Biological Effects of Ionising Radiation Flashcards
when ionisation occurs what is deposited locally
energy (35eV)
what happens when radiation passes through matter
it will ionise atoms along its path
where can evidence of DNA damage be seen
in the faulty repair of chromosome breaks
where is DNA damage seen
in individuals who are exposed to large doses
what is the direct effect of radiation damage on DNA
radiation interacts with the atoms of a DNA molecule or another important part of the cell
what is the indirect effect of radiation damage on DNA
radiation interacts with water in the cell, producing free radicals which can cause damage
why are double strands of DNA more difficult to repair
it usually occurs due to alpha radiation and if the repair is faulty it can lead to mutations which affects cell function
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
why is radiation delivered at a lower dose less damaging
cells can repair less serious DNA damage before further damage occurs
what organs are at risk from cancer following large radiation exposures
oesophagus, thyroid, lungs, skin, breast, stomach, liver, colon, gonads
what is the radiosensitivity of tissues dependent on
function of the cells that make up the tissues
if cells are actively dividing
what kind of cells are very radiosensitive
stem cells
why are stem cells radiosensitive
they divide very frequently
what cells are highly radiosensitive
bone marrow, lymphoid tissue, GI, gonads, embryonic tissues
what cells are moderately radiosensitive
skin, vascular endothelium, lungs, lens of eye
what are the least radiosensitive cells
CNS, bone and cartilage, connective tissue
what are the possible outcomes after radiation hits a cell nucleus
no change
mutation repaired
cell death
cell survives but is mutated - cancer?
what is absorbed dose
measures the energy deposited by radiation
in Grays
what is equivalent dose
absorbed dose multiplied by a weighting factor depending on the type of radiation
in Sieverts (Sv)
what does the linear no threshold model estimate
long term biological damage from radiation
what does the linear no threshold model assum
the damage is directly proportional to radiation dose and radiation is always harmful with no safety threshold
what is response linearity
several small exposures would have the same effect as one large exposure
what are the 2 types of radiation effects
deterministic and stochastic
what is the deterministic effects of radiation
tissue reactions
only occur above a certain dose
severity of effect is related to the dose received
what is the stochastic effects
probability of occurrence is related to the dose received
what is somatic stochastic effect
results in disease or disorder
what is genetic stochastic effect
abnormalities in descendents
what is the effect of radiation exposure during pregnancy
damage or kill enough of the cells for the embryo to undergo resorption
what dose can be lethal for an embryo
100mGy
what dose can lead to growth retardation in a foetus
> 250mGy
why does pregnancy not need to be taken into account for dental x-rays
because the dose is so low
what is the annual background radiation dose
2.2mSv
what is the equivalent dose of an intra oral
0.005mSv
how far should the controlled beam extend from the x-ray tube and patient
1.5m
what does justification mean when taking radiographs
practices must have sufficient benefit to individuals or society in order to offset the detriment
what does optimisation mean when taking radiographs
individual doses and the number of people exposed should be kept ALARP
what does dose limitation mean
system of individual dose limits so that the risks to individuals are acceptable
how can patient doses be reduced
use E speed film or faster
use a kV range of 60kV to 70kV
focus to skin distance should be >200m
use rectangular collimation
what are diagnostic reference levels
dose levels for typical examinations for standard sized patients
what does DRLs allow for
identification of units giving higher doses
what are the adult DRLs for intra oral examinations on phosphor plates
1.2mGy
what are the child DRLs for intra oral examinations on phosphor plates
0.7mGy