Radiation Protection Flashcards
what is the absorbed dose?
amount of energy deposited in a medium per unit mass of material
SI unit - gray Gy
measured in joules/kg
subunit - miligray mGy x 10-3
Equivalent dose H?
Take into account the different radio biological effectiveness of different types of radiation
what does the equivalent dose equal to?
absorbed dose x radiation weighting factor
what is weighting factor?
Wr
xrays, gamma rays, b particles Wr=1
alpha particles = 20
units of equivalent dose?
SI unit = sievert
milisieverts mSv x 10-3
microsievert uSv x 10-6
equivalent dose equals what if xrays weighting factor is 1?
absorbed dose
what is the effective dose?
allows doses from different investigations of different parts of the body to be compared
converts dose to an equivalent whole body dose
some body parts more susceptible to radiation than others
what is Wt?
tissue weighting factor
Effective dose equals?
= equivalent dose x tissue weighting factor
units of effective dose?
SI unit = sievert
sub unit = mSV
the term dose is actually what?
effective dose
what is the average yearly uk background radiation?
2.5mSv/year
radiation from a periapical? dpt?
1-8.3mSv ~ 8-40 hours
4-30mSv
Somatic?
affecting those irradiated
deterministic or non deterministic - stochastic
genetic?
affects offsrping of those irradiated
non deterministic - stochastic
deterministic affects of radiation?
will occur
threhsold of which symptoms will occur
above threshold - severity increases with dose
symptoms of deterministic radiation?
skin erythema hair loss cataracts GI upset suppression of erythropoiesis
does deterministic radiation occur in dentistry?
no
effects on an unborn child?
related to dose = deterministic
susceptible when organs are developing - 2-9 weeks
can cause malformation (reduced growth) and death
stochastic effects?
may occur/random development
no threshold at which events start to occur
any dose may cause stochastic effects
increased probability with increased dose
severity of effect not affected by dose
leukaemias/solid tumours
do non deterministic effetcs occur in dentistry?
yes
what cells are radiosensitive?
cells with high mitotic rate
cells undergoing many future mitoses
most primitive in differentiation
lymphocytes.oocytes are highly differentiated and non dividing
direct effects of radiation?
interacts with biologic macromolecules causing ionisation/damage
indirect effects of radiaiton?
water balance in body = most common damage
hydrogen/hydroxyl free radicals produced by action of radiation on water
free radicals = toxic substances e.g hydrogen peroxide
changes in biologic molecules?
DNA - breaks strands, loss/change of base, disrupt bonds between strands = cell death, mutation, carcinogenesis
what happens if both strands of DNA are broken?
misrepair
intact strand is usually the template
genetic effects?
radiation to reproductive organs can damage DNA in sperm/egg
may cause congenital abnormalities in offspring of those irradiated
no threshold
cancer risk from intra oral?
dpt?
- 06-0.7 in 1 000 000
0. 29-1.9 in 1 000 000
young pt’s more at risk?
yes
more radiosensitive cells
longer lifespan to develop a cancer
stages of radiation protection?
justfication
optimisation
dose limitation
what is justification?
every radiograph must be justified
benefit of exam must outweigh detrimental effects
what is optimisation?
doses kept as low as reasonably practicable and consistent with intended diagnostic purposes
distance from x ray?
inverse square law
staff sufficient distance from pt and not in direction of primary beam
what is the controlled area?
within 1.5m of tube and patient in any other direction
only pt in that area during exposure
size depends on kV of machine
1.5m
warnings?
noise/light when xrays produced
operator prevents access to controlled areas
switches outwith controlled area
monitoring of radiation to worker if?
> 1mSv / year
100 intra orals/week
50 dpt’s/week
lead protection used?
thyroid collar if thyroid in primary beam
lead aprons dont protect from radiation scattered in body
foetus most susceptible when?
2-9 weeks
