Inf. J. Rodiarim Pergamon Prrs\
Oncology Biol. Phys Vol 5. pp Ltd 1979. Prmted in the U.S.A
1893-1897
l Technical Innovations DOSE
RATES
and Notes
FOR
BRACHYTHERAPY 137Cs SOURCES-f
SUBHASH C. SHARMA, Ph.D.,
$
BRUCE GERBI, M.S.
MADOC-JONES, Washington
APPLICATORS
M.D.,
USING
and HYWEL
Ph.D.
University School of Medicine, Mallinckrodt Institute of Radiology, Division Oncology, 510 South Kingshighway, St. Louis, MO 63110, U.S.A. St. Louis, MO 63110, U.S.A.
of Radiation
We have computed the dose rates from brachytherapy 3M lnCs sources for different size ovoids and vaginal cylinders. They are expressed in tabular form. The dose rate tables thus generated compared with the widely used tables for ‘%Ra differ by as much as 9% for ovoids and up to 20% for the cylinders.’ These differences are mainly a consequence of differences in physical structure of the two types of sources. These tables will serve as a quick guide and reference and should be of great practical use to physicists and radiotherapists for planning implants. However, these tables are not meant to replace detailed computer isodose calculations. Brachytherapy
applicators,
13’Cs sources.
INTRODUCTION
applicable to a commonly used ‘37Cs source so it will be possible for the practicing radiotherapist and medical physicist to have a set of tables at hand with which he may quickly calculate the dose delivered to the surface of the vaginal mucosa or to the vaginal wall. There are 2 main advantages to these tables. First, at the time the intracavitary application is made, it is convenient to be able to give an accurate estimate of the expected duration of the intracavitary exposure immediately, before the computerized dosimetry has been completed. Second, it is always necessary to do a hand calculation as a check on the computerized calculations in case a mistake is made in entering data into the computer. Our method of data representation has the same format as the tables in Fletcher’s textbook.’ In effect, this paper is an extension of previously published work on dose distributions about single ‘37Cs sources’ and illustrates the change in dose rate around various size brachytherapy applicators.
Clinical radiotherapists in many institutions are accustomed to expressing the dose to the mucosa of the vaginal vault when using ovoids in terms of rad surface dose rather than simply in mg-hr. This is advantageous because it allows the rad surface dose to be expressed as a function of ovoid size. When treating the vagina using cylinders, it is customary to perform a hand calculation in addition to computerized isodose curves. For this purpose, tables have been generated for computing the rad surface dose or dose to the vaginal wall.’ These tables were developed at the M. D. Anderson Hospital and apply to the radium tubes used at that institution (written communication with V. Sampiere, June 1978). If radium sources are constructed differently from those at the M. D. Anderson Hospital or if another isotope such as cesium is used, the tables in Fletcher’s textbook may not be applicable. Furthermore, if those tables are used, an error may be produced which may be as much as 20% or more for vaginal cylinders when multiple sources are laid end to end. This difference could result in a significant increase in the complication rate to the patient. We have developed a new set of tables that are
METHODS
AND MATERIALS
Calculations were principally carried out for a Cs source§ and are reported here in detail. This particular
model
source
has a physical
length
of 20 mm,
420 Delaware St, S.E. Minneapolis, MN 55455, U.S.A. 93 M model 6D6C/CA, Radiation Therapy Products, Paul, Minn. Reprint requests to: S. C. Sharma, Ph.D. Accepted for publication 9 February 1979.
tsupported by United States Public Health Service (USPHS) Grant No. PO1 CA 13505, National Cancer Institute, National Institutes of Health. *Present address: University of Minnesota Hospitals, Dept of Therapeutic Radiology, Box 494, Mayo Memorial Bldg, 1893
St.
Radiation Oncology 0 Biology 0 Physics
I894
active length of 14 mm and a stainless steel wall thickness of 0.93 mm. This source was chosen because it has physical dimensions similar to a standard radium tube which has a physical length of 22 mm, active length of 15 mm and wall thickness of 1 mm of platinum. A dosimetry program? was used to generate the various dose rate tables. The energy absorption coefficient for 0.662 MeV gamma rays was taken as 0.221 cm-’ for iron, and the wall thickness entered was 0.93 mm. 2.55 mCi of ‘j’Cs was considered to be equivalent to 1 mg of radium.’ Comparison of the dosimetry program generated source data for a single 17’Cs source agrees well with the calculated dose distributions of Krishnaswamy’ which are generally accepted and supported by measured dose distributions of Saylor and Dillard’ and Marcia Urie, (unpublished data). For distances less than 4 cm from the center of the source, the difference was less than -~2% from the data of Krishnaswamy.’ At distances greater than 7 cm, our data showed an increase of 7% over that of Krishnaswamy. This is because tissue attenuation is not taken into account in the dosimetry program. The maximum contribution to the total dose rate comes from the sources adjacent to the point of interest. For a source at a distance greater than 7 cm, the relative contribution to the total dose rate is small. Therefore, the overall maximum error in the total weighted dose rates from the multiple source arrangement is of the order of 2-3%. The comparison of dose rate for cesium sources in air vs sources in tissue was shown experimentally4 and reveals the same type of differences. No correction for shielding is incorporated in the tabulation of the surface dose distributions for miniovoids. For ovoids larger than mini-ovoids, our tables reflect a 6% reduction in dose rate from the single source to account for shielding by the metal walls of the ovoids. This is the same reduction factor employed by Fletcher,’ to describe the dose rates around ovoids. A more sophisticated approach may be needed to describe the dose distribution completely around Fletcher-Suit applicators.’
RESULTS
AND DISCUSSION
Our computer generated dose rates are tabulated in Tables 1 and 2 for various diameter ovoids with single source and cylinders with multiple sources. The tables reported for 226Ra by Fletcher’ and our set of tables reported in this paper differ by as much as 20%. For ovoids, differences of the order of 10% may be explained and result from the difference between tArtronix System).
PC-12
Dosimetry
Program
(RTP-III.31
October 1979, Volume 5, Number 10
Table 1. Calculated dose rates for ovoids for “‘Cs s0urce.t All strengths of Cs are in mg Ra equivalent for 0.5 mm platinum
filtered radium source Mini-ovoids$--1.6
rayh
5 49.7
10 99.3
Small ovoid§-2.0 mg rad/h
5 31.7
10 63.3
Medium ovoid&2.5
rz?h
15 149.0
20 198.6
cm diameter I5 95.0
20 126.6
cm diameter
5
10
IS
20
21.2
42.3
63.5
84.6
Large ovoid&3.0 mg rad/h
cm diameter
5 15.1
10 30.2
cm diameter 15 45.3
20 60.4
+3M Cs Model 6D6C size CA, physical length = 20 mm, active length = 14 mm diameter = and 3.1 mm. SNo filtration corrections. O(-6%) ovoid absorption included in dose rates.
the source-wall filtration of 1 mm platinum-iridium steel for cesium. for radium tubes vs I mm stainless On the transverse axis through the cesium tube, 1 mm of stainless steel with 17’Cs gamma rays is approximately equivalent to 0.5 mm platinum with 22hRa gamma rays.* However, ‘37CsS tubes are standardized by calibration against radium tubes filtered by 0.5 mm of platinum in contrast to the 1 mm of platinum used in the standard radium tubes at the M. D. Anderson Hospital for which Fletcher’s’ tables are calculated. In the case where the sources are laid end to end in a vaginal cylinder, the remaining part of the increased dose from the cesium tubes results from the difference in physical length of the source. This results in a difference in concentration of the radioactive isotope per unit length of the vagina1 cylinder compared to a radium source. Additional differences arise because oblique filtration for 13’Cs gamma rays through stainless steel is different from the oblique filtration of the 226Ra gamma rays through Pt-Ir. CONCLUSION These tables for 13’Cs sources are of great practical usefulness; they may be used in the operating room $3M.
Dose
rates
Table 2. Vaginal
from
“‘Cs
sources
cylinders-dose
n
B
-2cm
p
_ _.
2 ---2cm
3 Without
n
at 0.25 cm beyond
7
-1--II
-‘_
cm
surface
: ~
4
5 2cm
2cm
spacers c
B
189.5
0 S. C. SHARMA et ul.
E I
D
I lh
-2cm With
Cesium Source
sources
Cesium Source
-
spacers
(Source
without
1.62 6.73 1.62 0.44 0.20
0.44 0.20 0.11
sources
without
1.45 4.50 1.45 0.43 0.19
A radlmg-h
1 2 3 4 5
3.21 1.27 0.42 0.19 0.11
1 2 3 4 5
A
D rad/mg-h 0.20 0.44 1.62 6.73 1.62
E rad/mg-h 0.11 0.20 0.44 1.62 6.73
with 2.0 cm diameter D rad/mg-h
0.43 1.45 4.50 1.45 0.43
E rad/mg-h
0.19 0.43 1.45 4.50 1.45
0.11 0.19 0.43 1.45 4.50
D
E
with 2.5 cm diameter B
C
rad/mg-h 1.27 3.21 1.27 0.42 0.19
Cylinder Source
rad/mg-h
v25
with 1.5 cm diameter
C
rad/mg-h
2cm
not to scale.)
0.44 1.62 6.73 1.62 0.44
B
Cylinder Source
rad/mg-h
spacers-cylinder
A
4.50 1.45 0.43 0.19 0.11
diameter
C
rad/mg-h
1.62
5
2cm
2 cm
spacers-cylinder B
6.73
rad/mg-h 1 2 3 4 5
-2cm
A rad/mg-h
1 2 3 4 5
-
M
rad/mg-h
rad/mg-h
0.42 1.27 3.21 1.27 0.42
rad/mg-h
0.19 0.42 1.27 3.21 1.27
0.11 0.19 0.42 1.27 3.21
D
E
with 3.0 cm diameter B
C
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
2.40 1.11 0.40 0.19 0.11
1.11 2.40 1.11 0.40 0.19
0.40 1.11 2.40 1.11 0.40
0.19 0.40 1.11 2.40 1.11
0.11 0.19 0.40 1.11 2.40
1896
Radiation Oncology 0 Biology 0 Physics
October 1979, Volume 5, Number IO
Table 2. (Cant&. Cesium
sources
Source
spacers-cylinder
A
B
rad/mg-h 1 2 3 4 5
without
1.48 0.86 0.36 0.18 0.11
Source
0.86 1.48 0.86 0.36 0.18
A
I
Cesium
Source
1.01 0.67 0.33 0.17 0.11
sources
0.67 1.01 0.67 0.33 0.17
6.73 1.09 0.28 0.12 0.07
B
1.09 6.73 1.09 0.28 0.12
A rad/mg-h
1 2 3 4 5
4.50 1.01 0.28 0.12 0.06
A rad/mg-h
1 2 3 4 5
3.21 0.92 0.28 0.12 0.06
rad/mg-h
0.18 0.36 0.86 1.48 0.86
0.11 0.18 0.36 0.86 1.48
D
E
rad/mg-h
0.33 0.67 1.01 0.67 0.33
rad/mg-h
rad/mg-h
0.17 0.33 0.67 1.01 0.67
0.11 0.17 0.33 0.67 1.01
per inch-cylinder
D rad/mg-h
0.28 1.09 6.73
with
E rad/mg-h
1.09
0.12 0.28 1.09 6.73
0.28
1.09
0.07 0.12 0.28 1.09 6.73
D
E
with 2.0 cm diameter B
C
rad/mg-h 1.01 4.50 1.01 0.28 0.12
Cylinder Source
radlmg-h
C
radlmg-h
Cylinder Source
C
rad/mg-h
A
rad/mg-h
0.36 0.86 1.48 0.86 0.36
with 2 (0.25 cm each) spacers 1.5 cm diameter
rad/mg-h 1 2 3 4 5
radlmg-h
E
D
with 5.0 cm diameter B
rad/mg-h
2 3 4 5
C
rad/mg-h
Cylinder
with 4.0 cm diameter
rad/mg-h
rad/mg-h
0.28 1.01 4.50 1.01 0.28
rad/mg-h
0.12 0.28 1.01 4.50 1.01
0.06 0.12 0.28 1.01 4.50
D
E
with 2.5 cm diameter B
rad/mg-h 0.92 3.21 0.92 0.28 0.12
C rad/mg-h 0.28 0.92 3.21 0.92 0.28
rad/mg-h 0.12 0.28 0.92 3.21 0.92
rad/mg-h 0.06 0.12 0.28 0.92 3.21
Dose
rates from “‘Cs sources 0 S. C. SHARMAet al.
1897
Table 2. (Contd). Cesium sources with 2 (0.25 cm each) spacers per inch-cylinder 3.0 cm diameter Source
1 2 3 4 5
with
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
2.40 0.84 0.27 0.12 0.07
0.84 2.40 0.“4 0.27 0.12
0.27 0.84 2.40 0.84 0.27
0.12 0.27 0.84 2.40 0.84
0.07 0.12 0.27 0.84 2.40
Cylinder with 4.0 cm diameter Source
/
1 2 3 4 5
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
1.48 0.69 0.26 0.12 0.07
0.69 1.48 0.69 0.26 0.12
0.12 0.26 0.69 1.48 0.69
0.07 0.12 0.26 0.69 1.48
0.26 0.69 1.48 0.69 0.26
Cylinder with 5.0 cm diameter Source
1 2 3 4 5
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
1.01 0.56 0.23 0.12 0.07
0.56 1.01 0.56 0.23 0.12
to give an immediate estimate of the length of time that ovoids or cylinders should be left in a patient. They also serve as an independent method to check computer calculations. They do not in any way
0.23 0.56 1.01 0.56 0.23
0.12 0.23 0.56 1.01 0.56
0.07 0.12 0.23 0.56 1.01
replace the need for computerized generation of isodose curves and they are applicable only to the size and dimensions of this particular 13’Cs source.
REFERENCES 2nd Edn, 1. Fletcher, G.H.: Textbook of radiotherapy, Lea & Febiger, Philadelphia, 1975, pp. 678-679. 2. Krishnaswamy, V.: Dose distributions about 13’Cs sources in tissue. Radiology 105: 181-184, 1972. 3. Saylor, W.L., Dillard, M.: Dosimetry of 13’Cs sources with the Fletcher-Suit gynecological applicator. Med.
Phys., Vol. 3, No. 2, Mar/Apr. 1976, pp. 117-119. 4. Shalek, R.J., Stovall, M.: Dosimetry in implant therapy. in Radiation Zhsimetry, Vol. III, ed. by Attix, F.H., Tochilin, E., New York, Academic Press, 1969, pp. 743-807.
Oncology Biol. Phys Vol 5. pp Ltd 1979. Prmted in the U.S.A
1893-1897
l Technical Innovations DOSE
RATES
and Notes
FOR
BRACHYTHERAPY 137Cs SOURCES-f
SUBHASH C. SHARMA, Ph.D.,
$
BRUCE GERBI, M.S.
MADOC-JONES, Washington
APPLICATORS
M.D.,
USING
and HYWEL
Ph.D.
University School of Medicine, Mallinckrodt Institute of Radiology, Division Oncology, 510 South Kingshighway, St. Louis, MO 63110, U.S.A. St. Louis, MO 63110, U.S.A.
of Radiation
We have computed the dose rates from brachytherapy 3M lnCs sources for different size ovoids and vaginal cylinders. They are expressed in tabular form. The dose rate tables thus generated compared with the widely used tables for ‘%Ra differ by as much as 9% for ovoids and up to 20% for the cylinders.’ These differences are mainly a consequence of differences in physical structure of the two types of sources. These tables will serve as a quick guide and reference and should be of great practical use to physicists and radiotherapists for planning implants. However, these tables are not meant to replace detailed computer isodose calculations. Brachytherapy
applicators,
13’Cs sources.
INTRODUCTION
applicable to a commonly used ‘37Cs source so it will be possible for the practicing radiotherapist and medical physicist to have a set of tables at hand with which he may quickly calculate the dose delivered to the surface of the vaginal mucosa or to the vaginal wall. There are 2 main advantages to these tables. First, at the time the intracavitary application is made, it is convenient to be able to give an accurate estimate of the expected duration of the intracavitary exposure immediately, before the computerized dosimetry has been completed. Second, it is always necessary to do a hand calculation as a check on the computerized calculations in case a mistake is made in entering data into the computer. Our method of data representation has the same format as the tables in Fletcher’s textbook.’ In effect, this paper is an extension of previously published work on dose distributions about single ‘37Cs sources’ and illustrates the change in dose rate around various size brachytherapy applicators.
Clinical radiotherapists in many institutions are accustomed to expressing the dose to the mucosa of the vaginal vault when using ovoids in terms of rad surface dose rather than simply in mg-hr. This is advantageous because it allows the rad surface dose to be expressed as a function of ovoid size. When treating the vagina using cylinders, it is customary to perform a hand calculation in addition to computerized isodose curves. For this purpose, tables have been generated for computing the rad surface dose or dose to the vaginal wall.’ These tables were developed at the M. D. Anderson Hospital and apply to the radium tubes used at that institution (written communication with V. Sampiere, June 1978). If radium sources are constructed differently from those at the M. D. Anderson Hospital or if another isotope such as cesium is used, the tables in Fletcher’s textbook may not be applicable. Furthermore, if those tables are used, an error may be produced which may be as much as 20% or more for vaginal cylinders when multiple sources are laid end to end. This difference could result in a significant increase in the complication rate to the patient. We have developed a new set of tables that are
METHODS
AND MATERIALS
Calculations were principally carried out for a Cs source§ and are reported here in detail. This particular
model
source
has a physical
length
of 20 mm,
420 Delaware St, S.E. Minneapolis, MN 55455, U.S.A. 93 M model 6D6C/CA, Radiation Therapy Products, Paul, Minn. Reprint requests to: S. C. Sharma, Ph.D. Accepted for publication 9 February 1979.
tsupported by United States Public Health Service (USPHS) Grant No. PO1 CA 13505, National Cancer Institute, National Institutes of Health. *Present address: University of Minnesota Hospitals, Dept of Therapeutic Radiology, Box 494, Mayo Memorial Bldg, 1893
St.
Radiation Oncology 0 Biology 0 Physics
I894
active length of 14 mm and a stainless steel wall thickness of 0.93 mm. This source was chosen because it has physical dimensions similar to a standard radium tube which has a physical length of 22 mm, active length of 15 mm and wall thickness of 1 mm of platinum. A dosimetry program? was used to generate the various dose rate tables. The energy absorption coefficient for 0.662 MeV gamma rays was taken as 0.221 cm-’ for iron, and the wall thickness entered was 0.93 mm. 2.55 mCi of ‘j’Cs was considered to be equivalent to 1 mg of radium.’ Comparison of the dosimetry program generated source data for a single 17’Cs source agrees well with the calculated dose distributions of Krishnaswamy’ which are generally accepted and supported by measured dose distributions of Saylor and Dillard’ and Marcia Urie, (unpublished data). For distances less than 4 cm from the center of the source, the difference was less than -~2% from the data of Krishnaswamy.’ At distances greater than 7 cm, our data showed an increase of 7% over that of Krishnaswamy. This is because tissue attenuation is not taken into account in the dosimetry program. The maximum contribution to the total dose rate comes from the sources adjacent to the point of interest. For a source at a distance greater than 7 cm, the relative contribution to the total dose rate is small. Therefore, the overall maximum error in the total weighted dose rates from the multiple source arrangement is of the order of 2-3%. The comparison of dose rate for cesium sources in air vs sources in tissue was shown experimentally4 and reveals the same type of differences. No correction for shielding is incorporated in the tabulation of the surface dose distributions for miniovoids. For ovoids larger than mini-ovoids, our tables reflect a 6% reduction in dose rate from the single source to account for shielding by the metal walls of the ovoids. This is the same reduction factor employed by Fletcher,’ to describe the dose rates around ovoids. A more sophisticated approach may be needed to describe the dose distribution completely around Fletcher-Suit applicators.’
RESULTS
AND DISCUSSION
Our computer generated dose rates are tabulated in Tables 1 and 2 for various diameter ovoids with single source and cylinders with multiple sources. The tables reported for 226Ra by Fletcher’ and our set of tables reported in this paper differ by as much as 20%. For ovoids, differences of the order of 10% may be explained and result from the difference between tArtronix System).
PC-12
Dosimetry
Program
(RTP-III.31
October 1979, Volume 5, Number 10
Table 1. Calculated dose rates for ovoids for “‘Cs s0urce.t All strengths of Cs are in mg Ra equivalent for 0.5 mm platinum
filtered radium source Mini-ovoids$--1.6
rayh
5 49.7
10 99.3
Small ovoid§-2.0 mg rad/h
5 31.7
10 63.3
Medium ovoid&2.5
rz?h
15 149.0
20 198.6
cm diameter I5 95.0
20 126.6
cm diameter
5
10
IS
20
21.2
42.3
63.5
84.6
Large ovoid&3.0 mg rad/h
cm diameter
5 15.1
10 30.2
cm diameter 15 45.3
20 60.4
+3M Cs Model 6D6C size CA, physical length = 20 mm, active length = 14 mm diameter = and 3.1 mm. SNo filtration corrections. O(-6%) ovoid absorption included in dose rates.
the source-wall filtration of 1 mm platinum-iridium steel for cesium. for radium tubes vs I mm stainless On the transverse axis through the cesium tube, 1 mm of stainless steel with 17’Cs gamma rays is approximately equivalent to 0.5 mm platinum with 22hRa gamma rays.* However, ‘37CsS tubes are standardized by calibration against radium tubes filtered by 0.5 mm of platinum in contrast to the 1 mm of platinum used in the standard radium tubes at the M. D. Anderson Hospital for which Fletcher’s’ tables are calculated. In the case where the sources are laid end to end in a vaginal cylinder, the remaining part of the increased dose from the cesium tubes results from the difference in physical length of the source. This results in a difference in concentration of the radioactive isotope per unit length of the vagina1 cylinder compared to a radium source. Additional differences arise because oblique filtration for 13’Cs gamma rays through stainless steel is different from the oblique filtration of the 226Ra gamma rays through Pt-Ir. CONCLUSION These tables for 13’Cs sources are of great practical usefulness; they may be used in the operating room $3M.
Dose
rates
Table 2. Vaginal
from
“‘Cs
sources
cylinders-dose
n
B
-2cm
p
_ _.
2 ---2cm
3 Without
n
at 0.25 cm beyond
7
-1--II
-‘_
cm
surface
: ~
4
5 2cm
2cm
spacers c
B
189.5
0 S. C. SHARMA et ul.
E I
D
I lh
-2cm With
Cesium Source
sources
Cesium Source
-
spacers
(Source
without
1.62 6.73 1.62 0.44 0.20
0.44 0.20 0.11
sources
without
1.45 4.50 1.45 0.43 0.19
A radlmg-h
1 2 3 4 5
3.21 1.27 0.42 0.19 0.11
1 2 3 4 5
A
D rad/mg-h 0.20 0.44 1.62 6.73 1.62
E rad/mg-h 0.11 0.20 0.44 1.62 6.73
with 2.0 cm diameter D rad/mg-h
0.43 1.45 4.50 1.45 0.43
E rad/mg-h
0.19 0.43 1.45 4.50 1.45
0.11 0.19 0.43 1.45 4.50
D
E
with 2.5 cm diameter B
C
rad/mg-h 1.27 3.21 1.27 0.42 0.19
Cylinder Source
rad/mg-h
v25
with 1.5 cm diameter
C
rad/mg-h
2cm
not to scale.)
0.44 1.62 6.73 1.62 0.44
B
Cylinder Source
rad/mg-h
spacers-cylinder
A
4.50 1.45 0.43 0.19 0.11
diameter
C
rad/mg-h
1.62
5
2cm
2 cm
spacers-cylinder B
6.73
rad/mg-h 1 2 3 4 5
-2cm
A rad/mg-h
1 2 3 4 5
-
M
rad/mg-h
rad/mg-h
0.42 1.27 3.21 1.27 0.42
rad/mg-h
0.19 0.42 1.27 3.21 1.27
0.11 0.19 0.42 1.27 3.21
D
E
with 3.0 cm diameter B
C
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
2.40 1.11 0.40 0.19 0.11
1.11 2.40 1.11 0.40 0.19
0.40 1.11 2.40 1.11 0.40
0.19 0.40 1.11 2.40 1.11
0.11 0.19 0.40 1.11 2.40
1896
Radiation Oncology 0 Biology 0 Physics
October 1979, Volume 5, Number IO
Table 2. (Cant&. Cesium
sources
Source
spacers-cylinder
A
B
rad/mg-h 1 2 3 4 5
without
1.48 0.86 0.36 0.18 0.11
Source
0.86 1.48 0.86 0.36 0.18
A
I
Cesium
Source
1.01 0.67 0.33 0.17 0.11
sources
0.67 1.01 0.67 0.33 0.17
6.73 1.09 0.28 0.12 0.07
B
1.09 6.73 1.09 0.28 0.12
A rad/mg-h
1 2 3 4 5
4.50 1.01 0.28 0.12 0.06
A rad/mg-h
1 2 3 4 5
3.21 0.92 0.28 0.12 0.06
rad/mg-h
0.18 0.36 0.86 1.48 0.86
0.11 0.18 0.36 0.86 1.48
D
E
rad/mg-h
0.33 0.67 1.01 0.67 0.33
rad/mg-h
rad/mg-h
0.17 0.33 0.67 1.01 0.67
0.11 0.17 0.33 0.67 1.01
per inch-cylinder
D rad/mg-h
0.28 1.09 6.73
with
E rad/mg-h
1.09
0.12 0.28 1.09 6.73
0.28
1.09
0.07 0.12 0.28 1.09 6.73
D
E
with 2.0 cm diameter B
C
rad/mg-h 1.01 4.50 1.01 0.28 0.12
Cylinder Source
radlmg-h
C
radlmg-h
Cylinder Source
C
rad/mg-h
A
rad/mg-h
0.36 0.86 1.48 0.86 0.36
with 2 (0.25 cm each) spacers 1.5 cm diameter
rad/mg-h 1 2 3 4 5
radlmg-h
E
D
with 5.0 cm diameter B
rad/mg-h
2 3 4 5
C
rad/mg-h
Cylinder
with 4.0 cm diameter
rad/mg-h
rad/mg-h
0.28 1.01 4.50 1.01 0.28
rad/mg-h
0.12 0.28 1.01 4.50 1.01
0.06 0.12 0.28 1.01 4.50
D
E
with 2.5 cm diameter B
rad/mg-h 0.92 3.21 0.92 0.28 0.12
C rad/mg-h 0.28 0.92 3.21 0.92 0.28
rad/mg-h 0.12 0.28 0.92 3.21 0.92
rad/mg-h 0.06 0.12 0.28 0.92 3.21
Dose
rates from “‘Cs sources 0 S. C. SHARMAet al.
1897
Table 2. (Contd). Cesium sources with 2 (0.25 cm each) spacers per inch-cylinder 3.0 cm diameter Source
1 2 3 4 5
with
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
2.40 0.84 0.27 0.12 0.07
0.84 2.40 0.“4 0.27 0.12
0.27 0.84 2.40 0.84 0.27
0.12 0.27 0.84 2.40 0.84
0.07 0.12 0.27 0.84 2.40
Cylinder with 4.0 cm diameter Source
/
1 2 3 4 5
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
1.48 0.69 0.26 0.12 0.07
0.69 1.48 0.69 0.26 0.12
0.12 0.26 0.69 1.48 0.69
0.07 0.12 0.26 0.69 1.48
0.26 0.69 1.48 0.69 0.26
Cylinder with 5.0 cm diameter Source
1 2 3 4 5
A
B
C
D
E
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
rad/mg-h
1.01 0.56 0.23 0.12 0.07
0.56 1.01 0.56 0.23 0.12
to give an immediate estimate of the length of time that ovoids or cylinders should be left in a patient. They also serve as an independent method to check computer calculations. They do not in any way
0.23 0.56 1.01 0.56 0.23
0.12 0.23 0.56 1.01 0.56
0.07 0.12 0.23 0.56 1.01
replace the need for computerized generation of isodose curves and they are applicable only to the size and dimensions of this particular 13’Cs source.
REFERENCES 2nd Edn, 1. Fletcher, G.H.: Textbook of radiotherapy, Lea & Febiger, Philadelphia, 1975, pp. 678-679. 2. Krishnaswamy, V.: Dose distributions about 13’Cs sources in tissue. Radiology 105: 181-184, 1972. 3. Saylor, W.L., Dillard, M.: Dosimetry of 13’Cs sources with the Fletcher-Suit gynecological applicator. Med.
Phys., Vol. 3, No. 2, Mar/Apr. 1976, pp. 117-119. 4. Shalek, R.J., Stovall, M.: Dosimetry in implant therapy. in Radiation Zhsimetry, Vol. III, ed. by Attix, F.H., Tochilin, E., New York, Academic Press, 1969, pp. 743-807.
