Biological Effects of Ionising Radiation and Radiation Risk Assessment Flashcards
What are the types of radiation?
Alpha - large particle, travels a few inches
Beta - very small particle, travels a few feet
Gamma - high energy, travels long distances
X-rays - high or low energy, travels long distances
What is ionising radiation?
Radiation with enough energy to turn atoms into ions
It does this by knocking away electrons orbiting the nucleus of an atom
What is the biggest effect of ionising radiation?
Damage to DNA
How does ionising radiation damage DNA directly?
Radiation interacts with the atoms of a DNA molecule
How does radiation damage DNA indirectly?
Radiation interacts with water in the cell, producing free radicals which cause damage
How does dose rate affect DNA damage?
Radiation delivered at a low dose rate is less damaging
Cells can repair less serious DNA damage before further damage occurs
At high dose rates, the DNA repair capacity if the cell is overwhelmed
What affects tissue radiosensitivity?
The function of the cells making up the tissue - differentiated cells don’t divide and so are less radiosensitive
If the cells are actively dividing - the more rapidly, the greater the radiosensitivity
Give examples of deterministic effects of radiation
Bone marrow blood cell depletion
Cataracts
Sterility
Hair loss
Skin damage
What are the different types of biological effects of radiation?
Deterministic effects
Stochastic effects
What is the effect of radiation during pregnancy?
Radiation exposure could damage or kill enough of the cell for the embryo to undergo resorption
How does patient pregnancy affect dental X-rays?
It doesn’t as the dose to the foetus is so low
The foetus will not be irradiated and the X-ray beam shouldn’t be directed towards the patients abdomen
Describe the controlled area for protection of staff?
Should extend at least 1.5m from the X-ray tube and patient
X-ray beam should always be directed away from staff members
What is included in the radiation protection philosophy?
Justification - sufficient benefit to individuals
Optimisation - doses and number of people exposed should be kept as low as reasonably practice
Dose limitation - system of individual dose limits so risks to individuals are acceptable
What should be used to keep dose optimisation ALARP?
Rectangular collimators
A kV range of 60-70kV
E speed film or faster (fewer X-ray photons required)
Focus to skin distance should be >200mm
