WO1988001848A1

WO1988001848A1 - Radiotherapy apparatus

Info

Publication number: WO1988001848A1
Application number: PCT/GB1987/000636
Authority: WO
Inventors: Douglas Gallie Clarkson
Original assignee: Greater Glasgow Health Board
Priority date: 1986-09-11
Filing date: 1987-09-11
Publication date: 1988-03-24
Also published as: GB2204470B; GB8621963D0; GB2204470A; GB8811088D0

Abstract

Radiotherapy apparatus of the isocentric type for use with high energy ionising radiations. In one embodiment a patient support assembly (24) is mounted to a gantry (12) so that when the gantry (12) is rotated through an angle of $g(a), the patient support assembly (24) is rotated by an angle of -$g(a) with respect to the gantry (12) about a separate horizontal axis (26) parallel to the gantry rotation axis (22) and moving with the gantry (12). This results in maintaining the couch top horizontal for all gantry angles. With the gantry (12) at an angle of 0, i.e. the radiation source (18) directly above the couch, the patient, instead of being at the height of the gantry rotation axis, is lower by the distance separating that axis from the horizontal axis of rotation of the patient support assembly (24). Because the radiation source (18) is still the same distance from the patient it is also lowered by the same amount, yet with the gantry at 180, that is the radiation beam pointing vertically upwards, the patient is no higher from the floor than with existing techniques. In another embodiment the patient support assembly (24b) is mounted separate from the gantry (12b) with the patient support assembly (24b) driven in response to the gantry rotation such that the couch top moves in a manner identical to that described above.

Description

RADIOTHERAPY APPARATUS

The present invention relates to radiotherapy apparatus particularly, but not exclusively, of the isocentric type for use with high energy ionising radiations. Modern radiotherapy equipment generally is of the isocentrically-mounted type, particularly where high-energy X-rays and electrons are used. The radiation source is mounted in a shielded head, called the treatment head, at the end of a horizontally extended arm on a rotating gantry. The axis of rotation of the gantry is horizontal and at some distance from the radiation source. The source produces a radiation beam which is first collimated to give a suitably shaped radiation field before being allowed to impinge on the patient and deposit its energy in the patient's tissues. The central axis of the radiation beam intersects the axis of rotation of the gantry at a point known as the isocentre. The central axis of the beam therefore describes a circular plane centred at the isocentre and orthogonal to the horizontal axis of rotation of the gantry. Full 360 gantry rotation is essential to accommodate the variety of treatment techniques.

The patient being treated normally lies on a flat surface, the treatment couch top, supported by a mechanism which allows complete freedom of movement of the couch in order to align the treatment volume in the patient with the radiation beam. The whole patient support assembly is usually mounted in a floor pit so that the assembly rotates about a vertical axis through the isocentre.

A major drawback of existing equipment is the height above floor level of the gantry axis of rotation. The distance of the radiation source from isocentre (focus- isocentre-distance, FID) is usually fixed at 100 cm.

Because the gantry is required to rotate through 360 , when the source is at its lowest position, beam pointing upwards, gantry at 180° (by convention) , the height of the isocentre in this position has to be well over 100 cm. Current manufacturers' units have isocentre heights between

125 cm and 134 cm and machine design dictates that the patie lies at or near that height for all gantry angles. The problem arises when the gantry is at 0 , beam pointing downwards, it is difficult for operators to set patients an correctly in line with the radiation beam since t&e,operator' of view is very oblique. Also, the treatment head is very high and operators have difficulty in reaching up to insert or remove accessories on the head unit. Techniques are such that most patients will have at least one field where the gantry is at 0 .

Further disadvantages are that. a floor pit is required when the patient support system is not attached to the gantry. Such a floor pit is very expensive and problematic to construct. High precision building work is also required on site because the gantry and patient support assembly should have rotational movements within 2 mm of the isocentre. Because of the requirements for a floor pit and considerable radiation shielding such treatment rooms are usually located in the basement or ground floor.

An object of the present invention is to provide an improved radiotherapy apparatus which obviates and mitigat the aforesaid disadvantages. This is achieved in its simplest forms by mounting th patient support assembly to the gantry such that when the gantry is rotated through an angle of=" ⁰, the patient supp assembly is rotated by an angle of.-o⁰ with respect to the gantry about a separate horizontal axis parallel to the gantry rotation axis and moving with the gantry. This results in maintaining the couch top horizontal for all gantry angles. With the gantry at an angle of 0°, i.e. th radiation source directly above the couch, the patient instead of being at the height of the gantry rotation axis, is lower by the distance separating that axis from the horizontal axis of rotation of the patient support assembl Because the radiation source is still the same distance fr the patient it is also lowered by the same amount, yet wit the gantry at 180 , that is the radiation beam pointing vertically upwards, the patient is no higher from the floor than with existing techniques.

Alternatively, the patient support assembly could be mounted separate from the gantry but with the patient suppo assembly driven in response to the gantry rotation such that the couch top moves in a manner identical to that which would result if the assembly were in fact attached to the gantry as described above.

According to the present invention there is provided a radiation treatment apparatus comprising, a rotatable gantry for rotation about a first substantially horizontal axis , a treatment arm coupled to said gantry and carrying a radiation source for rotation about said first axis, a movable patient support assembly coupled to said gantry, said patient support assembly oriented along a second substantially horizontal axis parallel to and spaced from said first horizontal axis, said second horizontal axis bein rotatable about said first horizontal axis in response to rotation of said gantry, said radiation source being adapted to produce a radiation beam substantially orthogonal to said first and said second horizontal axes and the intersection of said radiation beam and said second horizont axis being at a point defined as the isocentre, drive means for rotating said gantry about said first horizontal axis, said movable patient support assembly being coupled to said gantry drive means so that when said gantry rotates about said first axis to an angle<= , said patient support assembl and said second axis moves about said first axis through a substantially identical angle of -<_- , with respect to said gantry so that said patient support assembly remains in a substantially horizontal plane, and said second axis remains at a substantially constant distance from said radiation source during said rotation of said gantry.

Preferably said patient support assembly is a canti- levered horizontal platform for receiving a patient in a supine or a prone position. Alternatively said patient support assembly may be a chair for receiving a patient in a recumbent position.

Preferably the patient support assembly is mechanically coupled to the gantry. Alternatively the patient support assembly is physically separate and is electrically or optically coupled to the gantry so that the assembly is responsive to rotation of the gantry. Preferably the patient support assembly is rotatab about said first horizontal axis. Alternatively, the pat¬ ient support assembly can be moved laterally and vertically to effectively describe an arcuate path.

Preferably also, said drive means is disposed within said gantry for rotating said gantry about said first horizontal axis. Conveniently said patient support assembly is geared to said drive means simultaneously driv said patient support assembly through an angle of -= witi. respect to said gantry as said gantry rotates through an angle ^ ° about said first horizontal axis. Alternativ said gantry is a drum type gantry and drum drive means separate from said gantry are disposed in proximity to sai gantry for driving said gantry at its periphery about said first horizontal axis. Preferably said apparatus includes means for varying the distance between said patient support assembly and said radiation source. Conveniently said patient support assembly is cantilevered from said gantry.

In one embodiment the patient support assembly is a horizontal platform and the gantry includes a fixed floor stand for supporting said gantry for rotation about said first horizontal axis. In another embodiment the gantry is of the drum type and is adapted to be driven at its periphery by a drum drive disposed in a floor stand beneath the drum type gantry.

These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:-

Figs. 1(a) and (b) are respective end and side elevations of an embodiment of radiotherapy apparatus according to the present invention with the radiation source located directly above the patient at a gantry angle of 0°;

Figs. 2(a) and (b) depict similar views to Figs. 1(a) and 1(b) with the gantry shown rotated anti-clockwise by

45

Figs. 3(a) and (b) depict the gantry when rotated through 180 so that the radiation source is directly below the patient;

Fig.s. 4(a) and (b) are similar to Figs. 1(a) and (b) and depict a drum type gantry with the gantry at an angle of 0 directly above the patient, and Fig. 5 depicts a side elevation of an alternative embodiment of radiation therapy apparatus in accordance with the invention.

Reference is first made to Figs. 1(a) and 1(b) of the drawings which depict radiotherapy apparatus generally indicated by reference numeral 10 which consists of a gantry 12 carrying a cantilevered treatment arm 14, at one end of which is a radiation head 16 carrying a radiation source 18. The gantry is supported by a floor stand 20 which is fixed to the floor 21 and the fixed floor stand 20 includes drive means, not shown in the interests of clarity, for rotating the gantry 12 and the radiation source 18 about a horizontal axis of rotation 22. The gantry carries a patient support assembly 24 in the form of a cantilevered horizontal platform which is oriented along a horizontal axis 26 which is parallel to and spaced from axis of rotation 22. Gearing means generally indicated by reference numeral 28 couples the rotary drive to the gantry to the drive to the horizontal platform 24. The gearing means is typically toothed gears consisting of a first fixed gear 30 coaxial with the horizontal axis 22 coupled via an idler gear 32 to a rotary gear 34 which is coaxial with horizontal axis 26. Gears 30 and 34 are substantially identical.

The treatment head may be coupled to an accessory holder36 which can be removed if required. The central axi of the radiation beam indicated by broken line 38 inter- rotation 26 of sects the axis ofAthe platform 24 at a point known as the isocentre 40. As will be exlpained, as the gantry and the radiation source rotate, the central axis of the beam describes a circular plane containing the isocentre and orthogonal to the horizontal axis of rotation of the gantry and to the horizontal axis of the platform 24. It will be appreciated that the full 360 of rotation is essential to accommodate the variety of treatment technique The radiation beam of course, even though collimated, diverges and typical limits of the beam are specified by broken lines 42 and 44 respectively.

As best seen in Fig. 1(a) broken circle 46 depicts the path of the radiation source as the gantry 12 rotates about a horizontal axis 22 and broken circle 48 depicts the path of the isocentre 40 which rotates about axis 22 in response to rotation of the gantry as will be described. It will be seen that the distance of the isocentre from the radiation source is constant as the gantry rotates through 360 . In use, a patient is positioned on the horizontal platform 24 as shown in Figs. 1(a) and 1(b) with the gantry located directly above the patient's position turned 0 of rotation. Once the patient is in position the gantry can then be driven to rotate about horizontal axis 22. In the example shown, the gantry rotates in the anti-clockwise direction to reach a position shown for example in Figs. 2(a) and 2(b) in which the gantry is rotated anti-clockwise by 45O. As the gantry rotates the gearing 28 to the platform causes the horizontal platform and axis 26 to be rotated by an angle equal to the negative of the angle through which the gantry has rotated, i.e. by -45° with respect to the gantry. The effect of this is that the platform 24 remains in the horizontal plane so that the patient of course remains horizontal and the isocentre 40 remains at a fixed distance from the radiation source 18 as described above.

As the gantry continues to rotate the platform 24 is driven in the opposite direction by an equivalent angle and remains in the horizontal plane 24. In the position shown in Figs. 3(a) and 3(b) the gantry has been rotated by 180 so "that the radiation source is vertically beneath the patient so that the radiation beam impinges at the isocentre in the reverse direction from that shown in Figs. 1(a) and 1(b). It will be seen that the gantry 12 was mounted on the floor stand 20 such that there is sufficient clearance between the treatment arm and the floor 21 to permit full 360 rotation of the gantry to facilitate treatment. In this position it will be appreciated that the distance between the isocentre 40 and the radiation source 18 is the same as that shown in Figs. 1(a) and 1(b) and 2(a) and 2(b).

It will be appreciated that with the gantry at 0 as shown in Figs. 1(a) and 1(b) the distance separating the horizontal axis of rotation of the gantry and the horizontal axis 26 of the patient and support platform 24 is the amount by which the patient is lower than with existing apparatus. In addition, because the radiation source 18 remains at the same distance from the patient as with existing apparatus it is also lower by the same amount reducing space requirements. Finally, as illustrated in Figs. 3(a) and 3(b) with the gantry at a 180° rotated position and the beam 38 pointing upwards the patient is disposed no higher from the floor than with existing techniques.

Reference is now made to Figs. 4(a) and 4(b) of the drawings which depict an alternative gantry from that shown in Figs. 1 to 3(a) and (b) . For convenience. 848 _ _lQ _

like numerals will refer to like parts but with the suffix (a) added. In this embodiment the gantry is a drum type gantry 12a which is mounted on arcuate floor stand 20a mounted on floor 21a. The drive to the gantry 12a is effected by drum drive means 52 disposed at the periphery of the drum for driving the drum 12a to rotate through 360° about horizontal drum axis 22a. Platform 24a is mounted along horizontal axis 26a which is spaced from axis 22a by a fixed amount as indicated before. The drive to the axes 22a and 26a is coupled by gearing means 28a which results in the same rotational effect of the platform and axis 26a as described with reference to the first embodiment. Rotation of the drum 12a by drive means 52 has the same effect on platform 24a as earlier described with the isocentre 40a remaining the same distance from radiation source 18a throughout the rotation.

Reference is now made to Fig. 5 of the drawings which shows an alternative embodiment of radiation therapy apparatus in accordance with the invention. For convenience like numerals will refer to like parts already described but with the suffix (b) added. In this embodiment it will be seen that the patient support Platform 24b is not physically connected to the gantry 12b. Instead,the platform is cantilevered from a separate pedestal coupled to the floor 21b. The platform is electrically/optically coupled to the gantry 12b by means of a light beam 54 and photosensor 56 on the pedestal and has platform movement control means coupled to the photosensor. The platform movement control means is responsive to the light beam which includes a signal corresponding to the angular position of the gantry 12b, and causes the platform and axis 26b to be moved in a vertical plane, eg. X-"i plane, along an arcuate path by an angle which is the same as the angle by which the gantry rotates. The signal could be electronic instead of optical and the respective gearing is matched so that the distance moved by the patient support assembly is such that the second axis 26b. remains at a substantially constant distance from said radiation source.

It will be appreciated that various modifications may be made to the apparatus hereinbefore described without departing from the scope of the invention. For example, the horizontal table 24 and/or position of axis 26 can be adjustable so that the distance between the radiation source and the isocentre 40 can be varied. In addition, the platform 24 may be replaced by a cantilevered couch which may be floor mounted so a patient may be^' disposed in the recumbent or other suitable position depending on the treatment required.

Advantages of the invention are that there is no requirement for a floor pit, particularly if the patient support system is attached to the gantry, minimising the cost of constructing and modifying such pits which may be as much as 25% of the total cost of accommodating such apparatus. High precision building work is also minimised because the requirement of positioning the gantry on a fixed floor stand in relation to the patient support assembly to result in rotational movements within + or - 2mm of the isocentre is not required. The alignment of the gantry and platform can be done by the manufacturer on its own premises and the requirement of sending technical experts to supervise the installation of such structures is minimised.

The apparatus can be used for a wide variety of radiotherapy equipment; eg. linear accelerators, neutron generators, Cobalt-60, Caesium-137, orthovoltage and superficial X-ray machines and simulators can all be mounted in a similar manner. Variation adjustment of the distance between the gantry rotation axis and the patient support assembly horizontal axis ensures that the system remains truly isocentric for all such distances. With existing machines this requires that the radiation source be moved which is complex and often impossible. A larger focus-isocentre-distance, FID, is possible so that the dose at depth in the patient is enhanced. For example, 4 MV X-ray beam at 120 cm FID provides a depth dose similar to that of a 6 MV beam at 100 cm FID. Further advantages are that larger bending magnets are possible because of the larger space accommodation and this would permit better control and enable higher energies to be used clinically. The space required to accommodate such a new type of mounting is much less than with existing machines thus permitting upgrading of existing rooms for example, adding shielding inside the room because of the greater space. Furthermore new buildings will require less space from the outset. Because there is no require¬ ment for a floor pit of any depth radiotherapy rooms could be constructed above each other. If the wall of an upper storey room was situated in the path of the radiation beam from a machine in a lower room and vice versa, then the wall could be used to act as a primary radiation barrier for the radiation beam in the lower/upper room and as a secondary barrier for the upper/lower room. It is envisaged that such a construction would result in the saving of more than 20% of the cost of building each room. Because most radiotherapy departments are in long- established hospitals expansion is impossible because there is no free ground space butthis apparatus would now permit upward expansion for radiotherapy departments. A further advantage is that the manufacturing costs of the equipment may be reduced. For example, the patient support assembly attached to the gantry would reduce the requirement for counterweights and on-site installation is much simpler. More factory commissioning can be carried out eliminating the requirement for transporting delicate, expensive and often bulky test equipment to the site.

Claims

1. A rεdiation treatment r.pparatu? comprising a rotatable gantry for rotation about a first substantially horizontal axis, a treatment art coupled to said gantry and carrying a radiation source for rotation about said first axis, a movable patient support assembly coupled to said gantry, said patient support assembly oriented along a second substantially horizontal axis parallel to and spaced from said first horizontal axis, said second horizontal axis being rotatable about said first horizontal axis in response to rotation of said gantry, said radiation source being adapted to produce a radiation beam substantially orthogonal to said first and said second horizontal axes and the intersection of said radiation beam and said second horizontal axis being at a point defined as the isocentre, drive means for rotating said gantry about said first horizontal axis, said movable patient support assembly being coupled to said gantry drive means so that when said gantry rotates about said first axis to an angleoC⁰, said patient support assembly and said second axis moves about said first axis through a substantially identical angle of -aW , with respect to said gantry so that said patient support assembly remains in a substantially horizontal plane, and said second axis remains at a substantially constant distance from said radiation source during said rotation of said gantry.

2. Radiation treatment Apparatus as claimed in claim 1 wherein said patient support assembly is a cantilevered horizontal platform for receiving a patient in a supine or a prone position.

3. Radiation Treatment Apparatus as claimed in claim 1 wherein said patient support assembly is a chair for receiving a patient in a recumbent position.

4. Radiation Treatment Apparatus as claimed in claim 1, 2 or 3 wherein the patient support assembly is mechan¬ ically coupled to the gantry.

5. Radiation Treatment Apparatus as claimed in claim 1,

2 or 3 wherein the patient support assembly is physically separate and is electrically or optically coupled to the gantry so that the assembly is responsive to rotation of the gantry.

6. Radiation Treatment Apparatus as claimed in any preceding claim wherein the patient support assembly is rotatable about said first horizontal axis.

7. Radiation Treatment Apparatus as claimed in any one of claims 1 to 5 wherein the patient support assembly is movable laterally and vertically to effectively describe an arcuate path.

8. Radiation Treatment Apparatus as claimed in any preceding claim wherein said drive means is disposed within said gantry for rotating said gantry about said first horizontal axis.

9. Radiation Treatment Apparatus as claimed in any preceding claim wherein said patient support assembly is geared to said drive means simultaneously driving said patient support assembly through an angle of -o° with respect to said gantry as said gantry rotates through an angleo ° about said first horizontal axis. _ _χg _

10. Radiation Treatment Apparatus as claimed in any preceding claim wherein said gantry is a drum type gantry and drum drive means separate from said gantry are disposed in proximity to said gantry for driving said gantry at its periphery about said first horizontal axis.

11. Radiation Treatment Apparatus as claimed in any preceding claim wherein said apparatus includes means for varying the distance between said patient support assembly and said radiation source.

12. Radiation Treatment Apparatus as claimed in any preceding claim wherein said patient support assembly is cantilevered from said gantry.

13. Radiation Treatment Apparatus as claimed in any preceding claim wherein the patient support assembly is a horizontal platform and the gantry includes a fixed floor stand for supporting said gantry for rotation about said first -horizontal axis.

14. Radiation Treatment Apparatus as claimed in any one of claάms 1-12 wherein the gantry is of the drum type and is adapted to be driven at its periphery by a drum drive disposed in a floor stand beneath the drum type gantry.