Dosimetry Flashcards

Question

Answer 1

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The science of measuring/calculating dose levels

Answer 2

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the movement and transfer of energy through space/time/matter

Answer 3

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The amount or quantity of radiation absorbed by matter

Answer 4

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Definition: Ionizing radiation transfers its energy to air
How is it measured?
- Victoreen ‘R’ meters (ionization chambers)
Current uses:
- used in the measurement of skin dose (ESD)
- check calibration of xray equipment
Exposure facts:
- applies to x-ray/gamma radiation only, no particulates of energies up to 3 MeV
Units of Measurement:
- Traditional - (R) Roentgen
- S.I. - c/Kg
- 1 R = 2.58 x 10^-4 c/Kg

Answer 5

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↑ kVp = ↑ R value
↑ mAs = ↑ R value
↑ SID = ↓ R value
↑ collimation = ↓ R value
↑ filtration = ↓ R value.
intensity = quality

Answer 6

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Definition: The quantity of radiation deposited (transfered to) in an object (liquid or solid) per unit of mass
Unit of measurement:
- Traditional - Rad
- S.I. - Gray
- 1 Gray = 100 Rads
- 1 Rad = 100 ergs/g
- 1 Rad = 1 j/Kg
Facts:
- energy is transfered to the molecules of the absorbing material
- applies to all types of ionizing radiation at all enery levels
What influences absorbed does amount?
- Techincal factors:
- kVp
- mAs
- collimation
- filtration
- Material factors:
- Z#
- mass density
- thickness

Answer 7

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Currently two terms are used to define Biological dose:
- Equivalent dose (H_T) - dose specific to organ
- Effective dose (E) - whole body dose
Unit of measurement:
- Rem or Sievert (Sv)
- 1 Sv = 100 Rem
- 1 Rem = 10mSv
- 1 mSv = 100 mRem
- 1 Gy = 100 Rad
- 1 Rad = 10 mGy
- 1 mGy = 100 mRad
How are H_T and E the same?:
Both measurements of biological damage take into account the following:
- (D) = actual amount of energy absorbed by the tissue(s)
- the type of radiation the person was exposed to
- the actual tissues that were exposed to (D)
- both are ‘bio doses’ measured in rem/Sv

Answer 8

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Definition: It is the measure of the ability of a specific type of radiation to cause a biological effect to a living tissue or cells.
Facts:
- Laboratory experiments typically comparing 2 types of radiation and their ability to cause cellular damage (typically death)
- For given dose, some radiations do more damage than others
Equation: D= dose in Rads (Gy)
- D_ref / D _test
- D_ref = 250 kVp of x rays
- D _test= dose of ionizing radition being “compared” with the xray dose in terms of how many cells were killed
Summary :
- Not all radiations are created equal in the amount of cellular death they create, even if given in equal doses
- From RBE studies, a concept called Linear Energy Transfer was formulized
Unit of measurement:
- Traditional - Rem
- S.I. - Sievent

Answer 9

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1895 - 1930 - dosimetry was essentially non existent. No such thing as J.O.D.
up until the early 1930’s, an overdose of radiation was “measured” when your skin turned red.
- This was called skin erythema dose.
- This was considered the first dose limit
1934 Tolerance dose introduced
- 0.2 R/day
- 1.4 R/week
1936 (redefined Tolerance dose)
- 0.1 R/day
- 0.7 R/week
1937 - Roentgen (R) was defined and used as the unit of measurement for the Tolerance Dose.

Radiation quantities were not discovered at the same time, here is the order:

Air dose (exposure)
Absorbed dose
Biological dose

Answer 10

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Demonstrated that air exposed to x rays, ionizes
The more x rays, the more ionizations
Based on their experiments, the Roentgen became the unit for “air exposure”

Answer 11

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Air Dose(Exposure) (X) - measuring number of air molecules from ionization
Absorbed Dose (D) - number of molecules going into a mass
Biological Dose (H) -
1. Equivalent dose (H_T)
2. Effective dose (E)

Units of measurement for each:

Air Exposure (X):
1. Traditional - R
2. S.I. - c/Kg
Absorbed Dose (D):
1. Traditional - Rad
2. S.I. - Gray
Biological dose (H):
1. Traditional - Rem
2. S.I. Sievent

Answer 12

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Definition : The rate at which a specific type of ionizing radiation loses its energy (transfers its energy) as it traverses through a substance in a linear path
How does radiation lose it’s energy?
- removing electrons from its orbit
Unit of measurement:
- KeV/µm of absorbing material
Facts:
- Not all ionizing radiation loses their energy at the same rate
- High LET - loses it quickly
- Low LET - loses it slowly
LET value is related to RBE value of a specific type of radiation
- Alpha = ↑ RBE & ↑ LET
- x rays = ↓ RBE & ↓ LET

Answer 13

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creates a lot of ionizations (damage) in a short distance of travel
energy is expended quickly
not much penetration but high amounts of damage (bio effects) in a short distance of travel
Example:
- Alpha particles
- Neutrons
- Protons

Answer 14

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create much less ionizations (damage) over a given distance of travel.
They are not absorbed/scattered at a high rate, rather a low rate of ionizations
- less interactions
- more penetrating
Examples:
- electromagnetic ionizing radiations
- beta particles

Answer 15

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Two types of Weighting factors:
- Radiation Weighting Factor (W_R)
- Tissue Weighting Factor (W_T)
Why do we even need them?
1. Depending on their LET value, some radiations produce more bio damage than others.
- 1 Rad of Alpha particles will produce a lot more bio damage than 1 Rad of x rays would
1. Different types of tissues are more easily damaged (radiosensitive) than others.
Three factors needed to do calculation:

Absorbed Dose (D) - Rads/Gy
Type(s) of radiation exposed to LET
What tissue(s) were exposed on the person

What is W_R?
Radiation weighting factor is a numerical value (1-20) given to each type of known radiation based on LET value
- Alpha - 20
- x ray - 1
- gamma - 1
What is WT?
Tissue weighting factor. Numerical values based on radiosensitivity of specific organ
WT values are based on an arbitrary number system. The higher the number, the greater the sensitivity

Answer 16

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There is a Nuclear explosion and different types of radiation are released. These include gamma, neutrons and protons. Let’s see how H_T (Equivalent dose) would be calculated:
Step 1 - need to know the W_R for each type of radiation:
- Protons = 2
- Gamma = 1
- Neutrons = 10
Step 2 - the values of D (absorbed dose) would have to be known for each type of radiation… let’s say 2 Rads
Step 3 - use the equation
H_T = Σ D x W_Ror…
H_T = (2x2) protons + (2x1) gamma + (2x10) neutrons
H_T = 4 + 2 +20
H_T = 26 Rems

This is the biological dose, or risk of potential biological damage to an organ

Answer 17

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Definition: The amount of radiation absorbed by a specific tissue or organ
Formula:
- H_T = ΣD_T x W_R
- H_T - equivalent dose
- Σ - sum of
- D - Rad (or Gy) value
- W_R - radiation weighting factor

Answer 18

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Effective dose (E) - whole body dose
Defined by ICRP in 1991
Represents the end of the time-line for radiation quantities.
- 1930’s - Exposure (X)
- 1950’s - Absorbed dose (D)
- 1960’s/present - Biological dose
  - H_Tand E
Equation:
E = Σ H_T x W_T
H_T - equivalent dose
W_T - Tissue weighting factor
E - Effective dose
Units = Rems

Effective Dose is technically a whole body dose, even if the whole body was not irradiated. Whether one organ is exposed or multiple organs they each have an effect on the body as a whole.

Answer 19

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ColEfD has been designated for use in the description of population or group exposure from low doses of different sources of ionizing radiation.
it is determined as the product of the average EfD for an individual belonging to the exposed population or group and the number of persons exposed.
Unit of measurement:
- the person-sievert is the unit of choice
Example:
If 1000 people are exposed to low doses of different sources of ionizing radiation and recieve an average EfD of 0.5 mSv, the ColEfD is 500 person-mSv. Which equals 0.5 person-Sv.