X-ray or gamma ray systems or devices – Accessory – Object holder or support
Reexamination Certificate
2000-07-24
2003-10-21
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Object holder or support
C378S068000, C378S177000, C378S195000, C005S601000
Reexamination Certificate
active
06634790
ABSTRACT:
FIELD OF INVENTION
The invention relates to tomotherapy treatment and more particularly to an apparatus and method for precisely positioning a tomotherapy treatment table.
BACKGROUND
Intensity modulated radiation therapy (IMRT) is an emerging technique in the treatment of tumors. It involves the delivery of many small, concentrated “pencil beams” of radiation that can be varied in intensity. The primary goal of tomotherapy is to deliver a very high dose of radiation to the tumor, while sparing the surrounding tissue. In order to spare the surrounding tissue, this technique causes the high dose of radiation to conform to the shape of the tumor. Tomotherapy delivers a treatment to the tumor in a slice by slice procedure. One thin slice of the tumor is treated at a time before moving on to treat the next slice. The three dimensional shape of the tumor is programmed into a computer which controls the treatment. Because of the high doses of radiation involved and the desirability of having the high dose region essentially the exact size and shape of the tumor, extreme accuracy in positioning the patient is required. The necessary accuracy is maintained by aligning the linear accelerator's isocenter to a precise point within the patient. The isocenter is a single reference point in the x-y-z plane which serves to orient the radiation beams to the proper coordinates of the slices of the tumor.
FIG. 1
shows an example of equipment for performing such a technique. A linear accelerator
10
provides the radiation for the therapy. A multi-leaf collimator
14
concentrates the radiation into the pencil beams which are applied to the tumor. Each pencil beam is approximately one square centimeter in size. The multi-leaf collimator
14
is mounted on the head
13
of the linear accelerator
10
which rotates on a gantry
12
around the patient. The patient is immobilized on a treatment couch
16
which comprises a tabletop
18
, a positioning rail
20
, and a base
22
. The tabletop
18
is able to move independently of the base
22
in the lateral (x-axis) and/or longitudinal (y-axis) directions. The base
22
is moveable in the vertical directions (z-axis). This allows the patient, who is lying on the tabletop, to be positioned to the desired x, y, z location.
It is often advantageous to rotate the treatment couch
16
to a different angle (called a “couch angle”) with respect to the linear accelerator
10
in order to treat the tumor from a different direction (i.e., on a different plane). The entire couch assembly may be rotated about the isocenter line of the collimator
15
, because it is attached to a rotating disc assembly
24
mounted in the floor. The couch
16
is attached to the edge of the rotational disc
24
such that when the disc
24
is rotated, the couch angle is adjusted accordingly.
Research has shown that there are advantages to delivering IMRT treatments when the isocenter of the linear accelerator is intentionally placed somewhere other than the center of the tumor. For such “non-isocentric” delivery schemes, when the couch angle is changed, basic trigonometry dictates that the treatment couch must make lateral and longitudinal translations to maintain the original isocenter at the same point within the patient. These translations must be done With sub-millimeter accuracy relative to the isocenter. One prior art method performs these translations using a self-supporting positioning device known as the “Crane™” which is available from the Nomos Corporation as part of its Peacock System® radiosurgery device.
FIG. 2
shows a side view of the prior art positioning device.
FIG. 3
shows the overhead view of the same device. The positioning device
26
comprises a central vertical beam
28
which is supported by three legs
30
. The device
26
is moved by retractable wheels
32
which are recessed within the legs
30
when the device is stationary. The central beam
28
supports a lateral positioning arm
34
which extends through a lateral arm housing
35
. The location of the lateral positioning arm
34
is adjusted by a lateral movement crank
36
. The lateral positioning arm
34
is connected to the longitudinal arm housing
39
. A longitudinal positioning arm
38
extends through the longitudinal housing
39
. The location of the longitudinal arm
38
is controlled by a longitudinal movement crank
40
. Two attachment arms
42
are mounted on top of the longitudinal arm housing
39
. These arms
42
attach to the positioning rail
20
of the tabletop
18
(shown in
FIG. 1
) with attachment clamps
44
which are tightened with attachment cranks
46
.
A device of the type shown in
FIGS. 2 and 3
is, by design, very heavy (approximately 300 lbs.). When the couch angle is changed, the positioning device is elevated onto its wheels and dragged or pulled alongside the treatment couch as it rotates to the new angle. When the device is elevated onto the wheels, however, it exerts compressive, tensile, and/or shear forces on the attachment arms. These forces alter the position of the treatment couch relative to the device and, consequently, invalidate any previously set isocenter. Additional large forces also are exerted on the attachment arms when the device is dragged or pushed by the treatment couch while it is moving. These forces alter the position of the couch in relation to the device. Furthermore, the length of the lateral and vertical positioning alms, which is necessitated by the free standing design, makes the device prone to “flexing” of the system, which can induce clinically significant errors. In combination, these forces can, individually and collectively, result in significant errors of as much as 1 cm or more. Therefore, in practice, accurate treatment at multiple couch angles utilizing non-isocentric IMRT delivery schemes are currently not practical.
SUMMARY OF INVENTION
The invention relates to a tomotherapy treatment table positioning device for positioning the tabletop with a high degree of accuracy.
In general, in one embodiment, the invention relates to an apparatus for positioning a moveable tabletop on a treatment couch comprising: a central frame which is mounted to the treatment couch; a connecting mechanism attached to the moveable tabletop, the connecting mechanism extending from the central frame; and a positioning mechanism on the central frame which positions the moveable tabletop to a desired location in lateral and longitudinal directions.
In another embodiment, the invention relates to an apparatus for positioning a moveable tabletop on a treatment couch comprising: means for mounting a central frame to the base of the treatment couch; means for connecting the central frame to the moveable tabletop; means for positioning the moveable tabletop to a desired location in a lateral direction; and means for positioning the moveable tabletop to a desired location in a longitudinal direction.
In another embodiment, the invention relates to a method for positioning a moveable tabletop on a treatment couch to receive radiation treatment comprising: providing a central frame mounted on the treatment couch; attaching at least one connecting mechanism to the moveable tabletop, the connecting mechanism(s) extending from the central frame; and positioning the moveable tabletop to a desired location in lateral and longitudinal directions.
The advantages of the invention include, at least, an integrated positioning device that is mounted on the treatment couch. Another advantage is the capability of the device to position and lock the tabletop of the couch in the lateral and longitudinal positions to an accuracy of less than 0.01 mm. When the treatment couch is rotated to a different couch angle, the integrated positioning device rotates as an integral part of the couch and as a result, it maintains the positioning accuracy of the tabletop relative to the isocenter of the patient.
REFERENCES:
patent: 3240935 (1966-03-01), Dougall
patent: 3424470 (1969-01-01), Voster
patent: 3588500 (1971-06-01), Koerner
patent: 3783251 (1974-01-01), Pakovich
pat
Dunn Drew A.
Rosenthal & Osha L.L.P.
The University of Texas System
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