normal to the plane of said mounting plate, each of said supporting plates having an arced groove located on the inwardly directed face thereof, a first pair of heavy metal jaws, each of said jaws supported in said arced grooves of said first and second supporting plates and adapted and arranged to move in said grooves, and a second pair of heavy metal jaws, each of said jaws supported in said arced grooves of said third and fourth supporting plates and adapted and arranged to move in said grooves.

-16. The beam defining diaphragm system as defined in claim 15 wherein, each of said supporting plates has a second groove located on the inwardly directed faces thereof, a pair of elongated racks located in each of said second grooves of each of said supporting plates, each of said racks of each of said pairs having a toothed edge surface and a smooth edge surface, and a toothed pinion member positioned within each of said second grooves in each of said supporting plates, the teeth of said pinion member engaging the teeth of each of said rack members within each of said grooves and adapted and arranged to maintain said rack members within each of said grooves.

17. The system as defined in claim 16 wherein, each of said elongated rack members has a U-shaped slotted member depending from the end thereof in a direction normal to the length of said elongated racks, each of said jaws has a pin member protruding from each side surface thereof, each of said pin members is positioned within one end of said U-shaped slotted members, and electrical drive means are provided and adapted and arranged to rotate said pinions whereby one of said racks in each of said grooves is driven in a direction opposite to the other of said racks in each of said grooves.

18. The system as defined in claim 15 wherein each of said jaws of one of said pairs of jaws, has a radiation detector mounted thereon.

19. The system as defined in claim 15 wherein, optical field simulator means and optical range finder means are attached thereto, said optical field simulator means being adapted and arranged to provide a light image corresponding in size to that of the beam field defined by said jaws an in substantial registry with the beam field defined by said jaws, and said optical range finder means being adapted and arranged to provide an optical focal skin distance reference.

it. The system as defined in claim 15 wherein, an additional mounting plate is affixed to said mounting plate defining a first plane, said additional mounting plate being adapted and arranged relative to said mounting plate defining a first plane whereby said additional mounting plate is capable of at least 360 rotation relative to said first mounting plate.

21. Radiotherapy linear accelerator apparatus comprising, linear accelerator means for producing an electron beam, said beam defining a first central axis, means for bending said electron beam substantially 90 from said first central axis to thereby define a second central axis, target means for producing X-rays positioned along said second central axis, said X-ray beam emanating from said target means being axially aligned with said second central axis, a rotatable beam defining diaphragm apparatus positioned around said second central axis, said rotatable beam defining diaphragm means being rotatably mounted for rotation about said second axis, said means for producing said X-ray beam being disposed on said second axis at a position which is axially removed along said second axis from said rotatable beam defining means.

22. Radiotherapy linear accelerator apparatus comprising, linear accelerator means for producing an electron beam, said beam defining a first central axis, means for bending said electron beam substantially 9 from said first central axis to thereby define a second central axis, target means for producing X-rays positioned along said second central axis, said X-ray beam emanating from said target means being axially aligned with said second central axis, beam defining diaphragm means positioned around said second central axis, said beam defining diaphragm means being rotatably mounted about said second central axis, said beam defining diaphragm means including a pair of beam defining jaws adapted and mounted for movement in arcs of a circle subtending said target means.

23. Radiotherapy linear accelerator apparatus compris ing, linear accelerator means for producing an electron beam, said beam defining a first central axis, means for bending said electron beam substantially 90 from said first central axis to thereby define a second central axis, target means for producing X-rays positioned along said second central axis, said X-ray beam emanating from said target means being axially aligned with said second central axis, beam defining diaphragm means positioned around said second central axis, said beam defining diaphragm means being rotatably mounted about said second central axis, said beam defining diaphragm means including a first and second pair of beam defining jaws, each of said first and second pair of beam defining jaws mounted for movement in arcs of a circle subtending said target means.

24. A radiotherapy linear accelerator comprising, means for producing and directing a charged particle beam along a first axis, means for bending said charged particle beam substantially 90 from said axis to thereby define a second aixs, means for producing an X-ray beam directed along said second axis, means for defining said X-ray beam to a predetermined field about said second axis, and said means for defining said X-ray beam being adapted and arranged such that said means is capable of rotation about said second axis.

25. A radiotherapy linear accelerator comprising, means for producing and directing a charged particle beam along a first axis, means for bending said charged particle beam substantially 90 from said axis to thereby define a second axis, means for producing an X-ray beam directed along said second axis, means for defining said X-ray beam to a predetermined field about said second axis, and said means for defining said X-ray beam being adapted and arranged such that said means is capable of rotation about said secondaxis, said accelerator further including radiation detector means mounted in said beam defining means for monitoring the flatness of said X-ray beam.

26. Apparatus for controlling ionizing radiation derived from an electron beam, said ionizing radiation having an energy level greater than one mev. comprising, X-ray target means for producing and directing a beam of X- rays having a photon energy level greater than one mev. about a central axis, means for defining said X-ray beam within a predetermined field configuration, said means for defining said X-ray beam being adapted and arranged such that said means is capable of at least 360 rotation about said central axis, and said means for defining said X-ray beam being made of an X-ray absorbing material so dimensioned such as to have greater than A value layer thickness taken in the direction of primary transmission of the X-ray beam having photon energy level greater than one mev., said means for defining said X-ray beam including first and second pairs of heavy metal jaws mounted for movement in arcs of a circle subtending said X-ray target means, and a radiation detector means mounted in each of said jaws of one of said pairs of jaws.

27. Apparatus for controlling ionizing radiation derived from an electron beam, said ionizing radiation having an energy level greater than one mev. comprising X-ray target means for producing and directing a beam of X-rays having a photon energy level greater than one mev. about a central axis, means for defining said X-ray beam within a predetermined field configuration, said means for defining said X-ray beam being adapted and arranged such that said means is capable of at least 360 rotation about said central axis, and said means for defining said X-ray beam being made of an X-ray absorbing material so dimensioned such as to have greater than A value layer thickness taken in the direction of primary transmission of the X-ray beam having photon energy level greater than one mev., said means for defining said X-ray beam including first and second pairs of heavy metal jaws mounted for movement in arcs of a circle subtending said X-ray target means, said apparatus further including optical field simulator means and optical range finder means attached thereto, said optical field simulator means being adapted and arranged to provide a light image corresponding in size to that of the beam field defined by said jaws and in substantial registry with the beam field defined by said jaws, said optical range finder means being adapted and arranged to provide an optical focal skin distance reference.

28. Apparatus comprising, means for producing and directing a beam of X-rays about a central axis, means for defining said X-ray beam Within a predetermined field configuration, means for rotating said means for defining said X-ray beam at least 360 about said central axis, and means for monitoring the flatness of said X-ray beam disposed in said beam defining means.

29. Apparatus comprising, means for producing and directing a beam of X-rays about a central axis, means for defining said X-ray beam within a predetermined field configuration, means for rotating said means for defining said X-ray beam at least 360 about said central axis, a first mounting plate for said X-ray source means, said first mounting plate having an aperture therein whereby said X-ray beam may pass through said aperture, a second mounting plate afiixed to said first mounting plate and capable of rotation with respect thereto, said second mounting plate having an aperture therein whereby said X-ray beam may pass through said aperture, and, an annular enclosed ring-like space being provided between said first and said second mounting plates, a *wound electrical cable positioned Within said annular ring-like space, one end of said cable extending through an aperture in said first mounting plate, and the other end of said cable extending through an aperture in said second mounting plate.

30. A linear accelerator capable of producing ionizing radiation comprising, linear accelerator means for producing and directing a charged particle beam along a first axis, means coupled to said linear accelerator means for deflecting said particle beam from said first axis to thereby define a second axis, means surrounding said second axis for defining ionizing radiation traveling along said second axis to a predetermined field about said second axis said means for defining said ionizing radiation being rotatably mounted about said second axis for rotation about said second axis said defining means including pairs of relatively movable metal jaws.

31. A linear accelerator capable of producing ionizing radiation comprising, linear accelerator means for producing and directing a charged particle beam along a first axis, means coupled to said linear accelerator means for deflecting said particle beam from said first axis to thereby define a second axis, means surrounding said second axis for defining ionizing radiation traveling along said second axis to a predetermined field about said second axis, said means for defining said ionizing radiation being adapted and arranged such that said means is capable of rotation about said second axis, said linear accelerator being adapted and arranged for rotation about a third axis, said third axis being displaced from said first axis and from said second axis.

References (Iited UNITED STATES PATENTS 2,506,342 5/ 1950 Burke 250-86 2,637,818 5/1953 Gund et a1 250-495 2,910,603 10/ 1959 Van Dorsten et a1. 250-495 3,091,696 5/1963 Peyser 250- 3,120,610 2/1964 Fearon 250-495 3,152,238 10/1964 Anderson 250 49.5 3,163,762 12/1964 Peyser 250-105 3,230,409 1/1966 Farrell 250-495 RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

Claims

1. A RADIOTHERAPY LINEAR ECCELERATOR COMPRISING, MEANS FOR PRODUCING AND DIRECTING A CHARGED PARTICLE BEAM ALONG A FIRST AXIS, MEANS FOR BENDING SAID CHARGED PARTICLE BEAM SUBSTANTIALLY 90* FROM SAID FIRST AXIS TO THEREBY DEFINE A SECOND AXIS, MEANS FOR PRODUCING AN X-RAY BEAM DIRECTED ALONG SAID SECOND AXIS, ROTATABLE MEANS FOR DEFINING SAID X-RAY BEAM TO A PREDETERMINED FIELD ABOUT SAID SECOND AXIS, SAID ROTATABLE FROM DEFINING MEANS BEING ROTATABLY MOUNTED FOR ROTATION ABOUT SAID AXIS, SAID MEANS