RADIATION DOSIMETRY A THEORY RADIATION DOSES non-SI units (relationship between units) Dose Formula SI units ΔΕ J/kg = Gray (Gy) Absorbed Dose, rad 1 Gy = 100 rad Δm AE is the energy lost from the radiation beam, and Am is the mass of the material into which the energy is absorbed. ΔQ Roentgen (R) 1R = 2,58 · 104 C/kg Exposure dose, C/kg Δm where AQ is the electric charge freed by such radiation in a specified volume of air divided by the mass Am of that air. Relationship between absorbed dose and exposure dose D = f · X D is adsorbed dose , f is a coefficient depending on the kind of tissue being irradiated. H = Q · D where H is dose equivalent, Q is relative biological effectiveness of a particular kind of radiation, D is adsorbed dose. Equivalent Dose, Sievert rem Н (Sv) 1 Sv =100 rem Effective H ΣΗT Sievert rem 1 Sv =100 rem Equivalent Dose , Hef where HT = Wr · H, is the tissue-weighted dose equivalent to an organ or tissue, H, is the dose equivalent to the organ or tissue and the WT applicable to that organ or tissue. (Sv) Table 1 – Quality factors for different kinds of radiation Table 2 – Dimensionless weighting factors (Wr) Tissue WT Type of Radiation Gonads 0.25 Breast 0.15 х-гаys Red bone marrow 0.12 Lungs Thyroid 0.12 0.03 20 Bone surfaces 0.03 Neutrons (fast) 10 Remainder 0.30 Protons 10 Total body 1.00 1 DOSE RATES 1. Adsorbed dose rate: Np =" Table 3 – Exposure constants Radionuclides k, (µGy-m³/GBq-h at 1 m)" 137CS 99m'Tc 201TI н 2. Dose equivalent rate: Nµ = 88.11 15.95 3. Exposure rate: Nx = 12.16 Exposure rate at a distance r from the source of Mo radiation can be found as 39.46 67GA 20.54 1231 Ny = Y, where is ky is exposure constant for a ky'A 41.89 %3! "In 1251 57CO 131 55.41 given radioisotope, A is activity of the radioactive source, r is distance from the source of the radiation. 37.03 15.16 58.65 18ED 154.05 10. A person with lymphoma receives a dose of 35 Gy in the form of y radiation during a course of radiotherapy. Most of this dose is absorbed in 18 g of cancerous lymphatic tissue. (a) How much energy is absorbed by the cancerous tissue? (b) If this treatment consists of five 15 minute sessions per week over the course of 5 weeks and just 1% of the y photons in the y ray beam are absorbed, what is the power of the y ray beam? (c) If the y ray beam consists of just 0.5% of the y photons emitted by the y source, each of which has an energy of 0.03MeV, what is the activity (in Ci) of the y ray source?
RADIATION DOSIMETRY A THEORY RADIATION DOSES non-SI units (relationship between units) Dose Formula SI units ΔΕ J/kg = Gray (Gy) Absorbed Dose, rad 1 Gy = 100 rad Δm AE is the energy lost from the radiation beam, and Am is the mass of the material into which the energy is absorbed. ΔQ Roentgen (R) 1R = 2,58 · 104 C/kg Exposure dose, C/kg Δm where AQ is the electric charge freed by such radiation in a specified volume of air divided by the mass Am of that air. Relationship between absorbed dose and exposure dose D = f · X D is adsorbed dose , f is a coefficient depending on the kind of tissue being irradiated. H = Q · D where H is dose equivalent, Q is relative biological effectiveness of a particular kind of radiation, D is adsorbed dose. Equivalent Dose, Sievert rem Н (Sv) 1 Sv =100 rem Effective H ΣΗT Sievert rem 1 Sv =100 rem Equivalent Dose , Hef where HT = Wr · H, is the tissue-weighted dose equivalent to an organ or tissue, H, is the dose equivalent to the organ or tissue and the WT applicable to that organ or tissue. (Sv) Table 1 – Quality factors for different kinds of radiation Table 2 – Dimensionless weighting factors (Wr) Tissue WT Type of Radiation Gonads 0.25 Breast 0.15 х-гаys Red bone marrow 0.12 Lungs Thyroid 0.12 0.03 20 Bone surfaces 0.03 Neutrons (fast) 10 Remainder 0.30 Protons 10 Total body 1.00 1 DOSE RATES 1. Adsorbed dose rate: Np =" Table 3 – Exposure constants Radionuclides k, (µGy-m³/GBq-h at 1 m)" 137CS 99m'Tc 201TI н 2. Dose equivalent rate: Nµ = 88.11 15.95 3. Exposure rate: Nx = 12.16 Exposure rate at a distance r from the source of Mo radiation can be found as 39.46 67GA 20.54 1231 Ny = Y, where is ky is exposure constant for a ky'A 41.89 %3! "In 1251 57CO 131 55.41 given radioisotope, A is activity of the radioactive source, r is distance from the source of the radiation. 37.03 15.16 58.65 18ED 154.05 10. A person with lymphoma receives a dose of 35 Gy in the form of y radiation during a course of radiotherapy. Most of this dose is absorbed in 18 g of cancerous lymphatic tissue. (a) How much energy is absorbed by the cancerous tissue? (b) If this treatment consists of five 15 minute sessions per week over the course of 5 weeks and just 1% of the y photons in the y ray beam are absorbed, what is the power of the y ray beam? (c) If the y ray beam consists of just 0.5% of the y photons emitted by the y source, each of which has an energy of 0.03MeV, what is the activity (in Ci) of the y ray source?
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Transcribed Image Text:RADIATION DOSIMETRY
A THEORY
RADIATION DOSES
non-SI units
(relationship
between units)
Dose
Formula
SI
units
ΔΕ
J/kg =
Gray (Gy)
Absorbed Dose,
rad
1 Gy = 100 rad
Δm
AE is the energy lost from the radiation
beam, and Am is the mass of the material
into which the energy is absorbed.
ΔQ
Roentgen (R)
1R = 2,58 · 104
C/kg
Exposure dose,
C/kg
Δm
where AQ is the electric charge freed by
such radiation in a specified volume of air
divided by the mass Am of that air.
Relationship between absorbed dose and
exposure dose
D = f · X
D is adsorbed dose , f is a coefficient
depending on the kind of tissue being
irradiated.
H = Q · D
where H is dose equivalent, Q is relative
biological effectiveness of a particular kind
of radiation, D is adsorbed dose.
Equivalent Dose,
Sievert
rem
Н
(Sv)
1 Sv =100 rem
Effective
H ΣΗT
Sievert
rem
1 Sv =100 rem
Equivalent Dose
, Hef
where HT = Wr · H, is the tissue-weighted
dose equivalent to an organ or tissue, H, is
the dose equivalent to the organ or tissue
and the WT applicable to that organ or
tissue.
(Sv)
Table 1 – Quality factors for different kinds
of radiation
Table 2 – Dimensionless weighting factors
(Wr)
Tissue
WT
Type of Radiation
Gonads
0.25
Breast
0.15
х-гаys
Red bone marrow
0.12
Lungs
Thyroid
0.12
0.03
20
Bone surfaces
0.03
Neutrons (fast)
10
Remainder
0.30
Protons
10
Total body
1.00
1
DOSE RATES
1. Adsorbed dose rate: Np ="
Table 3 – Exposure constants
Radionuclides k, (µGy-m³/GBq-h at 1 m)"
137CS
99m'Tc
201TI
н
2. Dose equivalent rate: Nµ =
88.11
15.95
3. Exposure rate: Nx =
12.16
Exposure rate at a distance r from the source of Mo
radiation can be found as
39.46
67GA
20.54
1231
Ny = Y, where is ky is exposure constant for a
ky'A
41.89
%3!
"In
1251
57CO
131
55.41
given radioisotope, A is activity of the radioactive
source, r is distance from the source of the radiation.
37.03
15.16
58.65
18ED
154.05
Transcribed Image Text:10. A person with lymphoma receives a dose of 35 Gy in the form of y radiation during a course
of radiotherapy. Most of this dose is absorbed in 18 g of cancerous lymphatic tissue. (a) How much
energy is absorbed by the cancerous tissue? (b) If this treatment consists of five 15 minute sessions
per week over the course of 5 weeks and just 1% of the y photons in the y ray beam are absorbed,
what is the power of the y ray beam? (c) If the y ray beam consists of just 0.5% of the y photons
emitted by the y source, each of which has an energy of 0.03MeV, what is the activity (in Ci) of the
y ray source?
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