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Physics for FRCR CO1 > 4.11 Radiation Protection > Flashcards

4.11 Radiation Protection Flashcards

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1
Q

What are the 3 mainstays of radiation protection?

A
  1. Time
  2. Distance
  3. Shielding
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2
Q

How does time contribute to radiation safety?

A

Work with radiaition should be done as quickly as is safe

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3
Q

How does distance contribute to radiation safety?

A

Inverse square law principles
Maze - at least two corners

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4
Q

How does sheilding contribute to radiation safety?

A

Correct shield and thickness for type of radiation
e.g. thick walls, screens

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5
Q

What is the most common source of background radiation in the UK?

A

Radon gas

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6
Q

What is the average background exposure to radiation in the UK?

A

2.2mSv

cornwall 7.5 mSv/year
CT chest 8mSv
200mSv atomic bomb

1000mSv = 1Sv = 1 Gy

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7
Q

What are the deterministic effects of radiation exposure?

A
  • aka ‘Harmful tissue reactions’
  • Short term acute damage
  • This is caused by radiation inducing cell death (not all cell deaths are therapuetic)
  • This occurs after a certain threshold dose
  • Severity increases with dose
  • Severity increases with dose rate
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8
Q

What are the threshold doses for certain deterministic effects?

A

Skin erythema - 6Gy in one dose or 30Gy hyperfractionated

Hair loss - 3-5Gy or 50-60Gy in fractions

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9
Q

What are stochastic radiation effects?

A
  • Long-term damage
  • Future cancers
  • Hereditary defects if reproduction cells
  • No threshold doses
  • Probability increases linearly with dose
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10
Q

What does Equivalent dose measure?

A

Damage by radiation type using a radiation weighting factor

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11
Q

What is the weighting factor in equivalent dose?

A

Radiation weighting factor
Wr

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12
Q

What is the equation for Equivalent Dose?

A

Ht

Ht = absorbed dose (D) x radiation weighting factor Wr

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13
Q

What are the radiation weighting factors for different types of radiation?

A

1 for photons, x-rays, electrons, beta particles, gamma rays
20 for alpha particles
5-20 for neutrons (depending on their energies)

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14
Q

What units is Equivalent dose measured in?

A

Sievert

For most medical applications these are numerically equivalent to Gy

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15
Q

What does Effective dose (E) measure?

A

A dose measurement accouting for the type of radiation (Ht) and the sensitivity of exposed tissue (Wt)

Tissue radiosenstivity, stochastic risk

Assess the risk from the exposure to ionising radiation - liklihood of develoing a radiation idncued cancer or hereditary defect

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16
Q

What is the equation for Effective dose?

A

E = equivalent dose (Ht) x Tissue weighting factor (Wt)

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17
Q

What are the tissue weighting factors for different tissues?

A

The lower the weighting factor the less sensitive to radiation damage

1 = Whole body total
0.12 = red bone marrow, lungs, breast, stomach, colon
0.08 = gonads
0.04 = thyroid, oesophagus, liver, bladder
0.01 = brain, salivary glands, skin, bone surface

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18
Q

What is the weighting factor in Effective dose?

A

Tissue weighting factor (Wt)

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19
Q

What does IRR17 stand for?

A

Ionising Radiation Regulations?

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20
Q

Who is IRR17 enforced by?

A

HSE (Health and Safety at Work Act)

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21
Q

Who does IRR17 protect?

A
  1. Staff working with radiation
  2. The general public
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22
Q

What are the roles identified by IRR17?

A

Employer - holds legal responsiiblity for compliance - e.g. hospital ceo

Radation Protection Advisor (RPA) - Advises the employer e.g. senior physicist. They are registered and meet competency requirements.

Radation Protection Supervisor (RPS) - Ensure compiance with local rules e.g. senior radiographer

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23
Q

What does IRR17 cover?

A
  1. Workers - those who re occupationally exposed - must be trained in risks to health. Foetus in utero is member of public.
  2. Areas - identify supervised and controlled areas
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24
Q

What is ALARP?

A

As Low As Reasonably Practical

This accepts that at a certain point increasing protection against radiation stops being practicle or cost effective

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25
Q

What is ALARA?

A

As Low As Reasonably Acheivable

this does not consider practicalities/cost

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26
Q

What are the 9 key aspects of IRR17?

A
  1. Risk assessment
  2. Dose limits - set for workers, trainees, public
  3. Appoint RPA/RPS
  4. Controlled/supervised areas - designate areas based on exposure levels and ensure appropriate signage and safety features
  5. Personal dosimetry - monitor and record radiation doses reveived by employees and investigate if abnormal
  6. Provide training
  7. Report incidents - to HSE
  8. HSE approval for using radiation
  9. Medical surveillance - provide health monitoring for workers at risk
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27
Q

What is an Occupationally exposed worker in IRR17?

A

Anyone who works with radiation

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28
Q

What is a classified worker in IRR17?

A

Likely to receive >30% dose limit (>6mSv per year)

They require annual check up and individual dose monitoring

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29
Q

What is a supervised area in IRR17?

A

An area near the bunker likely to exceed public dose limits
>1 but <6 mSv per year

e.g. treatment control room

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30
Q

What is a controlled area in IRR17?

A

An area that has the potential to receive >6mSv per year, >15 to eye lens, 150 to skin/extremities

e.g. x-ray room, linac room

These require barriers, entry procedures, shielding, interlocks

31
Q

What is the ALARP Hierarchy of Controls?

A

From most to least effective:
1. Elimination - remove hasard
2. Substitution - use a lower risk option e.g. scan type
3. Engineering - isolate e.g. bunkers, interlocks, last one out button
4. Administration - local rules and policies
5. PPE - e.g. lead aprons

32
Q

What types of monitors can be used to monitor worker radiation exposures?

A
  1. Whole body
  2. Ring - for doses to hands
  3. Lens monitors - worn around head for dose to eye lens
33
Q

What types of whole body monitors are used to monitor worker radiation exposures?

A
  1. Thermoluminescent badges
  2. EPD - silicon - real time results can have alarms but no permanent records

These are worn on one part of the body but approximate dose to whole body. Worn under any PPE. Exchanged 1-2 months.
Invesitgate unusual results.

34
Q

What is the IRR17 threshold Effective dose to body and Equivalent doses to eye lens and skin/extremeties per year (mSv) to general public and pregnant women?

A

Body: 1

lens/extemities N/A

35
Q

What is the IRR17 threshold Effective dose to body and Equivalent doses to eye lens and skin/extremeties per year (mSv) to non-classified worker? e.g. a trainee <18years

A

Whole body: 6mSv

Lens: 15
Skin: 150

36
Q

What is the IRR17 threshold Effective dose to body and Equivalent doses to eye lens and skin/extremeties (over 1cm3) per year (mSv) to classified worker?

A

Whole body: 20 mSv

lens 20, skin 500

37
Q

What is the IRR17 threshold Effective dose to body and Equivalent doses to eye lens and skin/extremeties per year (mSv) to Supervised areas?

A

whole body >1
lens >5
skin >50

38
Q

What is the IRR17 threshold Effective dose to body and Equivalent doses to eye lens and skin/extremeties per year (mSv) to Controlled areas?

A

whole body >6
lens >15
skin/extrem >150

39
Q

What is IR(ME)R 2017?

A

Ionising Radition Medical Exposure

40
Q

Who is IR(ME)R 2017 enforced by?

A

CQC

41
Q

Who does IR(ME)R 2017 protect?

A

Patients - from unintended, excessive, or incorrect medical exposure

42
Q

What are the identified roles in IR(ME)R?

A
  1. Employer - overall repsonsibility and appoints MPE
  2. Medical Physics Expert
  3. Referrer
  4. Practitioner
  5. Operator
43
Q

What is the role of the MPE (Medical Physics Expert)?

A

Ensures employer understands requirements for complaince with the law
Advises on:
* Dosimetry
* Dose measurement
* Optimisation
* QA
* New equipmet installation and design

44
Q

What is the role of the Referrer in IR(ME)R 2017?

A

Person who identified patient who needs RT and refers patient to have an exposure.
Should provide relevant data about the patient e.g. LMP, breastfeeding

Usually consultant radiographer or oncologist

45
Q

What is the role of the Practitioner in IR(ME)R?

A

Person who justfiies and authorises exposure e.g. clinical oncologist or consultant radiphrapher

Requests localisation CT, prescribes RT dose, plans target volumes

46
Q

What is the role of the Operator in IR(ME)R?

A

Undertakes practical tasks relating to radiotherapy and imaging

e.g. physicist, radiographer

They would;
- consent patient
- define PTV
- Define and check plan and authorise
- Deliver RT
- Check patient ID
- Do quality assurance/control checks

47
Q

What does SAUE stand for? (IR(ME)R)

A

Significant Accidental or Unintentioned Exposure

48
Q

What are reportable doses under SAUE?

A

Anything ‘clinically signficiant’ which is determined by a threshold

49
Q

What is the notification threshold for all radiation modalities?

A

Adult >3mSv
Child >1mSv

50
Q

What is the notification threshold for all CT radiation planning?

A

If CT needs repeating twice (3 CTs in total)

51
Q

What is the notification threshold for RT verification images?

A

> 3 exposures per fraction
or 20% greater than intended over whole course

52
Q

What is the SAUE definition of over-exposure?

A

> 110% over whole course (including single fraction courses)
or
20% for any fraction

53
Q

What is the SAUE definition of under-exposure?

A

<90% over whole course

54
Q

What is a total geographical miss (SAUE)?

A

Complete miss of target volume
ALL notifiable

55
Q

What is a partial geogrpahical miss?

A

> 2.5x locally defined error margin for PTV or OAR

56
Q

What if the overdose is due to equipment failure?

A

Report to HSE rather than CQC

57
Q

What is meant by Accidental exposure?

A

Someone has been exposed when no exposure was intended e.g. wrong patient scanned

58
Q

What is meant by Unintended exposure?

A

Person was supposed to have exposure but what they got was different from what was intended to be given

59
Q

What is meant by justificaiton in radiation exposure?

A

exposure must provide sufficient benefit to the exposed individual to offset detriment it causes

(exception being screening programs)

60
Q

What is meant by Optimisation in radiation exposure?

A

Number of people exposed should be kept to a minimum (ALARP preiciple)

61
Q

What are the causes of Primary, Secondary and Tertiart radiation?

A

Primary: the primary beam (clincially useful radiation) that is highly collimated
Secondary: leakage from interactions within the head of the linac
Tertirary: unwanted scatter from within the patient or structures in the room. This is lower than the average energy of the beam but max possible is used for calculations
note: the larger the field the greater the scatter

62
Q

What are the key features of treatment room designs?

A
  1. Barriers
  2. Maze
  3. Doors
  4. Interlocks
  5. Last man out
63
Q

What are the types of barrier for treatment rooms?

A

Primary barrier: this is the wall directly in front or behind the primary beam to attenuate it. Usually 2.5m thick concrete

Secondary battier: the other 2 walls, designed to attenuate scatter. Usually 1.5m thick concerete.

64
Q

How is the attenuation of a barrier calculated?

A

HVT - Half Value Thickness - thickness of material needed to attenuate the beam by half

TVT - Tenth Value Thickness - thickness of material needed to attenuate the beam by a factor of 10 (e.g. 100 -> 10)

65
Q

What is the equation for attenuation?

A

I = Io * e^-ux

u = linear attenuation coefficient
x = thickness of material
Io = intensity with no attenuator present

66
Q

What is the formula for HVT?

A

HVT = ln2/ u

67
Q

What is the formula for TVT?

A

TVT = ln10/u

68
Q

What does the maze have to have?

A

At least 2 changes in direction

69
Q

What features to the room doors need to have?

A

Several tonnes and motorised (therefore slow)

70
Q

What does an interlock do?

A

automatically shuts off the linac if anyone enters the room

71
Q

What is the last man out?

A

2 switches which activate emergency cut off switch, warning lights, and light gates

(if someone passes through the light gate it will shut off the linac)

72
Q

What are the additional features needed for neutron beams?

A

If >15mV scatter is a big rpoblem
Need longer, narrower mazes which are lined with neutron absorbing material such as boron

73
Q

What is the Linear No-Threshold (LNT) model?

A

some data suggests cells are proportionally more sensitive to radiation carcinogenesis at lower doses than TNT would predict

Some data suggests cells are adaptive to damage at lower doses which may actually be beneficial

Physics for FRCR CO1 (11 decks)

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