1. Qing Liang, PhD Medical Physicist Mercy Health System, Janesville, WI
Radiation Dosimeters
Qing Liang, PhD
Medical Physicist
Mercy Health System, Janesville, WI

2. Learning Objectives Overview of different types of dosimeters
Understand the radiation-induced process and the meaning of measured signal
Learn about the clinical applications and advantages/issues with each type of dosimeter

4. Ionization Chamber

5. Ionization Chambers Work with electrometer (high V, charge collection)
Measure radiation dose from charge/current
Requires calibration

6. Ionization Chambers
Thimble ionization chamber
Farmer typed chamber

7. Ionization Chambers
Parallel plate chamber (electron dosimtery)

8. Ionization Chambers
Spherical chamber: Gamma Knife

9. Ionization Chambers
Well chamber: brachytherapy

10. Ionization Chambers Well chamber: brachytherapy
Sweet spot (maximum response)

11. Ionization Chambers
Pencil chamber: CT dosimetry for CTDI (CT dose index) measurements
10 cm nominal length

12. Chamber Reading Corrections
Pion: recombination correction
PTP: air density correction
Ppol: polarity correction
Pelec: electrometer calibration

13. Ionization Chambers: Other Issues
Stem effect: response from stem not thimble
Depends on chamber design (guarding)
Well guarded chamber: <0.1%
Guarded chamber: %
Unguarded chamber: %
Function of energy and beam size

14. Ionization Chambers: Other Issues
Leakage:
Source: chamber, cable, electrometer
Should measure leakage as a system before taking measurements
Leakage in the chamber is generally 1 to 10fA for a good chamber

15. Ionization Chambers: Other Issues
Energy response: It is desired to have a uniform energy response for all energies
Farmer chamber

16. TLD

17. Thermoluminescent Dosimeter (TLD)
Advantages
Small size
Wider linear dose response range
Reusable

18. Luminescence Process
Physics

19. Thermoluminescent Dosimeter (TLD)
Luminescence induced by heat
Impurities play important roles.
TLD readout process

20. TLD Glow Curve Time-temperature profile
Glow curve composed with difference peaks

21. Thermoluminescent Dosimeter (TLD)
Supralinearity
Materials:
LiF:Mg,Ti
LiF:Mn,Cu,P
CaF2:Mn
Li2B4O7:Mn
Dose response linearity: function of matieral
Dose response linearity

22. Energy Dependance of TLD

23. How to use TLD?
Annealing: oC for 1hour + 80 oC for 24 hours to reset the trap structure and eliminate any electrons in residual traps
Irradiation: wait 24 hours to let low temperature traps fade
Readout: to get the signal from high temperature traps
Annealing
Irradiation
Readout

24. TLD Applications Radiation therapy (external beam and brachy therapy):
Dose verification
In-vivo dosimetry: patient skin
Dose rate constant determination for BT

25. TLD Applications Diagnostic physics Health physics
Personnel exposure monitoring
Neutron measurements

26. OSLD

27. Optically Stimulated Luminescence Dosimeter (OSLD)
Instead of using heat, luminescence is stimulated with optical light
Material: Al2O3:C
Used in space by NACS
Used for personnel exposure monitoring
Now popular in radiation
therapy and diagnostic physics

28. OSLD
Readout system

29. OSLD
Dose response linearity: supralinearity

30. OSLD
Dose rate dependence:

31. OSLD
Energy dependence f(Q):
f(Q)
Al2O3
LiF
Al2O3/LiF

32. OSLD: signal fading

33. Characteristics of OSLD

34. Applications of OSLD External beam and brachytherapy
Output verification
In-vivo dosimetry
IROC uses OSLD to perform output audit

35. DIODE

36. Diode Dosimeter Designs
Cylindrical
Flat

37. Diode Dosimeter Theory
Semiconductor: narrow energy band width
n type: Doping “donor” impurity to produce additional electrons
P type: Doping “acceptor” impurity to produce additional holes

38. Diode Dosimeter Theory
Diode: p-n junction made by doping the semiconductor with donors and acceptors at adjacent junctions
Diode: no external voltage applied

39. Diode Dosimeter Theory
n-type diode: high doping level of n-type semiconductors, and low doping level of p-type conductors
p-type diode: high doping level of p-type semiconductors, and low doping level of n-type conductors

40. Dose Rate Dependence
p-type is less dependent on dose rate then n-type

41. Dose Rate Dependence

42. SSD Dependence
Related to dose rate

43. Accumulated Dose Dependence
Sensitivity of diode depends on accumulated dose.
Theory: crystal lattice gets changed with dose

44. Temperature Dependence

45. Energy Dependence
MV beams

46. Angular Dependence

47. Application of Diodes In-vivo dosimetry Small field dosimetry
TBI (Total Body Irradiation)
Dose verification
Small field dosimetry

48. MOSFET

49. MOSFET Metal Oxide Semiconductor Field Effect Transistor
Capable of dose measurements
immediately after irradiation or
can be sampled in predefined
time intervals
(on-line dosimetry)

50. Types of MOSFET

51. Dual-MOSFET

52. MOSFET Products
Mobile system
Wireless system

53. MOSFET Products
Implanted MOSFET detector: Dose Verified System

54. MOSFET: Temperature Dependence
TN dual-MOSFET-dual-bias detector: temperature independent
Other types of MOSFET: Temperature dependent
DVS MOSFET
3.3% more sensitive for 37 oC
Calibration should be performed
at 37 oC (body temp)

55. MOSFET: Energy Dependence

56. MOSFET: Dose Linearity
Dual-bias MOSFET

57. MOSFET: Accumulated Dose

58. MOSFET: Angular Dependence
Depends on design
Can be different for different
energies

59. MOSFET: Angular Dependence
To determine angular dependence

60. Characteristics of MOSFET

61. Clinical Applications MOSFET

62. Clinical Applications MOSFET
In-vivo dosimetry

63. Radiographic Film

64. Radiographic Film

65. Radiographic Film

66. Radiographic Film
Film development process

67. Radiographic Film: Temp. Dependence

68. Radiographic Film: Temp. Dependence

69. Radiographic Film: Optical Density
OD can be measured
with film scanner/digitize
or densitometer.

70. Radiographic Film: Dose Rate Dependence

71. Radiographic Film: Energy Dependence

72. Radiographic Film: Effect of Depth and Field Size

73. Radiographic Film: Clinical Application

74. Radiographic Film: Summery

75. Radiochromic Film

76. Radiochromic Film
Radiochromic film consists of a single or double layer of radiation-sensitive organic microcrystal monomers, on a thin polyester base with a transparent coating

77. Radiochromic Film
Color of the radiochromic films turns to a shade of blue upon irradiation.
Darkness of the film increases with increasing absorbed dose.
No processing is required to develop or fix the image.

78. Radiochromic Film
Flat bed film scanner

79. Radiochromic Film: Dose Linearity
Depends on scanning instruments

80. Radiochromic Film: Applications

81. Radiochromic Film: Summery
Advantage: high resolution, no processing necessary

82. Chemical Dosimeters

83. Chemical Dosimeters
Fricke

84. Chemical Dosimeters
Alanine

85. Chemical Dosimeters
Polymer Gel

86. Others Diamond detector Scintillator/plastic dosimeter
Optical fiber dosimeter ….

87. Summery

88. Thank you!