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Manual 3-D Treatment Planning
Medical Dosrmelry. Vol. 13. pp. 137-141 Printed I” the U.S.A. All rights reserved.
0739-021 l/88 Copyright 0 1988
MANUAL
3-D TREATMENT
$3.00 t .OO
American Associationof MedicalDosimetrists
PLANNING*
SHIRLEY ANN JOHNSTON R.T.(R)(T) Albert Einstein Medical Center, York and Tabor Roads, Philadelphia, PA 19I4 1 INTRODUCTION
lateral point of the volume of interest is measured from the midline. Multiply this distance (D) by both scale factors of the CT scan (SF CT) and film (SF F). This point (P) is now marked on the film with a small “X.” Therefore; P = D X (SF CT) X (SF F). This implies an overall scaling factor of (SF CT) X (SF F). This same procedure is repeated for each image. After all volumes of interest are measured, a line connecting all of the cross marks is drawn. The superior and inferior margins of the volume are closed by extending the borders to the level of the next CT slice. There is some uncertainty in determining where the edges of the volume are since all CT increments are for a finite thickness. It has been an accepted margin of error in our department to extend the superior and inferior borders to the next CT level. This allows for the possibility of the volume edges falling in between the image increments. On a lateral view, the measurements can be repeated using the anterior skin surface or the vertebral body as the reference point. Correct geometric proportions must be maintained using correct magnification factors specific to that film (SF F). The numbers employed in this technique are sometimes quite large; therefore, great care must be taken when the volume is marked by the radiation oncologist as well as when each measurement is done. The remainder of this article correlates the aforementioned procedure to the areas of the lung, prostate and uterus, and kidneys.
With the advent of the CT scan, more detailed information has become available to define the tumor volume in its entirety and thereby aid in treatment planning.* Ideally, it would be preferred to have this information relayed directly to the treatment planning computer, *6*‘ohowever, in many departments this is not yet available. An easy-to-use manual approach to project information from the CT cross-sectional image onto the initial portal or simulation film is presented in this paper. This technique allows the radiation oncologist a two dimensional projection of the involved three dimensional volume in juxtaposition to the surrounding normal structures. METHODS
AND MATERIALS
To minimize variability of anatomy from CT scan to film, it is preferred to have the patient scanned in the radiotherapy treatment position on a flat couch. If any patient positioning devices are used, the scanning should be done with the same support~.~ Any useful markers or catheters should be placed on the patient’ by a member of the treatment planning team or the physician responsible for the treatment. After completion of the scanning, the films of the CT scan are then reviewed by the radiation oncologist who will delineate the volume of interest using a wax pencil marker. The radiotherapy films and the CT images are now given to the treatment planning team. Since neither the CT images nor the portal film are the true size of the patient, the scale factors of both the CT scan (SF CT) and the simulation and/or portal film (SF F) being used must be determined. The positions of the CT slices are marked geometrically proportional to the magnification of the film along the central axis in the craniocaudad direction. For example, if the CT Scans are in increments of 1 cm, the levels should be marked on the film by (SF F) X 1. The image number of each CT slice as well as midline of the patient on both the CT scans and film are indicated. The anatomical content of each image is compared with each level projected on the film before proceeding. For an AP film, the most extreme medial and * 1988
Smithers
Writing
Competition
Lung A CT Scan of the lung in conjunction with the conventional X ray films can be helpful in ascertaining the full extent of the lesion.2,3*7Having compiled all of the information, the radiation oncologist can delineate the desired area to be irradiated on the CT Scan. Fig. 1 shows a patient’s CT scan with the indicated volume to be sketched onto the initial portal film (Fig. 2). The numbers on the film denote the level at which the correspondingly numbered CT scan images were taken. Anatomical references to correlate the sequence of the images were: (1) the apices of the lungs superiorly, (2) the carina, and (3) the diaphragm inferiorly. Measuring from the midsagittal plane as described previously, the extreme medial and lateral margins of the circumscribed were
entry. 137
138
Medical Dosimetry
Volume 13, Number 3, 1988
Manual 3-D treatment planning 0 S.A. JOHNSTON
139
Fig. 2. Information transferred from the CT Scan shows tumor extending laterally that would not have been encompassed within the initial treatment field. Fig. 3. Final radiotherapy treatment portal film using cerrobend blocks and amended field position.
Fig. 4. CT of a 54 year old patient having uterine carcinoma.
Medical Dosimetry
Figs. 5 and 6. Reconstructed tumor volume in the pelvis on orthogonal simulation films. Displacement of the bladder is due to the enlargement of the diseased uterus. marked with a small “X” on the film. This method was repeated for each circled area. At the completion of this, the radiation oncologist sketched the volumes of interest as seen in Fig. 3. The tumor volume could now be visualized in relation to the total lung volume. Appropriate field adjustments were made and field shaping blocks were designed to minimize unnecessary irradiation of normal tissues. The boost field could now be planned with very restrictive yet adequate margins. Pelvis
Structures in the pelvis not routinely seen on diagnostic films, for example, the prostate and the
Volume 13, Number 3, 1988
uterus, can be outlined on simulation films using this technique of “manually restacking” the CT scan. Studies have indicated the need for inclusion of the seminal vesicles in treating the prostate.“* With this in mind, field coverage must be adequate to ensure appropriate dose to this region. Obtaining orthogonal films at simulation, both bladder and rectum contrast filled, a reconstruction of the prostate and seminal vesicles can be readily accomplished. To initiate the process of reconstruction, align the mid-sagittal plane on the AP film and correlate the crania-caudad increments of the CT images. Use the iliac crests as an anatomical reference point superiorly and the pubic bone inferiorly. Measure the widest margin to the right and left of midline of both the seminal vesicles and prostate on each image. Mark accordingly on the AP film using P = D X (SF CT) X (SF F). Repeat the alignment on the lateral film and now remeasure the structures but for the most anterior and the most posterior margins. Use the anterior skin surface as the reference point when measuring for the lateral film. Remember to use the correct magnification factor (SF F) for each film. When all information is transferred onto the orthogonal films, these volumes are demonstrated in relation to the bladder and rectum. Frequently, contrast medium is used to opacify the bladder and rectal volumes. If an obstruction or a thickened wall is present in that organ of interest, full delineation is not possible due to the filling defect. The CT scan can well demonstrate the whole organ without contrast and can aid in completing the missing border of that structure on the film. From the CT scan shown in Fig. 4, a reconstructed uterine volume was drawn onto orthogonal simulation films (see Figs. 5 and 6). The same anatomical references were used for this CT scan-simulation film correlation as in the prostate discussion. A four field box treatment technique was to be employed. Note: the intended lateral field would not have given adequate anterior and posterior margins. The left field edge on the anterior-posterior field as well as the lateral field were adjusted by the radiation oncologist to satisfactorily encompass the desired volume. Kidneys
To avoid unnecessary irradiation of the kidneys, manually transferring their positions from the CT Table 1. Landmarks Brain Lung Abdomen Pelvis
and guidelines
sella turcica apices of lungs diaphragm top of iliac crest
for four general areas.
ear canal carina kidneys femoral heads
mastoids diaphragm top of iliac crest pubis
Manual 3-D treatment planning 0 S.A.
scan onto an initial portal film can: ( 1) document proximity to the treatment area, (2) aid in treatment planning, and (3) guide accurate shielding. Referring to the diaphragm and the iliac crests as anatomical landmarks, align the CT scan onto the AP film. Measuring from the mid-sagittal plane to the most medial and lateral aspects of the kidney on each slice, “reconstruct” each kidney using P = D X (SF CT) X (SF F) as described earlier. On a lateral film, repeat this technique using anterior vertebral bodies as the reference point. Although the skin surface could also be referred to, it is suggested to use the bony landmarks to alleviate discrepancies due to the prescence of gas or ascites. For patients who have a contraindication for the use of iodine-based contrast medium (used frequently to visualize kidneys in diagnostic studies) the CT scan is a valuable alternative. A CT scan through the abdominal area can show changes in kidney position due to surgery or displacement from tumor. During the course of treatment, a repeat CT scan can help the radiation oncologist redefine the tumor volume as well as an alteration of the kidneys without the need for multiple diagnostic studies or contrast. CONCLUSION Although there are many valuable diagnostic studies that can help define the diseased region and its relationship to the normal structures, adjuvant information can be obtained by manually measuring the
JOHNSTON
141
volumes from the CT scan and sketching them onto orthogonal films. This method can be employed in any anatomical area and gives the radiation oncologist the distinct advantage of seeing the structures encompassed within the treatment field from a “beam’s eye view,” REFERENCES I. Asbell, SO.; Schlager. B.A.; Baker, AS. Revision of treatment planning for carcinoma of the prostate. Int. J. Radiat. Oncol. Biol. Phys. 6:86 l-865; 1980. 2. Badcock, P.C. The role of computed tomography in the planning of radiotherapy fields. Radiobgy 147:24 l-244; 1983. 3. Gerbi. B.J.; Levitt, H.L. Treatment planning of radiotherapy for lung cancer. Front. Radiat. Thu. One. 21: 152- 180; 1987. 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. Therapeutic Radial. 158:537-540; 1986. 5. Kessler, M.L.; Pitluck, S.; Chen, G.T.Y. Techniques and applications of image correlation in radiotherapy treatment planning. Front. Radiat. Ther. Oncol. 21~25-32; 1987. 6. Korte. C.J.; Harrison, R.M.; Ross, W.M. A simulator based CT system for radiotherapy treatment planning. Br. J. Radio/. 57:631-635; 1984. 7. Mira. J.G.; Potter, J.L.; Fullerton, G.D.; Ezekiel, J. Advantages and limitations of computed tomography scans for the treatment planning of lung cancer. Int. J. Radiat. Oncol. Bioi. Ph.w 8:1617-1623; 1982. 8. Pilepich. M.V.; Perez. C.A.; Prasad, S. Computed tomography in definitive radiotherapy ofprostatic carcinoma. Int. J. Radiat. Oncol. Biol. Phys. 6:923-926: 1980. 9. Russell. W.J.; Murakami, J.: Kimura. S.: Hayabuchi, N. Computed tomography localizer. Cornput. Tomogr. 5:215220; 1981. 10. Wernik, J.A. Investigating 3-D radiation therapy. An interview with James A. Purdy, Ph.D. App. Radiol. 39-42: 1988.
0739-021 l/88 Copyright 0 1988
MANUAL
3-D TREATMENT
$3.00 t .OO
American Associationof MedicalDosimetrists
PLANNING*
SHIRLEY ANN JOHNSTON R.T.(R)(T) Albert Einstein Medical Center, York and Tabor Roads, Philadelphia, PA 19I4 1 INTRODUCTION
lateral point of the volume of interest is measured from the midline. Multiply this distance (D) by both scale factors of the CT scan (SF CT) and film (SF F). This point (P) is now marked on the film with a small “X.” Therefore; P = D X (SF CT) X (SF F). This implies an overall scaling factor of (SF CT) X (SF F). This same procedure is repeated for each image. After all volumes of interest are measured, a line connecting all of the cross marks is drawn. The superior and inferior margins of the volume are closed by extending the borders to the level of the next CT slice. There is some uncertainty in determining where the edges of the volume are since all CT increments are for a finite thickness. It has been an accepted margin of error in our department to extend the superior and inferior borders to the next CT level. This allows for the possibility of the volume edges falling in between the image increments. On a lateral view, the measurements can be repeated using the anterior skin surface or the vertebral body as the reference point. Correct geometric proportions must be maintained using correct magnification factors specific to that film (SF F). The numbers employed in this technique are sometimes quite large; therefore, great care must be taken when the volume is marked by the radiation oncologist as well as when each measurement is done. The remainder of this article correlates the aforementioned procedure to the areas of the lung, prostate and uterus, and kidneys.
With the advent of the CT scan, more detailed information has become available to define the tumor volume in its entirety and thereby aid in treatment planning.* Ideally, it would be preferred to have this information relayed directly to the treatment planning computer, *6*‘ohowever, in many departments this is not yet available. An easy-to-use manual approach to project information from the CT cross-sectional image onto the initial portal or simulation film is presented in this paper. This technique allows the radiation oncologist a two dimensional projection of the involved three dimensional volume in juxtaposition to the surrounding normal structures. METHODS
AND MATERIALS
To minimize variability of anatomy from CT scan to film, it is preferred to have the patient scanned in the radiotherapy treatment position on a flat couch. If any patient positioning devices are used, the scanning should be done with the same support~.~ Any useful markers or catheters should be placed on the patient’ by a member of the treatment planning team or the physician responsible for the treatment. After completion of the scanning, the films of the CT scan are then reviewed by the radiation oncologist who will delineate the volume of interest using a wax pencil marker. The radiotherapy films and the CT images are now given to the treatment planning team. Since neither the CT images nor the portal film are the true size of the patient, the scale factors of both the CT scan (SF CT) and the simulation and/or portal film (SF F) being used must be determined. The positions of the CT slices are marked geometrically proportional to the magnification of the film along the central axis in the craniocaudad direction. For example, if the CT Scans are in increments of 1 cm, the levels should be marked on the film by (SF F) X 1. The image number of each CT slice as well as midline of the patient on both the CT scans and film are indicated. The anatomical content of each image is compared with each level projected on the film before proceeding. For an AP film, the most extreme medial and * 1988
Smithers
Writing
Competition
Lung A CT Scan of the lung in conjunction with the conventional X ray films can be helpful in ascertaining the full extent of the lesion.2,3*7Having compiled all of the information, the radiation oncologist can delineate the desired area to be irradiated on the CT Scan. Fig. 1 shows a patient’s CT scan with the indicated volume to be sketched onto the initial portal film (Fig. 2). The numbers on the film denote the level at which the correspondingly numbered CT scan images were taken. Anatomical references to correlate the sequence of the images were: (1) the apices of the lungs superiorly, (2) the carina, and (3) the diaphragm inferiorly. Measuring from the midsagittal plane as described previously, the extreme medial and lateral margins of the circumscribed were
entry. 137
138
Medical Dosimetry
Volume 13, Number 3, 1988
Manual 3-D treatment planning 0 S.A. JOHNSTON
139
Fig. 2. Information transferred from the CT Scan shows tumor extending laterally that would not have been encompassed within the initial treatment field. Fig. 3. Final radiotherapy treatment portal film using cerrobend blocks and amended field position.
Fig. 4. CT of a 54 year old patient having uterine carcinoma.
Medical Dosimetry
Figs. 5 and 6. Reconstructed tumor volume in the pelvis on orthogonal simulation films. Displacement of the bladder is due to the enlargement of the diseased uterus. marked with a small “X” on the film. This method was repeated for each circled area. At the completion of this, the radiation oncologist sketched the volumes of interest as seen in Fig. 3. The tumor volume could now be visualized in relation to the total lung volume. Appropriate field adjustments were made and field shaping blocks were designed to minimize unnecessary irradiation of normal tissues. The boost field could now be planned with very restrictive yet adequate margins. Pelvis
Structures in the pelvis not routinely seen on diagnostic films, for example, the prostate and the
Volume 13, Number 3, 1988
uterus, can be outlined on simulation films using this technique of “manually restacking” the CT scan. Studies have indicated the need for inclusion of the seminal vesicles in treating the prostate.“* With this in mind, field coverage must be adequate to ensure appropriate dose to this region. Obtaining orthogonal films at simulation, both bladder and rectum contrast filled, a reconstruction of the prostate and seminal vesicles can be readily accomplished. To initiate the process of reconstruction, align the mid-sagittal plane on the AP film and correlate the crania-caudad increments of the CT images. Use the iliac crests as an anatomical reference point superiorly and the pubic bone inferiorly. Measure the widest margin to the right and left of midline of both the seminal vesicles and prostate on each image. Mark accordingly on the AP film using P = D X (SF CT) X (SF F). Repeat the alignment on the lateral film and now remeasure the structures but for the most anterior and the most posterior margins. Use the anterior skin surface as the reference point when measuring for the lateral film. Remember to use the correct magnification factor (SF F) for each film. When all information is transferred onto the orthogonal films, these volumes are demonstrated in relation to the bladder and rectum. Frequently, contrast medium is used to opacify the bladder and rectal volumes. If an obstruction or a thickened wall is present in that organ of interest, full delineation is not possible due to the filling defect. The CT scan can well demonstrate the whole organ without contrast and can aid in completing the missing border of that structure on the film. From the CT scan shown in Fig. 4, a reconstructed uterine volume was drawn onto orthogonal simulation films (see Figs. 5 and 6). The same anatomical references were used for this CT scan-simulation film correlation as in the prostate discussion. A four field box treatment technique was to be employed. Note: the intended lateral field would not have given adequate anterior and posterior margins. The left field edge on the anterior-posterior field as well as the lateral field were adjusted by the radiation oncologist to satisfactorily encompass the desired volume. Kidneys
To avoid unnecessary irradiation of the kidneys, manually transferring their positions from the CT Table 1. Landmarks Brain Lung Abdomen Pelvis
and guidelines
sella turcica apices of lungs diaphragm top of iliac crest
for four general areas.
ear canal carina kidneys femoral heads
mastoids diaphragm top of iliac crest pubis
Manual 3-D treatment planning 0 S.A.
scan onto an initial portal film can: ( 1) document proximity to the treatment area, (2) aid in treatment planning, and (3) guide accurate shielding. Referring to the diaphragm and the iliac crests as anatomical landmarks, align the CT scan onto the AP film. Measuring from the mid-sagittal plane to the most medial and lateral aspects of the kidney on each slice, “reconstruct” each kidney using P = D X (SF CT) X (SF F) as described earlier. On a lateral film, repeat this technique using anterior vertebral bodies as the reference point. Although the skin surface could also be referred to, it is suggested to use the bony landmarks to alleviate discrepancies due to the prescence of gas or ascites. For patients who have a contraindication for the use of iodine-based contrast medium (used frequently to visualize kidneys in diagnostic studies) the CT scan is a valuable alternative. A CT scan through the abdominal area can show changes in kidney position due to surgery or displacement from tumor. During the course of treatment, a repeat CT scan can help the radiation oncologist redefine the tumor volume as well as an alteration of the kidneys without the need for multiple diagnostic studies or contrast. CONCLUSION Although there are many valuable diagnostic studies that can help define the diseased region and its relationship to the normal structures, adjuvant information can be obtained by manually measuring the
JOHNSTON
141
volumes from the CT scan and sketching them onto orthogonal films. This method can be employed in any anatomical area and gives the radiation oncologist the distinct advantage of seeing the structures encompassed within the treatment field from a “beam’s eye view,” REFERENCES I. Asbell, SO.; Schlager. B.A.; Baker, AS. Revision of treatment planning for carcinoma of the prostate. Int. J. Radiat. Oncol. Biol. Phys. 6:86 l-865; 1980. 2. Badcock, P.C. The role of computed tomography in the planning of radiotherapy fields. Radiobgy 147:24 l-244; 1983. 3. Gerbi. B.J.; Levitt, H.L. Treatment planning of radiotherapy for lung cancer. Front. Radiat. Thu. One. 21: 152- 180; 1987. 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. Therapeutic Radial. 158:537-540; 1986. 5. Kessler, M.L.; Pitluck, S.; Chen, G.T.Y. Techniques and applications of image correlation in radiotherapy treatment planning. Front. Radiat. Ther. Oncol. 21~25-32; 1987. 6. Korte. C.J.; Harrison, R.M.; Ross, W.M. A simulator based CT system for radiotherapy treatment planning. Br. J. Radio/. 57:631-635; 1984. 7. Mira. J.G.; Potter, J.L.; Fullerton, G.D.; Ezekiel, J. Advantages and limitations of computed tomography scans for the treatment planning of lung cancer. Int. J. Radiat. Oncol. Bioi. Ph.w 8:1617-1623; 1982. 8. Pilepich. M.V.; Perez. C.A.; Prasad, S. Computed tomography in definitive radiotherapy ofprostatic carcinoma. Int. J. Radiat. Oncol. Biol. Phys. 6:923-926: 1980. 9. Russell. W.J.; Murakami, J.: Kimura. S.: Hayabuchi, N. Computed tomography localizer. Cornput. Tomogr. 5:215220; 1981. 10. Wernik, J.A. Investigating 3-D radiation therapy. An interview with James A. Purdy, Ph.D. App. Radiol. 39-42: 1988.