Radiation Safety Flashcards
KERMA
Kinetic energy released per unit mass
The initial large energy transfer involving one atom
Use for radiation with no charge (photos and neutrons)
Kerma K =
Kinetic energy of all charged particles liberated by protons in a small mass, m
1Gy = 1JKg-1
Dose =
Many small energy deposits involving many atoms along the electron track
Energy absorbed from a beam of radiation per unit mass up to material
1Gy = 1JKg-1
Difference between KERMA and absorbed dose is
Electron energy converted to bremsstrahlung radiation
K >D
Organ dose (DT) =
Average absorbed dose or energy over mass of organ
Equivalent dose =
Radiation factors applied to organ dose
Factors the damaging effects of radiation on tissue
More charge = Higher radiation weighting factor
Sv = 1JKg^-1
Radiation waiting factor depends on
Ionisation density tissue produced by the radiation
More charge or mass = ? radiation weighting factor
More charge or mass = Higher radiation weighting facto
XRs, gamma and electrons Wr =1
Protons = 2
Alpha particles = 20
Neutrons = 5-20 depending on energy
Effective dose =
Tissue weighting factors applied to effective dose
W(T) Factors the tissue radiation sensitivity
Also, how easily treatable the radiation harm is
Effective dose =
Gives information on overall risk of stochastic effects
Can be used to compare risk from different types of exposures
Ionising radiation interaction with tissue
Free radicals = chemical damage
Molecular changes = DNA or RNA damage
Sub-cellular and cellular changes =
- tissue effects such as cell death
- Cellular transformation (stochastic effect)
Free radical production
Ionisation of water:
H20 and radiation -> H20+ + e-
H20+ -> H+ + OH
OH is chemically damaging
Tissues at risk
Actively dividing:
Bone marrow
Gonadal germ cells
Intestinal epithelium
Skin
Tissue reactions or deterministic effects
Radiation-induced cell death
Does not occur below the threshold dose = 1% incidence
Threshold doses for acute exposures
Deterministic effects of foetal radiation
Stochastic effects
The increased probability of an effect occurring depending on dose
Due to cell mismatch or modification
Linear response with N threshold dose
Stochastic effect late period
Effect not seen until many years after the exposure
Radiation-induced carcinoma and genetic effects
ALARP = As low as reasonably practical
Risk Factors (ICRP 103)
Baseline adult risk of cancer = 1 in 3
Risk of radiation-induced cancer mortality
1 in 20,000 per mSV
(Across all ages and sexes)
Risk of radiation-induced severe hereditary effects
1 in 500,000 per mSV
(Across all ages and sexes)
Total Detriment
1 in 17,000
Stochastic effect of fetal radiation
Risk of childhood cancer induced by radiation exposure = 1 in 10,000 per mGy
Baseline risk of childhood cancer = 1 in 500
Dose for medical exposures
Typical Doses
Max potential for foetal abnormalities received during pregnancy weeks 3 - 8.
TRUE. Potential for the following foetal abnormalities is max if received during Weeks 3 - 8.
Mental retardation if max radiation during pregnancy weeks 8 - 15
TRUE. Mental retardation if max radiation during pregnancy weeks 8 - 15
Max potential for foetal death if max radiation given during 1st Trimester.
TRUE. Max potential for foeetal death if max radiation given during 1st Trimester.
The risk of fatal cancer from a uniform whole body irradiation is 5% or 1:20,000
