Dosimetry Flashcards
How can DNA be damaged directly?
Direct action: Photon causes ionisation as it hits electron with enough force that it is destroyed
How can DNA be damaged indirectly?
Photon interacts with electron and breaks down H2O by disassociation and free radical
Leads to heat production from a chemical reaction that destroys DNA
What is a double strand break?
Both strands break
Incorrect repair can lead to cell depth or mutation (not exact replica of parent) which can lead to cancerous cell
How is single strand break different to double strand break?
Single strand break can repair itself
What does a small dose change lead to?
Large biological response (including cell death)
Healthy tissue is not completely spared
What is fluence?
Number of particles going through an area
What is energy fluence?
A measure of the amount of radiant energy of each ray/particle that falls on a surface area
What is exposure?
A measure of flux at region of interest
Only applies to x-rays and gamma rays in air
X-rays ionise air and electrons have a charge
What is KERMA?
Kinetic Energy Released per unit Mass
Indirectly ionising radiation transfers energy to matter by 2 stage process:
x-ray which Compton scatters interacts with recoil electron
What is total KERMA?
total KERMA = K_c + K_r
K_r = radiative
K_c = collisional
(mainly use collision kerma)
What is absorbed dose?
How much energy is left in mass
How is dose deposited in depth?
In each layer of depth, electron will change direction and loose energy in each one
At different depths, electron will stop at different layers
When x-ray is far enough in, there is much more attenuation so x-ray stops
What type of relationship does KERMA follow?
Exponential relationship (and so does dose)
What can be done when dose and collisional kerma become equal after a certain point?
Can convert between both parameters when they become equal
What is Charged Particle equilibrium?
When there is no build up of charge: same number of energy and directions of electrons
