Radiation Biology 1 Flashcards
What are the 4 ways to measure the radiation dose?
Exposure dose
Absorbed dose
Equivalent dose
Effective dose
A measure of the capacity of radiation to ionize air
Exposure
-unit of radiation exposure that produces 2.08 x 109 ion pairs in 1.0 cc of air at standard temperature and pressure
Roentgen (R)
- To compare the biological effects of different types of radiation
- Radiation weighing factor (WR) depends on the type and energy of the radiation involved
Equivalent dose
Which 2 doses of radiation are usually equal in x rays?
Absorbed and Equivalent doses
-is a measure of the biological effectiveness of a radiation to ionize matter
Quality Factor(Q.F)
- This measure is used to specifically calculate risks of radiation to human tissues on a common scale.
- The calculation is a product of the sum of dose equivalence to the specific tissues or organs exposed and the biological tissue weighting factor.
Effective dose
- Use of the this allows comparisons of different imaging techniques to be made on a common scale.
- The value is an estimated measure of all somatic and genetic radiation-induced risk even if the entire body is not uniformly exposed.
Effective dose
______ is related to the maximum size of the beam
Area exposed
Used to assess risk of non-uniform radiation to localized part of body and degree to which this would increase a person’s “whole body” risk of
- cancer induction and/or
- induction of genetic mutations
Effective dose
What tissues have the highest weighting factor in the head and neck area?
Hematopoietic tissue
What is the standard unit (metric) for absorbed dose?
Gy
What is the standard unit (metric) for equivalent and effective dose?
Sv
Interactions of x radiation with matter
Ionization
X-ray photon enters object (eg. patient or other biologic tissues) and exits with no change in its energy
No interaction
______ interaction with xray matter:
•Accounts for 30% of all interactions•X-ray photon collides with an orbital electron and loses its energy•Ejected photoelectron loses it energy •Results in an atom with an altered electric state, i.e., “+” charge
Photoelectric effect
______ interaction with xray matter:
•The ionized matter is unstable and seeks a more stable configuration.
•The new configuration may include new ionic bonds, different covalent bonding, etc…
•If the degree of photoelectric effect is significant, this may affect, biologic structure, function or both.
•These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc.
Photoelectric effect
______ interaction with xray matter:
•accounts for 62% of interactions
•X-ray photon collides with an outer orbital electron losing some energy
•X-ray photon continues in different direction with less energy creating more scatter until all the energy is lost
•results in an atom with an altered electric state, i.e., “+” charge
•The ionized matter is unstable and seeks a more stable configuration.
•The new configuration may include new ionic bonds, different covalent bonding, etc…
•If the degree of photoelectric effect is significant, this may affect, biologic structure, function or both.
•These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…
Compton scatter
______ interaction with xray matter:
•accounts for 8% of all interactions
•X-ray photon of low energy interacts with an outer orbital electron and changes direction
•no photoelectron produced•no ionization occurs
Thompson scatter
Which 2 interactions with xray matter do not produce ionization and only excite electrons?
Thompson scatter and No interaction
_____ effect biologic injury
➢Directly ionizes biologic maromolecules
➢Contributes to 1/3 of biologic effects
Direct effect
_____ effect biologic injury
➢X-ray photons absorbed by H2O →free radicals →biologic damages
➢Contributes to 2/3 of biologic effects
Primary method of cell damage from radiolysis of water caused by x-radiation
Indirect effect
What are the 3 Outcomes of Direct Effect of UV Light on Skin DNA?
- Repair (healed)
- Inaccurate repair (mutation)
- No repair (death)
: a free atom or molecule carrying an unpaired orbital electron in the outer shell
Free radical
What do the free radicals from the indirect effect of radiations combine to produce?
Hydrogen peroxide
_____ dose curve:
•Small exposures do a substance do not produce measurable changes
•A threshold must be reached before changes are observed
•Most biologic effects are non-linear
Threshold nonlinear curve
_____ dose curve:
•Dose is proportional to the response
•No matter how small the dose, there is some damage or risk
Linear nonthreshold curve
_____ dose curve:
•No threshold
•Minimal damage at first with increased rate of damage with increased dose
Nonlinear non-threshold curve
_____ risk of radiation
•Have a threshold
•severity is proportional to the dose
•eg. ●Erythema ●xerostomia●cataract ●osteoradionecrosis●fertility ●fetal development●alopecia
Determinstic effect
Which risk of radiation is associated with cancer?
Stochastic effects
_____- risks of radiation
•Have no dose threshold
•Probability of occurrence is proportional to dose
•Severity of effects does not depend on dose
1.To somatic cells -genetic mutations cause malignancy
2.To germ cells -genetic mutations cause heritable
- any ionizing dose can produce cancer from diagnostic dental xrays
Stochastic effects
What are the only cancers that can be produced from diagnostic dental x rays?
Thyroid and Leukemia
\_\_\_\_ effects/ mutations –Somatic cells –all those except reproductive cells –Seen in the person irradiated –NOT transmitted to future generations •Induction of cancer, leukemia, cataracts
•Somatic effects/mutations
____ effects/ mutations
–NOT seen in the person irradiated
–Passed on to future generations
•Genetic effects/mutations
___ period of radiation damage:
•Time that elapses between exposure and appearance of clinical signs•May be short or long depending on:–Total dose–Dose rate•Shorter latent period if:–Increased amount of radiation–Faster dose rate•Genetic effects –may be generations before clinical effects are seen
Latent period
\_\_\_ period of radiation damage: •Cell death •Changes in cell function •Breaking or clumping of chromosomes •Giant cell formation •Cessation of mitotic activity •Abnormal mitotic activity
Period of injury
If you increase the total dose of radiation, how does this affect radiation damage to tissues?
Increases damage
If you increase the dose rate of radiation, how does this affect radiation damage to tissues?
Increases damage
If you increase the oxygen in the presence of radiation, how does this affect radiation damage to tissues?
If you increase the total dose of radiation, how does this affect radiation damage to tissues?
_____ –young, immature, rapidly growing and dividing, least specialized
Radiosensitive
–mature, specialized cells
Radioresistant
_____ age increases risk of damage from radiation:
•Rate of cellular and organ growth puts tissues at greatest level of radiosensitivity
•Greater life expectancy puts children at 2-10 greater risk of being afflicted with a radiation induced cancer
Younger age leads to greater risk of damage
