Copyright
0360.3016/90 $3.00 + .OO Cc 1990 Pergamon Press plc
0 Original Contribution CT SIMULATOR: A NEW 3-D PLANNING AND SIMULATING SYSTEM FOR RADIOTHERAPY: PART 2. CLINICAL APPLICATION NAGATA,
M.D.,’
TAKEHIRO
MASAJI TAKAHASHI,
M.D.,’
KAORU
YASUSHI
HIROSHI ISHIHARA, HIROSHI OHTA,
NISHIDAI, PH.D.,’
OKAJIMA, M.S.,*
M.S.3
M.D.,’
YASUFUMI
MITSUYUKI
NOBUYUKI
ABE, M.D.,’
YAMAOKA,
KUBO,
M.S.,3
AND CHUDO KAZUSA,
M.S.3
M.S.,2
‘Department of Radiology. Kyoto University, Kyoto 606: ‘Medical System Div., Shimadzu Corporation, Kyoto 604; and 3MedicalSystem Div., NEC Corporation. Tokyo 183, Japan performedradiotherapytreatment planning(RTP) with a new system called CT simulator in 72 patients. With the system, RTP is performedwith the patient lying on the CT couch within a short period of time. All the CT images scannedwere immediatelytransportedto the multi-imagemonitorsand to the treatment planningdevice. We have
Radiotherapy treatment planning could he performed not only at the beam center but also at any CT slice. Using a laser-beam field projector, field outlines were drawn over the patient’s skin. In clinical use, the system was useful for cases in which a target lies adjacent to dose limiting organs, cases with a complicated target shape, cases with complicated dose distribution curves, and cases treated with tangential fields. This system enables us to make optimum use of CT information and to make accurate 3-dimensional treatment planning programs. CT simulator,
Clinical
application,
Radiotherapy
treatment
INTRODUCTION
planning.
reconstructed images can also be viewed. With the laser beam field projector, the whole beam center and any shape of radiation field within 180” of the patient lying on the CT couch can be projected.
The introduction of CT in clinical medicine has enabled us to clearly define the extent of a tumor from the normal organ. and has brought a tremendous change in the field of radiotherapy (3). CT has become indispensable for radiotherapy treatment planning (RTP) (5), but all CT machines are developed mainly for diagnostic use and are separated from treatment planning machines and simulating systems. To take full advantage of this CT information, an integrated planning system is needed that can directly use the data from a transverse section for outlining the tumor while superimposing the isodose distribution (2). We have developed a new treatment planning system, “CT simulator”, that includes all the planning functions. The CT simulator consists of a CT scanner, two multiimage monitors, a 3-D treatment planning machine, and a laser beam field projector. With multi-image monitors, many CT slices can be viewed at the same time. The radiation fields over multiple CT images can also be checked. With the 3-D treatment planning machine, the visual optimization function and the fast dose calculation method (6, 7) can be used. A simulation image and other
METHODS
AND
MATERIALS
Since June 1987, radiotherapy treatment plans have been developed for 72 patients with this system. Patients whose target could not be clearly defined with CT and patients who could not lie still during CT scanning were excluded. This system was generally used more often for RTP in shrinking fields than for initial treatment because for initial treatment the x-ray simulator was used on a large field and later the field was reduced to the target using this system. The contrast enhancement examination was done on 73% to clearly define the target from vessels.
Clinicdjlowchurt Table 1 illustrates the flowchart of clinical application. The planning is to be carried out in the following way. 1. Initial CT scanning preparations. Before beginning CT simulation, all previous x-ray films, diagnostic CT
Reprints requests to: Yasushi Nagata M.D., Department of Radiology, Faculty of Medicine, Kyoto University, Sakyo, Kyoto 606, Japan. This work was supported by Grant-in-aid for Cancer Research from the Ministry of Health Welfare (6 l-26). Accepted for publication 9 August 1989.
Presented at the 9th International Conference of the Use of Computers in Radiation Therapy. Scheveningen, The Netherlands, June. 1987 and at the 29th annual meeting of the A.S.T.R.O.. Boston, USA, October, 1987 and at the 30th Annual Meeting of the A.S.T.R.O., New Orleans, LA, USA, November. 1988. 505
I. J. Radiation Oncology 0 Biology 0 Physics
506
Table 1. Clinical
flowchart
Initial CT scanning preparations 4 CT scanning with two different scannograms 4 Drawing target outlines 4 Make planning at the beam center 4 Make planning with all CT slices Make planning
with reconstructed c Laser beam held projection
images
scans and laboratory data of a patient are reviewed. After determining the target of the patient, the patient is immobilized on the CT couch for radiotherapy. To assure immobilization of the patient, fixing apparatus such as shell is used in some cases. The scanning parameters are selected at the CT operator console. 2. Scant& prc?jeYion radiogruphs (sc‘ann0~tatn.v). In diagnostic radiology, the scannogram is only used for locating the range of CT scanning, but for RTP by CT simulator, it is the only image scanned from the direction vertical to the CT slice. In this system. scannograms are taken from two different directions (A-P and lateral). They
March 1990. Volume IX. Number 3
with reconstructed target outlines and are superimposed with outlines of organs of interest later. 3. (‘7‘ .ccmning CT slices are taken at 5-10 mm intervals for a total of 1O-30 scans. For cancer patients, CT scanning must be hnished within a short period of time, usually within 15 minutes, because they are not always in good condition and can not lie still for a long time. To reduce scanning time. we used a high heat unit x-ray tube. The images scanned are instantly displayed on the multiimage monitor. After CT scanning, patients are allowed to leave the CT couch, after their skin has been marked so that they can be returned to the same position later. 4. 7ti,:q~ mllitwv. On each CT image. the outline of the body is automatically recognized by the computer. The outline of a target is drawn for each CT image by the digitizer (Fig. la). After the image is reconstructed during CT scanning. multiple CT slices on the monitor are used as references for drawing a target. Dose limiting organs, such as the spinal cord, liver, and kidney, which must be excluded from the radiation field as much as possible, are outlined at the same time. These outlines are instantly displayed on the CT slices of the multi-image monitors and reconstructed over the scannograms (Fig. I b). When the outline of the target is complete. the image of the target can be obtained from multiple CT slices, A-P and lateral scannograms. These target outlines give us an idea of the Sdimensional structure.
Fig. 1 A patient with esophageal cancer had been irradiated up to 45 Gy with A-P and P-A opposing fields. For residual tumor, we planned four oblique portals with blocking to the spinal cord. (a) The target outline is drawn over the CT image. (b) The target of each CT image is instantly reconstructed over A-P and lateral scannogram. (c) The planning with four portals at the center CT slice. (d) The reconstructed target and spinal cord outlines from oblique direction. We set the rectangle field with block to the spinal cord. (e) On the multi-image monitor, we can see dose distribution curves and beam mark over each CT image. (f) Over the reconstructed A-P view. we can check the dose distribution of the spinal cord. (g) The field shape and block is projected over the skin of the patient lying on the CT couch.
Clinical
application
of CT simulator
0 Y. NAGATA e’f (I/.
507
Fig. I. (Contd)
5. Treutment plunning at the beum center. With the target outlines and the dose limiting organ outlined, the ideal CT slice of the beam center is selected. First, we plan for this CT slice. Dose distribution curves of the CT slice are displayed on the treatment planning monitor (Fig. lc). In addition, the field direction and size and isocenter can be changed instantly using the visual optimization method. 6. Treatment planning with all CT slices. Formerly, a plan was made with only a single slice at the beam center. However, when the tumor is not symmetrical and is not single, plans made on the CT slice at the beam center are insufficient. It is necessary to know the dose distribution
of the CT slice out of the beam center. Using this system, the dose distribution curves of the CT slice out of the beam center are determined with the 3-dimensional dose reconstruction method. At this stage, we also use a newly reconstructed target outline seen from the radiation portal (beam’s eye view) and can make another 3-dimensional treatment plan such as block shielding (Fig. Id). These fields and blocks are displayed as beam marks over multiple CT images (Fig. 1e). We can make plans with all CT slices considering scattering radiation doses. 7. Treatment planning with reconstructed images (oblique image, simulation imuge). CT images, reconstructed in axial, coronal, sagittal and oblique views can
508
1. J. Radiation
Oncology
0 Biology 0 Physics
March
Fig.
I (C’ontd)
1990. Volume
18. Number
3
Clinical application
of CT simulator
Fig.
be superimposed with dose distribution curves (Fig. If). We can also check whether or not the target is included in the edge slice. The simulation image (Fig. 3c) is digitally reconstructed from multiple CT images, and has the same geometry as the simulation film of the portal. This view
1.
0 Y. NACATA e/ ul.
509
(Contd)
is used as verification film in comparison with the : portography. 8. Luser heum,field projecting system. After all pa rameters are set, the laser beam projecting system auto1 natitally controlled by the computer projects every 1>eam
510
I. J. Radiation
Oncology
0 Biology 0 Physics
center and radiation field shape successively over the skin of the patient (Fig. lg). At this stage. the patient is returned to the same position on the CT couch. RESULTS The clinical usefulness of this system was compared with that of our previous treatment planning by experienced radiation oncologists. This system has been useful on the following occasions.
Fig. 2. A patient with orbital lymphoma. oblique portal (b) shown in the figure.
The reconstructed
March
1990. Volume
18.Number 3
1. Cusc~s in M#lich the target lies udjacrnt to dose limiting orgum .mch us the spinal cord, liver, und lens In these cases. the relationship between the target and dose limiting organ is different on each CT slices. Using multi-image monitors, we can confirm it with beam marks and dose distribution curves over multiple CT images. Thus, the CT simulator was useful for the tumor near dose limiting organs, such as in cases of orbital tumors, mediastinal tumors and abdominal tumors. Figure 2 depicts a case of orbital lymphoma. All beam marks were
target shape and lens (a) are displayed
and we set the
Clinical
displayed over multiple out of the field.
application
of CT simulator
CT images and the right lens was
2. Cases with a complicated shape @target Generally, the head and neck or mediastinal tumors are complicated in shape because of their bony structure and spread route. In our system, the target outlines seen from any direction can be reconstructed from each CT slice. In the case of a bulky tumor, the outline of a target could be reconstructed over the scannogram. This was especially useful for RTP of brain tumor. head and neck tumor. lung tumor, abdominal and pelvic tumor. 3. Cases Mith a target ofcomplicated dose distribution ~IIY~L’S that should he planned \z*ithman)’ porta1.s More than three portals or rotating portals are commonly used for patients with abdominal or pelvic tumors (Fig. 3). Complicated dose distribution curves of such planning could be calculated instantly with our system and planning was completed within a few minutes. For lung or liver tumors. dose distribution curves of normal tissue are as important as those of the tumor (9). We used this system for liver tumors to reduce the treatment volume. The dose volume histogram (I) will be obtained with this system. 4. Cases with a target that .should be treated
with tangent ial jields Patients with skin or breast cancer are treated with tangential fields. With multiple CT slices and beam marks,
0 Y. NAGATA el a/
511
we could clearly define the relationship of the target and fields and select the direction and width of the portal beam. Treatment planning for the post-tumorectomy breast has been done using this system, which allowed including the residual mammary gland totally while sparing of normal lung. DISCUSSION As CT consists of multiple CT images, all the images are utilized for the RTP system. Most previous RTP systems were designed for single CT slice planning. Multiple CT images displayed simultaneously by our system are provided not only with target information but also with normal structure. Moreover, we can view multiple field outlines and dose distribution curves over multiple CT images. The dose distribution curves away from the central plane are very important when the tumor is not symmetrical and is irregularly shaped and when multiple tumors lie in the same field. Thus, we believe that this multiimage system is a practical 3-dimensional treatment planning system. The laser-beam field projector is fixed by a C-shaped arm about 60 cm caudal to the CT gantry, and controlled from the treatment console. Most of the field projectors currently used for radiotherapy are light projectors. However, for the CT simulator, it projects various kinds of field shapes (irregular fields) over the patient’s skin. It can project not only field shape and isocenter but also target shape over the skin. When all the components of the system are on line,
Fig. 3. A patient with stomach cancer. The planning with three portals at the beam center (a) and with all CT slices (b) are shown. Simulation image (c) of the antero-posterior field can be reconstructed from multiple CT slice.
512
1. J. Radiation
Oncology
0 Biology 0 Physics
March
Fig. 3. (C‘onrd)
1990. Volume
18, Number
3
Clinical
application
of CT simulator
and dose calculation is fast, we can use dose distribution curves more easily and more frequently than before. More complicated treatment plans can be developed within 30 minutes. With our previous treatment planning system, it took more than 2 hr for CT planning to be completed. The system provides many reconstructed images. We previously reconstructed the shape of the target from multiple CT slices over the A-P or lateral film without computer assistance. This was the only method to set the radiation fields using CT but it was very inaccurate. Now, all the targets are temporarily reconstructed by the computer and superimposed over scannograms (4). However, there are geometric differences between the scannograms and actual films: these images (CT beam’s view) are used only as a reference. True beam’s eye view considering isocenter and source-axis distance can be later reconstructed, and used for planning. The simulation image, digitally reconstructed radiographs, was used for confirming the radiation fields. It can be reconstructed from CT pixels by a summation method. With a CT scanner, a plain film can not be obtained for verification and a simulation film was taken with a x-ray simulator. This reconstructed film enables us to use this CT simulator without x-ray simulator. The portal film for the projected radiation fields over the skin can be compared with this simulation image. However, the quality of the simulation image is still not sufficient. There are a few problems with this system (8). With the CT simulator, the patient must lie still in the same position during the whole planning session. However, many patients requiring radiotherapy are not in good condition and can not lie still for 30 minutes. Thus. we
0 Y. NAGATA CYul.
513
must check the position ofthe patient at least three times: before scanning, after scanning, and before field projection. For patients who cannot lie still for a long time, we can perform CT scanning and planning and field projection separately. For patients who can not lie still during CT scanning, we must use a fixing apparatus. For a patient with a lower chest or upper abdominal tumor, moving artifacts due to respiratory movement are very important. Radiotherapy was previously carried out with no regard to respiration and CT scanning for RTP was done without breath holding. Therefore, the images were not good and targets could not be clearly outlined. Moreover, respiratory phases of each slice were different and 3-dimensional structures could not be reconstructed. In this system. CT slices are scanned while the patient holds his breath. The allowance of respiratory movement is considered later. Respiratory gating and intermittent irradiating system are now under development. The target is the area that we want to direct the treatment dose. However, in clinical cases, the shape of one target is very different from that of another. The most important point is that the imaging target of CT or MRI is not the same as the “clinical target” that is derived from the clinical experience of radiation oncologists. The establishment of a target definition for radiotherapy of each disease is an important problem. Even though there are problems remaining, the CT simulator is considered to be useful for clinical radiotherapy treatment planning, which can be accomplished within a short time and without the x-ray simulator. This system also allows more accurate 3-dimensional treatment planning.
REFERENCES I. Austin-Seymour, M. M.: Chen, G. T. Y.: Castro, J. R.: Saunders, W. M.; Pitluck. S.: Woodruff, K. H.: Kessler, M. Dose volume histogram analysis of liver radiation tolerance. Int. J. Radiat. Oncol. Biol. Phys. 12:31-35; 1986. 2. Dobbs, H. J.: Parker, R. P. The respective roles of the simulator and computed tomography in radiation planning. A review. Clin. Radiol. 35:433-439: 1984. 3. Glatstein, E.: Lichter, A.: Fraass, B. A.: Kelly. B. A.: Geijin. J. V. D. The imaging revolution and radiation oncology: the use ofCT, Ultrasound, and NMR for localization, treatment planning and treatment delivery. Int. J. Radiat. Oncol. Biol. Phys. Il:299-3 14; 1985. 4. Haynor, D. R.: Borning, A. W.; Griffin, B. A.; Jacky, J. P.; Kalet, I. J.; Shuman. W. P. Radiotherapy planning: direct tumor location on simulation and port films using CT. Radiology I58:537-540; 1986.
5. Holday. P.; Hodson, N. J.: Husband, J.: Parker, R. P.; Macdonald, J. S. Computed tomography applied to radiotherapy treatment planning: technique and results. Radiology 133: 417-482: 1979. 6. Inamura. K.; Abe, S.; Ueda, Y.: Shigaki, S.: Fujino, S. An application ofequivalent TAR method to fast reconstruction of three dimensional dose distribution. 8th ICCR Proc. 456460: 1984. 7. Inamura, K.; Ohta, H.; Kubo. Y. A new type of visual optimization method in treatment planning. 8th ICCR Proc. 230-234; 1984. 8. Ling, C.: Rogers, C. C.; Morton. R. J. Computed tomography in Radiation Therapy, New York: Raven Press; 1983. 9. Restock, R. A.; Fishman, E. K.; Order, S. E. CT scanning for radiotherapy treatment planning of hepatoma. Int. J. Radiat. Oncol. Biol. Phys. 1I : I4 l3- I4 18: 1985.
0360.3016/90 $3.00 + .OO Cc 1990 Pergamon Press plc
0 Original Contribution CT SIMULATOR: A NEW 3-D PLANNING AND SIMULATING SYSTEM FOR RADIOTHERAPY: PART 2. CLINICAL APPLICATION NAGATA,
M.D.,’
TAKEHIRO
MASAJI TAKAHASHI,
M.D.,’
KAORU
YASUSHI
HIROSHI ISHIHARA, HIROSHI OHTA,
NISHIDAI, PH.D.,’
OKAJIMA, M.S.,*
M.S.3
M.D.,’
YASUFUMI
MITSUYUKI
NOBUYUKI
ABE, M.D.,’
YAMAOKA,
KUBO,
M.S.,3
AND CHUDO KAZUSA,
M.S.3
M.S.,2
‘Department of Radiology. Kyoto University, Kyoto 606: ‘Medical System Div., Shimadzu Corporation, Kyoto 604; and 3MedicalSystem Div., NEC Corporation. Tokyo 183, Japan performedradiotherapytreatment planning(RTP) with a new system called CT simulator in 72 patients. With the system, RTP is performedwith the patient lying on the CT couch within a short period of time. All the CT images scannedwere immediatelytransportedto the multi-imagemonitorsand to the treatment planningdevice. We have
Radiotherapy treatment planning could he performed not only at the beam center but also at any CT slice. Using a laser-beam field projector, field outlines were drawn over the patient’s skin. In clinical use, the system was useful for cases in which a target lies adjacent to dose limiting organs, cases with a complicated target shape, cases with complicated dose distribution curves, and cases treated with tangential fields. This system enables us to make optimum use of CT information and to make accurate 3-dimensional treatment planning programs. CT simulator,
Clinical
application,
Radiotherapy
treatment
INTRODUCTION
planning.
reconstructed images can also be viewed. With the laser beam field projector, the whole beam center and any shape of radiation field within 180” of the patient lying on the CT couch can be projected.
The introduction of CT in clinical medicine has enabled us to clearly define the extent of a tumor from the normal organ. and has brought a tremendous change in the field of radiotherapy (3). CT has become indispensable for radiotherapy treatment planning (RTP) (5), but all CT machines are developed mainly for diagnostic use and are separated from treatment planning machines and simulating systems. To take full advantage of this CT information, an integrated planning system is needed that can directly use the data from a transverse section for outlining the tumor while superimposing the isodose distribution (2). We have developed a new treatment planning system, “CT simulator”, that includes all the planning functions. The CT simulator consists of a CT scanner, two multiimage monitors, a 3-D treatment planning machine, and a laser beam field projector. With multi-image monitors, many CT slices can be viewed at the same time. The radiation fields over multiple CT images can also be checked. With the 3-D treatment planning machine, the visual optimization function and the fast dose calculation method (6, 7) can be used. A simulation image and other
METHODS
AND
MATERIALS
Since June 1987, radiotherapy treatment plans have been developed for 72 patients with this system. Patients whose target could not be clearly defined with CT and patients who could not lie still during CT scanning were excluded. This system was generally used more often for RTP in shrinking fields than for initial treatment because for initial treatment the x-ray simulator was used on a large field and later the field was reduced to the target using this system. The contrast enhancement examination was done on 73% to clearly define the target from vessels.
Clinicdjlowchurt Table 1 illustrates the flowchart of clinical application. The planning is to be carried out in the following way. 1. Initial CT scanning preparations. Before beginning CT simulation, all previous x-ray films, diagnostic CT
Reprints requests to: Yasushi Nagata M.D., Department of Radiology, Faculty of Medicine, Kyoto University, Sakyo, Kyoto 606, Japan. This work was supported by Grant-in-aid for Cancer Research from the Ministry of Health Welfare (6 l-26). Accepted for publication 9 August 1989.
Presented at the 9th International Conference of the Use of Computers in Radiation Therapy. Scheveningen, The Netherlands, June. 1987 and at the 29th annual meeting of the A.S.T.R.O.. Boston, USA, October, 1987 and at the 30th Annual Meeting of the A.S.T.R.O., New Orleans, LA, USA, November. 1988. 505
I. J. Radiation Oncology 0 Biology 0 Physics
506
Table 1. Clinical
flowchart
Initial CT scanning preparations 4 CT scanning with two different scannograms 4 Drawing target outlines 4 Make planning at the beam center 4 Make planning with all CT slices Make planning
with reconstructed c Laser beam held projection
images
scans and laboratory data of a patient are reviewed. After determining the target of the patient, the patient is immobilized on the CT couch for radiotherapy. To assure immobilization of the patient, fixing apparatus such as shell is used in some cases. The scanning parameters are selected at the CT operator console. 2. Scant& prc?jeYion radiogruphs (sc‘ann0~tatn.v). In diagnostic radiology, the scannogram is only used for locating the range of CT scanning, but for RTP by CT simulator, it is the only image scanned from the direction vertical to the CT slice. In this system. scannograms are taken from two different directions (A-P and lateral). They
March 1990. Volume IX. Number 3
with reconstructed target outlines and are superimposed with outlines of organs of interest later. 3. (‘7‘ .ccmning CT slices are taken at 5-10 mm intervals for a total of 1O-30 scans. For cancer patients, CT scanning must be hnished within a short period of time, usually within 15 minutes, because they are not always in good condition and can not lie still for a long time. To reduce scanning time. we used a high heat unit x-ray tube. The images scanned are instantly displayed on the multiimage monitor. After CT scanning, patients are allowed to leave the CT couch, after their skin has been marked so that they can be returned to the same position later. 4. 7ti,:q~ mllitwv. On each CT image. the outline of the body is automatically recognized by the computer. The outline of a target is drawn for each CT image by the digitizer (Fig. la). After the image is reconstructed during CT scanning. multiple CT slices on the monitor are used as references for drawing a target. Dose limiting organs, such as the spinal cord, liver, and kidney, which must be excluded from the radiation field as much as possible, are outlined at the same time. These outlines are instantly displayed on the CT slices of the multi-image monitors and reconstructed over the scannograms (Fig. I b). When the outline of the target is complete. the image of the target can be obtained from multiple CT slices, A-P and lateral scannograms. These target outlines give us an idea of the Sdimensional structure.
Fig. 1 A patient with esophageal cancer had been irradiated up to 45 Gy with A-P and P-A opposing fields. For residual tumor, we planned four oblique portals with blocking to the spinal cord. (a) The target outline is drawn over the CT image. (b) The target of each CT image is instantly reconstructed over A-P and lateral scannogram. (c) The planning with four portals at the center CT slice. (d) The reconstructed target and spinal cord outlines from oblique direction. We set the rectangle field with block to the spinal cord. (e) On the multi-image monitor, we can see dose distribution curves and beam mark over each CT image. (f) Over the reconstructed A-P view. we can check the dose distribution of the spinal cord. (g) The field shape and block is projected over the skin of the patient lying on the CT couch.
Clinical
application
of CT simulator
0 Y. NAGATA e’f (I/.
507
Fig. I. (Contd)
5. Treutment plunning at the beum center. With the target outlines and the dose limiting organ outlined, the ideal CT slice of the beam center is selected. First, we plan for this CT slice. Dose distribution curves of the CT slice are displayed on the treatment planning monitor (Fig. lc). In addition, the field direction and size and isocenter can be changed instantly using the visual optimization method. 6. Treatment planning with all CT slices. Formerly, a plan was made with only a single slice at the beam center. However, when the tumor is not symmetrical and is not single, plans made on the CT slice at the beam center are insufficient. It is necessary to know the dose distribution
of the CT slice out of the beam center. Using this system, the dose distribution curves of the CT slice out of the beam center are determined with the 3-dimensional dose reconstruction method. At this stage, we also use a newly reconstructed target outline seen from the radiation portal (beam’s eye view) and can make another 3-dimensional treatment plan such as block shielding (Fig. Id). These fields and blocks are displayed as beam marks over multiple CT images (Fig. 1e). We can make plans with all CT slices considering scattering radiation doses. 7. Treatment planning with reconstructed images (oblique image, simulation imuge). CT images, reconstructed in axial, coronal, sagittal and oblique views can
508
1. J. Radiation
Oncology
0 Biology 0 Physics
March
Fig.
I (C’ontd)
1990. Volume
18. Number
3
Clinical application
of CT simulator
Fig.
be superimposed with dose distribution curves (Fig. If). We can also check whether or not the target is included in the edge slice. The simulation image (Fig. 3c) is digitally reconstructed from multiple CT images, and has the same geometry as the simulation film of the portal. This view
1.
0 Y. NACATA e/ ul.
509
(Contd)
is used as verification film in comparison with the : portography. 8. Luser heum,field projecting system. After all pa rameters are set, the laser beam projecting system auto1 natitally controlled by the computer projects every 1>eam
510
I. J. Radiation
Oncology
0 Biology 0 Physics
center and radiation field shape successively over the skin of the patient (Fig. lg). At this stage. the patient is returned to the same position on the CT couch. RESULTS The clinical usefulness of this system was compared with that of our previous treatment planning by experienced radiation oncologists. This system has been useful on the following occasions.
Fig. 2. A patient with orbital lymphoma. oblique portal (b) shown in the figure.
The reconstructed
March
1990. Volume
18.Number 3
1. Cusc~s in M#lich the target lies udjacrnt to dose limiting orgum .mch us the spinal cord, liver, und lens In these cases. the relationship between the target and dose limiting organ is different on each CT slices. Using multi-image monitors, we can confirm it with beam marks and dose distribution curves over multiple CT images. Thus, the CT simulator was useful for the tumor near dose limiting organs, such as in cases of orbital tumors, mediastinal tumors and abdominal tumors. Figure 2 depicts a case of orbital lymphoma. All beam marks were
target shape and lens (a) are displayed
and we set the
Clinical
displayed over multiple out of the field.
application
of CT simulator
CT images and the right lens was
2. Cases with a complicated shape @target Generally, the head and neck or mediastinal tumors are complicated in shape because of their bony structure and spread route. In our system, the target outlines seen from any direction can be reconstructed from each CT slice. In the case of a bulky tumor, the outline of a target could be reconstructed over the scannogram. This was especially useful for RTP of brain tumor. head and neck tumor. lung tumor, abdominal and pelvic tumor. 3. Cases Mith a target ofcomplicated dose distribution ~IIY~L’S that should he planned \z*ithman)’ porta1.s More than three portals or rotating portals are commonly used for patients with abdominal or pelvic tumors (Fig. 3). Complicated dose distribution curves of such planning could be calculated instantly with our system and planning was completed within a few minutes. For lung or liver tumors. dose distribution curves of normal tissue are as important as those of the tumor (9). We used this system for liver tumors to reduce the treatment volume. The dose volume histogram (I) will be obtained with this system. 4. Cases with a target that .should be treated
with tangent ial jields Patients with skin or breast cancer are treated with tangential fields. With multiple CT slices and beam marks,
0 Y. NAGATA el a/
511
we could clearly define the relationship of the target and fields and select the direction and width of the portal beam. Treatment planning for the post-tumorectomy breast has been done using this system, which allowed including the residual mammary gland totally while sparing of normal lung. DISCUSSION As CT consists of multiple CT images, all the images are utilized for the RTP system. Most previous RTP systems were designed for single CT slice planning. Multiple CT images displayed simultaneously by our system are provided not only with target information but also with normal structure. Moreover, we can view multiple field outlines and dose distribution curves over multiple CT images. The dose distribution curves away from the central plane are very important when the tumor is not symmetrical and is irregularly shaped and when multiple tumors lie in the same field. Thus, we believe that this multiimage system is a practical 3-dimensional treatment planning system. The laser-beam field projector is fixed by a C-shaped arm about 60 cm caudal to the CT gantry, and controlled from the treatment console. Most of the field projectors currently used for radiotherapy are light projectors. However, for the CT simulator, it projects various kinds of field shapes (irregular fields) over the patient’s skin. It can project not only field shape and isocenter but also target shape over the skin. When all the components of the system are on line,
Fig. 3. A patient with stomach cancer. The planning with three portals at the beam center (a) and with all CT slices (b) are shown. Simulation image (c) of the antero-posterior field can be reconstructed from multiple CT slice.
512
1. J. Radiation
Oncology
0 Biology 0 Physics
March
Fig. 3. (C‘onrd)
1990. Volume
18, Number
3
Clinical
application
of CT simulator
and dose calculation is fast, we can use dose distribution curves more easily and more frequently than before. More complicated treatment plans can be developed within 30 minutes. With our previous treatment planning system, it took more than 2 hr for CT planning to be completed. The system provides many reconstructed images. We previously reconstructed the shape of the target from multiple CT slices over the A-P or lateral film without computer assistance. This was the only method to set the radiation fields using CT but it was very inaccurate. Now, all the targets are temporarily reconstructed by the computer and superimposed over scannograms (4). However, there are geometric differences between the scannograms and actual films: these images (CT beam’s view) are used only as a reference. True beam’s eye view considering isocenter and source-axis distance can be later reconstructed, and used for planning. The simulation image, digitally reconstructed radiographs, was used for confirming the radiation fields. It can be reconstructed from CT pixels by a summation method. With a CT scanner, a plain film can not be obtained for verification and a simulation film was taken with a x-ray simulator. This reconstructed film enables us to use this CT simulator without x-ray simulator. The portal film for the projected radiation fields over the skin can be compared with this simulation image. However, the quality of the simulation image is still not sufficient. There are a few problems with this system (8). With the CT simulator, the patient must lie still in the same position during the whole planning session. However, many patients requiring radiotherapy are not in good condition and can not lie still for 30 minutes. Thus. we
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must check the position ofthe patient at least three times: before scanning, after scanning, and before field projection. For patients who cannot lie still for a long time, we can perform CT scanning and planning and field projection separately. For patients who can not lie still during CT scanning, we must use a fixing apparatus. For a patient with a lower chest or upper abdominal tumor, moving artifacts due to respiratory movement are very important. Radiotherapy was previously carried out with no regard to respiration and CT scanning for RTP was done without breath holding. Therefore, the images were not good and targets could not be clearly outlined. Moreover, respiratory phases of each slice were different and 3-dimensional structures could not be reconstructed. In this system. CT slices are scanned while the patient holds his breath. The allowance of respiratory movement is considered later. Respiratory gating and intermittent irradiating system are now under development. The target is the area that we want to direct the treatment dose. However, in clinical cases, the shape of one target is very different from that of another. The most important point is that the imaging target of CT or MRI is not the same as the “clinical target” that is derived from the clinical experience of radiation oncologists. The establishment of a target definition for radiotherapy of each disease is an important problem. Even though there are problems remaining, the CT simulator is considered to be useful for clinical radiotherapy treatment planning, which can be accomplished within a short time and without the x-ray simulator. This system also allows more accurate 3-dimensional treatment planning.
REFERENCES I. Austin-Seymour, M. M.: Chen, G. T. Y.: Castro, J. R.: Saunders, W. M.; Pitluck. S.: Woodruff, K. H.: Kessler, M. Dose volume histogram analysis of liver radiation tolerance. Int. J. Radiat. Oncol. Biol. Phys. 12:31-35; 1986. 2. Dobbs, H. J.: Parker, R. P. The respective roles of the simulator and computed tomography in radiation planning. A review. Clin. Radiol. 35:433-439: 1984. 3. Glatstein, E.: Lichter, A.: Fraass, B. A.: Kelly. B. A.: Geijin. J. V. D. The imaging revolution and radiation oncology: the use ofCT, Ultrasound, and NMR for localization, treatment planning and treatment delivery. Int. J. Radiat. Oncol. Biol. Phys. Il:299-3 14; 1985. 4. Haynor, D. R.: Borning, A. W.; Griffin, B. A.; Jacky, J. P.; Kalet, I. J.; Shuman. W. P. Radiotherapy planning: direct tumor location on simulation and port films using CT. Radiology I58:537-540; 1986.
5. Holday. P.; Hodson, N. J.: Husband, J.: Parker, R. P.; Macdonald, J. S. Computed tomography applied to radiotherapy treatment planning: technique and results. Radiology 133: 417-482: 1979. 6. Inamura. K.; Abe, S.; Ueda, Y.: Shigaki, S.: Fujino, S. An application ofequivalent TAR method to fast reconstruction of three dimensional dose distribution. 8th ICCR Proc. 456460: 1984. 7. Inamura, K.; Ohta, H.; Kubo. Y. A new type of visual optimization method in treatment planning. 8th ICCR Proc. 230-234; 1984. 8. Ling, C.: Rogers, C. C.; Morton. R. J. Computed tomography in Radiation Therapy, New York: Raven Press; 1983. 9. Restock, R. A.; Fishman, E. K.; Order, S. E. CT scanning for radiotherapy treatment planning of hepatoma. Int. J. Radiat. Oncol. Biol. Phys. 1I : I4 l3- I4 18: 1985.
