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THERMOLUMINESCENCE CHARACTERISTICS OF SILICON OPTICAL FIBRE
DOPED WITH YTTERBIUM AND YTTERBIUM – TERBIUM AS PHOTON
DOSIMETER.
MOHD. HILMI BIN SAHINI
UNIVERSITI TEKNOLOGI MALAYSIA
THERMOLUMINESCENCE CHARACTERISTICS OF SILICON OPTICAL FIBRE
DOPED WITH YTTERBIUM AND YTTERBIUM – TERBIUM AS PHOTON
DOSIMETER.
MOHD. HILMI BIN SAHINI
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Master of Science (Physics)
Faculty of Science
University Teknologi Malaysia
JUNE 2014
ACKNOWLEDGEMENT
My most humble and sincere thanks to first and foremost, my supervisor, Prof.
Dr. Husin Wagiran for his believe in me and opportunities given to further my studies.
Not to forget, Dr. Imam Hossain who also had helped throughout the completion of this
research.
To my extraordinary family, thanks for their endless love and support in
completing this study. My profound thanks to my fiancée, Nor Amiera for her patience
and support for me. They have truly been the foundation under this author.
I would like to express my immense gratitude to En. Hassan Ali, Science Officer
of Department of Oncology And Radiation Therapy, Hospital Sultan Ismail for his
generous assistance and expertise in this research.
I wanted to thank the government of Malaysia in providing a funded Master
scholarship. Not to forget also the Ministry of Higher Education of Malaysia for
providing research grant for this research.
ABSTRACT
The study of SiO2 commercial optical fiber explores the useful
thermoluminescence (TL) properties and reveals its potential as a TL dosimeter. The
present work describes the TL dose response, reproducibility, fading and minimum
detectable dose of SiO2: Yb and SiO2: Yb, Tb optical fibers as compared to TLD-100.
The optical fibers were placed in a solid phantom and irradiated with 6 and 10 MV X-
rays using LINAC Primus MC 3339 and 1.25 MeV gamma ray from gamma cell.
Scanning electron microscopy analysis was performed to determine the dopant
concentration and the effective atomic number, Zeff. The dopant concentration of Yb for
SiO2: Yb optical fiber was found ranging between 0.23 – 0.35 mol% and for SiO2: Yb,
Tb; the dopant concentration of Yb and Tb were in the range of 0.03 – 1.46 mol% and
0.12 – 0.39 mol% respectively. The Zeff value for SiO2: Yb and SiO2: Yb, Tb were
11.19 and 12.27 respectively, which is higher than that of soft tissue (7.42), but close to
bone (11.6 – 13.8). In term of TL dose response and sensitivity, SiO2: Yb, Tb optical
fiber demonstrated better results than SiO2: Yb optical fiber, but both TL materials were
still inferior when compared to TLD-100. SiO2: Yb, Tb optical fiber had the lowest
percentage lost in fading of about 5.83%, 15.65% and 18.55% for day 7, 21 and 28
respectively, compared to SiO2: Yb optical fiber which has higher fading of about
55.17% and 95.87% for day 14 and 30 respectively. SiO2: Yb, Tb optical fiber shows
good reproducibility results compared to SiO2: Yb optical fiber. The minimum
detectable dose of SiO2: Yb and SiO2: Yb, Tb optical fibers were 333 mGy and 19 mGy
respectively. In general, it can be concluded that SiO2: Yb, Tb optical fiber is a much
better optical fiber to be developed as a new TL dosimeter compared to SiO2: Yb
optical fiber.
ABSTRAK
Kajian gentian optik komersial SiO2 meneroka ciri luminesens terma (TL)
berguna dan keupayaan sebagai dosimeter TL. Kajian ini membincangkan sambutan
dos luminesens terma, kebolehulangan, kepudaran dan dos pengesanan minimum
gentian optik SiO2: Yb dan SiO2: Yb, Tb dan berbanding TLD-100. Gentian optik
diletakkan di dalam fantom pepejal dan disinarkan dengan sinar-X 6 dan 10 MV
menggunakan LINAC Primus MC 3339 dan sinar gama 1.25 MeV dari sel gama.
Analisis mikroskop pengimbas elektron (SEM) dilakukan bagi menentukan kepekatan
dopan dan nombor atom berkesan, Zeff. Kepekatan dopan Yb bagi gentian optik SiO2
ialah dalam julat 0.23 – 0.35 mol% dan kepekatan dopan Yb dan Tb bagi SiO2 : Yb, Tb
masing-masing ialah 0.03 – 1.46 mol% dan 0.12 – 0.39 mol%. Nilai Zeff bagi gentian
optik SiO2 : Yb dan SiO2 : Yb, Tb masing-masing ialah 11.19 dan 12.27, iaitu lebih
tinggi daripada nilai tisu lembut (7.42), tetapi hampir dengan tulang (11.6 – 13.8). Dari
aspek sambutan luminesens terma, SiO2 : Yb, Tb memberi keputusan yang lebih baik
berbanding SiO2 : Yb, tetapi kedua-dua bahan masih tidak dapat menandingi TLD-100.
Gentian optik SiO2 : Yb, Tb mempunyai peratus kepudaran yang lebih rendah iaitu
5.83%, 15.65% dan 18.55% masing-masing pada hari ke-7, 21 dan 28 berbanding
dengan SiO2 : Yb yang mempunyai peratus kepudaran yang lebih tinggi sebanyak
55.17% dan 95.17% pada hari ke-14 dan 30. Hasil kajian menunjukkan gentian optik
SiO2 : Yb, Tb menunjukkan keputusan sifat kebolehulangan yang lebih baik berbanding
gentian optik SiO2 : Yb. Dos pengesanan minimum bagi gentian optik SiO2 : Yb dan
SiO2 : Yb, Tb masing-masing ialah 333 mGy dan 19 mGy. Secara umum dapat
disimpulkan bahawa gentian optik SiO2 : Yb, Tb adalah lebih sesuai untuk dimajukan
sebagai dosimeter TL berbanding gentian optik SiO2 : Yb.
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION v
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF TABLES xiii
LIST OF FIGURES xv
LIST OF SYMBOLS xix
LIST OF ABRIVIATIONS xxi
LIST OF APPENDICES xxii
1 INTRODUCTION 1
1.1 Research Background 1
1.2 Objective of the Research 3
1.3 Statement of Problem 4
1.4 Scope of the Research 5
1.5 Significance of the Research 6
2 LITERATURE REVIEW 7
2.1 Introduction 7
2.2 Radiation Dosimeter 8
2.3 Thermoluminescence 8
2.3.1 Thermoluminescence Phenomena 9
2.3.2 Thermoluminescence Dosimeter System 10
2.3.3 Thermoluminescence Dosimeter 11
2.4 Characteristics of Thermoluminescence Material 13
2.4.1 Dose Linearity 14
2.4.2 Glow Curve 16
2.4.3 Energy Dependance 17
2.4.4 Fading 19
2.4.5 Sensitivity 20
2.4.6 Stability and Reproducibility 20
2.4.7 Effective Atomic Number 21
2.4.8 Minimum Detectable Dose 21
2.5 Silicon Dioxide Optical Fiber 22
2.5.1 SiO2 structure 24
2.5.2 Intrinsic Point-Defects 26
2.5.3 Oxygen Deficient Centers 27
2.5.4 Oxygen Associated Hole Center 28
2.5.5 Extrinsic Point-Defects 29
2.6 Rare Earth Impurity 30
3 RESEARCH METHODOLOGY 31
3.1 Material and Sample Preparation 31
3.2 Pre-Irradiation Annealing 32
3.3 Exposure to Irradiation 34
3.3.1 Linear Accelerator (LINAC) 34
3.3.2 Cobalt-60 36
3.3.3 Energy Response 38
3.3.4 Fading Determination 38
3.3.5 Reproducibility 38
3.3.6 Minimum Detectable Dose 38
3.4 Read-out Equipment 39
3.4.1 Dark Current 40
3.4.2 PMT Noise 41
3.4.3 Background Noise 41
3.5 Scanning Electron Microscope (SEM) 41
4 RESULTS AND DISCUSSION 44
4.1 Scanning Electron Microscope (SEM) Analysis 44
4.2 Dopant Concentration 46
4.3 Effective Atomic Number 49
4.4 TL Glow Curve 52
4.5 TL Dose Response 54
4.5.1 TL Response to X-ray Photon Irradiation 54
4.5.2 Comparison of Yb-doped with Yb-Tb
doped SiO2 Optical Fiber for 6 and 10 MV
Photons Irradiation
61
4.5.3 Comparison of SiO2 Doped Optical Fiber
with TLD-100 for 6 and 10 MV Photons
Irradiation
62
4.5.4 Comparison of Yb- and Yb-Tb Doped with
Ge- and Al-Doped SiO2 Optical Fibers for
6 and 10 MV Photons Irradiation
65
4.5.5 TL Response to Gamma Ray Irradiation 66
4.5.6 Comparison of Yb-Doped with Yb-Tb
Doped Optical Fiber for 1.25 MeV Gamma
Ray Irradiation
70
4.5.7 Comparison of Doped Optical Fiber with
TLD-100 for 1.25 MeV Gamma Ray
Irradiation
71
4.6 Energy Response 73
4.7 Fading 75
4.8 Reproducibility 78
4.9 Minimum Detectable Dose 81
5 CONCLUSION 82
5.1 Summary 82
5.2 Recommendation and Future Research 84
REFERENCES
Appendix A - D
85
91
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Characteristics of TL phosphors 15
3.1 TLDs material specification 36
3.2 Time of irradiation using Cobalt-60 41
4.1 Summary of dopant concentration for Yb-doped SiO2 optical
fiber
50
4.2 Summary of dopant concentration for Yb and Tb in Yb-Tb
doped SiO2 optical fiber
52
4.3 Summary of Zeff for Yb-doped optical fiber 54
4.4 Summary of Zeff for Yb-Tb doped optical fiber 55
4.5 TL response of Yb-doped SiO2 optical fiber for 6 MV
photons energy
59
4.6 TL response of Yb-Tb doped SiO2 optical fiber for 6 MV
photons energy
60
4.7 TL response of TLD-100 for 6 MV photons energy 61
4.8 TL response of Yb-doped SiO2 optical fiber for 10 MV
photons energy
63
4.9 TL response of Yb-Tb doped SiO2 optical fiber for 10 MV
photons energy
64
4.10 TL response of TLD-100 for 10 MV photons energy 65
4.11 Summary of sensitivity of TL materials compared with
TLD-100 for 6 MV photon.
69
4.12
Summary of sensitivity of TL materials compared with
TLD-100 for 10 MV photon
70
4.13 Summary of TL response of TL dosimeters for 6 and 10 MV
photons energy
71
4.14 TL response of Yb-doped SiO2 optical fiber for 1.25 MeV
gamma ray energy
72
4.15 TL response of Yb-Tb doped SiO2 optical fiber for 1.25
MeV gamma ray energy
73
4.16 TL response of TLD-100 for 1.25 MeV gamma ray
energy
75
4.17 Summary of sensitivity of TL materials compared with
TLD-100 for 1.25 MeV gamma ray energy
78
4.18 Reproducibility data for Yb-doped SiO2 optical fiber 86
4.19 Reproducibility data for Yb-Tb doped SiO2 optical fiber 86
4.20 Summary of minimum detectable dose 87
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Energy level diagram of the thermoluminescence process 11
2.2 Schematic diagram of a typical TLD reader 13
2.3 Linearity curve in a plot of TL as a function of dose 18
2.4 Comparison of first order (b=1), second order (b=2) and
intermediate order (b=1.5) TL glow peak
20
2.5 Photon energy response for a new indicated TLD materials 21
2.6 Different propagation mode in single-mode and multi-
mode optical fiber
26
2.7 Structure of an optical fiber 27
2.8 SiO4 tetrahedral structure is the most common structure
unit for SiO2
28
2.9 Structure of the amorphous silicon, with Si atom in grey
and O atoms in black
30
2.10 X-band electron paramagnetic resonance spectrum of E’
center
32
3.1 A furnace or TLD oven for annealing process 37
3.2 Linear accelerator Primus MLC 3339 used for photon
irradiation
39
3.3 A gamma cell used for gamma ray irradiation 41
3.4 Harshaw 3500 TL reader 44
3.5 Nova NanoSEM 450 used for SEM analysis 47
4.1 The spectrum of Yb-doped SiO2 optical fiber 49
4.2 The spectrum of Yb-Tb doped SiO2 optical fiber 49
4.3 The dopant concentration of Yb-doped SiO2 optical fiber 51
4.4 The dopant concentration of Yb in Yb-Tb doped SiO2
optical fiber
52
4.5 The dopant concentration of Tb in Yb-Tb doped SiO2
optical fiber
53
4.6 The Zeff of Yb-doped optical fiber 55
4.7 The Zeff of Yb-Tb doped optical fiber 56
4.8 The glow curve of Yb-Tb doped SiO2 optical fiber at 6 MV
photon irradiation for dose 1 -4 Gy
57
4.9 The glow curve of TLD-100 at 6 MV photon irradiation for
dose 1 -4 Gy
57
4.10 TL response (nC mg-1
) of Yb-doped SiO2 optical fiber
subjected to 6 MV photon irradiation
59
4.11 TL response (nC mg-1
) of Yb-Tb doped SiO2 optical fiber
subjected to 6 MV photon irradiation
61
4.12 TL response (nC mg-1
) of TLD-100 subjected to 6 MV
photon irradiation
62
4.13 TL response (nC mg-1
) of Yb-doped SiO2 optical fiber
subjected to 10MV photon irradiation
63
4.14 TL response (nC mg-1
) of Yb-Tb doped SiO2 optical fiber
subjected to 10 MV photon irradiation
65
4.15 TL response (nC mg-1
) of TLD-100 subjected to 10 MV
photon irradiation
66
4.16 The graph shows the TL response of Yb and Yb-Tb doped
SiO2 optical fiber for 6 MV photon energy versus dose
67
4.17 The graph shows the TL response of Yb and Yb-Tb doped
SiO2 optical fiber for 10 MV photon energy versus dose
67
4.18 TL response of Yb-, Yb-Tb doped SiO2 optical fiber and
TLD-100 for 6 MV photons
68
4.19 TL response of Yb-, Yb-Tb doped SiO2 optical fiber and
TLD-100 for 10 MV photons
69
4.20 TL response (nC mg-1
) of Yb-doped SiO2 optical fiber
subjected to 1.25 MeV gamma ray irradiation
72
4.21 TL response (nC mg-1
) of Yb-Tb doped SiO2 optical fiber
subjected to 1.25 MeV gamma ray irradiation
74
4.22 TL response (nC mg-1
) of TLD-100 subjected to 1.25 MeV
gamma ray irradiation
75
4.23 The graph shows the TL response of Yb- and Yb-Tb doped
SiO2 optical fiber for 1.25 MeV gamma ray energy versus
dose
76
4.24 TL response of Yb-, Yb-Tb doped SiO2 optica fiber and
TLD-100 for 1.25 gamma ray energy
77
4.25 The graph shows the energy response of Yb-doped SiO2
optical fiber for 6 and 10 MV photon irradiation
79
4.26 The graph shows the energy response of Yb-Tb doed SiO2
optical fiber for 6 and 10 MV photon irradiation
80
4.27 The graph shows the energy response of TLD-100 for 6
and 10 MV photon irradiation
80
4.28 The fading of Yb-doped SiO2 optical fiber subjected to 6
MV photon irradiation
82
4.29 The fading of Yb-Tb doped SiO2 optical fiber subjected to
6 MV photon irradiation
83
4.30 The reproducibility of Yb-doped SiO2 optical fiber at 6
MV photon irradiation
84
4.31 The reproducibility of Yb-Tb doped SiO2 optical fiber at 6
MV photon irradiation
85
LIST OF SYMBOLS
Zeff The effective atomic number
γ Gamma
β Beta
µ Micro
Gy Gray
ŋ The efficiency of the thermoluminescence emission
m Mass
ε Ratio between the energy
D Absorbed dose
M TL signal
k Boltzmann’s constant
Fc The inverse of the calibration factor
(µen / ρ)i The mass energy absorption coefficient
Wi The fraction of that element
S TL signal
k Kilo
s Second
ºC Degree Celsius
pC PikoCoulomb
nC NanoCoulomb
an Weight fraction contribution
Zn The atomic number of the element-n
mg Milligram
F(d) Dose response at dose D
Do The response at the lowest dose
B TL background signal
The standard deviation
F The calibration factor
MV Megavoltz
MeV Mega electron voltz
keV Kilo electron voltz
R Regression coeffiecient
LIST OF ABBREVIATIONS
TLD Thermoluminescence dosimetry
TL Thermoluminescence
SEM Scanning electron microscope
LINAC Linear accelerator
MOS Metal oxide semiconductor
CRN Continuous random network
ODC Oxygen deficient centers
EPR Electron paramagnetic resonance
NBOHC Non bridging oxygen hole center
UV Ultra violet
POR Peroxy radical
STH Self-trapped hole
RE Rare earth
CT Computed tomography
PMMA Polymethylmethacrylate
SSD Source-surface distance
MU Monitor unit
PMT Photomultiplier tube
LIST OF APPENDICES
Appendix Title Page
A Dopant Concentration Calculation 97
B Effective Atomic Number, Zeff Calculation 99
C Minimum Detectable Dose 102
D Propagation Error 104
CHAPTER 1
INTRODUCTION
1.1 Research Background
In radiotherapy and radio diagnosis, in order to map dose in tissues, there exist a
need for highly sensitivity in vivo dosimetry systems of high spatial resolution,
commercially available thermoluminescence dosimeters (TLDs) being limited to a
capability of few millimeters. The spatial resolution and dynamic range required of a
dosimeter to accurately evaluate the radiotherapy dose distribution of such complex
three-dimensional geometries, especially at the micro spatial resolution scale, is
becoming more challenging. Major advantages in using optical fibers or optical fibers
sensors for radiation detection and monitoring are: real-time interrogation capabilities,
possibility to design spatially resolved solutions and in-vivo investigation (Sporea et al.
2012).
The foundation of thermoluminescence (TL) theory appear to be due to Randall
and Wilkins (1945) and by Garlick and Gibson (1948) (Mckeever et al. 1988),
providing expressions for the shape of a glow peak in terms of temperature, heating
rate, and the characteristic of the trap. LiF has been developed commercially by
Harshaw Chemical Company and made available as TLD 100, TLD 100H, TLD 600
and TLD 700 depending on the quantity of Li present. The Li concentration determines
how the element will respond to neutrons, and an activator is required for the material to
be thermoluminescent. The effective atomic number of LiF (Zeff = 8.04) is close enough
to the value of Zeff for tissue make it almost tissue equivalent.
Studies of potential radiation therapy applications of the optical fiber TL
dosimetric system have been undertaken by several groups. Since then, much research
has been carried out for a better understanding and improvement of the material
characteristics as well as to develop new TL materials. As stated by Espinosa et al.
(2006), that optical fibers could be very attractive for using in a variety of radiation
dosimetry applications due to its small size, flexibility, low cost and commercially
available. Abdulla et al. (2001) has carried out a TL study on commercially available
Ge-doped silica based fiber optic in the dose range from 1 to 120 Gy and has fast fading
rate (2% within 6 hours and 6% within 30 days).
Hashim et al. (2009) work was also based on commercially available Ge-doped
optical fiber and compared to aluminum doped optical fiber. The TL dosimeters were
exposed by a wide range of sources, from low energy photons to megavoltage, through
neutrons and charged particles. The results showed that Ge-doped optical fiber had
linear dose response until at least 4 Gy for 6 MV photons, and up to 3.5 Gy for 6, 9and
12 MeV electrons irradiation. A linear dose response was found for 2.5 MeV protons
irradiations.
Another study from Hashim et al. (2010) was done by using oxygen atoms as a
dope to pure SiO2 optical fibers by using ion implantation technique. The O2- , Ge- and
Al- doped optical fibers were exposed to 6 MV photons and separately to 6, 9 and 12
MeV electrons. The results show the superior TL response to be that of the Ge-doped
optical fibers followed by the O2-doped fibers and lastly Al-doped fibers.
Encouraging results from such studies have paved the way in development of
the fiber radiation dosimeters specifically TL dosimetric characterization and properties
such as the glow curves parameters, energy dependence, relative energy response and
dose rate effect.
In many TLD applications, the main purpose is to determine the dose absorbed
in human tissue. For this reason, it is desirable that the TLD has an energy response
equal to that human tissue. In composite materials, for photon interactions the atomic
number cannot be represented uniquely across the entire energy region, as in the case of
elements, by a single number known as effective atomic number, Zeff (Shivaramu et al.
2000). It is very useful in medical radiation dosimetry for the calculation of dose in
radiation therapy and medical imaging. TL materials with Zeff = 7.42 or near this
number are called tissue equivalent.
1.2 Objectives of the Research
The objectives of this study are:
a) To determine the Zeff of Ytterbium, Yb and Ytterbium-Terbium, Yb-Tb doped
SiO2 and compare them with Zeff of tissue and bone.
b) To determine the dose response (dose linearity and sensitivity) and energy
response and compare them with LiF: Mg, Ti.
c) To determine the fading, reproducibility and minimum detectable dose of Yb
and Yb-Tb doped SiO2 optical fiber.
1.3 Statement of the Problem
Among the wide choice of radiation dosimeters that can be used for application
in radiotherapy, brachytherapy, diagnosis radiology and radiation protection of the
patient, thermoluminescence dosimetry (TLD) now become the well-established
technique for radiation detection. But it also has several restrictions including being
hygroscopic and having relatively poor spatial resolution – up to few millimeters.
In in-vivo dosimetry, the radiotherapist faces problem to set the exposure in
real-time to ensure that the proper dose is delivered to the desired region. Because, it
only provides integrated dose information after some time of irradiation of patient.
Other limitations of TLD are poor dose reproducibility, limited dynamic range and
sensitivity and in certain cases nonlinear response. This study intended to investigate
the alternative dosimetric material base on SiO2 optical fiber as a TL dosimeter.
Recently, several research groups have started to use SiO2 optical fibers as a
radiation dosimeter to measure the absorbed dose by patients, in particular overcoming
the spatial resolution limitations of existing TL dosimeter system (Yaakob et al., 2011)
and for certain dopant and dopants concentrations, sufficient TL yield to serve the
associated sensitivity needs (Wagiran et al., 2012). However, the manufacturers did not
specify the amount of dopant added in the optical fiber. Therefore, in this research, the
concentration of dopant for Tb-Yb and Yb-doped SiO2 optical fiber will also be
determined.
In regard to the potential of Ytterbium, Yb and Ytterbium-Terbium, Yb-Tb
doped optical fiber for therapeutic dosimetry application, studies have been carried out
to investigate the TL response of this candidate dosimeter for various types of radiation
beam. It is important to investigate the possible linear dose response between the
absorbed dose and the TL intensity over a wide range of dose as well as the energy
response of the dosimeters.
1.4 Scope of the Research
This study may provide a basis for applying TL phenomena in several
dosimetric situations. Their general characteristics such as linearity, energy response,
reproducibility, fading, sensitivity and atomic effective number, may provide
information to introduce Yb-Tb and Yb-doped SiO2 optical fiber as a new TL material.
This dosimeter may be suitable for many types of application particularly in radiation
therapy.
The irradiation of the core of the optical fiber exposed at dose level ranging
from 0.5 – 4.0 Gy of X-ray irradiation using Primus MLC 3339 linear accelerator
machine (LINAC) at 6 and 10 MV X-ray beams and 1.0 – 10.0 Gy for 1.25 MeV
gamma rays using Cobalt-60. The determination of fading effect of Tb-Yb and Yb-
doped optical fiber has been done using 6 MV X-ray irradiation at 4.0 Gy. Readings of
TL yield are obtained on 30 days following the time of exposure, and the
reproducibility characteristic were examined using 6 MV X-ray with dose 4 Gy
produced by LINAC.
This study has also been carried out to determine dopant concentration and
effective atomic number, with Zeff for Tb-Yb and Yb-doped optical fiber using a
scanning electron microscope (SEM). By using SEM, the composition of the elements
present in the fiber and the effective atomic number was determined.
1.5 Significance of the Research
The ability to manufacture silica fibers of relatively small diameter provides the
possibility of producing a thermoluminescence dosimeter offering high spatial
resolution. It is a further expectation that such fibers will provide radiation
measurements close to that of an ideal Bragg-Grayy cavity. This is important in the
accurate evaluation of absorbed radiation dose, being a critical consideration for non-
tissue equivalent probes such as doped silica glass.
There are a lot of advantages of doped silica glass fiber dosimeters. For
example, unlike conventional TLDs, the fibers are impervious to water; it then becomes
possible to locate the fiber dosimeter within a particular tissue of interest. With the
flexibility of silica glass fibers, this further suggests the possible use of fibers in a
variety of vascular procedures that involve appreciable radiation doses, in particular, in
intra-coronary artery brachytherapy.
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