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Preparation of phantom lung material
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 150 (http://iopscience.iop.org/0031-9155/21/1/117) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.113.111.210 This content was downloaded on 09/08/2015 at 11:54
Please note that terms and conditions apply.
PHYS. MED.BIOL.,
1976, VOL. 21,
NO.
1, 150-153. @ 1976
CORRESPONDENCE Preparation of Phantom Lung Material THE EDITOR, Sir, The purpose of this letteris to indicate the ratherwide range of lung densities that may result when granulated muscle-equivalentplasticis used to form phantom lungs and to suggest some alternative materials. The use of muscle-equivalent plastic (type A-150) for the construction of lung material for photon and neutrondose distribution measurements has been described in recent publications. A lung density of 0 . 3 8 g (3111-3 was obtained by McGinley (1 973)when granulated muscle-equivalent plastic, which is normally used for moulding operations, was packed into a thin-walled plastic container. The granulated muscle-equivalent plastic employed was in the form of thin flatparticles of rectangular cross-section withdimensions of approximately 2 x 2 x 0.1 mm and was purchased from the Physical Sciences Laboratory of Illinois Benedictine College, Lisle, Illinois. Garry, Stansbury and Poston (1974) used shavings ( 3 mm wide and 0 . 4 mm thick) of A-150 plastic turned by a lathe from solid pieces of plastic to produce phantom lungs with a density adensity of rangingfrom 0.1 to 0.2 g (3111-3. Phantomlungmaterialwith 0-2-0.3 g cm-3 was also formed by dicing the turnings with a food blender. The variabilityof the density of phantom lung material is caused by variation in the size and shape of the plastic particles. For example, Mijnheer (1974, private communication) found that a sample of granulated muscle-equivalent plasticobtainedfrom the Physical Sciences Laboratory was composed of particles with diameter ranging from 1 t o 5 mm and yielded a lung density of 0.6 g cm-3. The lung density was reduced to 0.4 g (3111-3 by filtering out the larger particles. A rangeof particle size and shape results fromthe procedure employed at the Physical Sciences Laboratory to prepare granulated muscle-equivalent plastic. I n this procedure, the components used in the A-150 plastic are ball milled while in powder form,then plasticized and mixed using a modified screw extrusion process, developed by the lateDr. F. R. Shonka, which ensures a high degree of uniformity. Following mixing, the plastic is prepared for moulding by granulating the extruded A-150 in a commercial Cumberland mill. Although a variety of screen sizes are available with this machine, Spokas (1974, private communication) has indicated that only two are routinely used. The coarse screen has 6 - 3 5 mm diameter holes, while the standard screen has 3.175 mm holes. An additional variable is introduced into the granulated A-l50 when sizeable clean pieces of the plastic left from moulding or machine operations areregranulatedforstock,This A-150 which has been subjected to high pressure moulding has a greater density than extruded material.
Correspondence
151
Instead of using the A - l 5 0 plastic one can prepare lung material by forming a mixture of 66% by weight Lucite (C,H,O,), chips and 34% by weight polyethylene (CH,), chips. As can be seen from table 1, this mixture is a better matchthan A - l 5 0 plastic to the composition suggested bySnyder,Ford, Warner and Fisher (1969) for Reference Man lung. I n addition, these plastics are more readily available and less expensive than A-l50 plastic. Table 1. Composition of lung and lung-equivalent materials Muscle-equivalent plastic (A-150), Smathers (1975, private 66% Lucite C,H,O,communicat'ion) 34% polyethylene CH, Yo by weight
Lung tissue, Snyder et al. (1969)
Constituent
H C
h' 0 Other
10.21 10.01 2.80 75.98 0.98
Modified sponge lung7 10.21 10.00 3.20 75.60 1.00
10.20 68.70 21.09 I
I
t Consists of the following in yo by weight: 68.5% H,O;
I
8 % NH,OH; 1 % NaCl; 22.50;b
C,H,,O, (vacuum oven dried sponge cellulose).
A third lung-equivalent material with hydrogen, oxygen and carbon contents similar to thatsuggested by Snyderet al. (1969) for lung was recently developed at the Oak Ridge National Laboratory by Stansbury and Poston (1974). This method uses sponge cellulose (C,H,,O,), salt (NaC1) and water. To obtain an accurate measure of the weight of the sponge, it was necessary to dry it in a vacuum oven overnight. Stansbury (1974, private communication) has found that a sealed container of sponge material with water and salt added shows no tendency t'o release water other than a slight condensation on the container walls. We have altered this material to introduce nitrogen into the sponge material a t levels found in lung by substituting other compounds for salt as shown in the last column of table 1 . A range of densities of the order of 0.15-0.30 g cm-3 can be achieved by cutting thesponge into small irregular sized pieces and packing the material in a container. I n table 2, the phantom lung materials arecompared with Snyder et al. lungtissuein terms of the percent difference between the mass attenuation coefficients for photon interactions (photoelectric, coherent and Compton scattering). A negative per centdifference is used to indicate that themass attenuation coefficient for the lung material is less than that of lung tissue. All mass attenuation coefficients were obtained by use of the TECALC program developed by Stansbury (1974). The Lucite-polyethylene mixture and A-150 plastic have mass attenuation coefficients that are about the same for coherentand Compton for photons photon interactions. Both materials are poor phantom materials
Correspondence
152
Table 2. 'Percentage difference between the mass attenuation coefficients for various phantom lung materials and lung t'issue Photon energy (hew
yo Difference photoelectric cross-section
Granulated A - l 5 0 plastic lung
10 20 40 60 80 100 150 200 500 1000
- 23.78 - 18'53 - 13.16 - 10.20 - 8.26 - 6.87 - 4.67 - 3.39 - 1.14 - 1.45
Lucitepolyethylene lung
10 20 40 60 80 100 150 200 500 1000
- 50.33 - 53.08 - 55.16 - 56'09 - 56.63 - 56'98 - 57.51
10 20 40 60 80 100 150 200 500 1000
Lung material
Modified sponge lung
yo Difference
yo Difference
coherent cross-section
Compton cross-section
- 26.25 - 25.64 - 24'86 - 24'45 - 24'22 -24.10 - 24.03 - 24.12 - 25.47 - 27.80
5.09 0.35 - 1.10 - 0.93 - 0.52 - 0.12 0.67 1.13 0.83 - 2.59
- 58.54
- 26.94 - 26.96 - 26.66 - 26.44 - 26.31 - 26.24 - 26.20 - 26'28 - 27.36 - 29.28
5.00 0.94 - 0.41 - 0.35 - 0.08 0.22 0.80 1.15 0.91 - 1.76
- 3.30
.- 0.50
- 4.2 1 - 5.01 - 5.40 - 5.65 - 5.83 - 6.12 - 6.31 - 6.92 - c1.91
- 0.62 - 0.62 - 0.61
0.04 0.02 0.01 0.01 0.00 0.00 0.00 0.00 0.00 - 0.01
-5i.80 - 58.36
- 0.55 - 0.59 - 0.61 - 0.62 - 0.62 - 0.62
Percentage difference for lung-equivalent material calculated as (PIP)
-
M P )
(luna-equivalent material) (Snyder lung tissue)
(PLIP)
x 100.
(Snyder lung tissue)
with energy below approximately 20 keV due to the low mass attenuation coefficients associatedwith the photoelectricinteraction. The sponge lung material is lung-equivalent for photons with energybetween 10 and 1000 keV.
P. H. MCGINLEY, J. J.SHONKA, School of Nuclear Engineering, Division of Radiation Therapy, Georgia Institute of Technology, Emory University Clinic, Atlanta, Georgia 30322, U.S.A. Atlanta, Georgia 30332, U.S.A. 18 July 1975
Correspondence
153
REFERENCES GARRY,S. M., STANSBURY, P. S., and POSTON, J. W., 1974, Measurement of Absorbed Fraction for Photon Sources Distributed Uniformly in Various Organs of a Heterogeneous Phantom, AEC Technical Report, ORNL-TM-4411. MCGINLEY,P. H., 1973, I n t . J . Appl. Radiat. Isotopes, 24, 477. SNYDER,W. S., FORD, M. R., WARNER,G. G., and FISHER, H. L., 1969, J . X u c l . M e d . , Suppl. 3, Pamphlet 5 . STANSBURY, P. S., 1974, T E C A L C - u Program to Calculate Compton, Coherent and Photoelectric Mass Attenuation Coeficients for Photons with Energies Less Than 1 M e V of Photon-equivalentMaterials, and to Assist in the EmluationandFormation AEC Technical Report, ORNL-TM-4451. STANSBURY, P. S., and POSTON, J. W., 1974, Health Physics Division Annual Progress Report for Period Ending July 1974, AEC Technical Report, ORNL-TM-4979.
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My IOPscience
Preparation of phantom lung material
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 150 (http://iopscience.iop.org/0031-9155/21/1/117) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.113.111.210 This content was downloaded on 09/08/2015 at 11:54
Please note that terms and conditions apply.
PHYS. MED.BIOL.,
1976, VOL. 21,
NO.
1, 150-153. @ 1976
CORRESPONDENCE Preparation of Phantom Lung Material THE EDITOR, Sir, The purpose of this letteris to indicate the ratherwide range of lung densities that may result when granulated muscle-equivalentplasticis used to form phantom lungs and to suggest some alternative materials. The use of muscle-equivalent plastic (type A-150) for the construction of lung material for photon and neutrondose distribution measurements has been described in recent publications. A lung density of 0 . 3 8 g (3111-3 was obtained by McGinley (1 973)when granulated muscle-equivalent plastic, which is normally used for moulding operations, was packed into a thin-walled plastic container. The granulated muscle-equivalent plastic employed was in the form of thin flatparticles of rectangular cross-section withdimensions of approximately 2 x 2 x 0.1 mm and was purchased from the Physical Sciences Laboratory of Illinois Benedictine College, Lisle, Illinois. Garry, Stansbury and Poston (1974) used shavings ( 3 mm wide and 0 . 4 mm thick) of A-150 plastic turned by a lathe from solid pieces of plastic to produce phantom lungs with a density adensity of rangingfrom 0.1 to 0.2 g (3111-3. Phantomlungmaterialwith 0-2-0.3 g cm-3 was also formed by dicing the turnings with a food blender. The variabilityof the density of phantom lung material is caused by variation in the size and shape of the plastic particles. For example, Mijnheer (1974, private communication) found that a sample of granulated muscle-equivalent plasticobtainedfrom the Physical Sciences Laboratory was composed of particles with diameter ranging from 1 t o 5 mm and yielded a lung density of 0.6 g cm-3. The lung density was reduced to 0.4 g (3111-3 by filtering out the larger particles. A rangeof particle size and shape results fromthe procedure employed at the Physical Sciences Laboratory to prepare granulated muscle-equivalent plastic. I n this procedure, the components used in the A-150 plastic are ball milled while in powder form,then plasticized and mixed using a modified screw extrusion process, developed by the lateDr. F. R. Shonka, which ensures a high degree of uniformity. Following mixing, the plastic is prepared for moulding by granulating the extruded A-150 in a commercial Cumberland mill. Although a variety of screen sizes are available with this machine, Spokas (1974, private communication) has indicated that only two are routinely used. The coarse screen has 6 - 3 5 mm diameter holes, while the standard screen has 3.175 mm holes. An additional variable is introduced into the granulated A-l50 when sizeable clean pieces of the plastic left from moulding or machine operations areregranulatedforstock,This A-150 which has been subjected to high pressure moulding has a greater density than extruded material.
Correspondence
151
Instead of using the A - l 5 0 plastic one can prepare lung material by forming a mixture of 66% by weight Lucite (C,H,O,), chips and 34% by weight polyethylene (CH,), chips. As can be seen from table 1, this mixture is a better matchthan A - l 5 0 plastic to the composition suggested bySnyder,Ford, Warner and Fisher (1969) for Reference Man lung. I n addition, these plastics are more readily available and less expensive than A-l50 plastic. Table 1. Composition of lung and lung-equivalent materials Muscle-equivalent plastic (A-150), Smathers (1975, private 66% Lucite C,H,O,communicat'ion) 34% polyethylene CH, Yo by weight
Lung tissue, Snyder et al. (1969)
Constituent
H C
h' 0 Other
10.21 10.01 2.80 75.98 0.98
Modified sponge lung7 10.21 10.00 3.20 75.60 1.00
10.20 68.70 21.09 I
I
t Consists of the following in yo by weight: 68.5% H,O;
I
8 % NH,OH; 1 % NaCl; 22.50;b
C,H,,O, (vacuum oven dried sponge cellulose).
A third lung-equivalent material with hydrogen, oxygen and carbon contents similar to thatsuggested by Snyderet al. (1969) for lung was recently developed at the Oak Ridge National Laboratory by Stansbury and Poston (1974). This method uses sponge cellulose (C,H,,O,), salt (NaC1) and water. To obtain an accurate measure of the weight of the sponge, it was necessary to dry it in a vacuum oven overnight. Stansbury (1974, private communication) has found that a sealed container of sponge material with water and salt added shows no tendency t'o release water other than a slight condensation on the container walls. We have altered this material to introduce nitrogen into the sponge material a t levels found in lung by substituting other compounds for salt as shown in the last column of table 1 . A range of densities of the order of 0.15-0.30 g cm-3 can be achieved by cutting thesponge into small irregular sized pieces and packing the material in a container. I n table 2, the phantom lung materials arecompared with Snyder et al. lungtissuein terms of the percent difference between the mass attenuation coefficients for photon interactions (photoelectric, coherent and Compton scattering). A negative per centdifference is used to indicate that themass attenuation coefficient for the lung material is less than that of lung tissue. All mass attenuation coefficients were obtained by use of the TECALC program developed by Stansbury (1974). The Lucite-polyethylene mixture and A-150 plastic have mass attenuation coefficients that are about the same for coherentand Compton for photons photon interactions. Both materials are poor phantom materials
Correspondence
152
Table 2. 'Percentage difference between the mass attenuation coefficients for various phantom lung materials and lung t'issue Photon energy (hew
yo Difference photoelectric cross-section
Granulated A - l 5 0 plastic lung
10 20 40 60 80 100 150 200 500 1000
- 23.78 - 18'53 - 13.16 - 10.20 - 8.26 - 6.87 - 4.67 - 3.39 - 1.14 - 1.45
Lucitepolyethylene lung
10 20 40 60 80 100 150 200 500 1000
- 50.33 - 53.08 - 55.16 - 56'09 - 56.63 - 56'98 - 57.51
10 20 40 60 80 100 150 200 500 1000
Lung material
Modified sponge lung
yo Difference
yo Difference
coherent cross-section
Compton cross-section
- 26.25 - 25.64 - 24'86 - 24'45 - 24'22 -24.10 - 24.03 - 24.12 - 25.47 - 27.80
5.09 0.35 - 1.10 - 0.93 - 0.52 - 0.12 0.67 1.13 0.83 - 2.59
- 58.54
- 26.94 - 26.96 - 26.66 - 26.44 - 26.31 - 26.24 - 26.20 - 26'28 - 27.36 - 29.28
5.00 0.94 - 0.41 - 0.35 - 0.08 0.22 0.80 1.15 0.91 - 1.76
- 3.30
.- 0.50
- 4.2 1 - 5.01 - 5.40 - 5.65 - 5.83 - 6.12 - 6.31 - 6.92 - c1.91
- 0.62 - 0.62 - 0.61
0.04 0.02 0.01 0.01 0.00 0.00 0.00 0.00 0.00 - 0.01
-5i.80 - 58.36
- 0.55 - 0.59 - 0.61 - 0.62 - 0.62 - 0.62
Percentage difference for lung-equivalent material calculated as (PIP)
-
M P )
(luna-equivalent material) (Snyder lung tissue)
(PLIP)
x 100.
(Snyder lung tissue)
with energy below approximately 20 keV due to the low mass attenuation coefficients associatedwith the photoelectricinteraction. The sponge lung material is lung-equivalent for photons with energybetween 10 and 1000 keV.
P. H. MCGINLEY, J. J.SHONKA, School of Nuclear Engineering, Division of Radiation Therapy, Georgia Institute of Technology, Emory University Clinic, Atlanta, Georgia 30322, U.S.A. Atlanta, Georgia 30332, U.S.A. 18 July 1975
Correspondence
153
REFERENCES GARRY,S. M., STANSBURY, P. S., and POSTON, J. W., 1974, Measurement of Absorbed Fraction for Photon Sources Distributed Uniformly in Various Organs of a Heterogeneous Phantom, AEC Technical Report, ORNL-TM-4411. MCGINLEY,P. H., 1973, I n t . J . Appl. Radiat. Isotopes, 24, 477. SNYDER,W. S., FORD, M. R., WARNER,G. G., and FISHER, H. L., 1969, J . X u c l . M e d . , Suppl. 3, Pamphlet 5 . STANSBURY, P. S., 1974, T E C A L C - u Program to Calculate Compton, Coherent and Photoelectric Mass Attenuation Coeficients for Photons with Energies Less Than 1 M e V of Photon-equivalentMaterials, and to Assist in the EmluationandFormation AEC Technical Report, ORNL-TM-4451. STANSBURY, P. S., and POSTON, J. W., 1974, Health Physics Division Annual Progress Report for Period Ending July 1974, AEC Technical Report, ORNL-TM-4979.
