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Flashcards in radiation protection Deck (15)
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1

how to express dose

absorbed dose
dose equivalent
effective dose

2

absorbed dose

radiation energy deposited in a unit mass of tissue

3

dose equivalent

absorbed dose weighed for harmfulness of different radiations

4

effective dose

dose equivalent weighted for radiation susceptibility of different tissues
(measure of risk, rather than a physical dose)

5

weighting factors

different parts of the body have different weighting factors

6

how does radiation affect DNA

1) Directly
- secondary electron breaks a DNA strand
2) Indirectly
- the electron leaves a trail of ionised water molecules behind the highly reactive OH free radicals created in this way are very damaging
- more frequent than direct

7

types of effect

1) Deterministic
- direct consequence of a dose above a minimum threshold, increasing in severity with dose
2) Stochastic
- increase likelihood but not severity with increasing dose, with no minimum threshold

8

somatic effects

- those occurring in the inviduial as a result of exposure to a dose of radiation

9

genetic effects

- those which arise in the offspring of an individual exposed to a dose of radiation

10

stochastic effects

Stochastic effects have no threshold but the probability of radiation induced effect increases with dose
Severity is independent of dose
- linear no threshold approach

11

factors to reduce an x ray dose

1) time
2) distance
3) shielding

12

time

- longer you spend near a source of radiation higher the dose
- minimise the exposure time

13

distance

- as you move away from the source the dose rate decreases rapidly according to the inverse square law
- Twise the distance – quarter the dose

14

sheilding

- where shieling is used, it attenuates the radiation reducing the dose
- attenuation is proportional to density

15

chose appropriate radiation factors

1) Filtration
2) kV
- High energy x-ray photons are more penetrating so are needed for thicker patients but will reduce image contrast
3) mA
- Increased current increases the number of photons, increasing the dose and improving image contrast
4) FSD (focus-to-skin distance)
- The closer the focus is to the patient the less the x-rays are scattered so the higher the dose but the image is less noisy
- normally fixed dependant on the collimator
5) Collimation
- Defines beam size. Must be no more than 6cm diameter
- Rectangular collimation will reduce dose