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Principles of Patient Management > Radiation protection > Flashcards

Radiation protection Flashcards

1
Q

Means of expressing dose

A

Radiation energy deposited in unit mass of tissue
-absorbed dose (Gray, Gy)(1Gy = 1J/kg)
Absorbed dose weighted for harmfulness of different radiations
-dose equivalent (Sievert, Sv)
Dose equivalent weighted for radiation susceptibility of different tissues. Mainly a measure of risk, rather than a physical dose
-Effective Dose (Sievert, Sv)

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2
Q

Tissue weighting factors: bone marrow, breast, colon, lung, stomach

A

0.12

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3
Q

Tissue weighting factors: bladder, oesophagus, gonads, liver, thyroid

A

0.05

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4
Q

Tissue weighting factors: bone surface, brain, kidneys, salivary glands, skin

A

0.01

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5
Q

Tissue weighting factors: remainder tissues

A

0.10

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6
Q

Summed total tissue weighting factors

A

1 = Whole body effective dose

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7
Q

Where does radiation come from?

A

14.3% medical
13.5% gamma from ground and buildings
11.6% internal (food)
10% cosmic
50.1% radon
0.5% other sources
(85% natural sources, 15% man-made)

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8
Q

Average annual UK background dose

A

2.5mSv

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9
Q

How can radiation affect DNA?

A

Directly: secondary electron breaks DNA strand
Indirectly: e- leaves trail of water molecules behind, highly reactive OH* free-radicals created in this way very damaging

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10
Q

Why is radiation so dangerous

A

Instantaneous whole body dose of 4Sv could potentially be fatal
!!!

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11
Q

Low risk

A

1 strand damage

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12
Q

High risk

A

Both strand breaks (more from indirect)

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13
Q

Consequences of DNA mutation

A

Mutation repaired –> viable cell
Cell death –> unviable cell
Cell survives but mutated –> cancer?

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14
Q

Cancer

A

Development of cancer has several stages, can take year
Cells not helpless, can repair DNA to some extent
Even in absence of radiation, each cell in body sustains 5-10000 DNA damage events an hour from constant onslaught of free radicals produced as by-product of reactions within cell

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15
Q

Two types of effect:

A

Deterministic and stochastic

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16
Q

Deterministic effect

A

Direct consequence of dose above minimum threshold, > in severity with dose
Threshold specific to tissue
Threshold normally of order of few Gy
LOOK AT GRAPH

17
Q

Stochastic effect

A

> in likelihood but not severity with > dose, with no minimum threshold
Severity is indipendent of dose
e.g. induction of cancer, where extremely low doses involve > risk of cancer. As dose > severity of individual malignancies does not >, but probability that larger proportion of exposed population may develop malignancy
LOOK AT GRAPH

18
Q

Who is affected?

A

Somatic effects are those occurring in individual as result of exposure to dose of radiation
Genetic effects are those which arise in offspring of individual exposed to dose of radiation

19
Q

Thresholds for deterministic effects: whole body exposure

A 
Detectable chromosome damage >0.1Sv
Detectable blood count change >1Sv
Radiation sickness >1
Possible death >3Sv
Certain death >10Sv
20
Q

Dental radiography risks

A

Intraoral/ periapical 2-10 μSv, cancer risk 0.06-0.7 per million exposure
CT Mandible 480-3300 μSv, cancer risk 24-242 per million exposures

21
Q

Levels of risk for common X-ray exams

A

Negligible risk (< 1 in 1,000,000): a few days of background radiation
-chest, teeth, arms and legs, hands and feet
Minimal (1 in 1,000,000 to 1 in 100,000): a few weeks
-skull, head, neck
Very low risk (1 in 100,000 to 1 in 10,000): few months to a year
-breast, hip, spine, abdomen, pelvis, CT scan of head
Low risk (1 in 10,000 to 1,000): a few years
-kidneys and bladder, stomach, colon, CT of chest, CT of abdomen

22
Q

Frequency of dental radiographs in UK

A

~20M radiographs in GDP

~3< panoramic (OPT) radiographs

23
Q

Three golden rules of radiation protection

A

Time
Distance
Shielfing

24
Q

Time

A

The longer you spend near a source of radiation, the higher your dose
Minimise the exposure time
LOOK AT GRAPH

25
Q

Distance

A

As you move away from source, the dose rate decreases rapidly according to inverse square law
Twice the distance = quarter the dose
LOOK AT GRAPH

26
Q

Shielding

A

Where possible use shielding, it attenuates the radiation, reducing the dose
Attenuation proportional to density
Might not make your job easier but it is there for your safety
Includes lead screens, aprons

27
Q

Room shielding

A

Normally room shielding specified by radiation protection advisor before build takes place
They will deicde how thick walls should be and what they should be made of and how much lead in foor
On existing builds where additional shielding needed, wall can be re-plastered in barium plaster or lead panels can be affixed

28
Q

Staff protection

A 
Dose limits (annual)
-6mSv to whole body
-50mSv to lens of eye
-150mSv to skin/ extremities
Scatter
PPE
Controlled areas
29
Q

How to keep staff protected

A

Training
-don’t do what you haven’t been trained to
Risk assessment-do risk assessment before starting new work with radiation
Local rules (RPS)
-read and understand them
Dose badges

30
Q

Patient protection

A

No legal dose limits for pxs but benefits must justify risk
Still expectation that doses will not be ‘much greater than intended’
DRLs (diagnostic reference levels) guidelines for px dose
Exposures must be optimised

31
Q

How to optimise px protection: choose appropriate factors

A

Filtration
kV
-high energy xray photons more penetrating so needed for thicker pxs but will reduce image contrast
mA
-> current > number of photons, > dose and improving image contrast
FSD (focus-to-skin distance)
-closer the focus to px the less xrays are scattered so higher the dose but image less noisy
Collimation
-defines beam size, must be no more than 6cm diameter

32
Q

Filtration

A

Gets rid of low energy x-rays that would get through px
1. spectrum with no filtration
2. spectrum through tube housing (inherent filtration)
3. Additional filtration
LOOK AT GRAPH

33
Q

Public protection

A 
IRR99 Dose Limits (annual)
-1mSv whole body
-15mSv to lens of eye
-50mSv to skin/ extremities
-HPA recommends 0.3mSv whole body
Room shielding (materials)
Warning lights/ notices
34
Q

People who can help

A

Radiation protection adviser
-will need one if you set up your own practice
Radiation protection supervisor
-RPS local to where x-rays being used
-make sure local rules are followed
Medical physic expert
-assist with optimisation - set exposure parameters to give best images to lowest dose
-may be same person as RPA, but separate responsibilities

35
Q

Thresholds for deterministic effects: localised exposures

A

Erythema >5Sv
Depilation temporary >4Sv
Permanent Depilation >7Sv
Desquamation >20Sv

Principles of Patient Management (15 decks)

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