Stereotaxic
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
MATS
A method
scribed.
for
A head
the exact ordinate diagnostic
stereotaxic
fixation
computed
system
Computed BERGSTROM1
tomography
has been devised
transfer of information system of the scanner coordinate systems.
AND
coor
Several authors have pointed out the potential of using CT to plan examinations such as biopsies [1 ] as well as types of treatment such as dose planning in radiotherapy [2]. An accurate fixation device is the necessary link connecting CT with other diagnostic and therapeutic procedures. We are now developing a fixation system flexible enough to fit various types of examinations and treatment which require accurate localization of the lesion. The prototype descnibed has yielded good results in transferring information obtained
at CT
cal treatment
investigation
[3, 4] and
to the planning
conventional
and
Therapeutic
placed
in position
in such
a manner
that
the
holes
in the
Use of Scanner
to Localize
Target
Point
of radiosurgi-
The coordinates of the chosen target point in the plane of the image may be determined from the printout. A fasten approach is to use the polaroid picture. The length A of the picture matrix across the picture and the distance a from the target point to the edge of the matrix are measured. The coordinate is calculated from x=axl6O/A (fig. 4). Using this procedure the influence of variations in picture size due to inconstancy of the oscilloscope is eliminated. A check of
neurosurgery.
Coordinate
GREITZ1
ring are guided into the holds (fig. 2D). The entire procedune takes about 30 mm. After the scan, the patient is transferred with the fixation device still on the head and is attached to another diagnostic device or therapy unit (fig. 3). The orthoplast bandage can be cut through and stored for future use.
Method
Diagnostic
TORGNY
material usually becomes rigid within 1 0 mm and the patient is then placed in a simulated EMI scanner, the position and angulation of the head being adjusted (fig. 2A). The orthoplast bandage is fixed using aluminium hooks onto a ring which may be applied to the front of the scanner (fig. 2B). The patient walks over to the scanner with the orthoplast bandage and the ring attached to the head (fig. 2C) and is
is de-
enabling
from the diagnostic to other therapeutic
Tomography
Systems
A diagnostic coordinate system is attached to the scanner in such a way that the position of each element in the tomographic picture is defined by a set of coordinates (x, y, z). This coordinate system has a fixed relationship to the opening of the scanner, and consequently any point in the tomographic picture may be related to it. The patient’s head is held in a fixed relationship to the coordinate system by a fixation device that immobilizes him in a given position in relation to the opening of the scanner. A therapeutic coordinate system is attached in an analogous manner to the therapeutic device so that any target point is defined by a set of coordinates (x’, y’, z’). By connecting the fixation device used for the diagnosis to the therapy unit in a well-defined manner, the coordinates of the diagnostic system may be transferred to the therapeutic system. An anatomical detail with coordinates (x, y, z) is chosen as target point and will have the coordinates (x’, y’, z’) which are given by a simple calculation (fig. 1). Hence the target point will be precisely defined in both coordinate systems without any reference to anatomical structures.
this
coordinate
is later
made
by computer
(see
below).
The
vertical coordinate is determined from the picture achieved by reconstruction of an orthogonal plane using densely applied, partly overlapping cuts [5, 6] (fig. 5). The vertical coordinate is defined by the cut intersecting the target point and may be expressed as a given measurement on a vernier scale mounted between the scanner gantry and its
Fixation Device A modified version has been developed of a fixation device used for radiosurgery at Karolinska Sjukhuset (L. Leksell, B. Jernberg, and G. Hammanstr#{246}m, personal communication, 1 975). A piece of thermoplast (Kerr#{174})is shaped to fit the root of the nose. A band of another type of thenmoplast (Orthoplast#{174}) is firmly applied around the patient’s head. Notches are made to leave the eyes free. The plastic Received This work I
Am
February 27, 1 976. was supported by a grant
Department J Roentgeno!
of Neuroradiology. 1 27:
167-1
from
Karolinska 70.
1 976
the
research
Sjukhuset,
funds
5-104
of the
B
A Fig.
1 -Information
therapeutic defines
Karolinska
01 Stockholm.
167
Institutet.
Sweden.
coordinate vertical
coordinate.
transfer
system
from
diagnostic
(B). Tomographic
coordinate
cut
(indicated
system
(A) to
by ellipse)
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
168
BERGSTROM
Simulated scanner opening and water box. B, Plastic of helmet to ring. D, Patient attached to scanner opening. mold over nose root was needed.
Fig. 2.-A.
C, Fixation no plastic
water
box
and
tomographic
used
for
determination
of Target
To check tomography,
the coordinates they are fed
of
the
back
into
the
Area
picture.
of the target into
the
The
area obtained
computer geometry
which of
the
by
the
aid
of a television
system)
and
by
placing
parencies with isodose curves over the monitor, a crude appreciation of the dose distribution can be obtained. When checking the target area, a simultaneous calculation of the coordinates of the therapeutic system is automatically made by computer. Discus&on
plots gamma
lesion is well anticipated in nadiosungical procedures. With the aid of the computer a 50% isodose curve can be plotted into the picture, roughly indicated as an ellipse on a circle [6] (fig. 6). Because the size of the picture element is 1 .5 x .5 mm, no precise isodose curve can be plotted at present. However, by using a magnified EMI picture (e.g., with
GREITZ
bandage fixed by adjustable aluminium hooks to metal ring fitting scanner opening. Since in this case fixation of helmet was improved by inserting screws into calvarium,
cuts.
Delineation
them
accurate
AND
trans-
A fixation device for stereotaxic CT scanning should meet the following criteria : (1 ) be efficient enough to cause a significant decrease in the occurrence of artifacts due to patient movement ; (2) allow reproducible positioning during
procedures
positional relationship interrelated diagnostic simple and accurate
of long
duration
of the patient and therapeutic transformation
; (3)
enable
constant
(target) to various devices and allow a of coordinates be-
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
STEREOTAXIC
3.-Procedure for attaching to fixation device. Coordinates CT scanning are directly transferred Fig.
ment
erence to anatomical
CT
169
Leksell stereotaxic instruof target point obtained at to this system without ref-
landmarks. Fig.
number
4.-Determination
of matrix
of
elements
horizontal
from
edge
=
coordinate. 60/A.
ax
Fig. 5.-Determination of vertical coordinate using reconstruction pictures in lateral and frontal planes. A and B, Reconstruction planes. C and 0, Corresponding results, C=lateral projections, D=frontal projections. Size and extension of pinealoma is clearly visible. Small white spots in C (bottom) and D (middle) represent tip of shunt catheter not seen in planes ofA and B.
Distance
in
BERGSTROM
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170
AND
GREITZ
are taken, the error in transforming the coordinates from the diagnostic to the therapeutic coordinate system is considerably reduced. In experimental models, tumors have been punctured with a standard deviation from the target point of 1 .1 mm. Movement between the plastic helmet and the skull was not taken into account in these studies. Also the center of the tumor model was determined more accurately by plotting attenuation profiles which allowed a target point to be chosen between the centers of adjacent elements. For many purposes the fixation requirements are not this exacting. The plastic helmet may then be applied without screws, becoming a simple procedure which requires no preparation of the patient and can be done outside the scanning room. This less elaborate fixation method has been used in CT examinations of about 50 patients. Three patients have been treated with radiosurgery based on information obtained from stereotaxic CT using the principles Fig.
curve
6.-Pinealoma.
plotted
into
point and rough
Target
picture
estimation
of 50%
described
here.
The
results
will
be published
[7].
isodose
by computer.
REFERENCES TF, Maclntyre WJ, Gonzalez L Tarar A, Zelch MG, Boiler M, Cook SA, Jelden G : Computed tomography of the thorax and abdomen ; a preliminary report. Radiology 1 1 7 : 257-264, 1975 Chernak ES, Rodriguez-Antunez A, Jelden GL Dhaliwal AS, Lavik PS : The use of computed tomography for radiation therapy treatment planning. Radiology 117:613-614, 1975 Leksell L : The stereotaxic method and radiosurgery of the brain. Acta Chir Scand 1 02 : 31 6-31 9, 1951 Leksell L : A note on the treatment of acoustic tumours. Acta Chir Scand 1 37 : 763-765, 1971 Glenn WV, Taveras JM, Johnston BJ, Morton PW, Dwyer SJ:
1 . Alfidi
tween ducibility
these
systems
of positioning
;
and
(4)
give
for examinations
an acceptable at different
reprotimes.
The methods of fixation and transformation of coordinates presented have been used in a limited number of patients. The results are promising and indicate that the fixation obtained in many respects meets the requirements listed above. Accordingly, EMI pictures of improved quality have been obtained due to the decrease in patient movement. It has been possible to pursue time-consuming procedures with good reproducibility of the tomognaphic cuts. Some improvement in the method is necessary since vertical movement of the head was observed in repeat examinations. The mean vertical movement was 3 mm but in one case was 1 3 mm. Work is now in progress to considerably reduce
this error.
The fixation of the plastic inserting two or three metal plastic being molded around
bandage may be improved by screws into the calvanium, the the screws. If these measures
2.
3. 4.
5.
RJ,
Clinical
Haaga
feasibility
transverse presented
of
reconstructing
coronal,
sagittal
Radiology
and
Nuclear
Medicine,
and
thin
CT scans. Paper Tomography in San
Juan,
Puerto
1975
6. BergstrOm tomography. 7.
Meaney
sections from overlapped 8.0 mm at the workshop on Reconstruction
Diagnostic Rico,
J,
M,
Sundman
Nor#{233}nG, Backlund
EO,
acoustic
using
Submitted
A : Picture processing 1 27 : 1 7-21 , 1976
in computed
Am J Roentgenol neuromas
for publication
Bergstrom stereotaxic
M,
Greitz
T : Radiosurgery
computerized
tomography.
of
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
MATS
A method
scribed.
for
A head
the exact ordinate diagnostic
stereotaxic
fixation
computed
system
Computed BERGSTROM1
tomography
has been devised
transfer of information system of the scanner coordinate systems.
AND
coor
Several authors have pointed out the potential of using CT to plan examinations such as biopsies [1 ] as well as types of treatment such as dose planning in radiotherapy [2]. An accurate fixation device is the necessary link connecting CT with other diagnostic and therapeutic procedures. We are now developing a fixation system flexible enough to fit various types of examinations and treatment which require accurate localization of the lesion. The prototype descnibed has yielded good results in transferring information obtained
at CT
cal treatment
investigation
[3, 4] and
to the planning
conventional
and
Therapeutic
placed
in position
in such
a manner
that
the
holes
in the
Use of Scanner
to Localize
Target
Point
of radiosurgi-
The coordinates of the chosen target point in the plane of the image may be determined from the printout. A fasten approach is to use the polaroid picture. The length A of the picture matrix across the picture and the distance a from the target point to the edge of the matrix are measured. The coordinate is calculated from x=axl6O/A (fig. 4). Using this procedure the influence of variations in picture size due to inconstancy of the oscilloscope is eliminated. A check of
neurosurgery.
Coordinate
GREITZ1
ring are guided into the holds (fig. 2D). The entire procedune takes about 30 mm. After the scan, the patient is transferred with the fixation device still on the head and is attached to another diagnostic device or therapy unit (fig. 3). The orthoplast bandage can be cut through and stored for future use.
Method
Diagnostic
TORGNY
material usually becomes rigid within 1 0 mm and the patient is then placed in a simulated EMI scanner, the position and angulation of the head being adjusted (fig. 2A). The orthoplast bandage is fixed using aluminium hooks onto a ring which may be applied to the front of the scanner (fig. 2B). The patient walks over to the scanner with the orthoplast bandage and the ring attached to the head (fig. 2C) and is
is de-
enabling
from the diagnostic to other therapeutic
Tomography
Systems
A diagnostic coordinate system is attached to the scanner in such a way that the position of each element in the tomographic picture is defined by a set of coordinates (x, y, z). This coordinate system has a fixed relationship to the opening of the scanner, and consequently any point in the tomographic picture may be related to it. The patient’s head is held in a fixed relationship to the coordinate system by a fixation device that immobilizes him in a given position in relation to the opening of the scanner. A therapeutic coordinate system is attached in an analogous manner to the therapeutic device so that any target point is defined by a set of coordinates (x’, y’, z’). By connecting the fixation device used for the diagnosis to the therapy unit in a well-defined manner, the coordinates of the diagnostic system may be transferred to the therapeutic system. An anatomical detail with coordinates (x, y, z) is chosen as target point and will have the coordinates (x’, y’, z’) which are given by a simple calculation (fig. 1). Hence the target point will be precisely defined in both coordinate systems without any reference to anatomical structures.
this
coordinate
is later
made
by computer
(see
below).
The
vertical coordinate is determined from the picture achieved by reconstruction of an orthogonal plane using densely applied, partly overlapping cuts [5, 6] (fig. 5). The vertical coordinate is defined by the cut intersecting the target point and may be expressed as a given measurement on a vernier scale mounted between the scanner gantry and its
Fixation Device A modified version has been developed of a fixation device used for radiosurgery at Karolinska Sjukhuset (L. Leksell, B. Jernberg, and G. Hammanstr#{246}m, personal communication, 1 975). A piece of thermoplast (Kerr#{174})is shaped to fit the root of the nose. A band of another type of thenmoplast (Orthoplast#{174}) is firmly applied around the patient’s head. Notches are made to leave the eyes free. The plastic Received This work I
Am
February 27, 1 976. was supported by a grant
Department J Roentgeno!
of Neuroradiology. 1 27:
167-1
from
Karolinska 70.
1 976
the
research
Sjukhuset,
funds
5-104
of the
B
A Fig.
1 -Information
therapeutic defines
Karolinska
01 Stockholm.
167
Institutet.
Sweden.
coordinate vertical
coordinate.
transfer
system
from
diagnostic
(B). Tomographic
coordinate
cut
(indicated
system
(A) to
by ellipse)
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
168
BERGSTROM
Simulated scanner opening and water box. B, Plastic of helmet to ring. D, Patient attached to scanner opening. mold over nose root was needed.
Fig. 2.-A.
C, Fixation no plastic
water
box
and
tomographic
used
for
determination
of Target
To check tomography,
the coordinates they are fed
of
the
back
into
the
Area
picture.
of the target into
the
The
area obtained
computer geometry
which of
the
by
the
aid
of a television
system)
and
by
placing
parencies with isodose curves over the monitor, a crude appreciation of the dose distribution can be obtained. When checking the target area, a simultaneous calculation of the coordinates of the therapeutic system is automatically made by computer. Discus&on
plots gamma
lesion is well anticipated in nadiosungical procedures. With the aid of the computer a 50% isodose curve can be plotted into the picture, roughly indicated as an ellipse on a circle [6] (fig. 6). Because the size of the picture element is 1 .5 x .5 mm, no precise isodose curve can be plotted at present. However, by using a magnified EMI picture (e.g., with
GREITZ
bandage fixed by adjustable aluminium hooks to metal ring fitting scanner opening. Since in this case fixation of helmet was improved by inserting screws into calvarium,
cuts.
Delineation
them
accurate
AND
trans-
A fixation device for stereotaxic CT scanning should meet the following criteria : (1 ) be efficient enough to cause a significant decrease in the occurrence of artifacts due to patient movement ; (2) allow reproducible positioning during
procedures
positional relationship interrelated diagnostic simple and accurate
of long
duration
of the patient and therapeutic transformation
; (3)
enable
constant
(target) to various devices and allow a of coordinates be-
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
STEREOTAXIC
3.-Procedure for attaching to fixation device. Coordinates CT scanning are directly transferred Fig.
ment
erence to anatomical
CT
169
Leksell stereotaxic instruof target point obtained at to this system without ref-
landmarks. Fig.
number
4.-Determination
of matrix
of
elements
horizontal
from
edge
=
coordinate. 60/A.
ax
Fig. 5.-Determination of vertical coordinate using reconstruction pictures in lateral and frontal planes. A and B, Reconstruction planes. C and 0, Corresponding results, C=lateral projections, D=frontal projections. Size and extension of pinealoma is clearly visible. Small white spots in C (bottom) and D (middle) represent tip of shunt catheter not seen in planes ofA and B.
Distance
in
BERGSTROM
Downloaded from www.ajronline.org by NYU Langone Med Ctr-Sch of Med on 05/02/15 from IP address 128.122.253.212. Copyright ARRS. For personal use only; all rights reserved
170
AND
GREITZ
are taken, the error in transforming the coordinates from the diagnostic to the therapeutic coordinate system is considerably reduced. In experimental models, tumors have been punctured with a standard deviation from the target point of 1 .1 mm. Movement between the plastic helmet and the skull was not taken into account in these studies. Also the center of the tumor model was determined more accurately by plotting attenuation profiles which allowed a target point to be chosen between the centers of adjacent elements. For many purposes the fixation requirements are not this exacting. The plastic helmet may then be applied without screws, becoming a simple procedure which requires no preparation of the patient and can be done outside the scanning room. This less elaborate fixation method has been used in CT examinations of about 50 patients. Three patients have been treated with radiosurgery based on information obtained from stereotaxic CT using the principles Fig.
curve
6.-Pinealoma.
plotted
into
point and rough
Target
picture
estimation
of 50%
described
here.
The
results
will
be published
[7].
isodose
by computer.
REFERENCES TF, Maclntyre WJ, Gonzalez L Tarar A, Zelch MG, Boiler M, Cook SA, Jelden G : Computed tomography of the thorax and abdomen ; a preliminary report. Radiology 1 1 7 : 257-264, 1975 Chernak ES, Rodriguez-Antunez A, Jelden GL Dhaliwal AS, Lavik PS : The use of computed tomography for radiation therapy treatment planning. Radiology 117:613-614, 1975 Leksell L : The stereotaxic method and radiosurgery of the brain. Acta Chir Scand 1 02 : 31 6-31 9, 1951 Leksell L : A note on the treatment of acoustic tumours. Acta Chir Scand 1 37 : 763-765, 1971 Glenn WV, Taveras JM, Johnston BJ, Morton PW, Dwyer SJ:
1 . Alfidi
tween ducibility
these
systems
of positioning
;
and
(4)
give
for examinations
an acceptable at different
reprotimes.
The methods of fixation and transformation of coordinates presented have been used in a limited number of patients. The results are promising and indicate that the fixation obtained in many respects meets the requirements listed above. Accordingly, EMI pictures of improved quality have been obtained due to the decrease in patient movement. It has been possible to pursue time-consuming procedures with good reproducibility of the tomognaphic cuts. Some improvement in the method is necessary since vertical movement of the head was observed in repeat examinations. The mean vertical movement was 3 mm but in one case was 1 3 mm. Work is now in progress to considerably reduce
this error.
The fixation of the plastic inserting two or three metal plastic being molded around
bandage may be improved by screws into the calvanium, the the screws. If these measures
2.
3. 4.
5.
RJ,
Clinical
Haaga
feasibility
transverse presented
of
reconstructing
coronal,
sagittal
Radiology
and
Nuclear
Medicine,
and
thin
CT scans. Paper Tomography in San
Juan,
Puerto
1975
6. BergstrOm tomography. 7.
Meaney
sections from overlapped 8.0 mm at the workshop on Reconstruction
Diagnostic Rico,
J,
M,
Sundman
Nor#{233}nG, Backlund
EO,
acoustic
using
Submitted
A : Picture processing 1 27 : 1 7-21 , 1976
in computed
Am J Roentgenol neuromas
for publication
Bergstrom stereotaxic
M,
Greitz
T : Radiosurgery
computerized
tomography.
of
