Biological Effects Of Ionising Radiation Flashcards
What is ionising radiation?
When photons interact with electrons in an atom and knock them out of the shell causing the atom to become an ion.
The radiation will do this along its path creating ions and depositing energy locally (35eV) - more than is needed to overcome atomic bonds (4eV)
What is the most significant effect of ionising radiation? How does this occur?
Damage to DNA directly or indirectly
Direct = radiation interacts with atoms of a DNA molecule in cell
Indirect = radiation interacts with water in cell, producing free radical which can cause damage as they are highly unstable and reactive
What determines tissue radiosensitivity?
Function of the cells making up the tissue
If the cells are actively dividing
E.g. stem cells very radiosensitive but differentiated cells are not
Give some highly radiosensitive tissues, moderate and least
High
- bone marrow, lymph, GIT, glands
Mid
- skin, lungs, vascular endothelium
Low
- CNS, bone and cartilage, connective tissue
What are the possible outcomes when radiation hits a cell nucleus?
What is absorbed dose and equivalent dose?
Absorbed dose measures energy deposited by radiation in grays (Gy)
Equivalent dose is absorbed dose multiplied by weighting factor depending on radiation
(Beta, gamma and x-rays = 1, alpha = 20) in units of sieverts Sv
What is the LNT model?
Linear no threshold model
Implies radiation damage is directly proportional to radiation dose
Assumes there is no safety threshold
What two types of radiation effects are there?
Deterministic
Stochastic
What is a deterministic effect
Tissue reactions
Only occur above a threshold dose
Severity is related to dose received
- cataracts
- hair loss
- skin damage
Etc
What is a stochastic effect
Probability of occurrence is related to dose received - no threshold of effects
Can’t predict how severe or what dose appear
Can develop years after
Somatic - disease or disorder
Genetics - abnormalities in descendants
What are sources of background radiation
Cosmic rays
Radon gas
Air travel
What is the dose of an intra oral x-ray?
0.005mSv
What are the three main points of radiation protection philosophy?
Justification - must have justification and sufficient benefit to offset detriment
Optimisation - must be ALARP taking into account economic and social factors. Use of rectangular collimator
Dose limitation - so risks are acceptable
How can dose be optimised?
- rectangular collimator
- 200mm focus to skin distance
- kV range of 60-70
