RAD 260: Saftey Flashcards
Unit of absorbed dose
1.Amount of energy absorbed per unit mass of tissue
2.Unit of measurement of tissue is gray (Gy); normally expressed as Gyt (t indicates tissue)
Mutation
Erroneous information passed to subsequent generations via cell division
Free radicals
Highly reactive ions that have an unpaired electron in the outer shell
Late tissue reactions (deterministic) include:
1.Cataractogenesis: Causes cataracts to form
2.Thyroid: cancer or cessation of function
3.Effect on fertility
Two types of filtration:
inherent and added
Added Filtration
1.Aluminum sheets placed in the path of the beam near the x-ray tube window
2.Mirror placed in the collimator head
Inherent filtration
1.Glass envelope of the x-ray tube
2.Insulating oil around the tube
3.Diagonal mirror used for positioning light
Measuring patient dose
Skin entrance dose
2.Mean marrow dose (MMD)
Mean Marrow Dose (MMD)
Average dose to active bone marrow
Three Cardinal Principals
Time, Distance, Shielding
Primary protective barriers
Must be at least -inch lead equivalent and extend from the floor to a height of 7 feet
Secondary protective barriers
Must be at least -inch lead equivalent and extend from the primary protective barrier to the ceiling with a ½-inch overlap
Determinants of barrier thickness
Distance, occupancy, workload, use
Handheld ionization chamber:
Used to measure radiation in an area; measures doses of 10 μGya per hour
Geiger-Mueller detector:
Used to detect radioactive particles; meter reads in counts per minute
Air Kerma
(units of exposure)
Used to define radiation exposure or radiation delivered to a specific point, measured in Gy
Coloumbs/kilograms
(units of exposure)
Sometimes used to measure exposure, but preferred unit is air kerma
General types of radiation damage
Somatic and Genetic
Somatic
damage to the exposed individual
Genetic
Damage to the genetic code of the germ cell contained in the DNA; may be passed to the next generation
Natural background radiation
- Contributes 3.0 mSv
- Approx. 48%
Largest source of natural background
radiation
Medical background radiation
- Contributes 3.2 mSv
- Approximately 50% of total radiation dose
Pair Production
Does not occur with radiography
Linear-nonthreshold relationship
Indicates that no level of radiation can be considered completely safe
b.A response occurs at every dose
c.The degree of response to exposure is directly proportional to the amount of radiation received
Linear-threshold relationship
a.Indicates that at lower doses of radiation exposure (to the left of the line intersecting the x-axis), no response is expected
b.When the threshold dose is exceeded, the response is directly proportional to the dose received
c.As an example, cataractogenesis does not occur at low levels of radiation exposure; there is a threshold dose below which cataractogenesis does not occur
Nonlinear-threshold relationship
a.Indicates that at lower doses of radiation exposure (to the left of the curve intersecting the x-axis), no response is expected
b.When the threshold dose is exceeded, the response is not directly proportional to the dose received and is increasingly effective per unit dose
Nonlinear-nonthreshold relationship
Indicates that no level of radiation can be considered completely safe
b.A response occurs at every dose
c.The degree of the response is not directly proportional to the dose received
d.The effect is large even with a small increase in dose
Stochastic effects
Randomly occurring effects of radiation; the probability of such effects is proportional to the dose
Tissue reactions
Effects that become more severe at high levels of radiation exposure and do not occur below a certain threshold dose
