Evaluation of the water equivalence of solid phantoms using gamma ray transmission measurements
ABSTRACT Gamma ray transmission measurements have been used to evaluate the water equivalence of solid phantoms. Technetium-99m was used in narrow beam geometry and the transmission of photons measured, using a gamma camera, through varying thickness of the solid phantom material and water. Measured transmission values were compared with Monte Carlo calculated transmission data using the EGSnrc Monte Carlo code to score fluence in a geometry similar to that of the measurements. The results indicate that the RMI457 Solid Water, CMNC Plastic Water and PTW RW3 solid phantoms had similar transmission values as compared to water to within ±1.5%. However, Perspex had a greater deviation in the transmission values up to ±4%. The agreement between the measured and EGSnrc calculated transmission values agreed to within ±1% over the range of phantom thickness studied. The linear attenuation coefficients at the gamma ray energy of 140.5 keV were determined from the measured and EGSnrc calculated transmission data and compared with predicted values derived from data provided by the National Institute of Standards and Technology (NIST) using the XCOM program. The coefficients derived from the measured data were up to 6% lower than those predicted by the XCOM program, while the coefficients determined from the Monte Carlo calculations were between measured and XCOM values. The results indicate that a similar process can be followed to determine the water equivalency of other solid phantoms and at other photon energies.
- SourceAvailable from: John Adamovics[Show abstract] [Hide abstract]
ABSTRACT: PRESAGE is a dosimeter made of polyurethane, which is suitable for 3D dosimetry in modern radiation treatment techniques. Since an ideal dosimeter is radiologically water equivalent, the authors investigated water equivalency and the radiological properties of three different PRESAGE formulations that differ primarily in their elemental compositions. Two of the formulations are new and have lower halogen content than the original formulation. The radiological water equivalence was assessed by comparing the densities, interaction probabilities, and radiation dosimetry properties of the three different PRESAGE formulations to the corresponding values for water. The relative depth doses were calculated using Monte Carlo methods for 50, 100, 200, and 350 kVp and 6 MV x-ray beams. The mass densities of the three PRESAGE formulations varied from 5.3% higher than that of water to as much as 10% higher than that of water for the original formulation. The probability of photoelectric absorption in the three different PRESAGE formulations varied from 2.2 times greater than that of water for the new formulations to 3.5 times greater than that of water for the original formulation. The mass attenuation coefficient for the three formulations is 12%-50% higher than the value for water. These differences occur over an energy range (10-100 keV) in which the photoelectric effect is the dominant interaction. The collision mass stopping powers of the relatively lower halogen-containing PRESAGE formulations also exhibit marginally better water equivalency than the original higher halogen-containing PRESAGE formulation. Furthermore, the depth dose curves for the lower halogen-containing PRESAGE formulations are slightly closer to that of water for a 6 MV beam. In the kilovoltage energy range, the depth dose curves for the lower halogen-containing PRESAGE formulations are in better agreement with water than the original PRESAGE formulation. Based on the results of this study, the new PRESAGE formulations with lower halogen content are more radiologically water equivalent overall than the original formulation. This indicates that the new PRESAGE formulations are better suited to clinical applications and are more accurate dosimeters and phantoms than the original PRESAGE formulation. While correction factors are still needed to convert the dose measured by the dosimeter to an absorbed dose in water in the kilovoltage energy range, these correction factors are considerably smaller for the new PRESAGE formulations compared to the original PRESAGE and the existing polymer gel dosimeters.Medical Physics 04/2011; 38(4):2265-74. · 2.91 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The measurement of absorbed dose to water in a solid-phantom may require a conversion factor because it may not be radiologically equivalent to water. One phantom developed for the use of dosimetry is a solid water, RW3 white-polystyrene material by IBA. This has a lower mass-energy absorption coefficient than water due to high bremsstrahlung yield, which affects the accuracy of absolute dosimetry measurements. In this paper, we demonstrate the calculation of mass-energy absorption coefficient ratios, relative to water, from measurements in plastic water and RW3 with an Elekta Synergy linear accelerator (6 and 10 MV photon beams) as well as Monte Carlo modeling in BEAMnrc and DOSXYZnrc. From this, the solid-phantom-to-water correction factor was determined for plastic water and RW3.Australasian physical & engineering sciences in medicine / supported by the Australasian College of Physical Scientists in Medicine and the Australasian Association of Physical Sciences in Medicine 09/2011; 34(4):553-8. · 0.89 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Estimation of the surface dose is very important for patients undergoing radiation therapy. The purpose of this study is to investigate the dose at the surface of a water phantom at a depth of 0.007 cm as recommended by the International Commission on Radiological Protection and International Commission on Radiation Units and Measurement with radiochromic films (RFs), thermoluminescent dosemeters and an ionisation chamber in a 6-MV photon beam. The results were compared with the theoretical calculation using Monte Carlo (MC) simulation software (MCNP5, BEAMnrc and DOSXYZnrc). The RF was calibrated by placing the films at a depth of maximum dose (dmax) in a solid water phantom and exposing it to doses from 0 to 500 cGy. The films were scanned using a transmission high-resolution HP scanner. The optical density of the film was obtained from the red component of the RGB images using ImageJ software. The per cent surface dose (PSD) and percentage depth dose (PDD) curve were obtained by placing film pieces at the surface and at different depths in the solid water phantom. TLDs were placed at a depth of 10 cm in a solid water phantom for calibration. Then the TLDs were placed at different depths in the water phantom and were exposed to obtain the PDD. The obtained PSD and PDD values were compared with those obtained using a cylindrical ionisation chamber. The PSD was also determined using Monte Carlo simulation of a LINAC 6-MV photon beam. The extrapolation method was used to determine the PSD for all measurements. The PSD was 15.0±3.6 % for RF. The TLD measurement of the PSD was 16.0±5.0 %. The (0.6 cm(3)) cylindrical ionisation chamber measurement of the PSD was 50.0±3.0 %. The theoretical calculation using MCNP5 and DOSXYZnrc yielded a PSD of 15.0±2.0 % and 15.7±2.2 %. In this study, good agreement between PSD measurements was observed using RF and TLDs with the Monte Carlo calculation. However, the cylindrical chamber measurement yielded an overestimate of the PSD. This is probably due to the ionisation chamber calibration factor that is only valid in charged particle equilibrium condition, which is not achieved at the surface in the build-up region.Radiation Protection Dosimetry 12/2013; · 0.91 Impact Factor
Radiation Measurements 43 (2008) 1258–1264
R.F. Hilla,b,∗, S. Browna,c, C. Baldocka
aInstitute of Medical Physics, School of Physics, University of Sydney, Australia
bDepartment of Radiation Oncology, Royal Prince Alfred Hospital, Sydney, Australia
cDepartment of Radiation Oncology, Royal North Shore Hospital, Sydney, Australia
Received 14 September 2007; received in revised form 6 January 2008; accepted 23 January 2008
Gamma ray transmission measurements have been used to evaluate the water equivalence of solid phantoms. Technetium-99m was used in
narrow beam geometry and the transmission of photons measured, using a gamma camera, through varying thickness of the solid phantom
material and water. Measured transmission values were compared with Monte Carlo calculated transmission data using the EGSnrc Monte
Carlo code to score fluence in a geometry similar to that of the measurements. The results indicate that the RMI457 Solid Water, CMNC
Plastic Water and PTW RW3 solid phantoms had similar transmission values as compared to water to within ±1.5%. However, Perspex had
a greater deviation in the transmission values up to ±4%. The agreement between the measured and EGSnrc calculated transmission values
agreed to within ±1% over the range of phantom thickness studied. The linear attenuation coefficients at the gamma ray energy of 140.5keV
were determined from the measured and EGSnrc calculated transmission data and compared with predicted values derived from data provided
by the National Institute of Standards and Technology (NIST) using the XCOM program. The coefficients derived from the measured data
were up to 6% lower than those predicted by the XCOM program, while the coefficients determined from the Monte Carlo calculations were
between measured and XCOM values. The results indicate that a similar process can be followed to determine the water equivalency of other
solid phantoms and at other photon energies.
© 2008 Elsevier Ltd. All rights reserved.
Keywords: Solid phantoms; Water equivalency; Technetium-99m; EGSnrc Monte Carlo; XCOM; Low energy photons
Solid water equivalent phantoms are used extensively for the
dosimetry of photon and electron beams as used in radiation
therapy, radiology, nuclear medicine and radiation safety. Water
is the phantom material of choice for both reference and rel-
ative dosimetry measurements in radiation therapy. There are
situations where a solid phantom is required (Andreo et al.,
2000; Badhwar et al., 2002; Metcalfe et al., 1997). Many radi-
ation detectors are not waterproof in which case a solid phan-
tom must be used (Mitchell et al., 1998). A solid phantom can
be designed into the required shape and/or size. In addition,
∗Corresponding author at: Department of Radiation Oncology, Royal
Prince Alfred Hospital, Missenden Road, Camperdown, NSW 2050,
E-mail address: firstname.lastname@example.org (R.F. Hill).
1350-4487/$-see front matter © 2008 Elsevier Ltd. All rights reserved.
measurements within high dose gradients can be difficult to
perform in water (Demir et al., 2005; Williams and Thwaites,
2000). Solid phantoms are also more useful for routine mea-
surements since they tend to be more robust and easier to set
up than water phantoms.
For a solid phantom to be considered water equivalent, it
must have similar radiological properties as that of water. These
properties include physical density, relative electron density
and effective atomic number as well as similar absorption and
scattering of radiation (Andreo et al., 2000; ICRU, 1989). For
higher energy photon beams as used in megavoltage radiother-
apy beams, the dominant interaction process is the Compton
effect, which has a dependence on the electron density of the
medium. The photons produced by therapeutic kilovoltage
X-ray units and some brachytherapy sources are lower in en-
ergy and the photoelectric effect becomes a more dominant
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
interaction processes. The photoelectric effect has a strong de-
pendence on the atomic number of the medium. This means
that at these lower energies, differences in the effective atomic
number of the solid phantom as compared to water may lead
to greater differences in measured dose.
The ICRU Report 44 recommends if any solid phantom
is to be considered water equivalent, it should not introduce
uncertainties to the absorbed dose of greater than 1% otherwise
correction factors may be required (ICRU, 1989). Testing the
radiological tissue equivalence in terms of the water equiva-
lency of a solid phantom for X-rays with lower energies can be
achieved by several methods: measurement of relative dosime-
try data such as percentage depth doses and output factors
(Allahverdi et al., 1999; Healy et al., 2005; Hill et al., 2005),
measurement of X-ray beam attenuation and/or back scatter
factors (Hermann et al., 1985), measurement of X-ray linear
attenuation coefficient, ?, using radioisotopes (Midgley, 2005)
and Monte Carlo dose calculations (Meigooni et al., 1994;
Reniers et al., 2004).
The results presented by Hermann found that the solid RW1
phantom material had good agreement with water for both
transmission and backscatter measurements in the energy range
10–100kV (Hermann et al., 1985). The epoxy resin material,
Plastic Water, has been shown to give significant dose differ-
ences as compared to water for X-rays with energies less than
100keV (Hill et al., 2005; Meigooni et al., 1994). These stud-
ies also found that the doses measured using the RMI457 Solid
Water epoxy resin phantom had good agreement with the doses
measured in water even at the lower energies.
Midgley measured the X-ray linear attenuation coefficient,
?, for a number of low atomic number materials using a
technetium-99m source and characteristic radiation in the en-
ergy range of 32.1– 62.2keV (Midgley, 2005). The difference
in ?, between Perspex and water, was up to 14% but for the
WT1 solid phantom, the maximum difference in the coefficient
was 3.6% over the same energy range.
In this paper, we used gamma ray transmission measure-
ments in solid phantoms to investigate the radiological water
equivalency of these phantoms. Linear attenuation coefficients
were determined for the solid phantoms and water using trans-
mission curves and compared with Monte Carlo calculations
and standard published data. An assessment of the dosimetric
response of the solid phantoms as compared to water was made.
2. Materials and methods
2.1. Experimental methods
All measurements were performed using a technetium-99m
radionuclide which has a half-life of 6.01h (Chu et al., 1999).
Technetium-99m emits a number of different gamma and beta
rays while undergoing radioactive decay. The main gamma ray
emissions have energies of 140.5 and 142.6keV with relative
amounts of 98.6% and 1.4%, respectively (Chu et al., 1999). It
is also noted that characteristic X-rays and Auger electrons are
emitted after internal conversion events and are not considered
in this work.
Elemental composition by relative weight and physical density of the five
phantom materials used in this study: Water, RMI457 Solid Water (RMI
Gammex), Plastic Water (Computerized Imaging Reference Systems), RW3
solid phantom (PTW Freiburg) and Perspex
Water RMI457 Plastic WaterRW3 Perspex
The following phantom materials were used in the com-
parison: water, Solid Water RMI457 (RMI Gammex, Mid-
dleton, WI, USA), Plastic Water (Computerized Imaging
Reference Systems Inc., Norfolk, VA, USA), RW3 Solid Water
(PTW Freiburg, Freiburg, Germany) and Perspex. The Plastic
Water and RMI457 Solid Water are made from epoxy resins.
Table 1 shows the elemental composition and physical charac-
teristics of each of the phantom materials (Andreo et al., 2000).
The solid phantom materials were in the form of blocks with
dimensions of at least 20 × 20cm2and different thicknesses.
The specified thickness of each block used was verified using
a vernier calliper and agreed to within ±0.2mm.
For each phantom material, ?, for the 140.5keV gamma ray
was determined using the Bouger–Lambert–Beer law which
states that the intensity of the gamma rays, I, is given by the
following equation (Johns and Cunningham, 1983):
I = I0× exp(−?x),
where I0 is the intensity of the primary beam and x is the
thickness of the phantom material.
The radionuclide source was located inside a custom de-
a beam diameter of 0.5cm (Brown et al., 2005). The geome-
try of the set-up used for the measurements is shown in Fig. 1.
A Philips SkyLight SPECT gamma camera (Philips Medical,
North Milpitas, CA, USA) using the Skylight software recorded
the total number of photons detected. The gamma camera was
positioned so that it was facing towards the floor. The lead con-
tainer with the source was placed on the floor and aligned with
the head of the gamma camera, which was 1m above the con-
tainer. The attenuating material was placed 10cm above the
source and aligned to be perpendicular to the beam. The gamma
camera had an energy window set to ±5% of the main gamma
ray energy of 140.5keV in order to remove low energy scat-
tered photons from the total number of counts (Jaszczak et al.,
Photons were counted for 60s for each measurement. For
each phantom material, the initial intensity, I0, was measured
with nothing in the beam, followed by measurements with
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
SPECT Gamma-Camera Head
Narrow beam of gamma-rays
passing through material
Stacked attenuating material
Two lead containers
inside glass vial
% of Initial Intensity
Material thickness (cms)
Fig. 1. A diagram of the equipment used to measure the transmission values for technetium-99m gamma rays passing through varying thicknesses of five
phantom materials. Shown are the lead container that held the radionuclide, the gamma camera and the support for the different phantom materials.
different thickness of the phantom material from 2 to 10cm.
The water was held in a thin plastic container, which was in-
cluded in all transmission measurements through water and
include for the initial intensity, I0.
Due to the short half-life of the technetium-99m isotope,
corrections were applied to take into account radioactive
decay during the experiment. The correction factor to the
total number of counts is given by ? as per the following
? = exp
?−t × ln(2)
where t is the time from the measurement of the initial intensity
and t1/2is the half-life of the source.
The error for each measurement was determined from the
uncertainty in the phantom thickness and the estimated uncer-
tainty from Poisson statistics.
2.2. Monte Carlo methods
Monte Carlo methods are widely used in solving radiation
dosimetry problems. In this work, we used the Electron Gamma
Shower (EGSnrc) version 4.2 Monte Carlo code to simulate
the gamma rays incident on the different phantom materials
(Kawrakow, 2000). The FLURZnrc user code was used to cal-
culate the energy fluence of the radiation beam for a cylindrical
geometry (Rogers et al., 2000).
The EGSnrc code is able to model the photoelectric ef-
fect, Compton scattering and Rayleigh scattering interaction
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
processes that occur for these photon energies. There are a
number of calculation options that were ‘switched on’ in the
software for all calculations: the inclusion of bound Compton
scattering, angular sampling of the direction of the emitted pho-
toelectron, Rayleigh scattering, atomic relaxations and electron
spin effects. The use of these parameters for our calculations
is consistent with the results of a previous study (Verhaegen,
2002). Photon and electron energy cut-off parameters (includ-
ing the electron rest mass), PCUT and ECUT, were set to val-
ues of 0.002 and 0.561MeV, respectively, for all calculations.
These cut-off parameters determine when a photon or electron
is no longer simulated and the energy is deposited in the local
The technetium-99m source was modelled in FLURZnrc as
a narrow parallel beam, with a diameter of 0.5cm, which cor-
responds to the size of the beam used in the measurements. The
source was simulated as a monoenergetic beam of photons with
energy of 140.5keV. It should be noted that the lead container
holding the source was not explicitly modelled in the Monte
Carlo simulations. The slab of phantom material was positioned
at a distance 10cm from the source. The total photon fluence
was scored in air within a 1mm thick and 15cm diameter voxel
situated on the central axis and at 1m distance from the start
of the attenuating phantom, with large diameter of the voxel
selected to be much larger than the radial dimension of the in-
cident radiation beam. The thickness of the phantom material
was varied, matching the thickness of the phantoms used in
the measurements. Photons in this voxel were scored into dif-
ferent energy bins in the range of 0–145keV with increments
of 5keV. The calculation of transmitted primary photons was
determined from the tally of photons in the top energy bin of
The EGSnrc code uses cross section data from a data file
created by the PEGS4 application. There were two options for
cross section data to be used by PEGS4 to generate the PEGS4
data file: (1) the default setting which photon cross section
data derived by Storm and Israel and (2) newer National In-
stitute of Standards and Technology (NIST) cross-section data
(Kawrakow, 2000). The NIST data set contains newer cross-
section data that is applicable at lower photon energies. Fluence
calculations were performed using each of the cross-sectional
a large number of incident photons were used for each calcu-
lation set: 2 × 107.
2.3. Determination of linear attenuation coefficients
The narrow-beam ?, for each material was determined using
curve fitting software within the Sigmaplot software program
(Systat Software Inc., San Jose, California) using an exponen-
tial function as per Eq. (1). The resulting output provides a
value of ?, and a calculated standard error. There were three
?’s determined for each of the phantom materials:
• Measured linear attenuation coefficient, ?measured, based on
the corrected counts recorded by the gamma-camera against
the thickness of attenuating material.
• Monte Carlo calculated linear attenuation coefficient,
?EGSnrc, using the transmission data from the Monte Carlo
• Calculated linear attenuation coefficients using data provided
by the NIST via their online XCOM data base found at
(Berger et al., 1998). The formulation for each material was
taken from Table 1 and used as an input in the XCOM
database, to give the total mass attenuation coefficient at
photon energy of 140.5keV. The total linear attenuation co-
efficient was determined from this by multiplying by the
physical density of the material as given in Table 1.
3. Results and discussion
The maximum uncertainty in the measured counts was cal-
culated to ±0.8% based on geometrical uncertainties and vari-
ations in the number of counts detected by the gamma camera.
The uncertainty in the phantom thickness was determined to be
±0.05cm for the solid phantoms and ±0.1cm for the water.
The measured transmission values as a function of phan-
tom thickness, based on the corrected counts of gamma rays,
are presented in Fig. 2. The results indicate that the transmis-
sion through Plastic Water, RMI 457 Solid Water and RW3
phantoms are in close agreement to that through water. The
agreement was in most cases within 1% and a maximum de-
viation of 1.5%. This level of agreement between doses mea-
sured in solid phantoms and in water is similar to previous
work using megavoltage X-ray beams (Allahverdi et al., 1999;
Liu et al., 2003) and in Monte Carlo calculations at similar
photon energies for brachytherapy sources (Meigooni et al.,
1994). The transmission values through Perspex are less than
those for water and with a greater deviation, being up to 4% at
Fig. 2. A comparison of measured transmission values of technetium-99m
gamma rays passing through varying thicknesses of 0–10cm of five phantom
materials. The measurements were done at the thicknesses indicated by the
symbols on the plots. The lines passing through the data points have been
applied for ease of reading the data.
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
Fig. 3. A comparison of measured and EGSnrc calculated transmission values for technetium-99m gamma rays passing through varying thicknesses of five
phantom materials. The phantom materials studied were water, RW3, Plastic Water, RMI 457 Solid Water and Perspex. The line passing through the measured
data points have been applied for ease of reading the data and are not the actual data.
One aspect of the solid phantoms that will contribute to un-
certainties in the transmission measurements is the inhomo-
geneity in the manufacture of the blocks, leading to variations
in density (Allahverdi et al., 1999; Seuntjens et al., 2005). The
results indicate that within the uncertainties, the Plastic Wa-
ter, RMI-457 Solid Water and RW3 phantom materials meet
the ICRU requirements for water equivalency at this particular
The maximum uncertainty of the Monte Carlo calculations
was less than 0.2%. The difference in transmission values be-
tween using the default and updated NIST cross-section data
was less than 0.1% for all calculations. From this, the calcu-
lations that used NIST cross-section data are presented in this
The Monte Carlo calculated and measured transmission val-
ues for the five phantom materials are presented in Fig. 3.
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
Linear attenuation coefficients, ? (cm−1), for the five phantoms studied deter-
mined using measured and Monte Carlo calculated transmission data and as
calculated by the XCOM program for gamma rays emitted by a technetium-
Water RMI-457 Plastic WaterRW3 Perspex
The line passing through the measured data points has been
applied for ease of reading the data and is not the actual data.
Each graph shows the Monte Carlo calculated and the mea-
sured transmission data as a function of phantom thickness.
The agreement between the Monte Carlo and measured data is
good with a maximum difference of 1.3%, but in most cases
the deviation was less than 1%.
The linear attenuation coefficients based on the measure-
ments, ?measured, the EGSnrc calculated transmission values, as
well as the coefficient calculated using XCOM, are presented
in Table 2. The results are such that the Monte Carlo calculated
linear attenuation coefficients agree with the measured values
to within 2.4%, with the standard error of the coefficient being
less than 0.7%. This level of agreement is acceptable due to the
variations that we expect as detailed above.
The value of the linear attenuation coefficient derived from
XCOM is greater than those derived from the measured and
the EGSnrc calculated transmission data. For the solid phan-
toms, the linear attenuation coefficient ? was 2% greater than
the Monte Carlo values, while for Perspex the coefficient was
4% greater. These results are consistent with Reniers et al.
(2004) who found differences of 3% between EGSnrc (using
updated cross-section data) and XCOM calculated attenuation
coefficients. In comparison, the linear attenuation coefficients
for water and Perspex as measured by Midgley (2005) are
in good agreement with the XCOM calculated coefficients,
but 3.3% and 5.4% greater, respectively, than the measured
coefficients in this paper. It should be noted that Midgley
used a different detector in his measurement of the gamma
The differences between the measured and calculated lin-
ear attenuation coefficients are attributed to (a) the energy
resolution of the inorganic scintillator crystal in the gamma-
camera (±10% FWHM at 140keV), (b) the partial energy
deposition of the gamma rays creating background noise,
(c) the Monte Carlo and XCOM calculated coefficients being
based on the attenuation of a monoenergetic gamma source
as compared to an actual spectrum, and (d) the lead colli-
mator used to hold the radionuclide generating X-rays via
emits gamma rays of other energies that may be within the en-
ergy window of the data acquisition system software. These
are not included in either the Monte Carlo or XCOM calcu-
lations that are expected to introduce additional deviations as
compared to the measured data.
In this project, transmission values of gamma rays have
been used as a method of testing the water equivalence of four
solid phantoms. To test the water equivalency of solid phan-
toms, we have used experimental and Monte Carlo methods
with the criteria for water equivalence being based on ICRU
The experimental data was measured by using a technetium-
99m radionuclide source in conjunction with a nuclear gamma
camera as the detector. The experimental results indicate that
for the photon energy tested of 140.5keV, the RMI457 Solid
Water, CMNC Plastic Water and PTW RW3 had transmission
values that were for most cases within 1.0% of those of wa-
ter thus meeting the ICRU requirements for water equivalency.
This means that these solid phantoms could be used for radi-
ation dosimetry of photons at this energy. Perspex cannot be
considered water equivalent for the photon energy tested. Veri-
fication of the experimental results by performing Monte Carlo
calculations shows similar results with the level of agreement
being within 1.3% after simulating the transport of gamma pho-
tons through the phantoms.
The agreement in linear attenuation coefficients calculated
from the transmission values of the experimental and Monte
Carlo values were within 2.4%, and greater disagreement with
those determined from NIST data. An improvement in the
Monte Carlo calculations could be achieved by modelling the
lead container holding the radionuclide. In addition, determi-
nation of the actual spectrum of photons that reach the gamma
camera could improve the agreement in the linear attenuation
coefficients from the three methods used.
All solid phantoms that claim to be water equivalent should
be checked in a similar manner before their use for dosime-
try measurements. This is particularly important if one will use
the solid phantom for photons with energies outside the range
specified by the manufacturer. By using other radionuclides that
emit lower energy gamma rays, further testing could be per-
formed at lower photon energies where the photoelectric effect
will become a more dominant interaction process. The experi-
mental procedure could also be used as a quality assurance tool
of the solid phantoms on a routine basis.
We would like to thank Dr. Dale Bailey from the De-
partment of Nuclear Medicine, Royal North Shore Hospital,
Sydney, Australia for allowing the use of equipment and pro-
viding the technetium-99m isotope.
Allahverdi, M., Nisbet, A., Thwaites, D.I., 1999. An evaluation of epoxy
resin phantom materials for megavoltage photon dosimetry. Phys. Med.
Biol. 44, 1125–1132.
Andreo, P., Burns, D.T., Hohlfield, K., Huq, M.S., Kanai, T., Laitano, F.,
Smyth, V., Vynckier, S., 2000. Absorbed dose determination in external
beam radiotherapy, an international code of practice for dosimetry based
on standards of absorbed dose to water. Technical Report Series No. 398,
International Atomic Energy Agency, Vienna.
R.F. Hill et al. / Radiation Measurements 43 (2008) 1258–1264
Badhwar, G.D., Robbins, D.E., Gibbons, F., Braby, L.A., 2002. Response
of a tissue equivalent proportional counter to neutrons. Radiat. Meas. 35,
Berger, M.J., Hubbell, J.H., Seltzer, S.M., Chang, J., Coursey, J.S., Sukumar,
R., Zucker, D.S., 1998. XCOM: Photon Cross Sections Database. Available
at ?http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html?. National
Institute of Standards and Technology, Physics Laboratory, Ionizing
Radiation Division, Gaithersburg, MD, USA.
Brown, S., Bailey, D.L., Baldock, C., 2005. An investigation of the relationship
between linear attenuation coefficients and CT Hounsfield units. Australas.
Phys. Eng. Sci. Med. 29, 140.
Chu, S.Y.F., Ekstrom, L.P., Firestone, R.B., 1999. The Lund/LBNL nuclear
data search. Available at ?http://nucleardata.nuclear.lu.se/nucleardata/
toi/index.asp?. Lunds Universitet, Sweden.
Demir, B., Bilge, H., Dincbas, F.O., Koca, A., Karacam, S., Gunhan, B.,
2005. The effect of pull back technique on dose distribution in the junction
region for 90Sr/90Y intravascular brachytherapy sources. Radiat. Meas.
Healy, B.J., Gibbs, A., Murry, R.L., Prunster, J.E., Nitschke, K.N., 2005.
Output factor measurements for a kilovoltage X-ray therapy unit. Australas.
Phys. Eng. Sci. Med. 28, 115–121.
Hermann, K.P., Geworski, L., Muth, M., Harder, D., 1985. Polyethylene-based
water-equivalent phantom material for X-ray dosimetry at tube voltages
from 10 to 100kV. Phys. Med. Biol. 30, 1195–1200.
Hill, R., Holloway, L., Baldock, C., 2005. A dosimetric evaluation of water
equivalent phantoms for kilovoltage X-ray beams. Phys. Med. Biol. 50,
ICRU, 1989. Tissue substitutes in radiation dosimetry and measurement.
Measurements, Bethesda, MD, USA.
Jaszczak, R.J., Greer, K.L., Floyd Jr., C.E., Harris, C.C., Coleman, R.E.,
1984. Improved SPECT quantification using compensation for scattered
photons. J. Nucl. Med. 25, 893–900.
Johns, H.E., Cunningham, J.R., 1983. The Physics of Radiology. Charles C.
Thomas, Springfield, IL, 796pp.
on Radiation Unitsand
Kawrakow, I., 2000. Accurate condensed history Monte Carlo simulation of
electron transport. I. EGSnrc, the new EGS4 version. Med. Phys. 27,
Liu, L., Prasad, S.C., Bassano, D.A., 2003. Evaluation of two water-equivalent
phantom materials for output calibration of photon and electron beams.
Med. Dosim. 28, 267–269.
Meigooni, A.S., Li, Z., Mishra, V., Williamson, J.F., 1994. A comparative
study of dosimetric properties of Plastic Water and Solid Water in
brachytherapy applications. Med. Phys. 21, 1983–1987.
Metcalfe, P., Kron, T., Hoban, P., 1997. The Physics of Radiotherapy
X-rays from Linear Accelerators. Medical Physics Publishing, Madison,
Midgley, S.M., 2005. Measurements of the X-ray linear attenuation coefficient
for low atomic number materials at energies 32–66 and 140keV. Radiat.
Phys. Chem. 72, 525–535.
Mitchell, G., Kron, T., Back, M., 1998. High dose behind inhomogeneities
during medium-energy X-ray irradiation. Phys. Med. Biol. 43, 1343–1350.
Reniers, B., Verhaegen, F., Vynckier, S., 2004. The radial dose function of
low-energy brachytherapy seeds in different solid phantoms: comparison
between calculations with the EGSnrc and MCNP4C Monte Carlo codes
and measurements. Phys. Med. Biol. 49, 1569–1582.
Rogers, D.W., Kawrakow, I., Seuntjens, J., Walters, B.R.B., Mainegra-Hing,
E., 2000. NRCC Report PIRS-702. NRC user codes for EGSnrc. Ionizing
Radiation Standards, National Research Council of Canada.
Seuntjens, J., Olivares, M., Evans, M., Podgorsak, E., 2005. Absorbed dose to
water reference dosimetry using solid phantoms in the context of absorbed-
dose protocols. Med. Phys. 32, 2945–2953.
Verhaegen, F., 2002. Evaluation of the EGSnrc Monte Carlo code for interface
dosimetry near high-Z media exposed to kilovolt and60Co photons. Phys.
Med. Biol. 47, 1691–1705.
Williams, J.R., Thwaites, D.I., 2000. Radiotherapy Physics in Practice. Oxford
University Press, Oxford, 332pp.