Dosimetry of ¹²⁵Iodine protons for in vivo mouse irradiation study

Dosimetry of

12

_{5Iodine 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 of Nuclear Science and Engineering Thesis Supervisor

Accepted by:

LIBRARIES

David Cory Professor of Nuclear Science and Engineering Chairman, NSE Committee for Undergraduate Students

ARCHIVES

MASSACHUSE'M

WAS11T

OF TECHNOLOGY

Dosimetry of

12

_{5Ilodine 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: Jacquelyn C. Yanch

Table of Contents:

1.

Introduction and Background...

4

1.1 Genetic Effects of Radiation ... 4

1.2 Radiation Dosimetry ... 5

1.3 Monte Carlo and MCNP... 5

1.4 Optically Stimulated Luminescence (OSL) Technology... 6

2.

Methods ...

7

2.1 Mouse and Source Cart Arrangement... 7

2.2 Flood Phantom Photon Source... 8

2.2.1 1251 Radioactive Properties... ... . 9

2.2.2 125I Initial A ctivity ... 11

2.2.3 Accounting for Activity Decay ... 12

2.3 Luxel® Dosimeters... 13

2.4 MCNP Code... ... 14

2.4.1 Calculating Dose Equivalent from MCNP output ... 15

2.4.2 MCNP Dosimeter Model ... 16

2.4.3 MCNP Cage Dose Profile... 17

3.

Results and Discussion...

...

19

3.1 Dosimeter Data ... ... ... ... 19

3.1.1 Dose Profiles... ... 19

3.1.2 Actual Activity Levels ... 21

3.1.3 Type of Radiation Reported ... 21

3.2 M CNP Data ... .. ... 22

3.2.1 MCNP Dosimeter Model... 22

3.2.2 MCNP Mouse Cage Dose Profile ... 23

4.

Conclusion...

25

Appendix A:

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...

37

Appendix E: MCNP Dose Profiles and Contour Maps...

43

Appendix F: Comparing MCNP and Dosimeters...

45

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}

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. Cage cart holding four cages identified as A, B, C, and D 2. Leaded acrylic shield to protect personnel

3. Rubbermaid cart holding metal box 4. Metal box containing phantom

5. 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 Biodex t 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

Figure 2: Flood Phantom Source [9]

2.2.1

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 is a combination of Auger electrons and X-rays from de-excitation of the electrons, and conversion electrons and gamma X-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

Energy (keV)

Figure 3: 125mTe Photon Energy Spectrum [11]

Figure 4: 125mTe Electron Energy Spectrum [11 ]

144.78

Te-125 Electron Energy Spectrum

160 140 -120 -L ,a 0UU -Z

80-C

Energy (keV)

I

2.2.2

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 ₂

(1) dt

where N1 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

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

N2 = 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,

'It

"!0

period of transient equilibrium

ingrowth

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.

_· ·_

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.

1-125 Activity Decay Over One Week

5.5 5 4.5 4 3.5 3 S2.5 2 1.5 1 0.5 0 0 1 2 3 4 5 6 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

N2 (t = 0) *

fexp(-0.01167

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:

--- 1

3.7*107 dps 60sec 60min 24hours

N2 (t = O)mCix x x - x x6.7217 (5)

ImCi I min lhour Iday

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 (6)

lmCi Iday 1decay 1Gy

= [(MCNPoutput) x (N₂ (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

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.

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 125I is added to maintain constant activity

levels. Prior to running tests with 125I, 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 Luxel Luxel Luxel Luxel Luxel Luxel Luxel Luxel

1&10 2&11 3&12 4&13 5&14 6&15 7&16 8&17 9&18

(mrem/ (mrem/ (mrem/ (mrem/ (mrem/ (mrem/ (mrem/ (mrem/ (mrem/ week) week) week) week) week) week) week) week) week)

264 198 251 465 961 442 227 267 286 120 275 259 406 1002 824 363 547 373 289 662 437 627 1079 783 259 771 248 457 913 346 608 1328 794 175 681 590 162 557 250 624 988 608 252 476 138 349 295 358 666 1027 495 250 669 163

Column Average Values (mrem/week)

273.50 483.33 316.83 566.00 1064.17 657.67 254.33 568.50 299.67 Column Standard Deviations (mrem/week)

123.04 276.50 76.33 104.55 135.29 165.77 61.47 180.93 165.74 Average Reported Error (15%) (mrem/week)

41.025 72.5 47.525 84.9 159.625 98.65 38.15 85.275 44.95

Is the Standard Deviation < Reported Error?

No No No I No Yes No 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.

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.)

'- CY)L) N- C)

Dose Over Cage Area (mremlweek)

3 1

E

800-1000

N-x-axis

(cm)

z-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 (N2(t = O)mCi)] x 2.8708 *101' (7)

Corresponding MCNP output = 655.6236re /week 4.5675 *10-17 Gy (8) 5mCi x 2.8708 *1018

y

Desired Average Dose = 2100 mrem/week

2100mrem / week

N2(t = O)mCi = (9)

[(4.5675 *10

_{1 GY)x (2.8707}

Y

N2(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

(%)

Table 2: 125mTe Electron Energy Spectrum [11]

Photon Origin Energy (keV) Relative Intensity

Auger L 3.19 152 ± 3 % Auger K 22.7 16.3 + 0.6 % CE K 3.690 _ 0.015 80.0 + 2.4 % CE L 30.565 ± 0.015 10.7 ± 0.3 % CE M 34.498 ± 0.015 2.15 ± 0.07 % CE K 77.462 ± 0.015 50.4 ± 1.7 % CE L 104.337 ± 0.015 36.2 ± 1.2 % CE M 108.270 ± 0.015 8.4 ± 0.3 % CE NP 109.108 ± 0.015 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 3 -1.19 -1 #3 4 -1.0 -2 3 -1.19 -3 2 -1.04 -6 48 -49 2 -1.04 -7 48 -49 2 -1.04 -8 48 -49 2 -1.04 -9 48 -49 2 -1.04 -10 48 -49 2 -1.04 -11 48 -49 2 -1.04 -12 48 -49 2 -1.04 -13 48 -49 2 -1.04 -14 48 -49 0 50

$PMMA phantom outside $water phantom inside $PMMA platform $luxel 1 $luxel 2 $luxel 3 $luxel 4 $luxel 5 $luxel 6 $luxel 7 $1uxel 8 $luxel 9 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 c/y -30 -20.65 2.0 $luxel 1 c/y -30 0 2.0 $luxel 2 c/y -30 20.65 2.0 $luxel 3 c/y 0 -20.65 2.0 $Iuxel 4 cy 2.0 $luxel 5 c/y 0 20.65 2.0 $luxel 6 c/y 30 -20.65 2.0 $luxel 7 c/y 30 0 2.0 $luxel 8 c/y 30 20.65 2.0 $luxel 9 py 12.03 py 12.33 so 100 $enviror $phantom outside $phantom nested $platform 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 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 7891011 12 13 14 15 fm6 1.6022e-10 ml 8016 -.2 $air 7014 -.8

m2 1001 -10.0 6012 -14.9 7014 -3.5 8016 -71.6 m3 1001 -.0805 6012 -.5998 8016 -.3196 m4 1001 -.11190 8016 -.88810 nps 1000000 $tissue $PMMA $water

MCNP Cage Dose Equivalent Profile Code, Mice column at x=0

1 -1.3e-3 -50 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11

3 -1.19 -1 #3 $PMMA phantom outside

4 -1.0 -2 $water phantom inside

3 -1.19 -3 $PMMA platform

3 -1.19 -4 #6 #7 #8 #9 #10 #11 $PMMA cage outside 1 -1.3e-3 -5 #7 #8 #9 #10 #11 $PMMA cage inside

2 -1.04 -6 7 -8 $mouse 2 -1.04 -6 9 -10 $mouse 2 -1.04 -6 11 -12 $mouse 2 -1.04 -6 13 -14 $mouse 2 -1.04 -6 15 -16 $mouse 0 50 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 $phantom outside $phantom nested $platform $cage outside $cage inside $mouse mode p print -86 -85 imp:p 1 1 1 1 1 1 1 1 1 1 10

sdef x dl y d2 z d3 erg d4 cel 3 par 2 $photon source def sil -30.45 30.45

spl 0 1 si2 .95 2.25 sp2 0 1

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

Deep Dose Equivalent Tables

Cart rear (close to wall)

227 267 286

465 961 442

264 198 251

Cart Front Week 1 Cart 1 Cart rear (close to wall)

363 547 373

406 1002 824

120 275 259

Cart Front Week 2 Cart 1

Cart rear (close to wall)

259 771 248

627 1079 783

289 662 437

Cart Front

Week 3 Cart 1 Cart rear (close to wall)

175 681 590

608 1328 794

457 913 346

Cart Front Week 3 Cart 2 Cart rear (close to wall)

252 476 138

624 988 608

162 557 250

Cart Front Week 4 Cart I Cart rear (close to wall)

250 669 163

666 1027 495

349 295 358

Cart Front Week 4 Cart 2

Lens Dose Equivalent Tables

Cart rear (close to wall)

233 553 286

579 1031 607

264 198 251

Cart Front Week 1 Cart 1 Cart rear (close to wall)

363 547 373

845 1106 824

429 693 324

Cart Front Week 2 Cart 1 Cart rear (close to wall)

259 771 425

800 1079 783

289 662 437

Cart Front Week 3 Cart 1 Cart rear (close to wall)

322 681 590

608 1328 794

457 913 346

Cart Front Week 3 Cart 2 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)

311 669 510

671 1566 981

585 295 573

Cart Front Week 4 Cart 2

Shallow Dose Equivalent Tables

Cart rear (close to wall)

232 768 323

837 1394 656

249 197 251

Cart Front Week 1 Cart 1 Cart rear (close to wall)

357 745 354

1412 1252 782

724 1002 325

Cart Front Week 2 Cart 1 Cart rear (close to wall)

246 732 600

1178 1037 744

274 629 456

Cart Front Week 3 Cart 1 Cart rear (close to wall)

420 646 560

577 1261 754

433 867 334

Cart Front Week 3 Cart 2 Cart rear (close to wall)

259 708 727

593 1640 607

764 531 371

Cart Front Week 4 Cart 1 Cart rear (close to wall)

312 636 849

672 2091 1576

873 296 958

Cart Front Week 4 Cart 2

Appendix D: Dosimeter Dose Equivalent Profiles and

Contour Maps

Deep Dose Equivalent

Week 1 Luxel Deep Dose Data

S900-100 5800-900 0700-800 " 600-700 m 500-600 0 400-500 0300-400 0200-300 S100-200 00-100

Week 3 Luxel Deep Dose Cart 1

e1000-12 S800-100 1 600-800 E 400-600 N 200-400 0 0-200 S3

Week 4 Deep Dose Data Cart I

S900-1000 m800-900 o 700-800 w 600-700 m 500-600 m 400-500 n •0lA S3 0200-300 SI uJV-U I o l100 II S2 EL30-100

Week 2 Luxel Deep Dose Data

m1000-12( M 800-100( 0 600-800 0 400-600 M 200-400 S3 ( 0-200 2

Week 3 Luxel Deep Dose Cart 2

U1200-14 .1000-12 U800-1 00 0 600-800 0400-600 S200-400 00-200 S3 900 800 700 600 500 400 300 200 10 04

K

Week 4 Deep Dose Data Cart 2

01000-1 2 0800-100

0

--

z--

I

__

I

-~--I

Week 2 Luxel Deep Dose Data 1 2 3 front of cart S3 S2 0 1000-15( 0500-100 0 0-500 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 Si Front of Cart

Week 1 Luxel Deep Dose D

front of cart

Lens Dose Equivalent

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

S3 2 01200-14( S1000-12 0800-100 0 600-800 0 400-600 0200-400 0l0-200 3

Week 4 Lens Dose Data Cart 2

16 14 12 1 800 600 400 200 0 N, J -S3 ;2 Week 1 Luxel Eye Dose Data

M1000-12 M800-100 0600-800 0400-600 M200-400 30-200 S3 2

Week 2 Luxel Eye Dose Data

31000-12( 3800-100( 0 600-800 0400-600 3200-400 S3 0-200 2 01400-16( 01200-14( 31000-12( 0800-100( 0 600-800 0400-600 0200-400 o 0-200 /r; i· ---·

I

Week 1 Luxel Eye Dose Data u 1000-15 oo500-1000 S0-500 1 2 3 front of cart Front of Cart

Week3 Luxel Lens Dose Cart1

S3 S2 131000-15S m500-100 S0-500 Si front of cart

Week 3 Luxel Lens Dose Cart2

-S3

-S2

So10oo-15

-Si

front of cart

Week 4 Lens Dose Data Cart I

2

0 1000-15

S500-100l

U 0-500

Week 4 Lens Dose Data Cart 2

01500-20C 0 1000-15C 0500-100C 50-500 3 IZ Front of Cart

Shallow Dose Equivalent

Week 2 Luxel Shallow Dose Data

0 1400-164 U 1200-141 *1000-124 1800-100( o 600-800 0 400-600 U 200-400 G 0-200 S3

Week 4 Shallow Dose Cart I

53 2 S1600-18( 01400-16( 0 1200-14( 0 1000-12( U 800-100( ] 600-800 o 400-600 S200-400 00-200

Week 4 Shallow Dose Cart 2

S2000-2500 a 1500-2000 [ 1000-1500

S500-1000

S3 o-500soo

Week 1 Luxel Shallow Dose Data

U 1200-14( U 1000-12( 1800-100( o 600-800 0 400-600 1 200-400 S3 0-200

Week 3 Luxel Shallow Dose Cart1

S1000-12C U 800-100 0 600-800 0 400-600 S200-400 0 0-200 S3

Week 3 Luxel Shallow Dose Cart2

S1200-14 U 1000-12 U 800-100 o 600-800 0400-600 S200-400 S 00-200 S3 ! #. Z5

Week 4 Shallow Dose Cart I ss3 S2 o 1500-20C 0 1000-15C I 500-100 O $ 0-500 S1 1 2 Front of cart 3

Week 2 Luxel Shallow Dose Data

o 1000-150(

50ooo1000

* 0-500

1 2

front of cart

Week 3 Luxel Shallow

53 S2 o 1000-15 • 500-100 So0-o500 Si 3 front of cart

Week 4 Shallow Dose Cart 2

^-2 n 2000-2500 0 1500-2000 S1000-1500 * 500-1000 * 0-500 1 Front of Cart Dose Cart 2 Front Cartof

Appendix E: MCNP Dose Profiles and Contour Maps

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

800-1000 0 600-800 o 400-600 S200-400 o0-200 2 3 Front of Cart

Lens Dose Equivalent

Cart rear (close to wall)

344.7271 ± 28.4400 617.4646 ± 33.5283 325.8573 ± 24.3090

646.675 ± 36.4725 1123.506 ± 46.5132 669.8796 ± 35.9725 361.8744 + 28.9500 623.9239 ± 36.2500 316.4526 ± 23.8605

Cart Front MCNP Luxel Deep Dose

I1 nn *800-1000 0 600-800 0400-600 m 200-400 S3 00-200 I 1

MCNP Luxel Lens Dose S3 S2 S2 1000-1500 m 500-1000 o 0-500 2 3 1 2 3

Shallow Dose Equivalent

Cart rear (close to wall)

341.4443 ± 34.8273 668.1514 ± 55.9920 341.9611 ± 29.6138

631.0607 ± 35.5287 1260.461 ± 89.3667 697.2656 ± 39.8139

346.0448 ± 30.7288 616.3966 ± 34.5182 354.5739 ± 38.1522

Cart Front

MCNP Luxel Shallow Dose

S3 2 M1200-144 aM1000-1 2 S800-100( 0600-800 0 400-600 S200-400 00-200

MCNP Luxel Shallow Dose

S3 0 1000-15 S500-1000 00-500 1 2 3 Front of Cart 01000-12( N800-100( 0600-800 0400-600 § 200-400 a0-200 S3 Front of Cart MCNP Luxel Lens Dose

S1

Appendix F: Comparing MCNP and Dosimeters

Deep Dose Comparison

Absolute value (MCNP - Dosimeter)

(mrem/week) Cart Rear (close to wall)

62.75946667 16.6404 4.91083334

9.9686 92.66636666 61.8507667

56.4784 82.01186667 17.6299333

Cart Front

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 69.39677

Cart Front

Is the Difference Within Combined Errors?

Cart rear (close to wall)

NO Yes Yes

Yes Yes Yes

Yes Yes Yes

Cart Front

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 NO

Yes Yes Yes

Yes 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 Yes NO

NO Yes Yes

NO Yes Yes

5.

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