Biological Effects of Radiation Flashcards
(29 cards)
What is apoptosis?
Cell death (before division)
Cell recognises damage and undergoes programmed cell death which happens within a few hours of irradiation
What are the main 5 outcomes after a cell is irradiated?
- Complete cell repair (error free)
- Partial repair
- Apoptosis (tissue/organ reactions)
- Unable to divide (reproductive death)
- Cell mutation (stochastic events)
What is reproductive failure of a cell?
Cell dies during subsequent mitosis
What is genomic instability?
Cell passes on reproductive issues to daughter cells and are more prone to damage, passing on incorrect DNA
What are the nine outcomes after a cell is irradiated?
- No effect
- Division delay
- Apoptosis
- Reproductive failure
- Genomic instability
- Mutation
- Transformation
- Bystander effects
- Adaptive response
What is mutation and transformation?
Cell mutates (altered structure), if the mutation is potentially carcinogenic, it is a transformation
What is the bystander effect?
Irradiated cell induces genetic, radiation-induced, damage in nearby cells, despite not being irradiated themselves
What is adaptive response?
Irradiated cell is primed for more radiation damage and potentially more resistant due to repair mechanisms being awoken
What is indirect action (cell damage)?
Radiation interacts with molecules in cell (e.g. water)
Free radicals are produced (e.g. OH-) causing chain reactions until damage is caused to a critical cell structure (e.g. DNA)
~2/3 low LET (e.g. gamma, electrons) damage is indirect
What is direct action (cell damage)?
Damage to critical cell structure
Dominant in high LET interactions (e.g. alpha)
How does radiation cause cell damage?
Ionising radiation is capable of ejecting atomic electrons
Electron causes further ionisation or free radical creation in the cell
Can be direct or indirect action
What is LET?
Linear energy transfer
Average energy, E, imparted to the medium by a charged particle, traversing a distance, x
dE/dx
What is a cell survival curve?
Fraction of cells that maintain reproductive integrity as a function of irradiated dose
High LET - linear
Low LET - linear quadratic
Limitation - studies done on cells not organs - doesn’t account for complex organ systems e.g oxygen supply
What are deterministic effects?
Threshold to the amount of radiation received before effects are observed, i.e. there is a safe ‘threshold’ before effects are definitely seen
Severity of the effect then depends on the amount of dose received
What causes deterministic effects?
Typically caused by cell death - organs can function with minimal impact until a certain quantity of cells are damaged, effect is then seen
What is an example of a deterministic effect?
- Erythema
- Cataracts
- Hairloss
- Sterility
When are deterministic effects typically seen after irradiation?
Hours to weeks after irradiation, up to months to years
What are stochastic effects?
Chance of developing condition is related to the quantity of dose received (i.e. cancer only needs one out of control mutation)
Severity of the effect is independent of dose received
What is an example of a stochastic effect?
Cancer
What is the cancer risk per Sv?
~5%/Sv
But in reality it depends of sex, age, dose distribution, genetics, lifestyle
What EAR?
Excess absolute risk
The absolute difference in risk between two populations (e.g. irradiated vs not irradiated)
Expressed per 10^4 person-years per Gy (or Sv) (for every Gy a population is irradiated, 1 cancer is observed for every 1000 people per year)
What is RR/ERR?
(Excess) Relative risk
The increased probability of seeing that event occur compared to another population
ERR = RR - 1
Expressed as fraction or % per Gy (or Sv)
For example, if we observed 75 events in a population of 100 and 25 events in the equivalent control population, the RR is 3 and the ERR is 2
Where does cancer risk data for irradiation come from?
Atomic bombs and tests
Radiotherapy applications
Early radiology
Radium workers
Uranium miners
Classified workers
Nuclear accidents
What is the linear no threshold model?
Assumes there is no safe level of radiation, just reduced likelihood
