Dosimetry of 125Iodine Photons for In Vivo Mouse
Irradiation Study
by
Sheena Hembrador
Submitted to the Department of Nuclear Science and Engineering
in partial fulfillment of the requirements for the degree of
Bachelor of Science
at the
Massachusetts Institute of Technology
June 2006
Copyright ©2006 Sheena Hembrador. All rights reserved.
The author hereby grants to MIT permission to reproduce and distribute publicly paper and electronic copies of this
thesis document in whole or in part.
Author:
Sheena Hembrador
Department of Nuclear Science and Engineering
May 12, 2006
Certified by:
Jacquelyn C. Yanch
Professor, Department ofNuclear Science and Engineering
Thesis Supervisor
Accepted by:
MASSACHUSE'M WAS11T
David Cory
Professor of Nuclear Science and Engineering
Chairman, NSE Committee for Undergraduate Students
OF TECHNOLOGY
OCT 12 2007
LIBRARIES
ARCHIVES
Dosimetry of 125Ilodine Photons for In Vivo Mouse
Irradiation Study
by
Sheena Hembrador
Submitted to the Department of Nuclear Science and Engineering on
May 12, 2006
In partial fulfillment of the requirements for the degree of
Bachelor of Science in Nuclear Science and Engineering
Abstract
The biological effects of acute, high doses of radiation are well understood. However, the
effects of chronic, low doses are not as clear. Mice irradiation experiments to study the
correlation of biological effects with chronic low dose rates are underway in order to make
conclusions about the effects of low doses. Yet, in order to do so, the level of dose provided to
the animals must be determined. This paper examines methods of ascertaining the dose rate
delivered to mice by photons from an 12 5Iodine filled flood phantom source. Two distinct
methods were used. First, Optically Stimulated Luminescence (OSL) Dosimeters were placed in
an array over an area slightly larger than the irradiation area. The dose equivalent they each
reported was recorded weekly. Secondly, a series of simulations were performed using MCNP to
calculate the expected dose equivalent reported by those dosimeters. Comparison of the
dosimeters' recorded dose to MCNP's calculated dose showed agreement within experimental
and statistical uncertainty for 82% of the measurements. This high level of agreement
demonstrates that the MCNP simulation approach produces reliable results. After this was
shown, other MCNP simulations were performed to determine the dose equivalent to the mice in
cages placed above the 1251 filled phantom. The simulation showed an average dose equivalent of
656 t 108 mrem per week, with a range of 866 t 33 mrem/week to 399 t 18 mrem/week. The
dosimetry methods developed in this report are not unique to this dose level, and can be used in
future mouse studies to determine dose rates at other orders of magnitude.
Thesis Supervisor:
Title:
Jacquelyn C. Yanch
Professor, Department of Nuclear Science and Engineering
Table of Contents:
1.
2.
Introduction and Background.....................................
4
1.1
1.2
1.3
1.4
4
5
5
6
Methods .................................................................
7
2.1
2.2
7
8
9
11
12
13
14
15
16
17
2.3
2.4
3.
Mouse and Source Cart Arrangement................................
Flood Phantom Photon Source...........................................
2.2.1 1251 Radioactive Properties...........
................
.
2.2.2 125I Initial A ctivity ................................................
2.2.3 Accounting for Activity Decay .................................
Luxel® Dosimeters..................................................
MCNP Code..................................
...................
2.4.1 Calculating Dose Equivalent from MCNP output ........
2.4.2 MCNP Dosimeter Model .......................................
2.4.3 MCNP Cage Dose Profile................................................
Results and Discussion.............................
3.1
3.2
4.
Genetic Effects of Radiation ........................................
Radiation Dosimetry .......................................................
Monte Carlo and MCNP...................................................
Optically Stimulated Luminescence (OSL) Technology..............
............
Dosimeter Data ... .......................................
...
.................
3.1.1 Dose Profiles................................
...............
3.1.2 Actual Activity Levels ................................
3.1.3 Type of Radiation Reported .....................................
M CNP Data ............................. .. ....................................
3.2.1 MCNP Dosimeter Model......................................
3.2.2 MCNP Mouse Cage Dose Profile ...............................
Conclusion.................................................................
19
19
19
21
21
22
22
23
25
Appendix A: 125mTe Radiation Spectra.....................................
30
Appendix B: Representative MCNP Codes................................
31
Appendix C: Dosimeter Raw Data Tables............
..............
34
Appendix D: Dosimeter Dose Equivalent
Profiles and Contour Maps...................................
Appendix E: MCNP Dose Profiles and Contour Maps..................
Appendix F: Comparing MCNP and Dosimeters........................
37
43
45
5.
47
References .................................................................
1. Introduction and Background
1.1. Genetic Effects of Radiation
Radiation affects the genome both directly and indirectly. An example of a direct
radiation effect would be the ionization of one or two strands of a DNA molecule by an X-ray
resulting in a DNA single or double strand break, respectively. Products of radiation in the cell
nucleus can also result in DNA damage. A track of radiation can cause the creation of free
radicals; i.e. ionized molecules, excited molecules, and free electrons. In water, radiation most
commonly produces H30 +,OH, e-, and H [1]. These free radicals could also cause DNA strand
breaks by chemical reactions. For example, an OH radical can attack a DNA sugar. Whether
direct or indirect, the most notable effects of radiation on the genome are DNA strand breaks.
Double strand breaks are more troublesome than single strand breaks. In the event of a
single strand break, enzymes can repair the break with the help of the intact adjacent strand of
DNA. Double strand DNA breaks are more complicated to repair. The two most prevalent
methods of repairing double strand breaks are Non-homologous End Joining (NHEJ) and
Homologous Recombination (HR) [2]. NHEJ is a much faster process than HR; it simply rejoins
the two broken ends of the DNA without the aid of a template. However, it often results in base
deletion at the breakage site, and thus this method of repair is prone to be mutagenic [2]. HR is a
much slower repair process, and less inclined to produce errors. It utilizes homologous DNA
sequences to facilitate accurate repair. HR typically occurs during cell mitosis, particularly
during the late S and G2 phases of the cell cycle, when the sister chromatid is present [2].
The presence of HR can be assessed by fluorescence imaging techniques. This
experiment aims to study the influence of chronic low dose radiation on the frequency of HR.In
particular it will use in situ fluorescence imaging techniques to study HR in mice pancreatic
cells. Also, it will measure the frequency of HR in skin fibroblasts and investigate the in rate of
HR in ear fibroblasts by flow cytometry techniques. Flow cytometry techniques are used to
count, sort, and/or examine microscopic particles suspended in a stream of fluid. It will use
similar techniques to study blood cells as well.
1.2. Radiation Dosimetry
Radiation dosimetry attempts to quantify amounts of energy deposited by radiation in
different materials. One of the most important quantities in Radiation Dosimetry is Absorbed
Dose. Absorbed Dose is defined as the amount of energy radiation deposits in a target material
per unit mass of the target material [1]. Absorbed Dose is typically measured in units of gray
(Gy), 1 Gy = 1 Joule/kg. It can also be measured by an older unit called the rad. 1 rad = 100
erg/g. Unit conversion shows us that 1 Gy = 100 rad. Often times Absorbed Dose is merely
referred to as Dose.
Another important dosimetric quantity is the Dose Equivalent. The idea of Dose
Equivalent came about because different kinds of radiation that provide the same Absorbed Dose
can affect biological material very differently. The biological effects of different types of
radiation are related very closely to the Linear Energy Transfer (LET) of that specific type of
radiation. LET is defined as the rate of energy loss over a linear distance [3]. Radiation with
higher LET, for example heavy charged particles like protons and alpha particles, will be more
damaging than radiation of lower LET like gamma Rays and X-rays. In order to quantify the
different biological effectiveness of different kinds of radiation, the concept of a unit-less Quality
Factor, Q, was created. Radiation of higher LET will have a higher Q value. For example, for a
particle with an LET between 53 - 175 keV/tm, the Q value ranges from 10 - 20 [1]. For
gamma and X-ray photons of any LET, the Q value equals 1. The Dose Equivalent is calculated
by multiplying the Absorbed Dose by the Q factor, and thus takes into account the effectiveness
of different kinds of radiation. If the Absorbed Dose is specified in units of Gy, the Dose
Equivalent is expressed in a unit called the Sievert (Sv). If the Absorbed Dose is in rad, the
corresponding Dose Equivalent unit is the rem. Since 1 Gy = 100 rad, 1 Sv = 100 rem.
1.3. Monte Carlo and MCNP
Monte Carlo is a numerical approach aimed at modeling a stochastic system. The
algorithm uses random numbers to sample a given probability distribution. Because of the
repetitiveness, and the large number of calculations involved, Monte Carlo is typically a
computer-based simulation.
MCNP5, the Monte Carlo code used for this experiment, was first developed at Los
Alamos National Lab. MCNP stands for Monte Carlo Neutral Particle [4]. It uses this numerical
method to analyze the transport of particles (unlike the name suggests, not just neutral particles),
namely neutrons, photons, and electrons, through materials. MCNP5 is a code in Fortran that
accepts input files that define a system. The input file for this experiment tracks the life of a
photon born from a defined source. The characteristics of every photon, in particular its energy,
are determined randomly according to a specified probability distribution. This experiment is
only interested in a photon if it deposits energy in a particular "cell" of the modeled geometry. In
this case the "cell" of interest is the model of a mouse. The input file was written to tally the
effects of all of the starting photons that deposit energy in the mouse cell. In the end it averages
the tally values and outputs the average energy deposited in the mouse cell per source photon.
1.4. Optically Stimulated Luminescence (OSL) Technology
Certain irradiated semiconductors will emit luminescence during exposure to light. The
intensity of the luminescence is a function of the dose absorbed by the material during
irradiation. Irradiation causes ionization of elements on the crystal, and thus creation of an
electron-"hole" pair (the positively charged, ionized element is the "hole"). Most OSL materials
have pre-existing defects in their crystal structure that serve as non-radiative charge traps [5].
The newly liberated electrons drift around the crystal, and eventually find their way into one of
these defects. Later, when the crystal is stimulated with light, these trapped electrons are excited
out of the defects and into the conduction band. Once in the conduction band, they drift around
until they find a hole. The recombination of an electron-hole pair causes luminescence. The
intensity of the luminescence is proportional to the number of electron-hole pairs, and the
number of electron-hole pairs is a function of the initial irradiation dose. Thus the intensity of the
luminescence is a function of the radiation dose. The energy spectrum of the dose can also be
determined by varying the energy of the stimulation light, and reading the relative intensity of
luminescence at these different stimulation energies [6].
Technology capitalizes on this natural relationship between luminescence and radiation
dose by creating dosimeters out of these semiconductors. One particular example of a
commercial OSL dosimeter is called the Luxel ®, which is a product of Landauer®, Inc. The Luxel
is made of A120 3crystal doped with Carbon. The detector is sealed inside a multi-element filter
pack. The filter pack has three windows; one open window, one with a 250 [tm thick Copper
layer, and one with a 500 pm thick layer of Tin [5]. These different filters allow the dosimeter to
discern the Shallow Dose Equivalent (SDE), Lens Dose Equivalent (LDE), and Deep Dose
Equivalent (DDE), respectively. DDE, LDE, and SDE are defined as the dose equivalent at a
tissue depth of 1 cm, 0.3 cm, and 0.007 cm, respectively [5]. Landauer claims that their Luxels
can read a photon dose range of 1 mrem - 1000 rem, for photons between the energies of 5 keV
- 40 MeV, and an electron dose range of 10 mrem - 1000 rem, for electrons between the
energies of 150 keV - 10 MeV [7]. Also, Landauer claims a 15% error in all of their reports.
2. Methods
This chapter begins by explaining the physical setup of the Engleward lab mice
irradiation experiment. It will detail the dimensions of the important components and their
relative distances, the geometry and radioactive characteristics of the
125I
source, and weekly
maintenance procedures.
A description of the dosimetric methods shall follow the setup description. Dose
measurement with Luxel OSL dosimeters will be delineated first, and MCNP dose models will
follow.
2.1. Mouse and Source Cart Arrangement
The irradiation facility consists of a row of three identical setups. Each setup consists of
two carts; one holds four mice cages and one holds the flood phantom photon source. Having
two carts allows isolation of the photon source so that the radiation dose to personnel is
minimized whenever they handle the mice and/or collect the dosimeters. Figure 1 shows a front
and back view of one setup.
Figure 1: One of three mice irradiation setups [8]
1.
2.
3.
4.
5.
Cage cart holding four cages identified as A, B, C, and D
Leaded acrylic shield to protect personnel
Rubbermaid cart holding metal box
Metal box containing phantom
Phantom filled with '25I in a sodium hydroxide solution, shielded with lead on all sides
except for the top
The mice cages and the platform they rest on are all made out of Polymethyl
methacrylate (PMMA). The dimensions of the platform and one mouse cage are 79.50 x 65.00 x
0.64 cm thick, and 28.07 x 18.75 x 21.00 cm tall, respectively. The cage walls are 0.32 cm thick.
2.2. Flood Phantom Photon Source
The flood phantom was purchased from Biodext
Medical Systems (Shirley, New York).
Flood phantoms provide a constant radiation flux over a large area. For this reason they are
typically used to determine the field uniformity of scintillation cameras.
Our phantom is made of PMMA and has a hollow inner cavity to hold the radiation
source solution. It also has a small hole in its side to allow filling and draining of the cavity. Its
outer dimensions are 71.1 x 52.0 x 3.2 cm thick, and the inner cavity is 41.9 x 60.9 x 1.3 cm [9].
Figure 2 shows an image of a flood phantom. The phantom material density is uniform
throughout; the inner cavity is transparent merely because the walls are thin enough.
Figure 2: Flood Phantom Source [9]
2.2.1 125sI Radioactive Properties
The inner cavity of the phantom holds a solution of 125Iodine in a NaOH (MP
Biomedicals, Irvine, CA) solution. 125I decays by electron capture to 125mTe with a half-life of
59.408 days [10]. This yields a decay constant X = 0.01167 days'. However, none of the
detectable radiation comes from
125I
decay, it actually results from the de-excitation of 125mTe
from its metastable state to its stable ground state. Since the electron capture decay of 1251 leaves
a vacancy in one of the lower electron orbitals, the 125STe nucleus and electron configuration are
both in excited states. Thus the radiation from 125Te isa combination of Auger electrons and Xrays from de-excitation of the electrons, and conversion electrons and gamma rays from decay of
the nucleus. Figure 3 displays the photon energy spectrum and Figure 4 displays the electron
energy spectrum. To see the information in tabular format, please see Appendix A. 125STe has a
half-life of 57.40 days (,. = 0.01208 days') [11].
Te-125 Photon Energy Spectrum
S40
30
20
10
0
I
3.77
27.202
27.472
30.944 30.995
31.704 35.504 109.276 144.78
Energy (keV)
Figure 3: 125mTe Photon Energy Spectrum [11]
Te-125 Electron Energy Spectrum
160 140 120 -L
,a
Z
0UU
-
80-
C 6040 20-
0-
I
I
3.19
3.69
22.7
I
k-
30.565 34.498 77.462 104.337 108.27 109.108
Energy (keV)
Figure 4: 125mTe Electron Energy Spectrum [11 ]
2.2.2
1251
Initial Activity
The goal of the Engleward mice irradiation experiments is to study the genetic effects of
constant exposure to radiation over a prolonged period of time, and over a wide range of
radiation dose rates. The dose rates of interest are three times the natural background level (30
gGy/day), 300 times background (3 mGy/day), and 30,000 times background (0.3Gy/day) [12].
The first set of experiments was conducted at approximately 300 times background.
In order to determine the activity level that corresponds to this dose rate, an MCNP
simulation was performed. The simulation modeled the mouse as a 6 cm long and 2 cm in
diameter tissue filled cylinder. The "mouse" sat centered 3 mm above a 3 mm thick PMMA box,
which represented the mouse cage floor. The PMMA box sat on top of a water-filled, rectangular
flood phantom. The source was defined in the phantom with a photon spectrum similar to that
displayed in Figure 3. (Note: For completeness, an MCNP model was also performed for an
electron source with the energy spectrum listed in Figure 4. The geometry was identical to the
geometry for the photon MCNP model. The simulation result showed that no source electrons
would deposit any energy in the mouse. This result was expected because it is well known
experimentally that electrons of these energies have a very short range. In water, electrons with
energy between 2 keV and 200 keV have a range between 2x10 -5 cm and 0.0440 cm [1]. This
indicates that nearly all of the source electrons would deposit their energy in the water of the
phantom. Therefore, source electrons were not considered in dosimetric calculations henceforth.)
The MCNP tally, results are given in units of (MeV/g) per starting photon. In order to attain
results in units of (Gy/photon), the MCNP output was multiplied by [1.6022x 10-' Gy/(MeV/g)]
[12].
MCNP determined that the average dose to a mouse modeled this way is (1.28 +
0.026)x10-16 Gy/photon. From a photon intensity spectrum (slightly different from the one listed
in Appendix A, and used in future calculations) it was determined that each decay produces on
average 1.47 photons by adding up the photon intensities. Multiplying this by the MCNP output,
we find that each decay results in a dose of 1.88x10- 16 Gy on average. Thus, to achieve the dose
level of interest, 300 times background (3 mGy/day), we need an activity level of 180 MBq (5
mCi) (= (0.003 Gy/day - 1.88x10.16 Gy/decay) + 86,400 sec/day) [12].
2.2.3 Accounting for Activity Decay
In order to keep dose levels constant, we need to model the decay of our source, and
"top-up" the phantom accordingly. Because the half lives of 125I and 12smTe are so close (T/2 =
59.408 days, 1i = 0.01167 days1' for 1251; Ti/2= 57.40 days, X2 = 0.01208 days' for 125mTe), our
source decay follows the Transient Equilibrium model [1]. Under this model, eventually the
activity of the daughter nuclide decays like that of the parent nuclide. The general differential
equation that governs the concentration of a decay product is:
dN2 = •1N -)N
dt
2
(1)
where N 1 and N2 are the number of atoms of the parent and daughter nuclide, respectively, and i
are their decay constants [1]. With the condition N2 (t=0) = 0, the solution to equation (1) is:
N2 =
N(t =0) -At _-et')
(2)
Since X2 > X1, eventually the daughter decay term dies out, and the parent decay term, e- y',
dominates the expression. We can see the time evolution of Transient Equilibrium in Figure 5.
We notice the initial growth of the daughter nuclide, and also that its eventual decay is
proportional to that of the parent.
Making the assumption that the
125I
we receive is far enough along its lifetime that the
daughter nuclide, 125mTe, is beyond its initial growth period, we can model the decay of 125mTe as
N 2 = N(t = 0) e
(3)
Substituting in the value for AX,
it was determined that 91.5% of the initial activity remains after
one week. Thus every week, the phantom has to be refilled with a concentration of the source
equivalent to 8.5% of the initial activity. For the dose level this experiment was concerned with,
5 mCi, the source was topped-up with 0.425 mCi of 1251 each week.
_·
·_
.1
'It
"!0
period of
ingrowth
transient equilibrium
Figure 5: Transient Equilibrium Model [13]
2.3. Luxel® Dosimeters
The Luxel OSL dosimeter was chosen to measure the dose integrated over a week. (The
dosimeters actually measure Dose Equivalent, but because the factor of proportionality between
Dose Equivalent and Dose, the quality factor, is one for photons and electrons of any LET [1],
the terms Dose and Dose Equivalent will be used interchangeably.) In order to minimize error,
and to get a profile of the dose over the whole active area, nine dosimeters were placed in a 3 x 3
array on each mouse cart platform, between the mice cages. Figure 6 shows a picture of the
dosimeter positioning on one cart. Each dosimeter had a unique number to identify it, and Figure
7 shows the Luxel numbering scheme. In order to keep the dosimeter in place, they were each
fastened to the cart with a strap of Velcro.
Every Wednesday morning at 9 AM, when the phantom was topped-up, campus
Radiation Protection Organization (RPO) representatives collected each badge and sent them to
Landauer to be read. Every Thursday or Friday, Landauer sent a document that detailed each
badge's dose equivalent readings in [mrem/week] for the week before. The document detailed
the DDE, LDE, and SDE; and it also reported the type and energy level of radiation responsible
for the dose.
_~_1
Figure 6: 3 x 3 Dosimeter array [8]
Wall
Wall
Wall
7
8
9
16
17
18
25
26
27
4
5
6
13
14
15
22
23
24
1
2
3
10
11
12
19
20
21
Front of Cart 1
Front of Cart 2
Front of Cart 3
Figure 7: Numbering System for Dosimeters
2.4. MCNP Code
MCNP simulations were used to evaluate the dose at several locations within the mouse
cages. The dosimeters could not be placed inside the cages, for the mice would have tampered
with them. Thus they could only provide limited information about the actual doses to the mice.
To rectify this, MCNP simulations were performed to probe the dose within the cages with finer
resolution. Detailed measurements of the source/cart system were taken, and these MCNP
simulations were run with a more complete geometry than those simulations that were performed
to determine the initial source activity.
The first set of MCNP runs simulated the dose specifically to the Luxel dosimeters on
one cart. This was done to compare the output of an MCNP simulation to actual measured data
and hopefully show that the MCNP results are realistic. The final set of simulations studied the
dose profile over the cage area. To see examples of the MCNP code used, please refer to
Appendix B.
2.4.1 Calculating Dose Equivalent from MCNP output
The MCNP code outputs its data in units of Gy per source photon. One has to multiply
this output by a factor that accounts for the source activity to receive results in units of
mrem/week. With results in mrem/week, we can compare the MCNP output to the dosimeter
data. We start determining this factor by finding out the number of source photons in one week.
In Section 2.2.3, we determined that the activity of the 125mTe source could be modeled by
Equation (3). If we integrate this function over one week, we can find the number of
disintegrations per week. Figure 8 shows a plot of the decay of 125mTe over one week.
1-125Activity Decay Over OneWeek
5.5
5
--- 1
4.5
4
3.5
3
S2.5
2
1.5
1
0.5
0
0
1
2
3
4
5
6
I
Time(days)
Figure 8: 125mTe Decay over one week
The integral of this function, where N2 is the activity of 125mTe in decays per day, over
seven days yields the number of decays per week:
7daus
N 2 (t = 0) *
fexp(-0.01167 * t)dt = N2 (t = 0)* 6.7217
0
Keeping this expression general with respect to the initial activity allows us to use it
again later for different activity levels and accordingly different dose levels. If N2 is in units of
mCi, we can multiply it by 3.7x107 to convert it to disintegrations per second, and then we can
multiply that by 86,400 to convert it to disintegrations per day. Thus the number of
disintegrations per week equals:
(4)
N 2(t =O)mCix
3.7*107 dps 60sec 60min 24hours
x
x x
x6.7217
ImCi
Imin lhour
Iday
(5)
Our photon spectrum in Appendix A tells us that, on average, each disintegration
produces 1.336 photons. Multiplying by this factor in the above expression, we now have the
number of photons produced by the source per week. If we multiply that whole expression by the
MCNP output, we can determine the Gy/week, and thus the energy deposition per week in the
mouse. Furthermore, since photons of any Linear Energy Transfer (LET) have a Quality Factor
of 1,the Dose Equivalent in mrem, can be found directly from the Dose in Gy by a conversion
factor: 1 Gy = 1 Sv = 100 rem = 105 mrem. Hence, the final expression to convert the MCNP
dose (Gy/photon) to the Dose Equivalent (mrem/week) is:
3.7*107dps 86400sec
1.336, 10 mrem
[(MCNPoutput)x N2 (t = )mCi]x 3.7
d
86400secx 6.7217 x 1.336y
mrem
lmCi
Iday
1decay
1Gy
=
(6)
[(MCNPoutput)x (N 2 (t = O)mCi)] x 2.8708 *1018 mrem / week
2.4.2 MCNP Dosimeter Model
The MCNP dosimeter model included the phantom source, the PMMA mouse cage
platform, and nine dosimeters. Figure 9 shows a profile of the Deep Dose MCNP dosimeter
model; the blue rectangles are the dosimeters, and the green rectangle is the cavity of the yellow
PMMA phantom that contains the
1251
source solution. The phantom source was defined as a
water-filled box, 60.9 x 41.9 x 1.3 cm thick, emitting photons of the previously defined energy
spectrum. This box was nested within a PMMA box of dimensions 71.1 x 52.0 x 3.2 cm. The
mouse cage platform was defined as a 79.50 x 65.00 x 0.58 cm PMMA box, and its bottom
surface floated 8.25 cm above the top surface of the phantom because there is an air gap of this
length between the phantom and the platform. Each Luxel dosimeter was modeled as a 4 cm
diameter, tissue-filled cylinder, with its center axis perpendicular to the platform. Models with
three different cylinder heights, 1 cm, 0.3 cm, and 0.007cm, were used to simulate the DDE,
LDE, and SDE that the real dosimeters report. Each simulation reported the dose to each of the
nine dosimeters in Gy/photon.
Figure 9: MCNP Deep Dose Dosimeter Model, x-y view
2.4.3 MCNP Cage Dose Profile
After the MCNP dosimeter model was performed, simulations were run to probe the dose
over the cart area. This geometry used the same source platform geometry as the previous model,
but it also included a PMMA mouse cage with outer dimensions of 56.15 x 37.5 x 21 cm high,
and 0.32cm thick walls. The mice were defined as 2 cm diameter, 6 cm long, tissue-filled
cylinders. All mice floated 1 cm above the cage floor to account for the length of their legs when
standing, and were oriented such that their cylindrical axis was parallel to the floor surface. In
each simulation 5 mice were aligned in a column, head to tail, with a 1.7 cm gap between each
mouse. Figure 10 shows 3 different views of the geometry.
-I
z-x view
Figure 10: Cage Dose Profile MCNP Simulation Geometry
Several runs were performed, and for each run, the column of mice was displaced 2 cm in
the x-direction until a dose in Gy/photon was determined for the whole cage area.
3. Results and Discussion
3.1. Dosimeter Data
First, one week of background radiation data were collected. However, none of the
dosimeters reported a significant background dose, thus there was no need to subtract a
background radiation factor from any of the future data. After that first week, four weeks worth
of data were collected in the presence of a radiation source. During the first two weeks, there
were only enough mice available to populate one cart of cages, and during the last two weeks,
there were enough mice to populate two carts of cages. A dose profile was created from the data
each week, for each cart, at each dose equivalent level, DDE, LDE, and SDE. See Appendix C to
view tables of the raw data, and see Appendix D to view all of the dose profiles created from the
raw data.
3.1.1 Dose Profiles
The most noticeable feature about the data is the wide dose fluctuation week to week. Not
only do the values change greatly week to week, but they also don't change uniformly over the
area of one cart. Table 1 shows reported DDE to the nine different dosimeter positions on one
cart and pertinent statistical values.
The standard deviation is greater than Landauer's reported error for all but one of those
Luxel positions. This is typical of all of the dose equivalent levels; none of the LDE standard
deviations are less than the reported error, and only one of the SDE standard deviations is greater
than reported error.
Why could this be happening? One suggested possibility was that the outer dosimeters
are positioned at the fringes of the source where the dose changes very rapidly with position, and
thus those data are more error prone. There is a ±1 cm error associated with the placement of the
dosimeters. (MCNP simulations were performed to examine the dose error associated with
changes in the placement of the dosimeters. The results will be explained in section 3.2.1.)
However, the standard deviation of the dosimeter over the center of the source is similar in
magnitude to those of the outer dosimeters, thus the mere placement on the fringe of the source
cannot be the source of all of the error. One more likely explanation is that the source is not
getting mixed sufficiently each week when more
levels. Prior to running tests with
125I,
125I
is added to maintain constant activity
the ability to uniformly mix a solution in the phantom was
tested with ink and water. Several of the initial runs were unsuccessful at getting a homogeneous
mixture. Adding more air bubbles before mixing the solution rectified the problem, however a
good mixture was still difficult to achieve even with more bubbles.
Table 1: Dosimeter Deep Doses and Statistics
Luxel
1&10
(mrem/
week)
Luxel
2&11
(mrem/
week)
Luxel
3&12
(mrem/
week)
Luxel
4&13
(mrem/
week)
Luxel
5&14
(mrem/
week)
Luxel
6&15
(mrem/
week)
Luxel
7&16
(mrem/
week)
Luxel
8&17
(mrem/
week)
Luxel
9&18
(mrem/
week)
264
198
251
465
961
442
227
267
286
120
289
275
662
259
437
406
627
1002
1079
824
783
363
259
547
771
373
248
457
913
346
608
1328
794
175
681
590
162
557
250
624
988
608
252
476
138
349
295
358
666
1027
495
250
669
163
254.33
568.50
299.67
180.93
165.74
85.275
44.95
Column Average Values (mrem/week)
273.50
483.33
316.83
566.00
1064.17
657.67
Column Standard Deviations (mrem/week)
123.04
276.50
76.33
104.55
135.29
165.77
61.47
Average Reported Error (15%) (mrem/week)
41.025
72.5
No
No
47.525
84.9
159.625
98.65
38.15
Is the Standard Deviation < Reported Error?
No I
No
Yes
No
No
No
Another noticeable characteristic is the vast range of dose levels. On average the center
dosimeter reports a DDE of 1064.17 mrem/week, whereas one in a corner reads 254.33
mrem/week; almost a factor of five less. This result is probably due to the positioning of the
outer dosimeters on the fringe of the source. However, the positioning of the dosimeters is
limited. The outer ones are already flush against the mouse cages, and cannot be positioned
closer to the center of the source. It would be more difficult to keep them fastened down if they
were placed inside the mouse cages, and they wouldn't be reading the true mouse dose if they
were placed under the cart since the photons are slightly attenuated through the PMMA platform
and mouse cage floor. Thus avoiding this large dose range can only be done if we increase the
source area, or decrease the mouse cage area.
No
3.1.2 Actual Activity Levels
In section 2.2.2 it was determined that in order to achieve a dose that is 300 times
background (3 mGy/day), we need an activity level of 180 MBq (5 mCi). From section 2.4.1, we
found that 1 Gy = 105 mrem, thus a dose of 3 mGy/day would result in a dose equivalent of
2100 mrem/week.
Unfortunately, none of the dosimeters reported values near to 2100 mrem/week. In fact
the highest readings are on average half of the target dose. The average dose values are even
lower; they are approximately one fourth of the target value. The average DDE is 498.22
mrem/week, the average LDE is 597.28 mrem/week, and the average SDE is 705.02mrem/week.
The average values are probably lower than the true average dose over the mouse cage area
because the outer dosimeters are on the edges of the source, but in any case the average dose
value is significantly lower than the target dose.
The vast disparity in target dose value and actual dose values is likely due to
discrepancies between the initial MCNP system model from which the necessary activity levels
were first calculated, and the true physical geometry of the system. At the beginning of this
experiment the mouse cart design took more time than expected, so the source specification
calculations were made with rough approximations of the source/target geometry. Recall from
section 2.2.2 that the initial MCNP model consisted of a cylindrical mouse atop a 3 mm thick
platform that directly rested on a 3 mm thick phantom source. However in the actual setup, the
platform is 5.8 mm thick - almost twice the initially modeled thickness. In addition, the platform
does not rest directly on the phantom. There is a 9 cm gap of air between the top of the phantom
and the bottom of the platform. Since we are dealing with a relatively soft photon spectrum,
photon attenuation over the thicker platform and the air gap between the source and the target
could be responsible for the lower dose levels. In fact, it will be shown in section 3.2 that when
MCNP simulations were performed with the correct geometry, the resulting dose is also lower
than the target dose, and about on the order of the dosimeter reported doses.
3.1.3 Type of Radiation Reported
In addition to the dose equivalent, the dosimeters also report the type of radiation
detected. The majority of reported radiation was from photons of energy between 10 keV and
250 keV. However some dosimeters reported an electron contribution to the Shallow Dose.
Despite the fact that the source readily emits Auger Electrons and Conversion Electrons, the
reported electrons probably do not find their origin in the phantom. As stated earlier in section
2.2.2, our source electrons only have a range between 2x10 -5 cm and 0.0440 cm [1]. The MCNP
model showed that the majority of the source electrons would deposit their energy in the
phantom. The electrons detected are most likely the result of photon interactions with matter.
The dominant interaction mechanism for our soft photon energy spectrum in water, tissue, and
air, is Compton Scattering. The first ionization energy for the most prevalent elements is only on
the order of tens of eV per ionization (For example: first ionization energies for Carbon = 11.260
eV, Oxygen = 13.618 eV, Nitrogen = 14.534 eV, Hydrogen = 13.598 eV) [14], thus since our
photons range in energy from 4 - 145 keV, ionized electrons will still have an appreciable
kinetic energy to provide a shallow dose.
3.2. MCNP Data
The first MCNP runs were modeled to mimic the geometry of the dosimeters positioned
on the cart. This was done to test the accuracy of the MCNP predictions of the dosimeters' doses.
If the dose equivalent reported by MCNP was similar to the dosimeter results, then the MCNP
models of dose to the mice can be expected to generate realistic results. After this test was
finished, an MCNP simulation was performed to examine the dose over the whole mouse cage
area to calculate the average mouse dose.
3.2.1 MCNP Dosimeter Model
The MCNP dosimeter model output information on the DDE, LDE, and SDE to each of
nine simulated dosimeters. The raw data were first converted to mrem/week according to the
procedure outlined in section 2.4.1. They were then tabulated, and a dose profile similar to those
made for the dosimeter data was made. See Appendix E to view all of the MCNP data and dose
profiles. As to be expected, since the MCNP source is modeled to emit radiation homogeneously
over its entire surface, the MCNP dose profiles were much more symmetric than the dosimeter
dose profiles.
The objective of creating this model was to see if MCNP could reproduce realistic
results. In order to determine that, first, average dosimeter dose profiles were created to
accumulate four weeks worth of data into three plots; one each for DDE, LDE, and SDE. Then
those three plots were compared to the analogous three MCNP plots. Both sets of data were
examined to determine if the agreed with each other within uncertainties. See Appendix F to
view the data for Combined Error, and MCNP and dosimeter differences.
Comparison of the data shows agreement between MCNP predictions and dosimeter data
22 out of 27 times. Since MCNP results have been shown to be accurate 81.5% of the time, it is
safe to trust other MCNP simulations, assuming the modeled geometry is true to real life
dimensions and materials.
Knowing that MCNP models are accurate, a simulation was performed to examine the
dose error associated with changes in the placement of the dosimeters. In this simulation, each of
the dosimeters was displaced 1 cm in different directions. Comparison of the MCNP results from
the displaced dosimeters to the original model show that for 19 out of 27 calculations, the dose
difference due to movement of the dosimeters is less than the statistical error associated with the
original dose calculation. Thus the dose error due to dosimeter positioning is only 30%
significant.
3.2.2 MCNP Mouse Cage Dose Profile
This experiment is most concerned with the doses that the mice receive, therefore it is
desirable to find the dose average over the area of the mouse cages. To do this, an MCNP model
was created with a row of five mice inside a cage. This row of mice was translated up and down
the length of the cage in increments of 2 cm, and the dose they received was recorded at each
location. With this information, a plot was created to model the dose over the area of the mouse
cages. Due to the sizes of the mice, and the increments of translation, the plot has a resolution of
2 cm in the x-direction, and 6 cm in the z-direction. See Figures 11 and 12 for the plot results.
The plots show that the source edge effects are not negligible, for there is a large dose
range from the center of the cage to one of the corners. The doses range from 866 _t 33
mrem/week close to the center, to 399± 18 mrem/week in one of the comers. This means that if
one mouse preferred to live in the center of the cage area, he would receive more than twice the
dose that another mouse that lived primarily in an outer comer would receive. Assuming that the
mice are more mobile and prefer to roam freely around their cages, according to the plot they
would receive an average dose of 656. 108 mrem/week.
Figure 11: Dose Profile Over the Mouse Cage Area in mrem/week.
(Note: The units of the x-axis and the y-axis are in cm. The units of the z-axis are in
mrem/week.)
Dose Over Cage Area (mremlweek)
C% r
3
1
z-axis
(cm)
'-
CY)L)
N-
C)
M-x-
O-c
, 0
N•-"
N-
M
N
CT
1
E 800-1000
o 600-800
[ 400-600
m200-400
go 0-200
P
N-
x-axis (cm)
Figure 12: Contour Map of the Dose Over the Mouse Cage Area in mrem/week
4. Conclusion
The dosimeters and the MCNP simulations make four important points. First of all,
comparison of the measured and calculated data show that MCNP simulations can be trusted to
report realistic mouse doses. A majority of the dosimeter measurements, 87%, agree with MCNP
calculations. This is useful for future mouse irradiation experiments, for it provides a sound
method for calculating doses provided to mice at any dose rate. Simulations like those described
in section 3.2.2 can be run to determine the average dose provided to mice. Knowing the doses
provided to the mice, and determining the amount of biological effects provided at that dose
level would clarify the effects of chronic low doses of radiation that this experiment intends to
study.
The second interesting result is that the mouse dose for this particular experiment varies
greatly over the cage area. One way to rectify this would be to increase the source area relative to
the target area. Either larger flood phantoms could be obtained, or less mouse cages could be
mounted above the platform. In either case, the result is unfavorable. Larger phantoms are more
expensive and would be difficult to maneuver each week when mixing had to be performed.
Also, since the current phantom fits snugly in its shielding box, to use a larger platform would
require re-engineering and re-manufacturing of the whole source cart/mouse cage system. The
alternative to a larger phantom would be a smaller cage area. This is unfavorable because the less
mice irradiated, the more error in the data. In order to irradiate the same number of mice with a
smaller cage area, assuming the number of mice per cage is limited, it would take a longer time
to complete the experiment.
One possible compromise to solve this problem would be to decrease the cage irradiation
area, but also include cages below the phantom. The setup could be engineered so that the mice
above the phantom receive the same dose as the mice below the phantom. All that would be
necessary would be that the attenuation characteristics between the cages above and below
would need to be symmetric, i.e. the thickness of the materials, and distance between the
phantom and the mice must be the same above and below. An MCNP simulation was run for the
hypothetical model that the phantom rested on a PMMA platform of the same thickness as the
platform that the mouse cages rest on, and that the tops of the mouse cages below the phantom
touch that platform. See Figure 13 for a picture of this model.
-
UIII
-
-
-
I
Figure 13: z-y view of the "Mice Under Phantom" model
The MCNP output for the mouse above the phantom was 844 ±t 32 mrem/week, and the
output for the mouse below the phantom was 576 ± 26 mrem/week. The dose to the mouse below
the phantom is probably lower because it is farther away from the phantom than the mouse
above. Another simulation was performed in which the distances and the thickness of materials
between the mice and the phantom were equivalent, and the cage below the phantom was
shorter. See Figure 14 for a picture. In this case, MCNP output a dose of 844 ± 32 mrem/week to
the mouse above the phantom, and 822 ± 31 mrem/week to the mouse below the platform. These
values are certainly within error of each other, and thus placing mice below the phantom would
be a viable solution to the problem of decreasing the source area relative to cage area, yet still
irradiating approximately the same number of mice in the same amount of time. The only thing
left to do would be to calculate the thickness of the PMMA platform necessary to support the
weight of the phantom, and optimize this thickness with a cage height such that the mice above
and below would receive equal doses.
Figure 14: MCNP model with shorter cage below phantom
In addition, the dosimeter data showed inhomogeneities and asymmetries in the dose
profile over the cart area. It was postulated that this could be due to poor mixing of the phantom
each week. The possible solutions to this problem are simpler than the previous solutions. In
order to provide a more homogeneous dose to the mice in spite of these asymmetries, either more
time could be devoted to the mixing process, the phantom could be mixed more than once a
week, or the mouse cages can be rotated often throughout the irradiation week.
Finally, they both show that the doses the mice are receiving are far lower than the
desired level of 300 times background. As stated earlier in Section 3.1.2, this disparity is most
likely the result of inaccurately modeling the system when the necessary source activity was first
calculated. Our photon spectrum is so soft that even attenuation over a few centimeters cannot be
neglected. In order to correct this, naturally more
1251
should be injected into the flood phantom.
If we neglect the large dose range, and wished to increase the average dose over the mice cage
area to the desired level of 2100 mrem/week, this would require an initial source activity level of
16.02 mCi. Equations (7) through (9) show the derivation of this result. In addition, the amount
of activity injected into the source each week to maintain constant activity levels would need to
be adjusted. Since it was determined that the source decays by 8.5% each week, to maintain an
initial activity of 16.02 mCi, 1.361 mCi of
1251
would need to be injected each week instead of
the 0.425 mCi that is currently being injected.
Current Average = 655.6236 mrem/week = [(MCNPoutput)x (N 2 (t = O)mCi)] x 2.8708 *101' (7)
Corresponding MCNP output = 655.6236re /week
5mCi x 2.8708 *1018
4.5675 *10 - 17 Gy
y
(8)
Desired Average Dose = 2100 mrem/week
2100mrem/ week
N 2 (t = O)mCi =
[(4.5675
*10-1
(9)
GY)x (2.8707 * 1018)]
Y
N 2(t=0) = 16.0158 mCi of 1251 per week
In summary, this paper has been concerned with the dose provided by a rectangular flood
phantom to mice. In order to discern the average dose, measurements were taken and simulations
were performed. The dosimetry methodology prepared for this study can be reproduced for
future mouse irradiation studies of different dose rates.
In addition to creating a dosimetry method, this study discovered interesting
characteristics about the mouse doses in the current experiment. Both the measurements and the
simulations showed problems in the dose, namely that there is a wide range of doses provided
over the area of the mouse cages due to the edge effects of the source, the wide dose range is
exacerbated by asymmetries in the source, and the doses provided are much lower than desired.
If the dose inhomogeneities were fixed, the standard deviation of the average dose would
decrease. Needless to say, a smaller dose error would make the correlation between biological
effects and radiation dose more conclusive.
Appendix A:
125mTe
Radiation Spectra
Table 1: 125mTe Photon Energy Spectrum [10]
Photon Origin
Energy (keV)
Relative Intensity
(%)
XR 1
XR ka2
XR kal
XR kp3
XR kpl
XR kp2
gamma
gamma
gamma
3.77
27.202
27.472
30.944
30.995
31.704
35.504 ± 0.015
109.276 ± 0.015
144.780 ± 0.025
14.4 ± 0.6 %
32.6 ± 1.1 %
60.3 ± 2.0 %
5.56 ± 0.18 %
10.7 ± 0.3 %
3.09 ± 0.10 %
6.67 ± 0.20 %
0.274 ± 0.009 %
3.9E-7 %
Table 2: 125mTe Electron Energy Spectrum [11]
Photon Origin
Energy (keV)
Relative Intensity
Auger L
Auger K
CE K
CE L
CE M
CE K
CE L
CE M
CE NP
3.19
22.7
3.690 _ 0.015
30.565 ± 0.015
34.498 ± 0.015
77.462 ± 0.015
104.337 ± 0.015
108.270 ± 0.015
109.108 ± 0.015
152 ± 3 %
16.3 + 0.6 %
80.0 + 2.4 %
10.7 ± 0.3 %
2.15 ± 0.07 %
50.4 ± 1.7 %
36.2 ± 1.2 %
8.4 ± 0.3 %
2.19 ± 0.07 %
Appendix B: Representative MCNP Codes
MCNP Dosimeter Lens Dose Equivalent Model Code:
bevin's Luxel Lens dose from 125-I photons
c
1 1 -1.3e-3-50#2#3#4#7#8#9#10#11#1 2 #13 #14 #15
$PMMA phantom outside
3 -1.19 -1 #3
$water phantom inside
4 -1.0 -2
$PMMA platform
3 -1.19 -3
$luxel 1
2 -1.04 -6 48 -49
$luxel 2
2 -1.04 -7 48 -49
$luxel 3
2 -1.04 -8 48 -49
$luxel 4
2 -1.04 -9 48 -49
$luxel 5
2 -1.04 -10 48 -49
2 -1.04 -11 48 -49
$luxel 6
$luxel 7
2 -1.04 -12 48 -49
2 -1.04 -13 48 -49
$1uxel 8
$luxel 9
2 -1.04 -14 48 -49
0 50
$phantom outside
rpp -35.55 35.55 0 3.2 -26 26
$phantom nested
rpp -30.45 30.45 0.95 2.25 -20.95 20.95
$platform
rpp -39.75 39.75 11.45 12.03 -32.5 32.5
$luxel 1
c/y -30 -20.65 2.0
$luxel 2
c/y -30 0 2.0
$luxel 3
20.65
2.0
c/y -30
$Iuxel 4
c/y 0 -20.65 2.0
$luxel 5
cy 2.0
$luxel 6
c/y 0 20.65 2.0
$luxel 7
c/y 30 -20.65 2.0
$luxel 8
c/y 30 0 2.0
$luxel 9
c/y 30 20.65 2.0
py 12.03
py 12.33
so 100
$enviror iment
mode p
print -86 -85
imp:p 11111111111110
sdef x dl y d2 z d3 erg d4 cel 3 par 2 $photon source def
sil -30.45 30.45
spl 01
si2 .95 2.25
sp2 01
si3 -20.95 20.95
sp 3 01
si4 L .00377 .027202 .027472.030944 .030995 .031704 .035504 .109276 .14478
sp4 14.4 32.6 60.3 5.56 10.7 3.09 6.67 .274 .00000039
f6:p 7891011 12 13 14 15
fm6 1.6022e-10
ml 8016 -.2
$air
7014 -.8
1001 -10.0
$tissue
6012 -14.9
7014 -3.5
8016 -71.6
m3 1001 -.0805 $PMMA
6012 -.5998
8016 -.3196
m4 1001 -.11190 $water
8016 -.88810
nps 1000000
m2
MCNP Cage Dose Equivalent Profile Code, Mice column at x=0
bevin's mouse dose from 125-I photons
1 -1.3e-3 -50 #2 #3 #4 #5 #6 #7
3 -1.19 -1 #3
4 -1.0 -2
3 -1.19 -3
3 -1.19 -4 #6 #7 #8 #9 #10 #11
1 -1.3e-3 -5 #7 #8 #9 #10 #11
2 -1.04 -6 7 -8
2 -1.04 -6 9 -10
2 -1.04 -6 11 -12
2 -1.04 -6 13 -14
2 -1.04 -6 15 -16
0 50
#8 #9 #10 #11
$PMMA phantom outside
$water phantom inside
$PMMA platform
$PMMA cage outside
$PMMA cage inside
$mouse
$mouse
$mouse
$mouse
$mouse
rpp -35.55 35.55 0 3.2 -26 26
rpp -30.45 30.45 0.95 2.25 -20.95 20.95
rpp -39.75 39.75 11.45 12.03 -32.5 32.5
rpp -28.075 28.075 12.03 33.03 -18.75 18.75
rpp -27.755 27.755 12.35 32.71 -18.43 18.43
c/z 0 14.03 1.0
pz -18.4
pz -12.4
pz -10.7
pz -4.7
pz -3
pz 3
pz 4.7
pz 10.7
pz 12.4
pz 18.4
so 100
$environment
mode p
print -86 -85
imp:p 1 1 1 1 1 1 1 111 10
sdef x dl y d2 z d3 erg d4 cel 3 par 2
sil -30.45 30.45
spl 0 1
si2 .95 2.25
sp2 0 1
$phantom outside
$phantom nested
$platform
$cage outside
$cage inside
$mouse
$photon source def
si3 -20.95 20.95
sp3 01
si4 L .00377.027202.027472.030944.030995.031704.035504.109276.14478
sp4 14.4 32.6 60.3 5.56 10.7 3.09 6.67 .274 .00000039
f6:p 7 8 9 10 11
$photon energy tally
fm6 1.6022e-10
ml 8016 -.2
$air
7014 -.
8
m2 1001 -10.0
$tissue
6012 -14.9
7014 -3.5
8016 -71.6
m3 1001-.0805
$PMMA
6012 -.
5998
8016 -.
3196
m4 1001-.11190 $water
8016 -.
88810
nps 1000000
Appendix C: Dosimeter Raw Data Tables
All data are in mrnem/week. Landauer claims 15% error on all readings.
Deep Dose Equivalent Tables
Cart rear (close to wall)
227
267
286
465
264
961
198
Cart Front
Week 1 Cart 1
442
251
Cart rear (close to wall)
363
547
406
1002
120
275
Cart Front
Week 2 Cart 1
Cart rear (close to wall)
259
771
627
1079
289
662
Cart Front
Week 3 Cart 1
Cart rear (close to wall)
175
681
608
1328
457
913
Cart Front
Week 3 Cart 2
Cart rear (close to wall)
252
476
624
988
162
557
Cart Front
Week 4 Cart I
Cart rear (close to wall)
250
669
666
1027
349
295
Cart Front
Week 4 Cart 2
373
824
259
248
783
437
590
794
346
138
608
250
163
495
358
Lens Dose Equivalent Tables
Cart rear (close to wall)
233
579
264
553
1031
198
286
607
251
Cart Front
Week 1 Cart 1
Cart rear (close to wall)
363
845
547
1106
373
824
429
693
Cart Front
Week 2 Cart 1
324
Cart rear (close to wall)
259
771
1079
800
662
289
Cart Front
Week 3 Cart 1
Cart rear (close to wall)
322
681
608
1328
457
913
Cart Front
Week 3 Cart 2
425
783
437
590
794
346
Cart rear (close to wall)
258
508
443
624
1223
608
474
557
347
Cart Front
Week 4 Cart 1
Cart rear (close to wall)
311
671
585
669
1566
295
Cart Front
Week 4 Cart 2
510
981
573
Shallow Dose Equivalent Tables
Cart rear (close to wall)
232
768
323
837
249
1394
197
Cart Front
Week 1 Cart 1
656
251
Cart rear (close to wall)
745
357
1412
1252
724
1002
Cart Front
Week 2 Cart 1
Cart rear (close to wall)
246
732
1178
1037
274
629
Cart Front
Week 3 Cart 1
Cart rear (close to wall)
420
646
577
1261
433
867
Cart Front
Week 3 Cart 2
Cart rear (close to wall)
259
708
593
1640
764
531
Cart Front
Week 4 Cart 1
Cart rear (close to wall)
312
636
672
2091
873
296
Cart Front
Week 4 Cart 2
354
782
325
600
744
456
560
754
334
727
607
371
849
1576
958
Appendix D: Dosimeter Dose Equivalent Profiles and
Contour Maps
Deep Dose Equivalent
---
-~-Week 1 Luxel Deep Dose Data
I
Week 2 Luxel Deep Dose Data
S900-100
5800-900
0700-800
" 600-700
m500-600
0 400-500
m1000-12(
M800-100(
0 600-800
0 400-600
0300-400
M200-400
0200-300
S3
2
S100-200
( 0-200
00-100
Week 3 Luxel Deep Dose Cart 2
Week 3 Luxel Deep Dose Cart 1
U1200-14
e1000-12
.1000-12
S800-100
U800-1 00
1 600-800
E
0 600-800
400-600
0400-600
N 200-400
0
S200-400
0-200
00-200
S3
S3
Week 4 Deep Dose Data Cart 2
Week 4 Deep Dose Data Cart I
900
-z-~---
800
700
600
500
400
300
K
J~F~-----R
I----2
S3
S2
04
I
__
0800-100
0600-800
0400-600
U200-400
0200-300
SIuJV-U
o l100
EL30-100
I
01000-1 2
n •0lA
200
10
S900-1000
m800-900
o 700-800
w600-700
m500-600
m400-500
S3
I
II
I
2
0 0-200
Week 2 Luxel Deep Dose Data
Week 1 Luxel Deep Dose D
S3
S2
0 1000-15(
0500-100
0 0-500
1
2
3
front
of cart
front of cart
front of cart
Week 3 Luxel Deep Dose Cart I
3
3o1000-15
S500-10
a 0-500
2
front of cart
Week 4 Deep Dose Data Cart 2
S3
S2
o1000-15
S500-100
200-500
Front
of Cart
Front of Cart
Si
Lens Dose Equivalent
Week 2 Luxel Eye Dose Data
Week 1 Luxel Eye Dose Data
M1000-12
31000-12(
M800-100
3800-100(
0600-800
0 600-800
0400-600
0400-600
M200-400
3200-400
30-200
S3
0-200
S3
2
2
Week 3 Luxel Lens Dose Cart2
*1200-14•
*1000-12C
U800-100C
0 600-800
0 400-600
0 200-400
a0-200
S3
Week 4 Lens Dose Data Cart I
Week 4 Lens Dose Data Cart 2
16
N,
14
12
01200-14(
S1000-12
S3
2
3
01400-16(
01200-14(
800
0600-800
600
0200-400
400
0l0-200
----·
1
0800-100
0400-600
J
200
0
/r; i·
31000-12(
0800-100(
0 600-800
0400-600
I
- S3
0200-400
;2
o 0-200
Week 1 Luxel Eye Dose Data
u 1000-15
oo500-1000
S0-500
1
2
3
front of cart
Week3 Luxel Lens Dose Cart1
Week 3 Luxel Lens Dose Cart2
S3
-S3
S2
-S2
131000-15S
m500-100
S0-500
So10oo-15
Si
-Si
front of cart
front of cart
Week 4 Lens Dose Data Cart I
Week 4 Lens Dose Data Cart 2
3
2
01500-20C
0 1000-15C
0500-100C
50-500
0 1000-15
S500-100l
U 0-500
IZ
Front of Cart
Front of Cart
Shallow Dose Equivalent
Week 1 Luxel Shallow Dose Data
Week 2 Luxel Shallow Dose Data
!
0
U 1200-14(
U
*1000-124
1800-100(
1800-100(
o 600-800
0 400-600
o 600-800
0 400-600
1 200-400
S3
1400-164
U 1200-141
1000-12(
0-200
U 200-400
S3
G 0-200
#.
Week 3 Luxel Shallow Dose Cart1
Week 3 Luxel Shallow Dose Cart2
S1200-14
S1000-12C
1000-12
U 800-100
U
0 600-800
0 400-600
U 800-100
S200-400
0400-600
0
o 600-800
S200-400
0-200
S
00-200
S3
S3
Week 4 Shallow Dose Cart I
Week 4 Shallow Dose Cart 2
S1600-18(
01400-16(
0 1200-14(
S2000-2500
0 1000-12(
a 1500-2000
U 800-100(
[ 1000-1500
] 600-800
o 400-600
53
2
Z5
S200-400
00-200
S500-1000
S3
o-500soo
Week 2 Luxel Shallow Dose Data
o 1000-150(
50ooo1000
*0-500
1
2
front of cart
Week 3 Luxel Shallow Dose Cart 2
53
S2
o 1000-15
• 500-100
So0-o500
Si
3
front of cart
Week 4 Shallow Dose Cart I
Week 4 Shallow Dose Cart 2
^-
ss3
S2
2
o 1500-20C
0 1000-15C
I 500-100
O
$ 0-500
S1
1
2
Front of cart
3
n 2000-2500
0 1500-2000
S1000-1500
* 500-1000
* 0-500
1
of
Cart
Front
Front of Cart
Appendix E: MCNP Dose Profiles and Contour Maps
All data are in mrem/week
Deep Dose Equivalent
Cart rear (close to wall)
317.0928 ± 21.9745
551.8596 ± 27.2067
304.5775 ± 20.8940
575.9686 ± 30.0080
971.5003 ± 36.9170
595.8159 ± 29.2546
329.9784 ± 22.9995
565.3452 ± 28.9457
299.2034 ± 21.8718
Cart Front
MCNP Luxel Deep Dose
MCNP Luxel Deep Dose
I1
nn
I
800-1000
*800-1000
S3
0 600-800
0 600-800
0400-600
m200-400
o 400-600
S200-400
o0-200
00-200
1
2
3
Front of Cart
Lens Dose Equivalent
Cart rear (close to wall)
344.7271 ± 28.4400
646.675 ± 36.4725
361.8744 + 28.9500
617.4646 ± 33.5283
1123.506 ± 46.5132
623.9239 ± 36.2500
Cart Front
325.8573 ± 24.3090
669.8796 ± 35.9725
316.4526 ± 23.8605
MCNP Luxel Lens Dose
MCNP Luxel Lens Dose
S3
01000-12(
S2
N800-100(
0600-800
S3
S2 1000-1500
0400-600
m500-1000
§ 200-400
o 0-500
a0-200
1
23S1
3
2
Front of Cart
Shallow Dose Equivalent
Cart rear (close to wall)
341.4443
631.0607
346.0448
±
±
±
34.8273
35.5287
30.7288
668.1514
1260.461
616.3966
±
±
±
55.9920
89.3667
34.5182
341.9611
697.2656
354.5739
±
±
±
29.6138
39.8139
38.1522
Cart Front
MCNP Luxel Shallow Dose
MCNP Luxel Shallow Dose
S3
M1200-144
aM1000-1 2
S800-100(
0600-800
0 1000-15
S500-1000
0 400-600
00-500
S200-400
S3
00-200
2
3
1
2
Front of Cart
3
Appendix F: Comparing MCNP and Dosimeters
Deep Dose Comparison
Absolute value (MCNP - Dosimeter)
(mrem/week)
Cart Rear (close to wall)
62.75946667
9.9686
56.4784
16.6404
92.66636666
82.01186667
Cart Front
4.91083334
61.8507667
17.6299333
Combined MCNP and Dosimeter
Errors (mrem/week)
Cart Rear (close to wall)
60.12453
112.4817
65.84402
114.908
196.542
127.9046
64.02449
101.4457
Cart Front
69.39677
Is the Difference Within Combined Errors?
Cart rear (close to wall)
NO
Yes
Yes
Yes
Yes
Yes
Cart Front
Yes
Yes
Yes
Lens Dose Comparison
Absolute value (MCNP - Dosimeter)
(mrem/week)
Cart Rear (close to wall)
53.7271
4.0354 111.9760333
41.15833333 98.6606666 96.28706666
54.45893333
70.9239 63.21406667
Cart Front
Combined MCNP and Dosimeter
Errors (mrem/week)
Cart Rear (close to wall)
72.08999
126.7533
89.98396
139.6475
229.8382
150.8975
91.39995
119.2
80.81053
Cart Front
Is the Difference Within Combined Errors?
Cart rear (close to wall)
Yes
Yes
Yes
Yes
Yes
Yes
Cart Front
NO
Yes
Yes
Shallow Dose Comparison
Absolute value (MCNP - Dosimeter)
(mrem/week)
Cart Rear (close to wall)
37.11096667 37.68193333
226.87223
247.1059666 185.372333
155.90107
206.7885333
29.3966
94.592767
Cart Front
Combined MCNP and Dosimeter
Errors (mrem/week)
Cart Rear (close to wall)
80.47732
161.8661
114.9388
167.2537
306.2417
167.7889
113.6538
122.5682
105.5272
Cart Front
Is the Difference Within Combined Errors?
Cart rear (close to wall)
Yes
NO
NO
Yes
Yes
Yes
Cart Front
NO
Yes
Yes
5.References:
"d ed.,
Toronto: John
[1]
Turner, James E., Atoms, Radiation, and Radiation Protection,
Wiley & Sons, Inc., 1995.
[2]
Helleday, Thomas, "Pathways for mitotic homologous recombination in mammalian
cells," Mutation Research, vol. 532, 2003, pp. 103 - 115.
[3]
Knoll, Glenn F., Radiation Detection and Measurement,
& Sons, Inc., 2000.
[4]
Faw, R.E.; Shultis, J.K., "A Primer Presenting an Introduction to the MCNP Code,"
Manhattan, KS: Dept. of Mechanical and Nuclear Engineering Kansas State University,
3 rd
2
ed., New York: John Wiley
2004.
[5]
Botter-Jensen, Lars; McKeever, Stephen, W.S.; Wintle, Ann, G., Optically Stimulated
Luminescence Dosimetry, 1st ed., Netherlands: Elsevier Science, B.V., 2003.
[6]
McKeever, Stephen, W.S., "Optically Stimulated Luminescence Dosimetry," SPIE-The
International Society for Optical Engineering, vol. 3534, November 1998.
[7]
Salasky, Mark; Yoder, R. Craig, "Optically Stimulated Luminescence - an alternative to
radiobiological monitoring films," Glenwood, IL: Landauer, Inc. and SPIE, vol. 2622, pp.
79 - 83.
[8]
Olipitz, Werner, "Standard Operating Procedure for Engleward 'Low Dose Radiation
Experiment' (CAC #1003-084-06)."
[9]
Biodex Medical Systems Web Page, Available at:
http://www.biodex.com/radio/phantoms/phantoms_054.htm
[10]
Brookhaven National Laboratory, National Nuclear Data Center, "NuDat 2.2 (database),"
Available at: http://www.nndc.bnl.gov/nudat2/decaysearchdirect.jsp?nuc=1251
[11]
Brookhaven National Laboratory, National Nuclear Data Center, "NuDat 2.2 (database),"
Available at: http://www.nndc.bnl.gov/nudat2/decaysearchdirect.jsp?nuc=125TE
[12]
Yanch, Jacquelyn C., "Absorbed Dose Determination from
Mouse Irradiations]," Nov. 2005.
[13]
U.S. Environmental Protection Agency, "Radioactive Equilibrium," Available at:
1251
Source [Engleward
http://,wyvw.epa. aoviradiatio n/understand/equ ilibrium.htm
[14]
Nave, C.R., "HyperPhysics," The Dept. of Physics and Astronomy at Georgia State
University, Available at: http://hyperphysics.phy-astr.gsu.ed u/hbase/h frame.htm 1,2005.