Development of breast tissue equivalent phantom made
from paraffin with some additives and its characterization by
using x-ray spectroscopy
Poster No.:
C-0145
Congress:
ECR 2015
Type:
Scientific Exhibit
Authors:
S. Cubukcu, H. Yücel; Ankara/TR
Keywords:
Breast, Radiation physics, Mammography, Acceptance testing,
Physics, Dosimetry, Cancer, Image verification
DOI:
10.1594/ecr2015/C-0145
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Page 1 of 12
Aims and objectives
The aim of this study is to develop a nearly breast tissue equivalent phantom. To do this,
paraffin was chosen as a base material since its chemical (e.g. hydrogen and carbon
contents) and physical properties (e.g. easily machinable and cheap) are suitable for
mimic the breast tissue.
In the mammographic energy region the characterization of the proposed phantom was
made by using x-ray spectroscopy with a CdTe detector. In literature for the testing the
equivalence of the materials to breast tissues, pulse height x-ray spectroscopy technique
is used for a complete characterization at diagnostic x-ray energies [Byng et al. 1998].
Thus the attenuation properties of the presently proposed phantom was determined from
the acquired x-ray spectra.
Methods and materials
1. Preparation of phantoms
In the preparation process, first paraffin wax was melt at a suitable temperature and then
the powder form of H3BO3 and CaSO4·2H2O compounds were added indivudually in
specified proportions. After that, disc shaped petriplates were filled with the mixtures and
allowed to cool down and become solid for a definite period.
The percentage of the additive compounds, weight and density of the disc phantoms
were written on the labels sticked on the phantoms.
In Fig.1 some examples of homogenous disk phantom samples are shown.
Page 2 of 12
Fig. 1: Paraffin disk phantoms
References: Medical Physics, Ankara University Institute of Nuclear Sciences Ankara/TR
2. Characterization of phantoms
The homogeneity of the phantoms was determined by a Carestream DRX-1C flat panel
x-ray imaging detector (amorfSi-CsI). The disk phantoms were placed in the centre of
detector and irradiated by GE Silhouette Radiographic System at 40 kVp and 5 mAs
beam quality. The homogeneity values were determined by using Image J software with
the relevant plug-in. Among the produced disc phantoms, the ones that have a better
homogeneity than %2.5 were chosen and then characterized by x-ray spectroscopy
system.
The experimental set up shown in Fig. 2 is used for the x-ray characterization. A CdTe
2
detector (Amptek, having 1 mm thick, 25 mm active area CdTe crystal and energy
57
resolution FWHM=1.28 keV @122keV ( Co)) was placed on the breast support table and
Page 3 of 12
the sensitive part of the detector was faced with the x-ray beam. The distance between
the detector window and the focal spot is 27.5 cm to obtain the sufficient photon flux.
The selected disc phantoms were then irradiated by GE Alpha RT mammographic xray unit which has Mo/Mo and Mo/Rh anode/filter combination 20-35 kVp energy range.
A phantom support table, having a gap for disc phantoms to be irradiated directly, was
placed between the detector and the x-ray tube. The detector side was collimated by
using Amptek EXVC tungsten collimator with 1000 µm and 200 µm hole diameters to
provide a pin hole beam. At six different beam energies in the range of 23 to 35 kVp, the
x-ray spectra were obtained without any sample. After that all phantom samples were
irradiated by adding a phantom disc on to the other phantom to see the transmission
properties depending on the thickness, as seen in Fig. 3.
Fig. 2: Irradiation and measurement geometry
References: Medical Physics, Ankara University Institute of Nuclear Sciences Ankara/TR
From the obtained spectra, the transmissions were determined, and plotted against the
thickness. The plots were then fitted to Archer equation [NCRP 147, 2004] by MATLAB
software and from the fits the total attenuation properties and half value layers (HVLs)
were calculated.
Page 4 of 12
Fig. 3: Transmission spectra obtained by CdTe detector with %10 H3BO3 mixed
paraffin
References: Medical Physics, Ankara University Institute of Nuclear Sciences Ankara/TR
The same procedure was repeated to commercially available BR12 [White et al. 1977]
and PMMA phantoms.
Images for this section:
Page 5 of 12
Fig. 1: Paraffin disk phantoms
Page 6 of 12
Fig. 2: Irradiation and measurement geometry
Fig. 3: Transmission spectra obtained by CdTe detector with %10 H3BO3 mixed paraffin
Page 7 of 12
Results
For the comparison, effective atomic number, effective atomic number to atomic weight
ratio, effective atomic weight, mass attenuation coefficient and mass energy attenuation
coefficients at the average energy of 28 kVp beam quality are given in Table 1 for
proposed disc phantoms, BR12 and PMMA phantoms [NIST, 2014].
Material
Zeff
(Z/A)eff
Aeff
µ/#
µen/#
2
(cm /g)
2
(cm /g)
(@19.5 keV) (@19.5 keV)
Paraffin only 4.99
0.60
5.39
0.49
0.25
Paraffin mixed with
%10 H3BO3
5.21
0.59
5.66
0.53
0.29
%20 H3BO3
5.42
0.58
5.95
0.57
0.33
%30 H3BO3
5.64
0.57
6.27
0.61
0.37
%5 CaSO4
5.42
0.59
5.68
0.80
0.58
%10 CaSO4
5.84
0.59
6.00
1.11
0.91
%15 CaSO4
6.26
0.58
6.34
1.43
1.25
PMMA
6.34
0.53
9.79
0.69
0.44
BR12
6.02
0.53
8.58
0.69
0.44
Table 1 - Some physical properties of prepared phantoms, PMMA and BR12 phantoms.
From Table 1, with the ideal mixing ratio, it is possible to simulate breast tissue with
paraffin and some additives. CaSO4 has higher attenuation properties because of
relatively high Z number of calcium element. So in the mixture, paraffin and H3BO3 should
be the major compounds and CaSO4 should be a trace amount.
From the measurements, the transmission values were calculated and plotted against
sample thickness, and an example is shown in Fig.3
Page 8 of 12
Fig. 4: Transmission values for phantoms made of paraffin mixtures, PMMA and BR12
References: Medical Physics, Ankara University Institute of Nuclear Sciences Ankara/TR
The HVL values and total attenuation coefficients were also calculated from the
transmission curves and given in Table 2 and Table 3.
Material %10
H3BO3
HVL
13.46
%20
H3BO3
%30
H3BO3
%5
CaSO4
%10
CaSO4
%15
CaSO4
PMMA
BR-12
10.62
10.40
8.44
6.80
6.24
8.55
8.35
(mm
Material)
Table 2 - HVL values of paraffin mixtures and PMMA and BR12 phantoms
Material %10
H3BO3
µtotal
0.050
%20
H3BO3
%30
H3BO3
%5
CaSO4
%10
CaSO4
%15
CaSO4
PMMA
BR-12
0.058
0.061
0.073
0.102
0.111
0.081
0.083
Table 3 - Total attenuation coefficients of paraffin mixtures and PMMA and BR12
phantoms
Page 9 of 12
Images for this section:
Fig. 4: Transmission values for phantoms made of paraffin mixtures, PMMA and BR12
Page 10 of 12
Conclusion
The results for the proposed phantoms are compared with commercially available
mammography phantoms BR12 and PMMA. The transmission curves of our proposed
phantoms indicated that the specific proportions of the additive compounds can be used
for simulating the breast tissue.
As a base material, paraffin is a good candidate for breast phantoms from point of
attenuation properties when mixed with different amounts of additives. Thus it can mimic
different density range of breast tissues such as adipose and glandular tissues. The
main advantage of proposed breast phantom is being cheap and easy machineable
in-house. They can be used for basic quality control tests of mammography units.
However the gained experience showed that paraffin has also some disadvantages in
view of mechanical strength, hardness and resistance to heat under normal environment
conditions. Hence we should try also another base material such as epoxy to obtain more
durable phantoms.
Personal information
Corresponding Author: S. Cubukcu, Ankara University, Faculty of Engineering,
Physics Engineering Department, 06100 Tandogan Ankara, Turkey, E-mail:
[email protected]
H. Yücel, Ankara University, Institute of Nuclear Sciences, 06100 Tandogan Ankara,
Turkey.
References
J.W. Byng, J.G. Mainprize, M.J. Yaffe, X-ray characterization of breast phantom
materials, Phys.Med.Biol., 43, 1367-1377, 1998.
NCRP Report No: 147, 2004.
D.R. White, J.R. Martin, R. Darlison, Epoxy resin based tissue substitutes, BRJ, 50,
814-821, 1977.
Page 11 of 12
NIST, 2014, "http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html",
accessible date 20.Dec.2014
Last
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