5 - Radiation Safety Flashcards
define the “absorbed dose”
- what is its SI unit?
- measured in?
- subunit?
absorbed dose is the measure of the amount of energy absorbed from the radiation beam per unit mass of tissue
- Gray (Gy)
- joules/kg
- miligray (mGy)
what does the equivalent dose take into account?
- it takes into account the different levels of radio-biological effectiveness of different types of radiation (radiation weighting factor)
what is the radiation weighting factor?
the biological effects of different types of radiation on different tissues
radiation weighting factor of:
x-rays, gamma rays, beta particles, and alpha particles
- what does this difference mean?
x-rays, gamma rays, beta particles = Wr 1
alpha particles = Wr 20
- the biological effect of a particular absorbed dose of alpha particles would be more severe than a absorbed dose of x-rays
how to calculate equivalent dose?
absorbed dose x radiation weighting factor
equivalent dose: what is the SI unit? what are its subunits?
SI unit: Sievert (Sv)
subunits: millisieverts (mSv), microsievert (uSv)
why is the equivalent dose same as the absorbed dose in x-rays?
because the radiation weighting factor for xrays is 1.
what does the effective dose allow?
it allows doses from different investigations of different parts of the body to be compared, by converting all doses to an equivalent whole body dose
what is tissue weighting factor?
the numerical value assigned to each different tissue based on its radiosensitivity
how is effective dose calculated?
SI unit?
subunit?
- equivalent dose x relevant tissue weighting factor
- Sievert (Sv)
- millisievert (mSv)
radon gas: how does it occur? where does it build up? what circumstances affect its level of buildup? yearly average dose?
- comes from naturally occurring uranium in the ground
- builds up indoors
- nature of the ground, atmospheric conditions, pattern of ventilation
- 1300 microsieverts
gamma rays:
emitted by?
dose depends on?
yearly average?
- natural radioactivity in the earth and building materials
- depends on rocks/soils and building materials
- 350 microsieverts
cosmic rays: radiation dose increases with?
latitude and altitude
arrange in descending order the dose from these radiographic examinations: CT head Chest xray Panoramic Periapical CT abdomen
CT abdomen (8 mSv) CT head (2 mSv) Chest xray (0.02 mSv/20 microSv) Panoramic (4-30 microSv) Periapical (1-8 microSv)
2 classifications of the biological effects of ionizing radiation?
- deterministic effects (tissue reactions)
- stochastic effects
explain the somatic and genetic effects of radiation?
- somatic: affect those irradiated
- genetic: affecting the offspring of those irradiated
what are deterministic effects of radiation?
should they occur in dentistry?
somatic, non-cancer damaging effects that will definitely result from a high specific dose of radiation.
- threshold dose exists at which effect begins to take place
- dose proportional to severity of effect
-they should not occur in dentistry
examples of deterministic effects?
- hair loss
- skin erythema
- cataracts
- GI upset
- suppression of erythropoiesis
effects on the unborn child:
related to?
susceptible when?
results in?
- dose (deterministic)
- when the organs are developing (2-9weeks)
- results in malformations or death
what are stochastic effects of radiation?
could they occur in dentistry?
those which occur or develop on a random basis without a threshold, meaning that any dose of radiation can bring on a stochastic effect. however, probability increases with dose
- stochastic effects of radiation do occur in dentistry
examples of non-deterministic (stochastic) effects?
leukaemia and solid tumours
genetic effects:
radiation to reproductive organs may lead to?
threshold?
radiation to reproductive organs may damage DNA in sperm/egg
lead to congenital abnormalities in offspring or those irradiated but no certainty
- no threshold
what are characteristics of the most radiosensitive cells?
- high mitotic rate
- undergo many future mitoses
- most primitive in differentiation
+ lymphocytes and oocytes which are highly differentiated and non-dividing
effects of radiation: explain the direct and indirect effects
direct: interacts with biologic macromolecules (DNA, RNA, proteins and enzymes) causing ionisation and damage
indirect: hydrogen and hydroxyl free radicals are produced by action of radiation on water (abundant in the body). free radicals form toxic substances such as hydrogen peroxide
- most common type of damage
changes in biological molecules: how is damage done to DNA?
damage to mechanism for cell death, mutation and carcinogenesis via:
- breaking strands
- loss/change of base
- disrupt bond between strands
young patients: are they more radiosensitive? why?
young patients have cells which are still dividing, therefore are more radiosensitive. they also have longer lifespan to allow the effect to develop
3 principles of radiation protection? + explain each
justification: exposure cannot be carried out until justified. benefit from examination but outweigh risk of exposure
optimisation: operator must ensure that exposure is kept as low as reasonably practicable, and consistent with intended diagnostic purpose
dose limitation
warnings for controlled area?
- visible light and audible noise when xrays being produced
- operator should be able to prevent access to controlled area
- use of control panels, switches, isolators outside controlled area
lead protection: justified? what to use when the thyroid may be in the primary beam?
- no justification for use of lead aprons, do not protect against radiation scattered internally within body
- thyroid collars should be used
pregnancy: when is fetus most susceptible?
during organogenesis (2-9weeks)
