Outcome 3 Flashcards
What are the five biological effects caused by radiation exposure?
- Genetic changes
- Growth increase or decrease
- Somatic change
- Lifespan change
- Carcinogenic growth
What are the three factors that impact the nature and severity of the biological damages?
- Quantity and nature of radiation
- Portion of body involved
- Rate of exposure
What are radiation effects in cells?
- They repair
- Repair incorrectly
- They die
What is the unit to describe quality of radiation? What is it measuring?
Bq; the amount of radioactivity
What is the relationship between the value of radioactivity and its ability to cause biological damage?
The higher the Bq dose, the higher the probability for creating bio damage
What is the nature of radiation?
It is the type of radiation. Whether it’s a particulate or non-particulate.
What is WB?
Whole body - radiation exposure is to the head, trunk, blood forming organs and gonads.
What is PE?
Partial exposure - only an extremity is exposed to radiation
How is dose rate calculated?
Dose/unit of time
What is an acute exposure?
High dose/SHORT time
What is a chronic exposure?
Low dose/LONG time
What is dose fractionation?
It is when you divide up the therapy dose into several treatments
What is the difference between stochastic and deterministic effects?
Stochastic (cancer) - effects that occur by chance and without a threshold level of dose of radiation, probability is proportional to the dose and it’s severity is not due to the dosage
Deterministic - has a known outcome; there is a threshold dose and severity of effects increases with dosage
What does ACTIVITY refer to?
It is the decay per second (by either the rearrangement of the nucleon or n—>p)
How is ACTIVITY measured? SI units? Common unit?
SI: Bq
Common: Ci
1 Bq = 2.7 x 10^-11 Ci
1 Ci = 3.7 x 10^10 Bq
1 mCi = 37 MBq
What does EXPOSURE mean?
It only applies to photons. It measures the charged ions created in air by radiation.
How is EXPOSURE measured? SI units? Common units?
SI: coulomb per kg (C/kg)
Common unit: roentgen (R)
1 C/kg = 3880 R
1 R = 2.58 x 10^-4 C/kg
What does ABSORBED DOSE mean?
It is the energy imparted by ionizing radiation in any matter that isn’t human tissue (per unit mass)
How is ABSORBED DOSE measured? si units? Common units?
SI: Gy (1 J/kg)
Common: rad (ergs/g)
1 Gy = 100 rad
1 rad = 0.01 Gy
What does DOSE EQUIVALENT mean?
It is the absorbed dose in humans!
How is DOSE EQUIVALENT measured? Si units? Common?
SI: Sv (J/kg)
Common: rem (Gy x weighting factors)
1 Sv = 100 rem
1 rem = 0.01 Sv
Eo = ?
exposure dose
- amount of energy delivered to an object
Ea = ?
Absorbed dose
- energy dissipated in object
Es = ?
Scatter
- energy only partially absorbed
Et = ?
Transmitted
- energy undergoes no interactions
Eo is directly proportional to Ea. T/F
True
What are factors that affect exposure dose?
- amount of activity in the source
- decay energy of the radionuclide
- source to object DISTANCE
- object surface area
- absorber between the source and object
What are factors that affect the absorbed dose?
- same factors that affect Eo
additionally: - nature or type of radiation - density and atomic number or irradiated objects
What does the Equivalent Dose account for?
the differences in biological damaging potential of various types of radiation
What is the formula for equivalent dose?
Htr = Dtr x Wr
Dtr [Gy]- average absorbed dose received by tissue (t) from radiation (r)
Wr = radiation weighting factor
Htr [Sv]
What is the radiation weighting factor (Wr) for gamma/x-rays/photons?
Wr = 1
What is the radiation weighting factor (Wr) for beta particles?
Wr = 1
What is the radiation weighting factor (Wr) for alpha particles?
Wr = 20
How is effective dose calculated?
It is the sum of all equivalent doses received by an organ x the tissue weighting factor
What is the effective dose formula?
E = sum(Htr x Wt)
E [Sv]
Htr [Sv]
What does tissue weighting factor tell us?
It is looking for the biological damage to specific tissues. The higher the weighting factor, the more sensitive it is.
It is based in comparison to damage to whole body doses.
What is the relationship between exposure and time?
time of exposure is directly proportional to exposure dose
(ie. 18 uSv/h if you cut the time to half, the dose will be half too)
What is the relationship between distance and exposure?
It is an inverse square law.
ex. if you double your distance, you decrease your dose by a rate by 4
What is the most effective means of protection (mathematically)?
Distance.
What is HVL?
Half value layer - thickness of any shielding material to reduce the intensity of the radiation by 50%
What is TVL?
Tenth value layer - thickness of any material necessary to reduce the original intensity to 1/10 (10%)
What is the formula for exposure rate?
exposure rate = ERC x A/d2
ERC - (exposure rate constant)
A - activity (Bq = 1 dps)
d = distance
What is the formula for time?
I = I0 x t
I - intensity of dose or dose rate after T
I0 - original intensity
t = time
What is the formula for distance?
I1/I2 = (d2/d1)^2
I1 - given intensity
I2 - asked intensity
d2 - asked distance
d1 - given distance
What is the formula for shielding?
HVL? TVL?
I = I0e^-ux
HVL = I = I0/2^n
TVL = I = I0/10^n
_____ ______ = radiobiology
_____ ______ = radiation protection
Biological effects = radiobiology
Radiation protection = stochastic or deterministic
What is stochastic effect?
Effects that occur by CHANCE and may occur without a threshold level of dose of radiation
- probability is proportional to the dose
- severity is independent to dose
Cancer.
What is deterministic effects?
Health effects
Severity varies with dose and the threshold is believed to exist
- generally resulted from high dose over a short time
