5. Radiation Biology, Safety & Protection Flashcards
What is the law of bergonie and tribondeau?
Most sensitive cells are those that are
1. Undifferentiated
2. Have high metabolic activity
3. Have high mitotic rate/high proliferation
4. Have a long dividing future (young tissues)
-> why children are more susceptible to radiation mutation than adults
List the low dose effects
- Cancer
- Heritable effects
- Effects on embryo/fetus (in utero)
=> primarily stochastic (random)
List the high dose effects
- Cell killing
- Tissue/organ effects
- Whole body effects
-> primarily determistic
Stochastic effects are..
- No threshold dose
- Severity is independent of dose
- all or none response - Random: Risk (probability) of effect is proportional to dose
Deterministic effects are..
- There is a threshold dose
- Severity is proportional to dose
- Risk (probability) of effect is independent of dose
- as long as threshold is met, effect occurs
E.g. sunburn, in-utero birth defects, radiation cataracts, radiation mucosistis, late tissue fibrosis
What is the primary concern in dental radiography?
Radiation-induced cancer
- a low dose effect, stochastic
What is the Linear Non-threshold Model?
‘Linear’ - linear rs between exposure & cancer risk
‘No threshold’ - risk is present at any exposure level
- a dose-response model used in radiation protection to estimate stochastic health effects
How is the LNT model derived?
- from historical events
- extrapolation to zero exposure for low doses
What is ALARA?
As Low As Reasonably Achievable
- risk of cancer is present at any radiation dose, no matter how low the dose is
- there is no ‘safe’ threshold
- higher the dose, the higher the risk
What is the excess relative risk of cancer for the entire population? (Based on ICRP)
5.5% per Sv
Can dental radiographs cause heritable effects?
TLDR: no statistically significant increase in genetically related disesase in the children of atomic bomb survivors
- cuz theoretically, mutations in germ cells can be passed on to the future
- but this has not been seen in human populations from past events
What is the dose threshold to fetus to produce xray induced birth defects?
100-250mSv (milli)
- but dental radiation doses are in microsieverts
- many thousand times lower than damaging doses
- neither primary dose nor scatter dose to fetus can produce birth defects
What are the principles of radiation protection?
- Principle of justification - potential benefit > potential risks of xray?
- Principle of optimization (ALARA) - minimise doses to px
- Dose limitation (more for working staff, there is no dose limitation for px) - but if px has exceeded recc doses, can try to use a lower procedure
List the 10 measures to reducing dental xray exposure to pxs.
- Px selection criteria (clinical examination, see if xray is beneficial to px)
- Film & digital imaging (digital smaller doses) (faster speed film -> less dose)
- Focal source to skin distance (length of collimator)
- Filtration (remove low energy photons)
- Rectangular collimation (reduce dose by 5x + reduced scatter=better contrast)
- Film n sensor holders (better alignment = less failed takes)
- Leaded aprons & thyroid collars
- Use of technique charts/protocols (optimized exposure)
- Exposure time (mAs) (mAs is directly correlated to dose. Also for pdn of image of adequate diagnostic quality)
- Operating potential (kVp) (in reality we dont touch this, unless u wanna change the contrast)
[T/F] you can prevent stochastic effects
False
- a wording issue
- can prevent deterministic effects
- only can reduce the probability of stochastic effects
