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Technique charts for Kodak’s new film-screen systems for portal localization 1
Medical Dosimetry, Vol. 23, No. 2, pp. 113–116, 1998 Copyright © 1998 American Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947/98 $19.00 1 .00
PII S0958-3947(98)00004-1
TECHNIQUE CHARTS FOR KODAK’S NEW FILM-SCREEN SYSTEMS FOR PORTAL LOCALIZATION PLATO C. LEE, PH.D. and GLENN P. GLASGOW, PH.D. Loyola University, Loyola-Hines Department of Radiotherapy, Maywood, IL 60153 Abstract—In July 1996, Kodak released new film-screen systems with enhanced contrast (EC) for portal localization with megavoltage therapeutic beams. This study presents the generation of general-purpose technique charts for Kodak’s new film-screen combinations: the Enhanced-Contrast localization (EC-L) film in EC-L cassette and the EC-L film in fast ECL (fECL) cassette for use with cobalt-60, 6 MV, 10 MV, and 18 MV beams. These technique charts were based on the assumption that a film with an optical density (OD) of 1.8 provides the best viewing density. The doses to produce such as OD, Dexp, were obtained from the H & D curves and were 1.5, 1.6, 1.7, and 1.8 cGy for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively, with the EC-L-film1EC-Lcassette combination. The corresponding values were 1.3, 1.3, 1.3, and 1.4 cGy, respectively, for the above four beams with the EC-L-film1fEC-L-cassette combination. The dose to the film is assumed to be proportional to the calibrated dose rate (D0), field size factor (FSF), inverse square factor relative to 100.0 cm (INV), and the transmission factor through the patient, which is equal to e2uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time or monitor unit, t, is then calculated from the following equation: t 5 Dexp/(D0*FSF*INV*e2uT). For an average port size of 15 3 15 cm, the attenuation coefficients were obtained from the fitting of TAR (cobalt-60) or TMR (6 MV, 10 MV, and 18 MV) as a function of depth from 10 to 30 cm and were 0.0564 cm21, 0.03714 cm21, and 0.02271 cm21 for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively. The FSF were explicitly obtained from the clinical physics data books and were 1.028, 1.032, 1.036, and 1.053 for cobalt-60, 6 MV, 10 MV, and 18 MV, respectively. For cobalt-60 beam, the D0 was assumed to be 100.0 cGy/min. For the 6 MV, 10 MV, and 18 MV beams, the D0 in cGy per monitor unit is 1.030, 1.051, and 1.061, respectively. Technique charts were then generated as a function of patient thickness from 10 to 45 cm for filming distance from 110 to 140 cm for all four beams. These technique charts can be easily customized to portal localization practices in a radiation therapy department. © 1998 American Association of Medical Dosimetrists. Key Words: Technique charts, Portal localization, Contrast-enhanced film-screen systems, H & D curves.
INTRODUCTION
on the film, Dexp, is assumed to be proportional to the calibrated dose rate at 100 cm, (D0), field size factor (FSF), inverse square factor relative to 100 cm (INV), and the transmission factor through the patient, which is equal to e2uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time (t) or monitor unit (MU) can be calculated from the following equation:
Presently, the only medium commonly employed to evaluate and document the accuracy of a radiation treatment is the weekly portal film.1 The image quality of the portal films taken with megavoltage beams are typically poor due to the predominance of Compton interactions in the filming process. Metal screens have been shown to enhance the contrast of the port films.2 In 1996 Kodak released the new Enhanced-Contrast Localization (EC-L) film-screen combinations for portal imaging with megavoltage beam.3 In this paper, we present the generation of the technique charts for these new film screen systems, both the EC-L film in EC-L cassette and the EC-L film in fast EC-L (fEC-L) cassette for radiation therapy with cobalt-60, 6 MV, 10 MV, and 18 MV beams. In the generation of the technique charts, it is assumed that an optical density (OD) of 1.8 provides the best viewing density.1,3 The dose to produce such an OD
t or MU 5
D exp D 0*FSF*INV*e2uT
(1)
The Dexps are to be experimentally obtained from the H & D curves of the EC-L films in EC-L cassette and the EC-L films in fEC-L cassette for all four beams. The attenuation coefficients of each beam are to be obtained from the fitting of either TAR (Co-60) or TMR (6 MV, 10 MV and 18 MV) as a function of the depth. Thus, by knowing the calibrated dose rate, (D0), and the FSF, the exposure time or MU, the technique charts can be easily generated as a function of the source-to-cassette distance (SCD) and the patient thickness, T, for all four beams.
Reprint requests to: Dr. Plato Lee, Alexian Brothers Cancer Care Center, 820 W. Biesterfield Road, Elk Grove Village, IL. E mail: [email protected]. Presented as a Work-In-Progress paper in the 39th Annual Meeting of the American Association of Physicists in Medicine (AAPM) in Milwaukee, WI, July 23–31, 1997. 113
114
Medical Dosimetry
Volume 23, Number 2, 1998
Fig. 3. TAR or TMR as a function of depth. Fig. 1. H & D curves for the EC-L film 1 EC-L cassette system.
MATERIALS AND METHODS In the determination of the H & D curves for both film-screen systems, the doses to the films were varied by changing the SCDs from 90 to 145 cm. Due to the speed of the film-screen systems, the exposure times or MUs were 0.02 minutes for co-60 and 2 MU for linac beams. (The reproducibility of dose delivery at such low time or MU settings was checked by repeatedly measuring the outputs of all the studied beams and was found to be better than 2%.) To collect all the exposures on a single
film for each H & D curve, a 6.0 3 6.0 cm field was used. A Nuclear Associate densitometer was used to read the ODs of all the films. The doses to cassette were calculated from the calibrated dose rates, field size factors and inverse square laws for all four beams: cobalt-60 from Theratronix 1000, 6 MV and 18 MV beams from Varian Clinac 1800 and 10 MV beam from Varian Clinac 18. The attenuation coefficients were obtained from the fitting of either the TAR (Co-60) or the TMRs (6 MV, 10 MV, and 18 MV) of a 15 3 15.0 cm field as a function of the depth from 10 to 30 cm. RESULTS Figure 1 shows the H and D curves of the EC-L film in EC-L cassette system for the Co-60, 6 MV, 10 MV, and 18 MV beams. This figure indicates that the sensitivity of the film-screen system is energy-dependent. The dose to produce an OD of 1.8 was determined to be 1.5, 1.6, 1.7, and 1.8 for the above four beams, respectively. Figure 2 shows the H and D curves for the EC-L film in fEC-L cassette for the four beams. Again, the figure indicates that the sensitivity of this film-screen system is energy-dependent. The dose to produce an OD of 1.8 was determined to be 1.3, 1.3, 1.3, and 1.4, respectively, for the above four beams. Table 1. Parameters related to technique charts Cobalt
Fig. 2. H & D curves for the EC-L film 1 fEC-L cassette system.
D0 100.0 (cGy/min or cGy/MU) FSF 1.028 u (cm21) 0.0564 Dexp-ECL cassette (cGy) 1.54 Dexp-fECL cassette (cGy) 1.29
6 MV
10 MV
18 MV
1.030
1.051
1.061
1.032 0.0371 1.67 1.29
1.036 0.0295 1.73 1.34
1.053 0.0227 1.82 1.40
Kodak’s new film screen systems ● P. LEE and G. GLASGOW
115
Table 2. Technique chart for various treatment machines (EC-L film 1 EC-L cassette) coa SFDc
63b
103b
183b
110
120
130
140
110
120
130
140
110
120
130
140
110
120
130
140
0.03 0.02 0.01 0.04 0.03 0.01 0.06 0.04 0.02 0.07 0.05 0.02 0.10 0.07 0.03 0.13 0.09 0.04 0.17 0.12 0.05 0.23 0.16 0.07
0.04 0.03 0.01 0.05 0.04 0.01 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.16 0.11 0.05 0.21 0.14 0.07 0.27 0.18 0.09
0.04 0.03 0.01 0.06 0.04 0.02 0.08 0.05 0.03 0.10 0.07 0.03 0.14 0.09 0.05 0.18 0.12 0.06 0.24 0.16 0.08 0.32 0.21 0.11
0.05 0.03 0.02 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.16 0.12 0.04 0.21 0.14 0.07 0.28 0.21 0.07 0.37 0.25 0.12
3 2 1 3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4
3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4 12 8 4
4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4 12 8 4 14 9 5
5 3 2 5 3 2 7 5 2 8 5 3 9 6 3 11 7 4 14 9 5 16 12 4
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 4 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 6 4 2 7 4 3 9 6 3
4 3 1 4 3 1 5 3 2 6 4 2 7 4 3 8 5 3 9 6 3 10 6 4
4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 9 6 3 10 7 3 12 8 4
2 1 1 3 2 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 3
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 6 4 2
3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 4 3 8 5 3
4 3 1 5 3 2 5 3 2 6 4 2 6 4 2 7 5 2 8 5 3 9 6 3
Thkd 10 15 20 25 30 35 40 45
a
Exposure time in minutes. Exposure time in monitor unit. SFD: source to film distance in cm. d Thk: patient thickness in cm. Note: The first, second and third times are the total, open field and blocked field exposure times, respectively. b c
Table 3. Technique chart for various treatment machines (EC-L film 1 fEC-L cassette) coa SFDc
63b
103b
183b
110
120
130
140
110
120
130
140
110
120
130
140
110
120
130
140
0.03 0.02 0.01 0.04 0.03 0.01 0.05 0.03 0.02 0.06 0.04 0.02 0.08 0.05 0.03 0.11 0.07 0.04 0.15 0.10 0.05 0.19 0.11 0.08
0.03 0.02 0.01 0.04 0.03 0.01 0.06 0.04 0.02 0.07 0.05 0.02 0.10 0.07 0.03 0.13 0.09 0.04 0.17 0.12 0.05 0.23 0.16 0.07
0.04 0.03 0.01 0.05 0.03 0.02 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.15 0.10 0.05 0.20 0.12 0.08 0.27 0.18 0.09
0.04 0.03 0.01 0.06 0.04 0.02 0.08 0.05 0.03 0.10 0.06 0.04 0.13 0.09 0.04 0.18 0.12 0.06 0.23 0.16 0.07 0.31 0.21 0.10
2 1 1 3 2 1 3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 8 5 3 9 6 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 8 5 3 9 6 3 11 7 4
3 2 1 4 3 1 5 3 2 6 4 2 7 4 3 9 6 3 11 7 4 13 9 4
2 1 1 2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2
2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 3 2 7 5 2
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 9 6 3
2 1 1 2 1 1 2 1 1 3 2 1 3 2 1 3 2 1 4 3 1 4 3 1
2 1 1 2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2
3 2 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2
3 2 1 4 3 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 5 2
Thkd 10 15 20 25 30 35 40 45
a
Exposure time in minutes. Exposure time in monitor unit. SFD: source to film distance in cm. d Thk: Patient thickness in cm. Note: The first, second and third times are the total, open field and blocked field exposure times, respectively. b c
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Medical Dosimetry
Figure 3 shows the TAR or TMR as a function of the depth from 10 to 30 cm. From this figure, attenuation coefficients were determined to be 0.0564 cm21, 0.0371 cm21, 0.0285 cm21, and 0.0227 cm21 for the Co-60, 6 MV, 10 MV, and 18 MV beams, respectively. Table 1 summarizes some of the parameters related to the generation of the technique charts. It is assumed that the average portal film size is 15 3 15 cm. Table 2 summarizes the technique charts for all four beams as a function of patient thickness and source-tofilm distance (SFD) for the EC-L film in EC-L cassette system. Table 3 shows similar technique charts for the EC-L film in fEC-L cassette system. DISCUSSIONS This paper shows that the sensitivity of Kodak’s new film-screen systems is energy-dependent and that
Volume 23, Number 2, 1998
fEC-L film in EC-L cassette system is faster than EC-L film in EC-L cassette system. General purpose technique charts have been generated for both systems for the four most popularly used radiation therapy beams. These technique charts can be easily customized to portal localization practice in a radiation therapy department.
REFERENCES 1. Radiotherapy portal imaging quality. AAPM Report No. 24. AAPM; 1987. 2. Droege, R.T.; Bjarngard, B.E. Influence of metal screens on contrast in megavoltage x-ray imaging. Med. Phys. 6:487– 493; 1979. 3. A new imaging standard for radiation oncology. Eastman Kodak Company; 1996. 4. Droege, R.T.; Stefanakos, T.K. Portal film technique charts. Int. J. Radiat. Oncol. Biol. Phys. 11:2027–2031; 1985. 5. Faermann, S.; Krutman, Y. Generation of portal film charts for 10 MV x-rays. Med. Phys. 19:351–353; 1992.
PII S0958-3947(98)00004-1
TECHNIQUE CHARTS FOR KODAK’S NEW FILM-SCREEN SYSTEMS FOR PORTAL LOCALIZATION PLATO C. LEE, PH.D. and GLENN P. GLASGOW, PH.D. Loyola University, Loyola-Hines Department of Radiotherapy, Maywood, IL 60153 Abstract—In July 1996, Kodak released new film-screen systems with enhanced contrast (EC) for portal localization with megavoltage therapeutic beams. This study presents the generation of general-purpose technique charts for Kodak’s new film-screen combinations: the Enhanced-Contrast localization (EC-L) film in EC-L cassette and the EC-L film in fast ECL (fECL) cassette for use with cobalt-60, 6 MV, 10 MV, and 18 MV beams. These technique charts were based on the assumption that a film with an optical density (OD) of 1.8 provides the best viewing density. The doses to produce such as OD, Dexp, were obtained from the H & D curves and were 1.5, 1.6, 1.7, and 1.8 cGy for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively, with the EC-L-film1EC-Lcassette combination. The corresponding values were 1.3, 1.3, 1.3, and 1.4 cGy, respectively, for the above four beams with the EC-L-film1fEC-L-cassette combination. The dose to the film is assumed to be proportional to the calibrated dose rate (D0), field size factor (FSF), inverse square factor relative to 100.0 cm (INV), and the transmission factor through the patient, which is equal to e2uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time or monitor unit, t, is then calculated from the following equation: t 5 Dexp/(D0*FSF*INV*e2uT). For an average port size of 15 3 15 cm, the attenuation coefficients were obtained from the fitting of TAR (cobalt-60) or TMR (6 MV, 10 MV, and 18 MV) as a function of depth from 10 to 30 cm and were 0.0564 cm21, 0.03714 cm21, and 0.02271 cm21 for cobalt-60, 6 MV, 10 MV, and 18 MV beams, respectively. The FSF were explicitly obtained from the clinical physics data books and were 1.028, 1.032, 1.036, and 1.053 for cobalt-60, 6 MV, 10 MV, and 18 MV, respectively. For cobalt-60 beam, the D0 was assumed to be 100.0 cGy/min. For the 6 MV, 10 MV, and 18 MV beams, the D0 in cGy per monitor unit is 1.030, 1.051, and 1.061, respectively. Technique charts were then generated as a function of patient thickness from 10 to 45 cm for filming distance from 110 to 140 cm for all four beams. These technique charts can be easily customized to portal localization practices in a radiation therapy department. © 1998 American Association of Medical Dosimetrists. Key Words: Technique charts, Portal localization, Contrast-enhanced film-screen systems, H & D curves.
INTRODUCTION
on the film, Dexp, is assumed to be proportional to the calibrated dose rate at 100 cm, (D0), field size factor (FSF), inverse square factor relative to 100 cm (INV), and the transmission factor through the patient, which is equal to e2uT, where u is the broad beam attenuation coefficient and T is the patient thickness. With the above assumptions, the exposure time (t) or monitor unit (MU) can be calculated from the following equation:
Presently, the only medium commonly employed to evaluate and document the accuracy of a radiation treatment is the weekly portal film.1 The image quality of the portal films taken with megavoltage beams are typically poor due to the predominance of Compton interactions in the filming process. Metal screens have been shown to enhance the contrast of the port films.2 In 1996 Kodak released the new Enhanced-Contrast Localization (EC-L) film-screen combinations for portal imaging with megavoltage beam.3 In this paper, we present the generation of the technique charts for these new film screen systems, both the EC-L film in EC-L cassette and the EC-L film in fast EC-L (fEC-L) cassette for radiation therapy with cobalt-60, 6 MV, 10 MV, and 18 MV beams. In the generation of the technique charts, it is assumed that an optical density (OD) of 1.8 provides the best viewing density.1,3 The dose to produce such an OD
t or MU 5
D exp D 0*FSF*INV*e2uT
(1)
The Dexps are to be experimentally obtained from the H & D curves of the EC-L films in EC-L cassette and the EC-L films in fEC-L cassette for all four beams. The attenuation coefficients of each beam are to be obtained from the fitting of either TAR (Co-60) or TMR (6 MV, 10 MV and 18 MV) as a function of the depth. Thus, by knowing the calibrated dose rate, (D0), and the FSF, the exposure time or MU, the technique charts can be easily generated as a function of the source-to-cassette distance (SCD) and the patient thickness, T, for all four beams.
Reprint requests to: Dr. Plato Lee, Alexian Brothers Cancer Care Center, 820 W. Biesterfield Road, Elk Grove Village, IL. E mail: [email protected]. Presented as a Work-In-Progress paper in the 39th Annual Meeting of the American Association of Physicists in Medicine (AAPM) in Milwaukee, WI, July 23–31, 1997. 113
114
Medical Dosimetry
Volume 23, Number 2, 1998
Fig. 3. TAR or TMR as a function of depth. Fig. 1. H & D curves for the EC-L film 1 EC-L cassette system.
MATERIALS AND METHODS In the determination of the H & D curves for both film-screen systems, the doses to the films were varied by changing the SCDs from 90 to 145 cm. Due to the speed of the film-screen systems, the exposure times or MUs were 0.02 minutes for co-60 and 2 MU for linac beams. (The reproducibility of dose delivery at such low time or MU settings was checked by repeatedly measuring the outputs of all the studied beams and was found to be better than 2%.) To collect all the exposures on a single
film for each H & D curve, a 6.0 3 6.0 cm field was used. A Nuclear Associate densitometer was used to read the ODs of all the films. The doses to cassette were calculated from the calibrated dose rates, field size factors and inverse square laws for all four beams: cobalt-60 from Theratronix 1000, 6 MV and 18 MV beams from Varian Clinac 1800 and 10 MV beam from Varian Clinac 18. The attenuation coefficients were obtained from the fitting of either the TAR (Co-60) or the TMRs (6 MV, 10 MV, and 18 MV) of a 15 3 15.0 cm field as a function of the depth from 10 to 30 cm. RESULTS Figure 1 shows the H and D curves of the EC-L film in EC-L cassette system for the Co-60, 6 MV, 10 MV, and 18 MV beams. This figure indicates that the sensitivity of the film-screen system is energy-dependent. The dose to produce an OD of 1.8 was determined to be 1.5, 1.6, 1.7, and 1.8 for the above four beams, respectively. Figure 2 shows the H and D curves for the EC-L film in fEC-L cassette for the four beams. Again, the figure indicates that the sensitivity of this film-screen system is energy-dependent. The dose to produce an OD of 1.8 was determined to be 1.3, 1.3, 1.3, and 1.4, respectively, for the above four beams. Table 1. Parameters related to technique charts Cobalt
Fig. 2. H & D curves for the EC-L film 1 fEC-L cassette system.
D0 100.0 (cGy/min or cGy/MU) FSF 1.028 u (cm21) 0.0564 Dexp-ECL cassette (cGy) 1.54 Dexp-fECL cassette (cGy) 1.29
6 MV
10 MV
18 MV
1.030
1.051
1.061
1.032 0.0371 1.67 1.29
1.036 0.0295 1.73 1.34
1.053 0.0227 1.82 1.40
Kodak’s new film screen systems ● P. LEE and G. GLASGOW
115
Table 2. Technique chart for various treatment machines (EC-L film 1 EC-L cassette) coa SFDc
63b
103b
183b
110
120
130
140
110
120
130
140
110
120
130
140
110
120
130
140
0.03 0.02 0.01 0.04 0.03 0.01 0.06 0.04 0.02 0.07 0.05 0.02 0.10 0.07 0.03 0.13 0.09 0.04 0.17 0.12 0.05 0.23 0.16 0.07
0.04 0.03 0.01 0.05 0.04 0.01 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.16 0.11 0.05 0.21 0.14 0.07 0.27 0.18 0.09
0.04 0.03 0.01 0.06 0.04 0.02 0.08 0.05 0.03 0.10 0.07 0.03 0.14 0.09 0.05 0.18 0.12 0.06 0.24 0.16 0.08 0.32 0.21 0.11
0.05 0.03 0.02 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.16 0.12 0.04 0.21 0.14 0.07 0.28 0.21 0.07 0.37 0.25 0.12
3 2 1 3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4
3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4 12 8 4
4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 10 6 4 12 8 4 14 9 5
5 3 2 5 3 2 7 5 2 8 5 3 9 6 3 11 7 4 14 9 5 16 12 4
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 4 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 6 4 2 7 4 3 9 6 3
4 3 1 4 3 1 5 3 2 6 4 2 7 4 3 8 5 3 9 6 3 10 6 4
4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 9 6 3 10 7 3 12 8 4
2 1 1 3 2 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 3
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 6 4 2
3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 4 3 8 5 3
4 3 1 5 3 2 5 3 2 6 4 2 6 4 2 7 5 2 8 5 3 9 6 3
Thkd 10 15 20 25 30 35 40 45
a
Exposure time in minutes. Exposure time in monitor unit. SFD: source to film distance in cm. d Thk: patient thickness in cm. Note: The first, second and third times are the total, open field and blocked field exposure times, respectively. b c
Table 3. Technique chart for various treatment machines (EC-L film 1 fEC-L cassette) coa SFDc
63b
103b
183b
110
120
130
140
110
120
130
140
110
120
130
140
110
120
130
140
0.03 0.02 0.01 0.04 0.03 0.01 0.05 0.03 0.02 0.06 0.04 0.02 0.08 0.05 0.03 0.11 0.07 0.04 0.15 0.10 0.05 0.19 0.11 0.08
0.03 0.02 0.01 0.04 0.03 0.01 0.06 0.04 0.02 0.07 0.05 0.02 0.10 0.07 0.03 0.13 0.09 0.04 0.17 0.12 0.05 0.23 0.16 0.07
0.04 0.03 0.01 0.05 0.03 0.02 0.07 0.05 0.02 0.09 0.06 0.03 0.12 0.08 0.04 0.15 0.10 0.05 0.20 0.12 0.08 0.27 0.18 0.09
0.04 0.03 0.01 0.06 0.04 0.02 0.08 0.05 0.03 0.10 0.06 0.04 0.13 0.09 0.04 0.18 0.12 0.06 0.23 0.16 0.07 0.31 0.21 0.10
2 1 1 3 2 1 3 2 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 8 5 3 9 6 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 8 5 3 9 6 3 11 7 4
3 2 1 4 3 1 5 3 2 6 4 2 7 4 3 9 6 3 11 7 4 13 9 4
2 1 1 2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2
2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 3 2 7 5 2
3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3
3 2 1 4 3 1 4 3 1 5 3 2 6 4 2 7 5 2 8 5 3 9 6 3
2 1 1 2 1 1 2 1 1 3 2 1 3 2 1 3 2 1 4 3 1 4 3 1
2 1 1 2 1 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2
3 2 1 3 2 1 3 2 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2
3 2 1 4 3 1 4 3 1 4 3 1 5 3 2 5 3 2 6 4 2 7 5 2
Thkd 10 15 20 25 30 35 40 45
a
Exposure time in minutes. Exposure time in monitor unit. SFD: source to film distance in cm. d Thk: Patient thickness in cm. Note: The first, second and third times are the total, open field and blocked field exposure times, respectively. b c
116
Medical Dosimetry
Figure 3 shows the TAR or TMR as a function of the depth from 10 to 30 cm. From this figure, attenuation coefficients were determined to be 0.0564 cm21, 0.0371 cm21, 0.0285 cm21, and 0.0227 cm21 for the Co-60, 6 MV, 10 MV, and 18 MV beams, respectively. Table 1 summarizes some of the parameters related to the generation of the technique charts. It is assumed that the average portal film size is 15 3 15 cm. Table 2 summarizes the technique charts for all four beams as a function of patient thickness and source-tofilm distance (SFD) for the EC-L film in EC-L cassette system. Table 3 shows similar technique charts for the EC-L film in fEC-L cassette system. DISCUSSIONS This paper shows that the sensitivity of Kodak’s new film-screen systems is energy-dependent and that
Volume 23, Number 2, 1998
fEC-L film in EC-L cassette system is faster than EC-L film in EC-L cassette system. General purpose technique charts have been generated for both systems for the four most popularly used radiation therapy beams. These technique charts can be easily customized to portal localization practice in a radiation therapy department.
REFERENCES 1. Radiotherapy portal imaging quality. AAPM Report No. 24. AAPM; 1987. 2. Droege, R.T.; Bjarngard, B.E. Influence of metal screens on contrast in megavoltage x-ray imaging. Med. Phys. 6:487– 493; 1979. 3. A new imaging standard for radiation oncology. Eastman Kodak Company; 1996. 4. Droege, R.T.; Stefanakos, T.K. Portal film technique charts. Int. J. Radiat. Oncol. Biol. Phys. 11:2027–2031; 1985. 5. Faermann, S.; Krutman, Y. Generation of portal film charts for 10 MV x-rays. Med. Phys. 19:351–353; 1992.