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Claims  |
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What is claimed is:
1. Apparatus for monitoring and sensing changes in position of a patient
from a prior position at a prior time to a current position at a current
time, which apparatus comprises:
a source of radiation for applying radiation to a patient;
a plurality of individual targets adapted to be releasably affixed at both
a current time and a prior time to the patient, for reflecting radiation
impinging thereon;
camera and computer means for detecting the reflected radiation from
individual ones of the targets, uniquely identifying individual ones of
said targets from which radiation was detected, and for individually
determining current and prior positions of the uniquely identified targets
in three-dimensional space, based on the target fixation to the patient at
the current and prior times, respectively;
data storage means for storing data representative of at least the prior
position of the uniquely identified targets;
computer means for comparing the current position of the uniquely
identified targets with the prior position data stored in the data storage
means for those identified targets, and developing from said comparing
position signals representative of a difference in position of said
identified targets, and therefore said patient from said prior time to
said current time; and
display means responsive to said position signals for displaying indicators
representative of said difference in position of said patient.
2. The apparatus of claim 1 which further comprises means for user
interaction for receiving and storing data from the user, the data
comprising user-set tolerances; and wherein the display means displays the
indicators so that they have a size which is proportional to the magnitude
of the difference, and a color which is dependent upon the magnitude that
the difference exceeds a percentage of the tolerance stored in the data
storage means.
3. The apparatus of claim 2 which further comprises means for sending a
position signal to a table means which supports the patient, wherein
the table means, in response to the position signal, comprises means for
moving the patient so that the differences do not exceed the tolerances.
4. The apparatus of claim 2 wherein the display means comprises means for
displaying an indicator in a first color if the difference exceeds a first
limit and in a second color if the difference exceeds a second limit.
5. The apparatus of claim 2 wherein the display means further comprises
means for displaying the differences in a predetermined color if the
differences do not exceed the tolerance.
6. The apparatus of claim 1 wherein the data further comprises a treatment
fraction requirement for a user defined modality of treatment and wherein
the computer means further comprises means for comparing the treatment
fraction with a time of application of radiation and means for signaling
the operator that the time of treatment for the fraction has expired.
7. The apparatus of claim 1 wherein the data further comprises a treatment
fraction requirement for a user defined modality of treatment and wherein
the apparatus further comprises means for signaling that a radiation
therapy machine is active and the computer means further comprises:
means for receiving the signal and determining a time of radiation;
means for comparing the treatment fraction with the time of radiation and
means for signaling the operator that the time of treatment for the
fraction has expired.
8. The apparatus of claim 7 which further comprises means for sending a
turnoff signal to the radiation therapy machine for causing the radiation
therapy machine to cease being active.
9. The apparatus of 6 wherein the computer means for comparing further
comprises:
means for storing the fraction of treatments provided for a patient in the
storage means for each treatment along with an indicator of the data of
the treatment;
means for displaying the stored treatment fractions and sums of the
treatment fractions.
10. The apparatus of claim 5 wherein the predetermined color is green.
11. The apparatus of claim 4 wherein the first color is orange and the
second color is red.
12. The apparatus of claim 4 wherein the first limit comprises a first
percentage of the tolerance and the second limit comprises a second
percentage of the tolerance.
13. The apparatus of claim 1 wherein the source of radiation comprises a
source of infrared radiation.
14. The apparatus of claim 1 wherein the camera means comprises CCD camera
means.
15. The apparatus of claim 14 wherein the camera means further comprises
infrared filter means.
16. The apparatus of claim 1 wherein the target means comprises
retroreflective reflector means.
17. The apparatus of claim 16 wherein the retroflector means comprises at
least one reflector, the reflector being comprised of a first portion
which is retroreflective and a second portion which is not
retroreflective.
18. The apparatus of claim 17 wherein the first portion has a first
predetermined shape and the second portion has an aperture, wherein the
aperture is large enough so that a mark placed the surface of the patient
may be seen when the target is affixed to the patient.
19. The apparatus of claim 1, wherein a target comprises:
a body of substantially flat material;
means disposed on one side of the body for releasably affixing the body to
a patient; and
means disposed on the other side of the body for retroreflecting radiation;
wherein:
the retroreflecting means comprises a first portion which is
retroreflective and a second portion which is not retroreflective.
20. The target of claim 19 wherein the first portion has a first
predetermined shape and the second portion has an aperture, wherein the
aperture is large enough so that a mark placed on the surface of the
patient may be seen when the target is affixed to the patient.
21. The apparatus of claim 2 wherein the targets comprises at least three
reflectors and wherein the computer means further comprises means for
determining a position of a plane of at least three of the at least three
reflectors.
22. The apparatus of claim 21 wherein the targets comprises more than three
reflectors and the computer means further comprises means for determining
a plane by a least squares fit between planes determined by groups of
three reflectors.
23. The apparatus of claim 2 wherein the computer means further comprises
means for determining a position of the patient as a center of mass of the
Positions of the targets.
24. Apparatus for monitoring and sensing changes in position of a patient
from a prior position at a prior time to current position at a current
time, which apparatus comprises:
a plurality of individual phosphorescent targets adapted to be releasably
affixed to the patient at both the current time and the prior time, for
generating radiation;
camera and computer means for detecting the radiation from individual ones
of the targets, uniquely identifying individual ones of said targets from
which radiation was detected, and for individually determining current and
prior positions of the uniquely identified targets in three-dimensional
space, based on the target fixation at the current and prior times;
data storage means for storing data representative of at least the prior
position of the uniquely identified targets;
computer means for comparing the current position of the uniquely
identified targets with the prior position stored in the data storage
means for those identified targets, and developing from said comparing
position signals representative of a difference in position of said
identified targets, and therefore said patient, from said prior time to
said current time; and
display means responsive to said position signals for displaying indicators
representative of said difference in the position of said patient.
25. The apparatus of 24 wherein the camera means further comprises filter
means for passing radiation substantially in the range of wavelengths
emitted by the targets.
26. The apparatus of claim 24 wherein the phosphorescent means comprises at
least one generator, the generator being comprised of a first portion
which is phosphorescent and a second portion which is not phosphorescent.
27. The apparatus of claim 24, further comprising:
means for user interaction for receiving and storing data from the user,
the data comprising a user-set tolerance; and
wherein the display means displays the indicators so that they have a size
which is proportional to the magnitude of the difference, and a color
which is dependent upon the magnitude that the difference exceeds a
percentage of the user-set tolerance stored in the data storage means.
28. Apparatus for monitoring and sensing changes in position of a patient
from a prior position at a prior time to a current position at a current
time, which apparatus comprises:
a source of radiation for applying radiation to a patient;
a plurality of targets adapted to be releasably affixed at both a current
time and a prior time to the patient, for reflecting radiation impinging
thereon;
camera and computer means for detecting the reflected radiation from the
targets and for determining current and prior positions of the targets in
three-dimensional space, based on the target fixation at the current and
prior times, respectively;
data storage means for storing data representative of at least the prior
position of the targets;
computer means for comparing the current position of the targets with the
stored prior position data for those targets, and developing from said
comparing position signals representative of a difference in position of
said patient from said prior time to said current time;
user means for causing input to and storage by said data storage means of
user-set tolerances; and
display means responsive to said position signals for displaying indicators
which are representative of said difference in position of said patient by
causing the indicators to have a size which is proportional to the
magnitude of the difference, and a color which is dependent upon the
magnitude that the difference exceeds a percentage of the user-set
tolerance stored in the data storage means.
29. The apparatus of claim 28 wherein the display means further comprises
means for displaying an indicator in a first color if the difference
exceeds a first limit and in a second color if the difference exceeds a
second limit.
30. The apparatus of claim 28 wherein the display means further comprises
means for displaying the differences in a predetermined color if the
differences do not exceed the percentage of the user-set tolerance.
31. The apparatus of claim 29 wherein the first color is orange and the
second color is red.
32. The apparatus of claim 29 wherein the first limit comprises a first
percentage of the user-set tolerance and the second limit comprises a
second percentage of the user-set tolerance.
33. The apparatus of claim 30 wherein the predetermined color is green.
34. Apparatus for monitoring and sensing changes in the position of a
patient from a prior position at a prior time to a current position at a
current time, which apparatus comprises:
a source of radiation for directing a predetermined narrow spectral
bandwidth of radiation towards a patient;
a plurality of targets adapted to be releasably affixed at both a current
time and a prior time to the patient, said targets having a reflecting
surface thereon for reflecting the predetermined narrow spectral bandwidth
of radiation directed to the patient and impinging thereon;
camera means having an optical bandpass filter at its optical input which
passes substantially only said predetermined narrow bandwidth, and which
is directed to said targets for detecting the reflected radiation from the
targets and providing at an output an image signal representative of said
detection;
position determining means coupled to said camera means and responsive to
said image signal for determining current and prior positions of the
targets in three-dimensional space, based on the target fixation at the
current and prior times, respectively;
data storage means for storing at least the prior position data of the
targets;
computer means for comparing the current position of individual ones of the
uniquely identified targets with the prior position data stored in the
data storage means for those targets, and developing from said comparing
position signals representative of a difference in position of said
patient from said prior time to said current time; and
display means responsive to said position signals for displaying indicators
which are representative of said difference in position of said patient.
35. The apparatus of claim 34, wherein said source of radiation comprises
an infrared light source, and said optical filter comprises a infrared
light filter.
36. A method for monitoring and sensing changes in the position of a
patient from a prior time to a current time, said method comprising the
following steps:
applying a plurality of indicating marks to a surface portion of a patient
whose position is to be monitored, said applying being done before the
prior time;
releasably affixing a plurality of individual radiation reflecting targets
to the patient so that each target of said plurality is aligned with an
indicating mark at the current time and prior time;
directing radiation towards the patient;
detecting radiation reflected from individual ones of the targets at the
current time and prior times, uniquely identifying individual ones of said
targets from which radiation was detected, and determining current and
prior positions for individual ones of the uniquely identified targets in
three-dimensional space, based on the target fixation at the current and
prior times, respectively;
storing data representative of at least the prior position of the targets;
comparing the current position of the targets with the prior data stored
for those identified targets, and developing from said comparing position
signals representative of a difference in position of said patient from
said prior time to said current time; and
displaying said position signals as an indication of the difference in
position of the patient from said prior time to said current time, thereby
monitoring the position of the patient.
37. The method of claim 36, wherein:
said displaying step comprises displaying indicators in a three-dimensional
coordinate system, which indicators have a size which is proportional to
the magnitude of the difference, and a color which is dependent upon the
magnitude that the difference exceeds a percentage of the tolerance stored
in the data storage means.
38. The method of claim 36, wherein said affixing step comprises:
affixing individual radiation reflecting targets to the patient at the
current time and prior time, each target comprising a body of
substantially flat material having affixing means disposed on one side of
the body for affixing the body to the patient, and retroreflecting means
disposed on the other side of the body for retroreflecting radiation, the
retroreflector means comprising a first portion which is retroreflective
and a second portion which is not retroreflective and allows said
indicating marks to be visible therethrough, so that during this affixing
step said second portion of each of said targets is aligned with said
indicating marks on said surface of said patient.
39. The method of claim 36, wherein:
said comparing step comprises comparing a center of mass calculated for the
current position of said targets to a center of mass calculated for the
prior position of said targets.
40. The method of claim 36, wherein said detecting step comprises:
calculating position vectors between each one of a plurality of said
target, and a relative angular relationship between each one of said
vectors at both of the current and prior times, and comparing the
calculated vectors and their relative angular relationship at said current
time to the calculated vectors and their angular relationship at said
prior time, for uniquely identifying a plurality of said targets and their
current position, and therefor said patient, in three-dimensional space.
41. The method of claim 40, wherein:
said comparing step comprises individually comparing the current position
of individual ones of said uniquely identified targets to the prior
position of those identified targets; and
said displaying step comprises displaying magnitudes in a three-dimensional
coordinate system, said magnitudes being representative of the difference
between the current three-dimensional position and a prior
three-dimensional position of the patient, thereby monitoring the position
of the patient. |
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Claims |
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Description |
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TECHNICAL FIELD OF THE INVENTION
The present invention relates to methods and apparatus for patient
positioning and for verifying treatment fields in the delivery of
radiation therapy.
BACKGROUND OF THE INVENTION
Accurate placement and verification of treatment fields remain as principal
problems in the delivery of radiation therapy. Measurements of patient
setup and field positioning errors have been reported by many authors. For
example, many published reports document positioning errors having mean
deviations of the order of 5 to 8 mm, wherein a significant percentage of
positioning errors occur in excess of 15 mm. One example of such reports
can be found in an article entitled "Quality Assurance in Radiation
Therapy: Physics Efforts" by Svensson, G. K., Int. J. Rad. Onc. Biol.
Phys., Vol. 10, Sup 1, 23-29, 1983.
As is well known, such positioning errors lead to a decrease in Tumor
Control Probability (TCP) which can be as large as 20 percent (20%). One
example of such results can be found in an article entitled "Uncertainty
Analysis of Field Placement Error Measurements Using Digital Portal and
Simulation Image Correlations" by McParland, B. J., Med. Phys., 20(3),
679-685, May/June 1993.
Many groups have attempted to address this issue by using "port films" or
real time portal imaging technology. One example of such attempts is
described in an article entitled "Automatic On-line Inspection of Patient
Set-up in Radiation Therapy Using Digital Portal Images" by Gilhuijs, K.
G. A. and van Herk, M., Med. Phys., 20(3), May/June 1993. See also U.S.
Pat. No. 5,138,647 entitled "Portal Imaging Device" issued Aug. 11, 1992
to Nguyen, J. and Yu, C. X. and assigned to Siemens Medical Laboratories,
Inc.
Presently, routine clinical implementation of the above-described
techniques suffers from drawbacks in that they: (a) are labor intensive;
(b) require human judgment; and (c) require delivery of radiation before
patient/field position can be determined. In addition, most analysis is
done off-line after patient treatment has been completed.
At present, no commercial system exists which can rapidly, reliably,
remotely and accurately measure the orientation/position of a patient in
Cartesian space by performing the following tasks: (a) resolve target
position on a patient to better than 1 mm absolute in Cartesian space and
determine patient rotation about any of the three principal axes; (b)
provide sufficient reproducibility so that an operator/technologist can
reposition targets on the patient with a reproducibility of better than 2
mm, from day to day; (c) warn the operator/technologist if the patient,
i.e., the targets, are not in the correct position before treatment; (d)
report patient position with respect to an initial, i.e., reference,
patient setup or with respect to a setup for a particular treatment; and
(e) provide a method for quality assurance of a linac ODI, laser, light
field position and digital couch. Thus, there is a need in the art for a
system for accurate patient setup and day-to-day patient position
verification which provides these capabilities.
SUMMARY OF THE INVENTION
Advantageously, embodiments of the present invention solve the
above-identified problems by providing a remote sensing system capable of
real time monitoring of patient position which can report variations in
patient setup from day to day as well as motion during individual
treatments. In particular, an embodiment of the present invention is a
system which can rapidly, reliably, remotely and accurately measure the
orientation/position of a patient in Cartesian space by performing the
following tasks: (a) accurately resolve target position on a patient,
e.g., to better than 1 mm absolute, in Cartesian space and determine
patient rotation about any of the three principal axes; (b) provide
sufficient reproducibility so that an operator/technologist can reposition
targets on the patient with high reproducibility, e.g., of better than 2
mm, from day to day; (c) warn the operator/technologist if the patient,
i.e., the targets, are not in the correct position before treatment; (d)
report patient position with respect to an initial, i.e., reference,
patient setup or with respect to a setup for a particular treatment; and
(e) provide a method for quality assurance of a linac ODI, laser, light
field position and digital couch. Specifically, an embodiment of the
present invention comprises: (a) a source of radiation for applying
radiation to a patient; (b) target means affixed to the patient for
reflecting radiation impinging thereon; (c) camera and computer means for
detecting the reflected radiation and for determining the position of the
targets in three-dimensional space; (d) data storage means for storing the
position of the targets; (e) computer means for comparing the position of
the targets with positions stored in the data storage means; and (f)
display means for displaying indicators whenever differences between the
position and the stored position exceed tolerances stored in the data
storage means.
In accordance with further embodiments of the present invention, an
inventive user interface enables a user to define tolerance tables for
position differences based on clinical application where, for example, a
stereotactic motion tolerance table may be assigned a tighter tolerance
than that required for breast setup. Further in accordance with the
present invention, displays are made of position differences which exceed
predefined tolerance values wherein a displays of predetermined colors,
such as a red bar, indicate the severity of position mismatches. Still
further in accordance with the present invention, displays of patient
motion are made, which displays can be stored and/or printed.
In particular, embodiments of the present invention comprise a computerized
video based system capable of measuring Cartesian coordinates of small
optical targets placed on a surface of a patient and a user interface and
analysis software package. A preferred embodiment of the inventive system
comprises two CCD cameras mounted in a treatment roomed and focused on a
treatment unit isocenter. The cameras are interfaced to a 486 33 MHz PC
via a two channel video board. Inventive passive targets (retroreflective
in the preferred embodiment) are attached to a surface of the patient. The
targets are automatically recognized and extracted by a three-dimensional
(3-D) vision system and the three-dimensional position of each target is
determined using a triangulation algorithm. When the patient moves, the
system senses motion of the targets and reports a change in patient
position. When the targets are placed in the same position on the patient,
from day to day, in accordance with a preferred embodiment of the present
invention, patient setup is reproducibly determined.
As those in the art can readily appreciate, embodiments of the present
invention advantageously enable the positions of the targets, and by
inference the patient, to be determined accurately before radiation is
delivered. In addition, in accordance with such embodiments, relative
motion, i.e., setup position, of the patient from day to day is
determined.
For a fuller understanding of the present invention, reference should now
be made to the following detailed description of the preferred embodiments
of the invention and the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURE
FIG. 1 shows, in pictorial form, an embodiment of the present invention;
FIG. 1a shows, in pictorial form, a target for use in an embodiment of the
present invention;
FIG. 2 shows a device comprised of a set of well-defined targets mounted at
various heights disposed on one side of a thermally stable plate which is
used for calibration in an embodiment of the present invention;
FIG. 3 shows an example of the display of patient treatment and position in
accordance with the present invention; and
FIG. 4 shows base line length B between cameras 150 and 160 and standoff
distance S.
DETAILED DESCRIPTION
FIG. 1 shows, in pictorial form, an embodiment of the present invention. As
shown in FIG. 1, a patient 100 lies on table 110 under gantry 120 of a
radiation therapy machine. Targets 111-114 have been affixed to the chest
of patient 100. As will be described in detail below, in a preferred
embodiment of the present invention, targets 111-114, formed of
retroreflective material which is disposed on one side of a substantially
flat tape and a pressure sensitive adhesive tape disposed on the other
side, are affixed to the patient.
Light sources 130 and 140 provide radiation which impinges upon targets
111-114. In the preferred embodiment of the present invention, light
sources 130 and 140 produce infrared radiation. Infrared radiation is
advantageous in that it enables the system to more readily distinguish
light reflected from the targets, as opposed to background radiation
(interference) that might be available in a therapy room under ambient
lighting conditions. In the preferred embodiment, light sources 130 and
140 are infrared lasers which are commercially available and whose
radiation is spread by lenses so as to illuminate targets 111-114. The use
of laser light sources is advantageous in that the spectral bandwidth of
the radiation is narrow and provides, thereby, a further reduction in
background interference.
Cameras 150 and 160 are focused substantially on table 110 and are standard
512.times.480 pixel CCD cameras which are commercially available.
(Alternatively, higher resolution cameras, such as 1320.times.1035 pixels
available from Videk Megaplus may be used.) In the preferred embodiment,
the cameras are equipped with infrared filters to further reduce detection
of background radiation. Further, the cameras are fixed in position so
that they do not have to be recalibrated often in accordance with the
method described in detail below. The outputs from cameras 150 and 160 are
applied to image acquisition and processing boards (not shown) which are
disposed within a PC-type computer 200. In the preferred embodiment, the
image acquisition boards were purchased from Matrox Corporation as IM-1280
with ASD digitizer and RTP board. Computer 200 is associated with store
210 which is used to store software used in operating computer 200 and is
used to store data received from cameras 150 and 160, from users inputting
data from a keyboard 230, and data produced, in a manner which will be
described in detail below in accordance with the present invention, by
computer 200. A display 220 is utilized to provide the results of
analyses, in a manner which will described in detail below in accordance
with the present invention, by computer 200.
Interface 250 provides communication between the therapy machine, of which
gantry 120 forms a part, and computer 200, which communication will be
described in detail below. Further, positioning apparatus 240 is
configured to receive positioning signals from computer 200 in order to
adjust the position of table 110 and, thereby, patient 100 in a manner
which will be described in detail below.
Embodiments of the present invention include a Vision-based Coordinate
Measurement (VCM) system which is used to measure the positions of the
targets. The VCM software is comprised of a set of library routines which
are utilized to design application programs and to combine the application
programs with application-specific user interface software. In accordance
with a preferred embodiment of the present invention, the library routines
are dynamic link libraries (DLLs) written in C for Microsoft Windows. The
VCM system has been under development at the National Research Council of
Canada for several years and has been described in an article entitled "A
Hierarchical Approach to Stereo Vision" by El-Hakim, S. F.,
Photogrammetric Engineering and Remote Sensing, 55(4), 443-448 (1989), an
article entitled "The VCM Automated 3-D Measurement System--Theory,
Application, and Performance Evaluation" by El-Hakim, S. F., Applications
of Artificial Intelligence X: Machine Vision and Robotics, Proc. SPIE
1708, 460-482 (1992), and an article entitled "Multicamera Vision Based
Approach to Flexible Feature Measurement For Inspection and Reverse
Engineering" by El-Hakim, S. F. and Pizzi, N.J., Optical Engineering,
32(9), 1993, all three articles being incorporated herein by reference. As
shown in the above-described articles, the VCM system is a software
package which can be integrated with commercially available solid-state
cameras, image grab and processing boards, and computer hardware. As | | |
