Biological effects of Ionising Radiation and Radiation Risk Assessment Flashcards
what are the two main types of radiation that ionising radiation can be divided into
by-products of radioactive decay
artificially produced electromagnetic radiation
what categories can you divide by-products of radioactive decay into
alpha particles
beta particles
gamma rays
what is ionising radiation
ionising radiation has enough energy to turn atoms into ions by knocking away electrons
what is an ion pair
free electron and positively ionised atom
what is the most significant effect of ionising radiation
DNA damage
what can DNA damage be seen in
faulty repair of chromosome breaks, development of abnormal cell populations and development of cancer
what types of DNA damage is there
direct or indirect
what is direct DNA damage
radiation interacts with the atoms of a DNA molecule or another important part of the cell
what is indirect DNA damage
radiation interacts with water in the cell - when water molecule becomes ionised a highly reactive free radical ion is formed, two of these can combine to form a hydroxyl radical which can diffuse short distances and cause DNA damage
what is one advantage of DNA being a double helix
if one strand breaks it can still be held together by the strand that hasnt broken
why do double strand DNA breaks usually occur
alpha radiation
what does the biological effect of DNA damage depend on
type of radiation
amount of radiation
time over which the dose is received
the tissue or cell type irradiated
at what rate of delivering radiation is damage less likely to occur
low doses
what two factors is the radiosensitivity of tissue divide on
the function of the cells that make up the tissues
if the cells are actively dividing
what is an example of cells that divide frequently and are very radiosensitive
stem cells
what cells are less sensitive to radiation damage
differentiated cells
what are examples of highly radiosensitive tissues
bone marrow
lymphoid
GI
gonads
embryonic
what tissues are moderately radiosensitive
skin
vascular endothelium
lung
lens of the eye
what tissues are least radiosensitive
central nervous system ‘bone and cartilage
connective tissue
what are the two outcomes of radiation hitting nucleus
no change or DNA mutation
what can happen if the cell is mutated
can repair
cell death
cell survives but mutated
what is the absorbed dose
a quantity that can be measured - measures the energy deposited by radiation
what is equivalent dose
a derived quantity - absorbed dose multiplied by a radiation weighting factor depending on type of radiation
what is an effective dose
derived quantity - equivalent dose to each organ multiplied by the tissue weighting factor and summed (probability of cancer)
what is the linear no threshold (LNT) model
estimates the long term biological damage from radiation - several small exposures can have same effect of one large exposure
what are the two types of radiation effects
deterministic effects
stochastic effects
what is a deterministic effect
tissue reactions
only occur above a certain threshold dose
the severity of the effect is related to the dose received
what is stochastic effects
the probability of occurrence is related to the dose received
what are two categories stochastic effects can be divided into
somatic - disease or disorder
genetics - abnormalities in descendants of those exposed
what are some sources of background radiation
cosmic rays
internal radionuclides
what is the effective dose value for an intra oral x-ray
0.005 mSv - negligible risk of cancer
what is the controlled area
should extend at least 1.5m from the x-ray tube and patient
what is justification of the x-ray
sufficient benefit to the individual to offset the detriment
what is the optimisation of the optimisation
individual doses and number of people exposed should be kept as low as reasonably practicable
how can you reduce damage to CR plates
insert plates between two plastic sheets
damaged detectors should be cleaned or replaced
