Week 7

Question 1

What are stochastic effects?

Answer 1

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)

Question 2

What happens in regards to cell mutations and the body’s defence mechanisms?

Answer 2

very likely that these mutations will be eliminated by the body’s defence mechanisms

Question 3

What the affecting parameters for stochastic effects?

Answer 3

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

Question 4

What is the percentage of deaths caused by cancer? (how does this relate to radiation?)

Answer 4

25% of deaths are due to cancer,

very few of these cancer deaths are caused by radiation

Question 5

Are radiation induced cancers distinguishable from other types of cancer?

Answer 5

no

Question 6

What sort of study shows statistics of radiation-induced cancer?

Answer 6

epidemiological studies

Question 7

What is the Lifespan Study? (LSS)

Answer 7

study of life-long health impact of radiation (e.g. atomic bomb survivors)

Question 8

Where do we get statistic of radiation-induced cancer from?

Answer 8

The Lifespan Study (LSS) (study of life-long health impact of radiation (e.g. atomic bomb survivors))
Radiation Patients
Occupationally expose group (uranium miners)

Question 9

are the cancer risks of low doses of ionising radiation clear?

Answer 9

no

Question 10

Which set of people provide the most accurate representation of LSS? (Lifespan Study)

Answer 10

the Hiroshima and Nagasaki people (largest group exposed to high dose exposure)

Question 11

What was the average dose in the LSS group?

Answer 11

200mSv with more than 50% receiving less than 50mSv

Question 12

How are risk estimates given?

Answer 12

in the number of cases expected if a million people were given 10mSv dose per year

Question 13

What is the Linear No Threshold (LNT)?

Answer 13

model that uses linear extrapolation and is based on the large amount of statistical data
-standard model for stochastic effects of exposure to radiation

Question 14

What is a hormetic relationship?

Answer 14

favourable biologic response to low doses of radiation exposure (hormesis) has been noted in some animal studies

Question 15

Based on the LNT model, at zero dose (0Gy) what is the chance that a person would get a radiation induced cancer?

Answer 15

zero, but as you increase the dose that person receives, the chance of getting a radiation induced cancer increases linearly

Question 16

What are the assumption of the linear no threshold (LNT) model?

Answer 16

• 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

Question 17

What is an uncertainty and scientific debate over the LNT?

Answer 17

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

Question 18

Cells are not passively affected by the accumulation of IR induced lesions, rather they react through which three mechanism?

Answer 18

• 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)

Question 19

In regards to the LNT model, what happens at low doses (<10mSv)?

Answer 19

lesions are eliminated by cell death

the probability of misrepair is smaller (because the more damage, the longer the cell repair process is)

Question 20

In regards to the LNT model, what happens at slightly higher doses (>10mSv)?

Answer 20

a significant number of cells may be damaged but repair mechanisms are activated (this allows cell survival but disrepair or irreversible lesions may occur)

Question 21

What dose range is the LNT model based on?

Answer 21

0.2Sv to 5Sv

Question 22

What types of radiation-induced cancer dose the LNT look at?

Answer 22

thyroid cancer
leukaemia
bone cancer
lung cancer
breast cancer

Question 23

For thyroid cancer where has data come from?

Answer 23

atomic bomb survivors
Marshall Islander (exposed to radioactive fallout following US nuclear testing 1046-1958)
therapy patients (children treated for enlarged thymus)

Question 24

Where does most of the information about Leukaemia by IR come from?

Answer 24

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

Question 25

Where does most of the information regarding induction of bone cancer by IR come from?

Answer 25

watch dial painters (female factory workers in 20th century who used radioactive paint (glow in the dark)

Question 26

Where does most of the information regarding induction of lung cancer by IR come from?

Answer 26

studies of uranium miners (in 1900s 50% of pitch pitchblende miners in Bohemia died from lung cancer)

Question 27

Where does most of the information regarding induction of breast cancer by IR come from?

Answer 27

patients treated with IR for postpartum mastitis
atomic bomb survivors
female patients in a Canadian sanatorium who received fluoroscopies for tuberculosis

Question 28

What is the total risk of death from exposure to IR?

Answer 28

500 per million of general population exposed to 10msV

Question 29

What is the risk estimate for radiation workers?

Answer 29

400 per million per year exposed to 10mSv

Question 30

What are the objectives of radiation protection in regards to deterministic and stochastic effects?

Answer 30

prevent deterministic

reduce the probability of stochastic effects