Inf J. Radiation Oncology @ Pergamon Press Ltd..
Bid. Phys., Vol. 5, pp. 573-519 Printed in the U.S.A. 1979.
??Technical Innovation
and Note
COMPUTERIZED INTERNAL MAMMARY LYMPHOSCINTIGRAPHY IN RADIATION TREATMENT PLANNING OF PATIENTS WITH BREAST CARCINOMA? MICHAEL J. BRONSKILL, Ph.D.,* GEORGE HARAUZ, B.A.Sc.6 and G~~NEZ N. EGE, M.D., F.R.C.S., D.M.R.T., F.R.C.R., F.R.C.P.(C)y University of Toronto, Canada A method is described which uses a minicomputer system to obtain full size plots of internal mammary lymphoscintigrams. In order to facilitate accurate radiation therapy treatment planning, individual lymph nodes are outlined and their positions determined precisely with respect to sternal notch and xiphisternal markers. Computerized
lymphoscintigraphy,
Parasternal
radiation
INTRODUCTION
treatment,
Carcinoma
of the breast.
3. In a multiple field technique, the junction between supraclavicular and parasternal portals gives rise to inhomogeneity of radiation dose to retroclavicular nodes. Internal mammary lymphoscintigraphy provides not only a technique for visualization and comparison of the parasternal nodes, but also the means of localizing individual lymphatic aggregates in relation to standard landmarks for greater accuracy in treatment planning. Attempts to overcome the problems discussed above can thus be made. We have developed a computerized system designed to produce a full size plot of the lymphatics invisualized with lymphoscintigraphy, for dividualized treatment planning. The development, implementation, and features of this system are described in this article.
It has been the policy in the primary
management of patients with breast carcinoma and histological evidence of axillary involvement to supplement surgery with external radiation to ipsilateral lymph node drainage areas, in an attempt to eliminate tumor residues. In spite of sophisticated advances in external radiation technology, doubt persists regarding the contribution of radiation to the control of breast carcinoma.’ Recent articles24 on the use of interstitially introduced radiocolloids for visualization of parasternal lymphatics have revealed shortcomings in the attempted management of breast carcinoma without an accurate knowledge of the anatomy and pathology of the parasternal lymphatics in the individual patient. Specific inadequacies in conventional management, including radiation techniques, which have been brought to light by internal mammary lymphoscintigraphy include the following observations: 1. In 30% of patients, parasternal nodes lie outside standardized radiation portals. 2. 15% of patients demonstrate cross drainage between parasternal lymphatics, implying significant risk of extension of disease to contralateral parasternal nodes.
METHODS AND MATERIALS Internal mammary lymphoscintigraphy was carried out in patients with breast carcinoma with the ipsilateral subcostal injection of 500 PCi of 99mT~antimony colloid,]) followed at 3 hr with a scintigraphic image. The contralateral injection was then performed and the final image obtained 3 hr later. Delaying the second injection makes it possible to demonstrate
tThis work was supported by the Ontario Cancer Treatment and Research Foundation (Grant No. 356) and the National Cancer Institute of Canada. SStaff Physicist, The Ontario Cancer Institute (incorporating the Princess Margaret Hospital), and Assistant Professor, Department of Medical Biophysics. §Graduate Student, Department of Medical Biophysics. THead, Department of Nuclear Medicine, The Princess Margaret Hospital, and Assistant Professor, Department of Radiology.
[(For information on commercial availability, contact Union Carbide Corp., Tuxedo, New York, U.S.A. Reprint requests to: M. J. Bronskill, Ph.D., The Ontario Cancer Institute 500 Sherbourne Street, Toronto, Ontario, M4X lK9, Canada. Acknowledgements-John Watts and Lee Santon constructed and calibrated the scintillation camera-minicomputer interface. Barbara MataniC assisted in the preparation of the manuscript. Accepted for publication 15 November 1978. 573
514
Radiation Oncology 0 Biology 0 Physics
crossover in lymphatic drainage pathways, anatomic variants and other parameters relevant to the interpretation of the study. Images were obtained with scintillation camera,? interfaced’ to a remote computer.+ The lymphoscintigram was recorded as a 64 x 64 matrix in the computer memory, representing a single 7.5 min image or node frame. The positions of the sternal notch and xiphisternum were obtained by imaging superimposed ‘33Ba spot markers (= 25 PCi distributed within the center 3 mm of a 2.5 cm plastic disk) for a 15 set marker frame prior to the node frame. The x and y coordinates of the two markers were obtained by dividing the field of view into upper and lower halves and calculating the mean x and y coordinates for all counts greater than 20% of the maximum count recorded in the field of view. This calculation is described in Fig. 1. The position of the individual lymph nodes was more difficult to obtain. Interpolated isocount lines were found to be incapable of detecting nodes against background noise, especially of liver activity, and individual nodes were portrayed much larger than in the 70 mm 1ymphoscintigram.B A method for outlining individual or aggregated lymph nodes using spatial differentiation and the calculation of isogradient lines
Fig. 1. Procedure for calculating position of the sternal notch and xiphisternal markers. The marker frame is shown at left with a hexagonal pattern because of septal penetration around each marker. The equations for calculating the sternal notch coordinates (X,,, Y,,) are shown at right. Only the upper half of the matrix (above the arrow) is considered. The coordinates of the xiphisternum are calculated similarly using the lower half of the matrix. Here, s(i, j) is the (i, j)th element of the digitized marker frame and sthr is a threshold value chosen as 20% of the maximum element to eliminate background.
SOhio-Nuclear Inc., Cleveland, Ohio, U.S.A. Model 110. *Digital Equipment Corp., Maynard, Mass., U.S.A., PDP 1 l/40.
April 1979, Volume 5, Number 4
was developed and proved to be satisfactory. Specific details of this procedure are given in the Appendix. The actual plots are produced using digital plotter1 with data transmission from the computer at 30 characters per sec. All data acquisition and processing programs were written in Fortran with the exception of a few Macro subroutines. Two operating systems have been used.11
RESULTS Because the resultant plots were to be used for individualized radiation therapy planning, the accuracy and linearity of this plotting method were tested carefully. Analog-to-digital converter gains in the computer interface were adjusted precisely. Marker position accuracy was then tested with a sheet of graph paper taped to the face of the collimator. Calculated marker position was compared to actual position and the largest discrepancy observed was 4mm. This error is comparable to that made positioning the marker on the patient. Typically about 20,000 counts are recorded in the 15 set marker frame. The accuracy of the isogradient technique in locating lymph nodes was tested similarly using 57Co spot markers which duplicated the size and number of counts observed with nodes. The spatial accuracy achieved was slightly worse than that with the ‘33Ba markers, because individual nodes have fewer counts and are distributed in relatively few matrix elements. The depicted size of the nodes depends on the isogradient level chosen for the plot. Using edge detection we find an isogradient level of 200 to yield a plot with node size slightly smaller than that observed in the 70 mm scintigram (see Appendix). Using this isogradient level, the center of the isogradient contour around a j7Co marker was always located within 5 mm of its true position, usually within 2 or 3 mm. Note that these tests of positional accuracy also include the nonlinearity of the scintillation camera itself. During the 7.5 min node frame, approximately 800,000 counts are accepted by the scintillation camera (mainly in the injection sites) and less than 1% are not recorded by the computer, primarily the result of analog-to-digital converter deadtime. The actual spatial differentiation and isogradient calculation followed by the plotting takes approximately one minute on the computer, depending on the complexity of the node pattern for individual patients. In Fig. 2 the plot obtained for a normal parasternal
$Kodak PF film. TTektronix Inc., Beaverton, Oregon, Model 4662. IIDigital Equipment Corp., RT-11 and RSX-1lM.
575
Computerized internal mammary lymphoscintigraphy 0 M. J. BRONSKILL etal.
‘w’ '5
CM
1
,
+SN
‘8310 AM 25-APQ-78 ISCGRADIENT = 200 TOTAL COgNTS = 647-32
Fig. 3. Following the left subcostal injection, right upper parasternal nodes are demonstrated in continuity with left parasternal nodes, indicating presence of substernal cross drainage.
--
5c1.1 SN
1 A 0
>i L
i8313 PM 25-APR-78 ISOGRADIENT = 200 TOTAL COUWTS = 909934
1
Fig. 2. (A) Normal internal mammary lymphoscintigram demonstrating subcostal injection sites and bilateral parasternal nodes. (B) Corresponding computerized lymph node plot; actual plot is full size.
lymph node pattern is compared to the corresponding 70 mm scintigram. The data for the two images is usually captured simultaneously. An example of cross
drainage is shown in Fig. 3. The discrepancy between conventional radiation portals (6 x 18 cm) and a laterally situated parasternal node shown in Fig. 4 demonstrates how easy it is to exclude nodes from standardized treatment fields. DISCUSSION This computerized plotting system produces full scale plots of the parasternal lymphatics, as imaged by lymphoscintigraphy, maintaining spatial accuracy within a few millimeters. Using these plots, and the
9
$XPU
i 16974 PM 4-NOV.77 SOGRADIENT : ZOO TOTAL COUNTS =653927
Fig. 4. Lymph node plot with superimposed conventional radiation portal. Upper left parasternaf node is partially excluded from the treatment field.
sternal notch and xiphisternum as landmarks, the radiation oncologist can determine the optimum field size and configuration while taking into consideration the presence or absence of cross drainage, the level of cross drainage and the contralateral lymphatics which may be at risk. The controversy concerning the efficacy of radia-
576
Radiation Oncology 0 Biology 0 Physics
tion in the management of breast carcinoma will, no doubt, continue. The disparity between parasternal lymphatics and standard radiation portals (Item 1, above and Fig. 4) can, however, be resolved with
lymphoscintigraphy and the plotting system described. The radiation oncologist is now in a position to assess and treat accurately the potential of parasternal lymphatics as a tumor reservoir which is often overlooked because of the low incidence of clinicallyapparent parasternal recurrence. The isogradient plotting technique described has a potential application in the quantifying of individual lymph node radiocolloid uptake. Work is underway to determine accurately the number of counts enclosed within individual isogradient contours. This capability will alleviate the present influence of film type and film processing on the interpretation of the lymphoscintigram.? Quantified isogradient plots should
April 1979, Volume 5, Number 4
also be kinetics.
useful
tools
for
investigating
lymphatic
CONCLUSION
date, 1009 patients have had the benefit of computerized internal mammary lymphoscintigraphy in the planning of their radiation therapy at this institute. Knowledge of the precise location of parasternal nodes and any lymphatic communication between parasternal chains eliminates the inaccuracy and inhomogeneity of dose distribution inherent in standardized multiple field techniques. It is anticipated that the refinement of such individualized radiation treatment planning may alter favorably the prognosis of early breast carcinoma in circumstances where disease may still be confined to drainage lymphatics. To
REFERENCES Brinkley, D.: The role of postoperative radiotherapy. In Breast Cancer Management-Early and Late, ed. by Stoll, B.A., Chicago, Heinemann Medical Books, 1977, pp. 67-76. Ege, G.N.: Internal mammary lymphoscintigraphy-the rationale, technique, interpretation and clinical application: a review based on 848 cases. Radiology 118: 101-107, 1976. Ege, G.N.: Internal mammary lymphoscintigraphy in breast-carcinoma: a study of 1072 patients. Int. J. Radiat. Oncol. Biol. Phys. 2: 755-761, 1977. Rose, C.M., Kaplan, W.D., Marck, A.: Lymphoscintigraphy of internal mammary lymph nodes. Int. J. Radiat. Oncol. Biol. Phys. 2: 102, 1977.
5. Santon, L.W., Prato, F.S., Aspin, N.: Long-distance transmission of digital scintillation camera signals. J. Nucl. Med. 17: 394-3%, 1976. 6. Sutro, L.L., Kilmer, W.L.: Assembly of computers to command and control a robot. In 1%9 Spring Joint Computer Conf. 14-16 May, Boston, Mass., AFZPS Conf. Proc. Vol. 34. Mount Vale, New Jersey, American Federation of Information Processing Societies Press, 1%9, pp. 113-137. S.A., Aggarwal, J.K.: Methods of edge 7. Underwood, detection in visual scenes. In Proc. of the 1973 IEEE Symposium on Circuit Theory, IEEE Cat. No. 73CH0 Institute of Electrical and Electronics 7658CT. Engineers, New York, pp. 45-51.
APPENDIX Edge detection in the digitized lymphoscintigram
Individual lymph nodes in the lymphoscintigrams represent structures varying in size from 3 to 10 mm and contain several times more counts than the surrounding background. As seen in Fig. 2, however, background levels differ significantly in the image, especially over the liver and near the injection sites. The individual lymph nodes are best characterized by edges or sharp changes in intensity. In order to detect edges, the digitized 64 x 64 lymphoscintigram matrix (or node frame) is processed with a small, square, 3 x 3 window or local differential operator which accentuates the presence of edges. The 3 X 3 operator is a good size for this application. A 2 x 2 operator is too small because the finite spatial resolution of the scintillation camera tends to smear
tWe have found that the clinical interpretation influenced by film type, and recommend at present
can be the use
structures across adjacent matrix elments. Larger operators tend to miss the small node structures. Underwood and Aggarwal describe several 3 x 3 differential operators.’ In general, the results of an edge detection procedure depend on prior image processing such as smoothing or nonlinear enhancement. In our case no prior image processing is done and good edge detection in our application is achieved with a method from Sutro and Kilmer.6 The differential image is calculated according to: d(i, j)=
s g k=i-1
(s(i, j)-
s(k, I))
(1)
[=j-1
where s(k, 1) is the (k, 1)th element (or pixel) of the original digitized lymphoscintigram and d(i, j) is the
of Kodak PF 70 mm film for lymphoscintigraphy.
Computerized
internal
mammary
lymphoscintigraphy
0 M. J. BRONSKILL etal.
577
, b)
64 18359 1 .........
PM ,
Z-MAY-78
lSOGRADlENT=200
rl,
I
,
................. ......... * ........................... t
!
,I , ......
/
..(. , ,‘,
1
1
I
........
..
‘-COLUMN I .........
...................
1
........ -39.
Fig. Al. (a) Broad Gaussian, u = 10.0. (b) The differential matrix for (a). The central peak is narrower than the original Gaussian. :o:
48
._:d
I’:““’ .,...I
I....
-.
)..‘.
P.O:@
56_.
:
_.........,
:
:
:
:
0
I
: .,. f 0. ,
.,
:.:.
,. ::..
1
.-
-
&
zoi
bl MAXIMUM
100
ELEMENT
=
Fig. A3. (a) Normal internal mammary lymphoscintigram. (b) Corresponding lymph node plot with a grid superimposed, indicating the centers of differential matrix elements, d(i, i).
i
Fig. A2. (a) Narrow Gaussian, (T = 1.0. (b) The differential matrix for (a). Figs. Al(B) and A2(B) have similar shapes.
(i j)th element of the differential matrix. Each pixel represents a square area of 0.44 cm* and s(k, 1) is in units of counts/pixel. Parasternal lymph nodes are usually small structures and may be considered as point sources. They are embedded in tissue, a scattering medium, at a depth of at least 5 cm from the face of the scintillation camera collimator. The full width at half maximum (FWHM) of the point spread function at such a depth is about 8 mm for our scintillation camera, ignoring scattering. Thus, the lymph node images are approximately Gaussian in shape and are larger than the lymph nodes themselves. The following one-dimensional Gaussian function was used to
518
Radiation Oncology 0 Biology 0 Physics
r
PROFILE
OF ROW 29;
PROFILE
OF COLUMN
April 1979, Volume 5, Number 4
MAXIMUM
39 ;
ELEMENT
MAXIMUM
= 6247
ELEMENT=
I
243356
b)
Fig. A4. (a) Profile through row 29 of the lymph node matrix in A3(b), showing 2 lymph nodes. These profiles
are similar to those of Fig. A2(b). The isogradient level of 200 is sufficient to distinguish lymph nodes from background noise. (b) Profile through column 39, showing a lymph node (small bump at pixel 45) and an injection site. This profile is shown on a scale approximately 40 times less sensitive than Fig. A4(a). On this scale the tendency of this differential operator to produce concentric circles for large structures such as the injection
site is revealed.
represent
lymph node images:
s(i) = 100 exp (- (i - 50)*/2o*), i = 1,100
(2)
u = 1.0 was chosen to represent a small node and u = 10.0 was chosen to represent a very large node. The differential matrix in one dimension is calculated according to: d(i) = 2 X s(i) - s(i + 1) - s(i - 1).
(3)
The effect of this edge detection operator is shown in Figs. Al and A2; the edges of the simulated node are detected and the size of the node is reduced somewhat. Because this operator also amplifies background “noise” in the image, an appropriate isogradient level which separates nodes from noise can only be chosen by detailed examination of actual lymphoscintigram matrices. In Fig. A3, a grid is superimposed on the isogradient plot and profiles through row 29 and column
Computerized
18359 PM ISOGRADIENT
2-MAY-78 = 100
internal mammary lymphoscintigraphy
161116
Fig. A5. The lymphoscintigram of Fig. A3(a) plotted at a lower isogradient level (100.) than in A3(b). Note the increased amount of noise in this plot, particularly over the liver.
0 M. J. BRONSKILL et al.
579
39 of the differential matrix are shown in Fig. A4. An isogradient of amplitude 200 is usually adequate to suppress background and outline individual nodes by interpolation between differential matrix elements. As shown in Fig. AS, a lower isogradient contour tends to find structures in background noise. This technique is effective only for small structures, however, and large structures (such as injection sites) with a broad, flat-topped profile tend to appear as 2 concentric circles. This effect is shown for one injection site in Figs. A3 and A4. Only a portion of the field of view of the scintillation camera can be plotted full size on a sheet of 11 x 14 in graph paper. The positions of the sternal notch and xiphisternum, obtained from the marker frame, are used to center an 8 x 12.5 in window on the differential matrix and only isogradient contours within this window are calculated and plotted. This feature has the added advantage of compensating for the off-center positioning of the patient under the scintillation camera.
Bid. Phys., Vol. 5, pp. 573-519 Printed in the U.S.A. 1979.
??Technical Innovation
and Note
COMPUTERIZED INTERNAL MAMMARY LYMPHOSCINTIGRAPHY IN RADIATION TREATMENT PLANNING OF PATIENTS WITH BREAST CARCINOMA? MICHAEL J. BRONSKILL, Ph.D.,* GEORGE HARAUZ, B.A.Sc.6 and G~~NEZ N. EGE, M.D., F.R.C.S., D.M.R.T., F.R.C.R., F.R.C.P.(C)y University of Toronto, Canada A method is described which uses a minicomputer system to obtain full size plots of internal mammary lymphoscintigrams. In order to facilitate accurate radiation therapy treatment planning, individual lymph nodes are outlined and their positions determined precisely with respect to sternal notch and xiphisternal markers. Computerized
lymphoscintigraphy,
Parasternal
radiation
INTRODUCTION
treatment,
Carcinoma
of the breast.
3. In a multiple field technique, the junction between supraclavicular and parasternal portals gives rise to inhomogeneity of radiation dose to retroclavicular nodes. Internal mammary lymphoscintigraphy provides not only a technique for visualization and comparison of the parasternal nodes, but also the means of localizing individual lymphatic aggregates in relation to standard landmarks for greater accuracy in treatment planning. Attempts to overcome the problems discussed above can thus be made. We have developed a computerized system designed to produce a full size plot of the lymphatics invisualized with lymphoscintigraphy, for dividualized treatment planning. The development, implementation, and features of this system are described in this article.
It has been the policy in the primary
management of patients with breast carcinoma and histological evidence of axillary involvement to supplement surgery with external radiation to ipsilateral lymph node drainage areas, in an attempt to eliminate tumor residues. In spite of sophisticated advances in external radiation technology, doubt persists regarding the contribution of radiation to the control of breast carcinoma.’ Recent articles24 on the use of interstitially introduced radiocolloids for visualization of parasternal lymphatics have revealed shortcomings in the attempted management of breast carcinoma without an accurate knowledge of the anatomy and pathology of the parasternal lymphatics in the individual patient. Specific inadequacies in conventional management, including radiation techniques, which have been brought to light by internal mammary lymphoscintigraphy include the following observations: 1. In 30% of patients, parasternal nodes lie outside standardized radiation portals. 2. 15% of patients demonstrate cross drainage between parasternal lymphatics, implying significant risk of extension of disease to contralateral parasternal nodes.
METHODS AND MATERIALS Internal mammary lymphoscintigraphy was carried out in patients with breast carcinoma with the ipsilateral subcostal injection of 500 PCi of 99mT~antimony colloid,]) followed at 3 hr with a scintigraphic image. The contralateral injection was then performed and the final image obtained 3 hr later. Delaying the second injection makes it possible to demonstrate
tThis work was supported by the Ontario Cancer Treatment and Research Foundation (Grant No. 356) and the National Cancer Institute of Canada. SStaff Physicist, The Ontario Cancer Institute (incorporating the Princess Margaret Hospital), and Assistant Professor, Department of Medical Biophysics. §Graduate Student, Department of Medical Biophysics. THead, Department of Nuclear Medicine, The Princess Margaret Hospital, and Assistant Professor, Department of Radiology.
[(For information on commercial availability, contact Union Carbide Corp., Tuxedo, New York, U.S.A. Reprint requests to: M. J. Bronskill, Ph.D., The Ontario Cancer Institute 500 Sherbourne Street, Toronto, Ontario, M4X lK9, Canada. Acknowledgements-John Watts and Lee Santon constructed and calibrated the scintillation camera-minicomputer interface. Barbara MataniC assisted in the preparation of the manuscript. Accepted for publication 15 November 1978. 573
514
Radiation Oncology 0 Biology 0 Physics
crossover in lymphatic drainage pathways, anatomic variants and other parameters relevant to the interpretation of the study. Images were obtained with scintillation camera,? interfaced’ to a remote computer.+ The lymphoscintigram was recorded as a 64 x 64 matrix in the computer memory, representing a single 7.5 min image or node frame. The positions of the sternal notch and xiphisternum were obtained by imaging superimposed ‘33Ba spot markers (= 25 PCi distributed within the center 3 mm of a 2.5 cm plastic disk) for a 15 set marker frame prior to the node frame. The x and y coordinates of the two markers were obtained by dividing the field of view into upper and lower halves and calculating the mean x and y coordinates for all counts greater than 20% of the maximum count recorded in the field of view. This calculation is described in Fig. 1. The position of the individual lymph nodes was more difficult to obtain. Interpolated isocount lines were found to be incapable of detecting nodes against background noise, especially of liver activity, and individual nodes were portrayed much larger than in the 70 mm 1ymphoscintigram.B A method for outlining individual or aggregated lymph nodes using spatial differentiation and the calculation of isogradient lines
Fig. 1. Procedure for calculating position of the sternal notch and xiphisternal markers. The marker frame is shown at left with a hexagonal pattern because of septal penetration around each marker. The equations for calculating the sternal notch coordinates (X,,, Y,,) are shown at right. Only the upper half of the matrix (above the arrow) is considered. The coordinates of the xiphisternum are calculated similarly using the lower half of the matrix. Here, s(i, j) is the (i, j)th element of the digitized marker frame and sthr is a threshold value chosen as 20% of the maximum element to eliminate background.
SOhio-Nuclear Inc., Cleveland, Ohio, U.S.A. Model 110. *Digital Equipment Corp., Maynard, Mass., U.S.A., PDP 1 l/40.
April 1979, Volume 5, Number 4
was developed and proved to be satisfactory. Specific details of this procedure are given in the Appendix. The actual plots are produced using digital plotter1 with data transmission from the computer at 30 characters per sec. All data acquisition and processing programs were written in Fortran with the exception of a few Macro subroutines. Two operating systems have been used.11
RESULTS Because the resultant plots were to be used for individualized radiation therapy planning, the accuracy and linearity of this plotting method were tested carefully. Analog-to-digital converter gains in the computer interface were adjusted precisely. Marker position accuracy was then tested with a sheet of graph paper taped to the face of the collimator. Calculated marker position was compared to actual position and the largest discrepancy observed was 4mm. This error is comparable to that made positioning the marker on the patient. Typically about 20,000 counts are recorded in the 15 set marker frame. The accuracy of the isogradient technique in locating lymph nodes was tested similarly using 57Co spot markers which duplicated the size and number of counts observed with nodes. The spatial accuracy achieved was slightly worse than that with the ‘33Ba markers, because individual nodes have fewer counts and are distributed in relatively few matrix elements. The depicted size of the nodes depends on the isogradient level chosen for the plot. Using edge detection we find an isogradient level of 200 to yield a plot with node size slightly smaller than that observed in the 70 mm scintigram (see Appendix). Using this isogradient level, the center of the isogradient contour around a j7Co marker was always located within 5 mm of its true position, usually within 2 or 3 mm. Note that these tests of positional accuracy also include the nonlinearity of the scintillation camera itself. During the 7.5 min node frame, approximately 800,000 counts are accepted by the scintillation camera (mainly in the injection sites) and less than 1% are not recorded by the computer, primarily the result of analog-to-digital converter deadtime. The actual spatial differentiation and isogradient calculation followed by the plotting takes approximately one minute on the computer, depending on the complexity of the node pattern for individual patients. In Fig. 2 the plot obtained for a normal parasternal
$Kodak PF film. TTektronix Inc., Beaverton, Oregon, Model 4662. IIDigital Equipment Corp., RT-11 and RSX-1lM.
575
Computerized internal mammary lymphoscintigraphy 0 M. J. BRONSKILL etal.
‘w’ '5
CM
1
,
+SN
‘8310 AM 25-APQ-78 ISCGRADIENT = 200 TOTAL COgNTS = 647-32
Fig. 3. Following the left subcostal injection, right upper parasternal nodes are demonstrated in continuity with left parasternal nodes, indicating presence of substernal cross drainage.
--
5c1.1 SN
1 A 0
>i L
i8313 PM 25-APR-78 ISOGRADIENT = 200 TOTAL COUWTS = 909934
1
Fig. 2. (A) Normal internal mammary lymphoscintigram demonstrating subcostal injection sites and bilateral parasternal nodes. (B) Corresponding computerized lymph node plot; actual plot is full size.
lymph node pattern is compared to the corresponding 70 mm scintigram. The data for the two images is usually captured simultaneously. An example of cross
drainage is shown in Fig. 3. The discrepancy between conventional radiation portals (6 x 18 cm) and a laterally situated parasternal node shown in Fig. 4 demonstrates how easy it is to exclude nodes from standardized treatment fields. DISCUSSION This computerized plotting system produces full scale plots of the parasternal lymphatics, as imaged by lymphoscintigraphy, maintaining spatial accuracy within a few millimeters. Using these plots, and the
9
$XPU
i 16974 PM 4-NOV.77 SOGRADIENT : ZOO TOTAL COUNTS =653927
Fig. 4. Lymph node plot with superimposed conventional radiation portal. Upper left parasternaf node is partially excluded from the treatment field.
sternal notch and xiphisternum as landmarks, the radiation oncologist can determine the optimum field size and configuration while taking into consideration the presence or absence of cross drainage, the level of cross drainage and the contralateral lymphatics which may be at risk. The controversy concerning the efficacy of radia-
576
Radiation Oncology 0 Biology 0 Physics
tion in the management of breast carcinoma will, no doubt, continue. The disparity between parasternal lymphatics and standard radiation portals (Item 1, above and Fig. 4) can, however, be resolved with
lymphoscintigraphy and the plotting system described. The radiation oncologist is now in a position to assess and treat accurately the potential of parasternal lymphatics as a tumor reservoir which is often overlooked because of the low incidence of clinicallyapparent parasternal recurrence. The isogradient plotting technique described has a potential application in the quantifying of individual lymph node radiocolloid uptake. Work is underway to determine accurately the number of counts enclosed within individual isogradient contours. This capability will alleviate the present influence of film type and film processing on the interpretation of the lymphoscintigram.? Quantified isogradient plots should
April 1979, Volume 5, Number 4
also be kinetics.
useful
tools
for
investigating
lymphatic
CONCLUSION
date, 1009 patients have had the benefit of computerized internal mammary lymphoscintigraphy in the planning of their radiation therapy at this institute. Knowledge of the precise location of parasternal nodes and any lymphatic communication between parasternal chains eliminates the inaccuracy and inhomogeneity of dose distribution inherent in standardized multiple field techniques. It is anticipated that the refinement of such individualized radiation treatment planning may alter favorably the prognosis of early breast carcinoma in circumstances where disease may still be confined to drainage lymphatics. To
REFERENCES Brinkley, D.: The role of postoperative radiotherapy. In Breast Cancer Management-Early and Late, ed. by Stoll, B.A., Chicago, Heinemann Medical Books, 1977, pp. 67-76. Ege, G.N.: Internal mammary lymphoscintigraphy-the rationale, technique, interpretation and clinical application: a review based on 848 cases. Radiology 118: 101-107, 1976. Ege, G.N.: Internal mammary lymphoscintigraphy in breast-carcinoma: a study of 1072 patients. Int. J. Radiat. Oncol. Biol. Phys. 2: 755-761, 1977. Rose, C.M., Kaplan, W.D., Marck, A.: Lymphoscintigraphy of internal mammary lymph nodes. Int. J. Radiat. Oncol. Biol. Phys. 2: 102, 1977.
5. Santon, L.W., Prato, F.S., Aspin, N.: Long-distance transmission of digital scintillation camera signals. J. Nucl. Med. 17: 394-3%, 1976. 6. Sutro, L.L., Kilmer, W.L.: Assembly of computers to command and control a robot. In 1%9 Spring Joint Computer Conf. 14-16 May, Boston, Mass., AFZPS Conf. Proc. Vol. 34. Mount Vale, New Jersey, American Federation of Information Processing Societies Press, 1%9, pp. 113-137. S.A., Aggarwal, J.K.: Methods of edge 7. Underwood, detection in visual scenes. In Proc. of the 1973 IEEE Symposium on Circuit Theory, IEEE Cat. No. 73CH0 Institute of Electrical and Electronics 7658CT. Engineers, New York, pp. 45-51.
APPENDIX Edge detection in the digitized lymphoscintigram
Individual lymph nodes in the lymphoscintigrams represent structures varying in size from 3 to 10 mm and contain several times more counts than the surrounding background. As seen in Fig. 2, however, background levels differ significantly in the image, especially over the liver and near the injection sites. The individual lymph nodes are best characterized by edges or sharp changes in intensity. In order to detect edges, the digitized 64 x 64 lymphoscintigram matrix (or node frame) is processed with a small, square, 3 x 3 window or local differential operator which accentuates the presence of edges. The 3 X 3 operator is a good size for this application. A 2 x 2 operator is too small because the finite spatial resolution of the scintillation camera tends to smear
tWe have found that the clinical interpretation influenced by film type, and recommend at present
can be the use
structures across adjacent matrix elments. Larger operators tend to miss the small node structures. Underwood and Aggarwal describe several 3 x 3 differential operators.’ In general, the results of an edge detection procedure depend on prior image processing such as smoothing or nonlinear enhancement. In our case no prior image processing is done and good edge detection in our application is achieved with a method from Sutro and Kilmer.6 The differential image is calculated according to: d(i, j)=
s g k=i-1
(s(i, j)-
s(k, I))
(1)
[=j-1
where s(k, 1) is the (k, 1)th element (or pixel) of the original digitized lymphoscintigram and d(i, j) is the
of Kodak PF 70 mm film for lymphoscintigraphy.
Computerized
internal
mammary
lymphoscintigraphy
0 M. J. BRONSKILL etal.
577
, b)
64 18359 1 .........
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lSOGRADlENT=200
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Fig. Al. (a) Broad Gaussian, u = 10.0. (b) The differential matrix for (a). The central peak is narrower than the original Gaussian. :o:
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Fig. A3. (a) Normal internal mammary lymphoscintigram. (b) Corresponding lymph node plot with a grid superimposed, indicating the centers of differential matrix elements, d(i, i).
i
Fig. A2. (a) Narrow Gaussian, (T = 1.0. (b) The differential matrix for (a). Figs. Al(B) and A2(B) have similar shapes.
(i j)th element of the differential matrix. Each pixel represents a square area of 0.44 cm* and s(k, 1) is in units of counts/pixel. Parasternal lymph nodes are usually small structures and may be considered as point sources. They are embedded in tissue, a scattering medium, at a depth of at least 5 cm from the face of the scintillation camera collimator. The full width at half maximum (FWHM) of the point spread function at such a depth is about 8 mm for our scintillation camera, ignoring scattering. Thus, the lymph node images are approximately Gaussian in shape and are larger than the lymph nodes themselves. The following one-dimensional Gaussian function was used to
518
Radiation Oncology 0 Biology 0 Physics
r
PROFILE
OF ROW 29;
PROFILE
OF COLUMN
April 1979, Volume 5, Number 4
MAXIMUM
39 ;
ELEMENT
MAXIMUM
= 6247
ELEMENT=
I
243356
b)
Fig. A4. (a) Profile through row 29 of the lymph node matrix in A3(b), showing 2 lymph nodes. These profiles
are similar to those of Fig. A2(b). The isogradient level of 200 is sufficient to distinguish lymph nodes from background noise. (b) Profile through column 39, showing a lymph node (small bump at pixel 45) and an injection site. This profile is shown on a scale approximately 40 times less sensitive than Fig. A4(a). On this scale the tendency of this differential operator to produce concentric circles for large structures such as the injection
site is revealed.
represent
lymph node images:
s(i) = 100 exp (- (i - 50)*/2o*), i = 1,100
(2)
u = 1.0 was chosen to represent a small node and u = 10.0 was chosen to represent a very large node. The differential matrix in one dimension is calculated according to: d(i) = 2 X s(i) - s(i + 1) - s(i - 1).
(3)
The effect of this edge detection operator is shown in Figs. Al and A2; the edges of the simulated node are detected and the size of the node is reduced somewhat. Because this operator also amplifies background “noise” in the image, an appropriate isogradient level which separates nodes from noise can only be chosen by detailed examination of actual lymphoscintigram matrices. In Fig. A3, a grid is superimposed on the isogradient plot and profiles through row 29 and column
Computerized
18359 PM ISOGRADIENT
2-MAY-78 = 100
internal mammary lymphoscintigraphy
161116
Fig. A5. The lymphoscintigram of Fig. A3(a) plotted at a lower isogradient level (100.) than in A3(b). Note the increased amount of noise in this plot, particularly over the liver.
0 M. J. BRONSKILL et al.
579
39 of the differential matrix are shown in Fig. A4. An isogradient of amplitude 200 is usually adequate to suppress background and outline individual nodes by interpolation between differential matrix elements. As shown in Fig. AS, a lower isogradient contour tends to find structures in background noise. This technique is effective only for small structures, however, and large structures (such as injection sites) with a broad, flat-topped profile tend to appear as 2 concentric circles. This effect is shown for one injection site in Figs. A3 and A4. Only a portion of the field of view of the scintillation camera can be plotted full size on a sheet of 11 x 14 in graph paper. The positions of the sternal notch and xiphisternum, obtained from the marker frame, are used to center an 8 x 12.5 in window on the differential matrix and only isogradient contours within this window are calculated and plotted. This feature has the added advantage of compensating for the off-center positioning of the patient under the scintillation camera.
