Week 7 Flashcards
What are stochastic effects?
as dose increases the probability that a stochastic effect will result, increases
- there is no dose threshold
- random in nature, and show up as cell mutations (not cell death)
What happens in regards to cell mutations and the body’s defence mechanisms?
very likely that these mutations will be eliminated by the body’s defence mechanisms
What the affecting parameters for stochastic effects?
dose: stochastic effects are applicable at all dose levels
Number of affected cells: the mores the greater the chance of one survive
health status of patient
What is the percentage of deaths caused by cancer? (how does this relate to radiation?)
25% of deaths are due to cancer,
very few of these cancer deaths are caused by radiation
Are radiation induced cancers distinguishable from other types of cancer?
no
What sort of study shows statistics of radiation-induced cancer?
epidemiological studies
What is the Lifespan Study? (LSS)
study of life-long health impact of radiation (e.g. atomic bomb survivors)
Where do we get statistic of radiation-induced cancer from?
The Lifespan Study (LSS) (study of life-long health impact of radiation (e.g. atomic bomb survivors))
Radiation Patients
Occupationally expose group (uranium miners)
are the cancer risks of low doses of ionising radiation clear?
no
Which set of people provide the most accurate representation of LSS? (Lifespan Study)
the Hiroshima and Nagasaki people (largest group exposed to high dose exposure)
What was the average dose in the LSS group?
200mSv with more than 50% receiving less than 50mSv
How are risk estimates given?
in the number of cases expected if a million people were given 10mSv dose per year
What is the Linear No Threshold (LNT)?
model that uses linear extrapolation and is based on the large amount of statistical data
-standard model for stochastic effects of exposure to radiation
What is a hormetic relationship?
favourable biologic response to low doses of radiation exposure (hormesis) has been noted in some animal studies
Based on the LNT model, at zero dose (0Gy) what is the chance that a person would get a radiation induced cancer?
zero, but as you increase the dose that person receives, the chance of getting a radiation induced cancer increases linearly
What are the assumption of the linear no threshold (LNT) model?
- constant probability of mutation of a cell per unit pose (i.e. any radiation dose is potentially harmful)
- radiation damage is not repairable
- the probability of biologic damage has a linear relationship with the absorbed dose
What is an uncertainty and scientific debate over the LNT?
the LNT requires extrapolation between 0.2Sv and 5Sv, which can have many uncertainties
- dose received in MI is lower (0.1mSv to 20mSv)
- RT dose exposure may depend on background radiation
- all studies in the dose rang <100mSv have failed to detect any statistically significant risks for the carcinogenic effect
Cells are not passively affected by the accumulation of IR induced lesions, rather they react through which three mechanism?
- by fighting against reactive oxygen species
- by eliminating injured cells (mutated or unstable) through apoptosis
- by stimulating DNA repair mechanisms (occurs at doses slightly above 10mSv)
In regards to the LNT model, what happens at low doses (<10mSv)?
lesions are eliminated by cell death
the probability of misrepair is smaller (because the more damage, the longer the cell repair process is)
In regards to the LNT model, what happens at slightly higher doses (>10mSv)?
a significant number of cells may be damaged but repair mechanisms are activated (this allows cell survival but disrepair or irreversible lesions may occur)
What dose range is the LNT model based on?
0.2Sv to 5Sv
What types of radiation-induced cancer dose the LNT look at?
thyroid cancer leukaemia bone cancer lung cancer breast cancer
For thyroid cancer where has data come from?
atomic bomb survivors Marshall Islander (exposed to radioactive fallout following US nuclear testing 1046-1958) therapy patients (children treated for enlarged thymus)
Where does most of the information about Leukaemia by IR come from?
survivors of atomic bombing in Hiroshima and Nagasaki
-those treated with IR for ankylosing spondylitis, hyperthyroidism
HOWEVER: a similar increase was noted in patients who had the thyroid removed
