- Email: [email protected]
Simulation by a diagnostic CT for the early vocal cord carcinoma
Copyright
Medical Dosimetry, Vol. 22, No. I. pp. 13- 16. 1997 0 1997 American Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947/97 $17.00 + .OO
PI1 SO958-3947( 96)00133-l
ELSEVIER
SIMULATION
BY A DIAGNOSTIC CT FOR THE EARLY CORD CARCINOMA
VOCAL
A. ROVIROSA, M.D.,’ J. BERENGUER, M.D.,2 A. SANCHEZ-REYES, PH.D.,' M. TORRES,’ J. M., CASALS, M.D.,’ B. FARRUS,M.D.,’ and A. BIETE, PH.D., M.D.lT3 ’ Radiation Oncology Department, ’ Neuroradiology Section, Hospital Clinic I Universitari of Barcelona. Barcelona, Spain; 3 University Autonoma of Barcelona, Barcelona, Spain Abstract-The CT-based simulation with a 3D planning system permits the optimization of radiotherapy treatments. The goal is to obtain an increase in the local control and survival with a reduction of the treatment related toxicity. In our hospital, we do not have a CT simulator and our 3D planning system is not yet working, therefore, we have developed a system to simulate radiotherapy treatments using a diagnostic CT. We began by simulating an early vocal cord carcinoma. The rules of this simulation are presented using a clinical case as an example. 0 1997 American Association of Medical Dosimetrists Key Words:
CT-simulation,
Early
vocal
cord
carcinoma,
Radiotherapy.
INTRODUCTION
MATERIALS
In radiotherapy treatments of early vocal cord carcinomas, a number of anatomical differences between each patient must be considered; the size and location of the tumor, the size of vocal cords, the location of vocal cords in the neck relative to the skin, and the difference in the contour at different levels of the neck. These differences produce variations in the dose distribution in each patient. Moreover, the use of distinct treatment energies (Co60, 4MV, 6MV, 1OMV) can cause important variations in the dose distribution in the same patient.‘.2 It seems clear that we need to keep all of these considerations in mind, and offer an individualized treatment plan for each patient. A perfect knowledge of the gross and clinical tumoral volume is needed to offer an accurate radiotherapy treatment. Several image techniques have been employed, such as CT, MRI and PET to allow for this goal.jm5 In previous years, a CT based simulation with a 3D planning system seemed to offer the best way to optimize radiotherapy treatments.6 Although there has been a progressive increase in the number of centers with 3D planning systems, few radiotherapy departments have a CT-simulator. In our hospital, a CTsimulator is not available and our 3D planning system is not yet operating; therefore, we developed a system to simulate early vocal cord carcinoma with a diagnostic CT. We will describe how this simulation is performed in a patient with a TlNO vocal cord carcinoma.
To show the technique of simulation we shall present a clinical case of TlNO left vocal cord carcinoma affecting the anterior one third, treated by xphotons of 6 MV. An immobilization thermoplastic mask is made with the patient correctly aligned in the treatment position. Three hyperdense CT markers are placed on the mask longitudinally in the median line and in the lateral sides, all coinciding with the simulator lasers (Fig. 1). Afterwords, the patient is referred to the radiology department for the simulation by a diagnostic CT. A wooden board is placed over the table of the CT to reproduce the same table simulator conditions. The patient is aligned with the CT lasers in the same position that the mask was made. Real size CT slices every 2 millimeters are performed to determine the placement of the vocal cord (Fig. 2). The slice which coincides with the center of the vocal cord is selected, using this as the central plane of the treatment. After the dimensions of the tumor’s affected vocal cord are known, the superior and inferior limits of the field (2 cm above and below the tumoral vocal cord) are determined by motion of the CT table. The CT lasers permit us to place the central plane, the superior and inferior limits of the field on the mask. The transverse dimension of the field is ascertained by measuring the distance from the anterior portion of the vertebral body in the central plane to the metallic reference in the median line of the patient. The center of the field is then placed in the median value of this dimension. A line perpendicular to the floor in this point will intersect the mask in two points, so that these two points of intersection will coincide with the center of the two
Reprint requests to: Dr. A. Rovirosa, RadiationOncology Department, Hospital Clinic i Universitari of Barcelona.CI Villarroel no 170, 08036
Barcelona,
Spain,
Presentedas communicationin the ing. Granada,September24-26, 1994.
XIII
AND METHODS
Annual ESTRO Meet13
Medical Dosimetry
Volume22, Number1, 1997
Fig. 2. Scanogrammadein the treatmentposition.
Fig. 1. Thermoplasticmaskwith hyperdensemarkers
fields. The latter can be placed on the patient mask, the distance to the metallic lateral references measured by CT (Fig. 3a). Likewise, the posterior limit of the field is establishedin relation to the hyperdense metallic markers by measuring the distance given by CT (Fig. 3b). The superior, posterior and inferior limits, as well as the center of the field are placed over the mask. The patient is then referred to the simulator for an X-ray with the dimensions of the fields chosen by CT (Fig. 4). After the dosimetric study was done, our patient was treated with different weight in each field, and wedges adapted to the tumor volume and the patient’s contour need. The size of the field was 5 X 5 cm. Because there is a 6 MV Linac in our department and the tumor was in the anterior third of the vocal cord, our patient needed to be treated with a bolus to give
Fig. 3. In the centralplane: (A) Determinationof the center of the field and (B) the posteriorlimit of the field.
15
Simulation by a diagnostic CT for early vocal cord carcinoma 0 A. ROVIROSA et al.
Fig. 4. Simulator X-ray of the patient presented. Wires show the center and limits of the fields determined by CT. The small differences seen in the simulator X-ray between the limits of the fields and the wires are due to the x-ray projection.
a correct dose distribution in the anterior part of the vocal cord. After 46 Gy, the exclusion of the arythenoid could be done accurately due to the knowledge of their location (Fig. 5). DISCUSSION
these cases. The treatment of the vocal cord carcinoma affecting the commissura and the anterior third with an energy of 6 MV is adequate if all of these factors are considered, and if the best treatment technique is studied.‘,‘-” The size of the fields has been correlated with local control and to arythenoid edema; large fields more than 6 x 6 cm have been associated with an increase of local control but an increase of the arythenoid edema.1’-‘3 These considerations show that careful attention to the technique of treatment and dosimetric study is a critical factor in obtaining optimal results in treatment of vocal cord carcinoma. CT-based simulation permits correct location of the vocal cords in the neck, and determination of the tumoral volume. The center of the field can then be placed where the vocal cord is, allowing the field dimensions to be adjusted more accurately to the necessity of each patient. We developed a system to simulate patients with a diagnostic CT, permitting individualized treatment in each case, taking into account the correct location of the tumor in the vocal cord and the differences in the contour of the patient. It is also possible to adjust the fields or the technique for the treatment that every tumor requires. The hyperdense CT markers permit us to correlate the different slices and make a good assessment of the treatment volume. In addition, by knowing the correct placement of the arythenoid, we can exclude these accurately when possible. The real size CT slices are the real contour of the patient in the
-
- - e-.
AND CONCLUSION
In radiotherapy of vocal cord carcinoma, some technical considerations must be taken into account. When parallel opposing fields are used, the dose inhomogeneity occurs at anterior and posterior extremities of the treatment volume. Thus, depending on the location of the tumor in the vocal cord and the tumor size, the dose distribution may not be adequate in the tumoral volume. Moreover, we must be aware that anatomical variations exist in patients relative to the contour of the neck, size of the vocal cord and location of the vocal cords in relation to the skin.’ This has repercussions in the dose received by the tumor. In patients with short necks, the shoulders can be included in the treatment fields when lateral opposing fields are used; oblique treatment fields are the best option in
\
: 1 :’ / /I
Fig. 5. Dosimetric study. Sixty Gy covering the tumor were administered. Two opposite lateral fields were used, weighing 1:2,2. The posterior half of the arythenoid area received less than 50 Gy after the treatment was finished.
16
Medical Dosimetry
treatment position. In our case, we use it to perform the dosimetric study in all slices of interest. Real size CT slices may permit the undertaking of an accurate dosimetric study with the knowledge of the exact clinical tumor volume and the location of healthy neighboring structures.‘4 Dose distribution can then be adjusted for each case, permitting us to correlate the dose received by various structures with acute and late treatment toxicity. We believe that this technique can offer a good optimization of early vocal cord carcinoma treatment in centers without a 3D planning system and CT simulator.
REFERENCES 1. Akin, Y; Tokita, N; Ogino, Takashi; Tsukiyama, I; Egawa, S; Saikawa, M; Ohyama, W; Yoshizumi, T; Ebihara, S. Radiotheraov of Tl elottic cancer with 6 MeV X rays. Inf. J. R&at. b&l. BioZ.-Phys. 20:1215-1218; 1991. 2. Fein, D.A.; Mendenhall, W.M.; Parsons, J.T.; Million, R.R. TlT2 squamous cell carcinoma of the glottic larynx treated with radiotherapy: a multivariate analysis of variables potentially influencing local control. Int. J. Radiat. Oncol. Biol. Phys. 25:605611; 1993. 3. Glatstein, E.; Litchter, AS.; Fraas, B.A. The imaging revolution in radiation oncology: use of CT, ultrasound and MRI for localization, treatment planning and treatment delivery. Int. J. Rudiaf. Oncol. Biol. Phys. 11: 229-314; 1985. 4. Thorton, A.F.; Haken, R.K.H. Three dimensional motion analysis on an improved head immobilization system for simulation, CT, MRI and PET imaging. Radiother. Oncol. 20:224-228; 1991.
Volume 22, Number 1, 1997 5. Thorton, A.F.; Haken, R.K.H.; Weeks, K.J.; Gerardsson, K.; Correll, L.; Lash, K.A. A head immobilization system for radiation simulation, CT, MRI and PET imaging. Med. Dosim. 16:5 l56; 1992. 6. Nagata, Y.; Nishiday, K. CT simulator: a new 3-D planning and simulation system for radiotherapy: Part 2. clinical application. Znt. J. Radiat. Oncol. Biol. Phys. 18(3):505-513; 1990. 7. Rovirosa, A.; Berenguer, J.; Ferrer, F.; Sanchez-Reyes, A.; Torres. M.: Casals. .I; Farrtls. B.: Biete. A. Planificacion Y simulation por tomografia computarizada (TC) de 10s tumor& de cuerda vocal: resultados preliminares en 10 pacientes TlNO Oncologia, 18(8):S119; 1995. 8. Rovirosa, A.; Berenguer, J.; Ferrer, F.; Casals, J.; SanchezReyes, A.; Arias, C.; Farrds, B.; Traserra, J. Simulation by a diagnostic CT in the vocal cord carcinoma. Preliminary resnlts in ten patients. ECCOI. EJC, 31A: 179; 1995. 9. Wiggenraad, R.G.; Terhaard, C.H.; Hordijk, G.J.; Ravasz, L.A. The importance of vocal cord mobility in T2 laryngeal cancer. Radiother.
Oncol.
l&321-327:
1990.
10. Zohar, Y.; Rahima, M.; Shvili, Y.; Talmi, Y.P.; Lurie, H. The controversial treatment of anterior commissure carcinoma of the larynx. Laryngoscope. 102:69-72; 1992. Il. Cellai, E.; Chiavacci, A.; Olmi, P. Causes of failure of curative radiation therapy in 205 early glottic cancers. Int. J. Radiat. Oncol.
Biol.
Phys. 19: 1139-
1142; 1990.
12. Terhaard, C.H.J.; Snippe, K.; Ravasz, L.A.; Van der tweel, I.; Hordijk, G.J. Radiotherapy in Tl laryngeal cancer: prognostic factors for locoregional control and survival, uni-, and multivariate analysis. Int. J. Radiat. Oncol. Biol. Phys. 21: 1179- 1186; 1991. 13. Teshima, T.; Chatani, M.; moue, T. Radiation therapy for early vocal glottic cancer (Tl NOMO) : II. Prospective randomized studv concernine radiation field. Int. J. Radiat. Oncol. Biol. Phys. 18:i19-123; 1<90. 14. Rovirosa, A.; Berenguer, J.; Sanchez-Reyes, A.; Farms, B.; Casas. F.; Biete. A. A CT-based simulation for head and neck tumors’in centers without CT-simulator and 3D-planning system. Med. Dosim. 20(2):111-115; 1995.
Medical Dosimetry, Vol. 22, No. I. pp. 13- 16. 1997 0 1997 American Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947/97 $17.00 + .OO
PI1 SO958-3947( 96)00133-l
ELSEVIER
SIMULATION
BY A DIAGNOSTIC CT FOR THE EARLY CORD CARCINOMA
VOCAL
A. ROVIROSA, M.D.,’ J. BERENGUER, M.D.,2 A. SANCHEZ-REYES, PH.D.,' M. TORRES,’ J. M., CASALS, M.D.,’ B. FARRUS,M.D.,’ and A. BIETE, PH.D., M.D.lT3 ’ Radiation Oncology Department, ’ Neuroradiology Section, Hospital Clinic I Universitari of Barcelona. Barcelona, Spain; 3 University Autonoma of Barcelona, Barcelona, Spain Abstract-The CT-based simulation with a 3D planning system permits the optimization of radiotherapy treatments. The goal is to obtain an increase in the local control and survival with a reduction of the treatment related toxicity. In our hospital, we do not have a CT simulator and our 3D planning system is not yet working, therefore, we have developed a system to simulate radiotherapy treatments using a diagnostic CT. We began by simulating an early vocal cord carcinoma. The rules of this simulation are presented using a clinical case as an example. 0 1997 American Association of Medical Dosimetrists Key Words:
CT-simulation,
Early
vocal
cord
carcinoma,
Radiotherapy.
INTRODUCTION
MATERIALS
In radiotherapy treatments of early vocal cord carcinomas, a number of anatomical differences between each patient must be considered; the size and location of the tumor, the size of vocal cords, the location of vocal cords in the neck relative to the skin, and the difference in the contour at different levels of the neck. These differences produce variations in the dose distribution in each patient. Moreover, the use of distinct treatment energies (Co60, 4MV, 6MV, 1OMV) can cause important variations in the dose distribution in the same patient.‘.2 It seems clear that we need to keep all of these considerations in mind, and offer an individualized treatment plan for each patient. A perfect knowledge of the gross and clinical tumoral volume is needed to offer an accurate radiotherapy treatment. Several image techniques have been employed, such as CT, MRI and PET to allow for this goal.jm5 In previous years, a CT based simulation with a 3D planning system seemed to offer the best way to optimize radiotherapy treatments.6 Although there has been a progressive increase in the number of centers with 3D planning systems, few radiotherapy departments have a CT-simulator. In our hospital, a CTsimulator is not available and our 3D planning system is not yet operating; therefore, we developed a system to simulate early vocal cord carcinoma with a diagnostic CT. We will describe how this simulation is performed in a patient with a TlNO vocal cord carcinoma.
To show the technique of simulation we shall present a clinical case of TlNO left vocal cord carcinoma affecting the anterior one third, treated by xphotons of 6 MV. An immobilization thermoplastic mask is made with the patient correctly aligned in the treatment position. Three hyperdense CT markers are placed on the mask longitudinally in the median line and in the lateral sides, all coinciding with the simulator lasers (Fig. 1). Afterwords, the patient is referred to the radiology department for the simulation by a diagnostic CT. A wooden board is placed over the table of the CT to reproduce the same table simulator conditions. The patient is aligned with the CT lasers in the same position that the mask was made. Real size CT slices every 2 millimeters are performed to determine the placement of the vocal cord (Fig. 2). The slice which coincides with the center of the vocal cord is selected, using this as the central plane of the treatment. After the dimensions of the tumor’s affected vocal cord are known, the superior and inferior limits of the field (2 cm above and below the tumoral vocal cord) are determined by motion of the CT table. The CT lasers permit us to place the central plane, the superior and inferior limits of the field on the mask. The transverse dimension of the field is ascertained by measuring the distance from the anterior portion of the vertebral body in the central plane to the metallic reference in the median line of the patient. The center of the field is then placed in the median value of this dimension. A line perpendicular to the floor in this point will intersect the mask in two points, so that these two points of intersection will coincide with the center of the two
Reprint requests to: Dr. A. Rovirosa, RadiationOncology Department, Hospital Clinic i Universitari of Barcelona.CI Villarroel no 170, 08036
Barcelona,
Spain,
Presentedas communicationin the ing. Granada,September24-26, 1994.
XIII
AND METHODS
Annual ESTRO Meet13
Medical Dosimetry
Volume22, Number1, 1997
Fig. 2. Scanogrammadein the treatmentposition.
Fig. 1. Thermoplasticmaskwith hyperdensemarkers
fields. The latter can be placed on the patient mask, the distance to the metallic lateral references measured by CT (Fig. 3a). Likewise, the posterior limit of the field is establishedin relation to the hyperdense metallic markers by measuring the distance given by CT (Fig. 3b). The superior, posterior and inferior limits, as well as the center of the field are placed over the mask. The patient is then referred to the simulator for an X-ray with the dimensions of the fields chosen by CT (Fig. 4). After the dosimetric study was done, our patient was treated with different weight in each field, and wedges adapted to the tumor volume and the patient’s contour need. The size of the field was 5 X 5 cm. Because there is a 6 MV Linac in our department and the tumor was in the anterior third of the vocal cord, our patient needed to be treated with a bolus to give
Fig. 3. In the centralplane: (A) Determinationof the center of the field and (B) the posteriorlimit of the field.
15
Simulation by a diagnostic CT for early vocal cord carcinoma 0 A. ROVIROSA et al.
Fig. 4. Simulator X-ray of the patient presented. Wires show the center and limits of the fields determined by CT. The small differences seen in the simulator X-ray between the limits of the fields and the wires are due to the x-ray projection.
a correct dose distribution in the anterior part of the vocal cord. After 46 Gy, the exclusion of the arythenoid could be done accurately due to the knowledge of their location (Fig. 5). DISCUSSION
these cases. The treatment of the vocal cord carcinoma affecting the commissura and the anterior third with an energy of 6 MV is adequate if all of these factors are considered, and if the best treatment technique is studied.‘,‘-” The size of the fields has been correlated with local control and to arythenoid edema; large fields more than 6 x 6 cm have been associated with an increase of local control but an increase of the arythenoid edema.1’-‘3 These considerations show that careful attention to the technique of treatment and dosimetric study is a critical factor in obtaining optimal results in treatment of vocal cord carcinoma. CT-based simulation permits correct location of the vocal cords in the neck, and determination of the tumoral volume. The center of the field can then be placed where the vocal cord is, allowing the field dimensions to be adjusted more accurately to the necessity of each patient. We developed a system to simulate patients with a diagnostic CT, permitting individualized treatment in each case, taking into account the correct location of the tumor in the vocal cord and the differences in the contour of the patient. It is also possible to adjust the fields or the technique for the treatment that every tumor requires. The hyperdense CT markers permit us to correlate the different slices and make a good assessment of the treatment volume. In addition, by knowing the correct placement of the arythenoid, we can exclude these accurately when possible. The real size CT slices are the real contour of the patient in the
-
- - e-.
AND CONCLUSION
In radiotherapy of vocal cord carcinoma, some technical considerations must be taken into account. When parallel opposing fields are used, the dose inhomogeneity occurs at anterior and posterior extremities of the treatment volume. Thus, depending on the location of the tumor in the vocal cord and the tumor size, the dose distribution may not be adequate in the tumoral volume. Moreover, we must be aware that anatomical variations exist in patients relative to the contour of the neck, size of the vocal cord and location of the vocal cords in relation to the skin.’ This has repercussions in the dose received by the tumor. In patients with short necks, the shoulders can be included in the treatment fields when lateral opposing fields are used; oblique treatment fields are the best option in
\
: 1 :’ / /I
Fig. 5. Dosimetric study. Sixty Gy covering the tumor were administered. Two opposite lateral fields were used, weighing 1:2,2. The posterior half of the arythenoid area received less than 50 Gy after the treatment was finished.
16
Medical Dosimetry
treatment position. In our case, we use it to perform the dosimetric study in all slices of interest. Real size CT slices may permit the undertaking of an accurate dosimetric study with the knowledge of the exact clinical tumor volume and the location of healthy neighboring structures.‘4 Dose distribution can then be adjusted for each case, permitting us to correlate the dose received by various structures with acute and late treatment toxicity. We believe that this technique can offer a good optimization of early vocal cord carcinoma treatment in centers without a 3D planning system and CT simulator.
REFERENCES 1. Akin, Y; Tokita, N; Ogino, Takashi; Tsukiyama, I; Egawa, S; Saikawa, M; Ohyama, W; Yoshizumi, T; Ebihara, S. Radiotheraov of Tl elottic cancer with 6 MeV X rays. Inf. J. R&at. b&l. BioZ.-Phys. 20:1215-1218; 1991. 2. Fein, D.A.; Mendenhall, W.M.; Parsons, J.T.; Million, R.R. TlT2 squamous cell carcinoma of the glottic larynx treated with radiotherapy: a multivariate analysis of variables potentially influencing local control. Int. J. Radiat. Oncol. Biol. Phys. 25:605611; 1993. 3. Glatstein, E.; Litchter, AS.; Fraas, B.A. The imaging revolution in radiation oncology: use of CT, ultrasound and MRI for localization, treatment planning and treatment delivery. Int. J. Rudiaf. Oncol. Biol. Phys. 11: 229-314; 1985. 4. Thorton, A.F.; Haken, R.K.H. Three dimensional motion analysis on an improved head immobilization system for simulation, CT, MRI and PET imaging. Radiother. Oncol. 20:224-228; 1991.
Volume 22, Number 1, 1997 5. Thorton, A.F.; Haken, R.K.H.; Weeks, K.J.; Gerardsson, K.; Correll, L.; Lash, K.A. A head immobilization system for radiation simulation, CT, MRI and PET imaging. Med. Dosim. 16:5 l56; 1992. 6. Nagata, Y.; Nishiday, K. CT simulator: a new 3-D planning and simulation system for radiotherapy: Part 2. clinical application. Znt. J. Radiat. Oncol. Biol. Phys. 18(3):505-513; 1990. 7. Rovirosa, A.; Berenguer, J.; Ferrer, F.; Sanchez-Reyes, A.; Torres. M.: Casals. .I; Farrtls. B.: Biete. A. Planificacion Y simulation por tomografia computarizada (TC) de 10s tumor& de cuerda vocal: resultados preliminares en 10 pacientes TlNO Oncologia, 18(8):S119; 1995. 8. Rovirosa, A.; Berenguer, J.; Ferrer, F.; Casals, J.; SanchezReyes, A.; Arias, C.; Farrds, B.; Traserra, J. Simulation by a diagnostic CT in the vocal cord carcinoma. Preliminary resnlts in ten patients. ECCOI. EJC, 31A: 179; 1995. 9. Wiggenraad, R.G.; Terhaard, C.H.; Hordijk, G.J.; Ravasz, L.A. The importance of vocal cord mobility in T2 laryngeal cancer. Radiother.
Oncol.
l&321-327:
1990.
10. Zohar, Y.; Rahima, M.; Shvili, Y.; Talmi, Y.P.; Lurie, H. The controversial treatment of anterior commissure carcinoma of the larynx. Laryngoscope. 102:69-72; 1992. Il. Cellai, E.; Chiavacci, A.; Olmi, P. Causes of failure of curative radiation therapy in 205 early glottic cancers. Int. J. Radiat. Oncol.
Biol.
Phys. 19: 1139-
1142; 1990.
12. Terhaard, C.H.J.; Snippe, K.; Ravasz, L.A.; Van der tweel, I.; Hordijk, G.J. Radiotherapy in Tl laryngeal cancer: prognostic factors for locoregional control and survival, uni-, and multivariate analysis. Int. J. Radiat. Oncol. Biol. Phys. 21: 1179- 1186; 1991. 13. Teshima, T.; Chatani, M.; moue, T. Radiation therapy for early vocal glottic cancer (Tl NOMO) : II. Prospective randomized studv concernine radiation field. Int. J. Radiat. Oncol. Biol. Phys. 18:i19-123; 1<90. 14. Rovirosa, A.; Berenguer, J.; Sanchez-Reyes, A.; Farms, B.; Casas. F.; Biete. A. A CT-based simulation for head and neck tumors’in centers without CT-simulator and 3D-planning system. Med. Dosim. 20(2):111-115; 1995.