X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-08-06
2001-04-17
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S205000
Reexamination Certificate
active
06219403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiation therapy method, and a radiation therapy system including a radiation therapy planning apparatus and radiation therapy apparatus, for determining the irradiation range of radiation to be aimed at a certain portion within the body of a subject such as a tumor, and controlling the actual irradiation of radiation based on a therapy plan that takes into consideration bodily movement of the patient during the irradiation period.
2. Description of the Related Art
In an arrangement wherein radiation is to be aimed at a certain portion in the body of a subject such as a tumor, determining the range of irradiation and matching the range of irradiation with the affected part by displaying the determined range of irradiation on the surface of the subject are extremely important tasks.
Known radiation therapy apparatus arrangements involve watching a tomography image from a CT apparatus or the like and a fluoroscopy image from an x-ray simulator or the like to determine the irradiation range.
That is, the tomography image from the CT apparatus con display the interior of the body of the subject with high contrast resolution, and the area to which radiation should be irradiated (i.e., the area of interest) can be relatively easily determined on the tomography image. The portion corresponding with the area of interest on the tomography image is obtained on the fluoroscopy image. With the fluoroscopy image from the X-ray simulator, the perspective of the fluoroscopy image matches the center of the irradiation of radiation, so the area of interest on the fluoroscopy image can be correlated with a corresponding portion on the surface of the subject. The range of irradiation has thus been determined qualitatively, which has been marked on the uneven surface of the subject using a marker or the like.
Also, the radiation therapy plan generally includes, as shown in
FIG. 9A
, determining a part
50
on a slice image reflecting the physical status of a subject
4
at a certain time t
1
, to the determining of an optimal irradiation method with the part
50
as a target
8
, and the simulation thereof (In the Figure, “O” denotes a hypothetical radiation source, and the dotted arrows imply the radiation cone).
However, in the case of creating a therapy plan for a part which is easily affected by bodily moving caused by breathing, variations are taken into consideration for the exhaling period (shrunk) and inhaling period (stretched) of the part
50
displayed on-the slice image of the subject
4
, as shown in
FIGS. 10A and 10B
. That is, a irradiation part including a so-called safety margin Ma is set, so as to be somewhat larger that the part
50
.
Accordingly, the range of the therapy plan is set larger than the form of the part
50
which is a tumor or the like, due to bodily moving caused by breathing.
However, it is difficult to distinguish fine differences in contrast with fluoroscopy using X-ray simulators, and particularly in the event that the contrast between the area of interest and other areas is small, the area of interest determined in the tomography image has not been able to be identified in the fluoroscopy image. Thus, judging at which position in the fluoroscopy image the area of interest identified in the tomography image exists has been a troublesome task which requires much experience. Also, owing to such, it has been difficult to precisely determine the range for irradiation of radiation beams.
Also, the slice images which have been used for the therapy plan are images taken of the physical state of the patient at the time of examination, and this is also problematic in that these images do not reflect the constantly-changing bodily movements.
For example, with actual irradiation of radiation beams, the position of the part
50
serving as the target
8
is constantly moving from the position of the target
8
in the plan, due to bodily movement of the subject
4
such as breathing, but actual irradiation is performed according to the therapy plan with the target
8
fixed, so there has been a problem in that the target
8
of the irradiation shifts away from the actual part
50
at a time t
2
during the irradiation period, as shown in FIG.
9
B. This shifting of the irradiation target owing to bodily movement increases in magnitude in the case that the patient has to be subjected to the therapy for prolonged sessions.
On the other hand, setting of the irradiation portion including the safety margin Ma (See
FIG. 10
) depended greatly on the experience and instincts of the operator (physician), so however carefully the safety margin may be set, there has been no guarantee that the margin is sufficiently large.
Accordingly, in the event that the irradiation portion including the safety margin Ma is set to a size greater than necessary, there has been the possibility that non-tumor parts outside of the tumor portion may be subjected to excessive irradiation of radiation. Conversely, in the event that the set size is smaller than necessary, there have been problems that the amount of radiation is less than the planned standard, resulting in repeating the radiation treatment.
SUMMARY OF THE INVENTION
The present invention has been made in light of the above-described problems, and accordingly, it is an object of the present invention to provide a radiation therapy method and a radiation therapy system wherein an image suitable for determining the range for irradiation of radiation can be synthesized, and a fluoroscopy image of the subject can be synthesized on an X-ray TV simultaneously with the irradiation, thereby solving the problem of deterioration in precision of the therapy plan due to bodily movement during the irradiation period.
In order to realize the above object, according to the present invention, a radiation therapy method includes a center projection image synthesizing method for creating an image for determining the range of irradiation of radiation beams, in an arrangement wherein irradiation of radiation beams is aimed at a specific portion such as a tumor within the body of a subject, the projection image synthesizing method comprising: a step for establishing a marker at the specific portion such as tumor, or nearby (including the surface of the subject); a step for obtaining 3-D data regarding inside of the body of the subject with a CT apparatus or the like; and a step for obtaining from the 3-D data a center projection image for 3-D data according to a center-of-projection point determined beforehand and the marker, and/or an area of interest within the 3-D data; wherein the relative positions of the established marker and the specific portion are clarified, and irradiation of radiation beams is terminated in the event that the relative positions shift.
The center projection image may be an image of the subject which changes over time, and the obtained projection image data may be output to a recording medium.
According to another aspect of the present invention, the projection image synthesizing method comprises: a step for specifying as an area of interest an area corresponding with the specific portion in the 3-D data regarding inside of the body of the subject which has been obtained with a CT apparatus or the like; and a step for calculating a center projection image for the area of interest according to a center-of-projection point at geometric conditions set for the area of interest and the established marker, and/or the 3-D data; wherein the geometric conditions are the same as the geometric conditions for the point of origin for irradiation of radiation beams to the portion corresponding with the area of interest in the body of the subject.
According to another aspect of the present invention, the geometric conditions are the same as the geometric conditions for the focal point of an X-ray tube in an X-ray TV apparatus on the portion corresponding with the area of interest in the body of the subject.
The projection image obtained by the center project
Kiknadze Irakli
Kim Robert H.
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
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