Dosimetry Flashcards
What are the radiation core safety principles?
(3)
Justification
Optimisation
Limitation
How do we know that radiation is harmful?
Atomic bomb survivors
How do atomic bomb survivors tell us that radiation is harmful?
Survivors were tested for how close they were from the epicentre, which indicated the dose that they received. The further they were, the less dose they got. They compared the number of cancers these people got to a normal population.
The further the distances from the epicentre, the lower occurrence of cancer. This allowed the creation of the linear non-threshold model for stochastic effects
What does the linear non-threshold model for stochastic effects say?
The higher the dose of radiation someone receives, the higher their risk of cancer
Why may the linear non-threshold model for stochastic effects be inaccurate?
Because the information to create it was from atomic bomb survivors, yet all of them had high doses- just in different quantities
What are the 2 types of quantities of radiation?
Direct quantities (radiation that’s directly measured)
Derived quantities (radiation that’s not directly measured)
What are the direct quantities of radiation?
(3)
Exposure
KERMA
Absorbed dose
What are the derived quantities of radiation?
(5)
Equivalent dose
Effective dose
DAP
DLP
Personal dose equivalent
What is exposure?
The amount of ionisation caused by an x-ray or a gamma ray in air
What does the exposure measure?
The total charge produced in air by ionising radiation
What does the exposure not include?
The extra ionisation caused by the slowing of electrons (brehmstrahlung)
What is the unit of exposure?
Coulombs per kilogram (C/kg)
What direct quantity is usually used instead of exposure?
KERMA
What is KERMA?
A measure of kinetic energy released per unit mass. It includes the effects of brehmstrahlung
What is the unit for KERMA?
Gray (Gy)
What is the absorbed dose?
The amount of energy deposited in a material
What is the absorbed dose equal to?
KERMA in air
What is the unit for the absorbed dose?
Gray (Gy)
What is linear energy transfer (LET)?
It defines how damaging a radiation is based on charge, mass and energy
What does it mean if there’s a higher LET?
The DNA breaks are more irreparable
Do alpha particles have a high or low LET?
Why?
High LET
So that they can slow down quickly in tissue and cause more damage in the DNA
Do gamma rays, x-rays and electrons have a high or low LET?
Low LET
What is the relative biological effectiveness (RBE) determined by?
(3)
The LET of the radiation
The dose rate
The particle type
What is the equivalent dose?
It considers the harmfulness of the radiation
What is the unit for the equivalent dose?
Sievert (Sv)
What is the weighting factor for beta, gamma and electrons?
1
What is the weighting factor for protons?
5
What is the weighting factor for neutrons?
5-20
What is the weighting factor for alpha?
Why?
20
Because it causes more damage
When can DNA only be damaged?
When it’s condensed
What is the main unit when looking at the risk of radiation?
Effective dose
Why are some organs in the body more sensitive to radiation than others?
Because the faster the organs divide, the more of them are in the stationary (S) phase in the cell cycle, so the DNA is condensed and can be more easily damaged
What is the unit of the effective dose?
Sievert (Sv)
Which type of dose do we use to find out the risk?
Effective dose
What is the effective dose of ultrasound and MRI?
Why?
0
Because they don’t involve ionising radiation
Why do children and foetuses have a greater risk associated with radiation exposures?
(2)
Because they live longer, so there’s more time for cancers to develop
Because they’re growing
What does DAP stand for?
Dose
Area
Product
What is the exposure area product?
The exposure measured using a transparent flat-bed ion chamber attached to an x-ray collimator
What is the exposure area product commonly known as?
Te absorbed dose that’s being delivered to the patient in the air
What does ESD stand for?
Entrance
Surface
Dose
What is the entrance surface dose?
The absorbed dose at the entrance surface of the patient (the dose to the skin). It includes back-scattered radiation
What does CTDI stand for?
CT
Dose
Index
What is the CTDI?
The dose that would’ve been measured if the output had been equal to the chosen slide width
What is CTDIvol?
How to measure the absorbed dose with a rotational x-ray beam
What does CTDIvol stand for?
CT
Dose
Index for a
Volume
What factors impact what CTDI volume is delivered?
(2)
Collimation
Pitch
What are occupational exposures?
Exposures to a risk in the workplace (doses expoed to staff)
What can be used to measure the dose of staff?
Dosimeters
What are AECs?
The use of ionisation chambers to optimise exposure
What does AEC do?
It monitors the dose received at the detector and terminates x-rays when the dose is what has been specified
What are the 3 AEC chambers?
A
B
C
What AEC chambers do we use for a thicker material?
(2)
A
B
What AEC chambers do we use for a thinner material?
C
