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Medical Physics > Random DR/RP > Flashcards

Random DR/RP Flashcards

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1
Q

Who is responsible for implementing regulations and how is this usually done

A

Employer has responsibility, usually delegated to radiation protection committee

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2
Q

Who is RPA

A

Radiation protection adviser - individual or body appointed by radiation employer and meeting criteria of competence specified by HSE.

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3
Q

Advice on compliance that RPA might give

A

Radiation risk assessment
Designation of controlled and supervised areas
Handling of investigations
Contingency plans
Dose assessment and recording

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4
Q

What must RPAs be consulted on

A

Implementation of requirements for controlled and supervised areas
Plans for future installations
Calibration and use of equipment for monitoring
Periodic testing of control and safety features and systems of work

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5
Q

HSE graded approach

A

Notification (low risk) - electronic submission
Registration (includes all x-ray work) - submission, statements to agree to, small fee
Consent (licensing) - administering radionuclides, use of LINACs, more evidence and higher fee

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6
Q

Designated area

A

Work area where special procedures are needed to restrict dose (access, training, work practice). Person working here likely to receive dose over threshold.

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7
Q

Values for dose rate

A

Instantaneous dose rate
Dose rate (DR) - over 1 minute
Time-averaged dose rate (TADR) - over 8 hours
TADR2000 (same over 2000 hours)

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8
Q

Requirements for designated areas

A

Warning signs
Systems of work to restrict exposures
Environmental monitoring
Assessment of dose (personal and environmental) to ensure dose limits not exceeded

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9
Q

What should local rules contain

A

Description of area and its identification (controlled or supervised)
Name of RPS
Arrangements to restrict access
Conditions for entry for non-classified persons
Instructions for safe working
Dose investigation levels
Contingency plans

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10
Q

RPS

A

Should be appointed when local rules are needed, preferably full time and sufficiently senior.

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11
Q

Classified workers

A

Receive effective dose >20mSv or equivalent dose > a dose limit in a few minutes
Anyone likely to get an annual effective dose >6mSv or 3/10 any other dose limit

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12
Q

What does classification involve

A

Regular medical surveillance, personal monitoring performed by an approved lab and person dose record kept on CIDI

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13
Q

Pregnant staff

A

Dose to foetus should be ALARP and unlikely to exceed 1mSv - equivalent to 2mSv on abdomen

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14
Q

Diagnostic reference levels

A

A dose reference level set for a specific standard examination type and standard patient
cohort
Represents an upper level for acceptable dose
National and local
Expressed in easily measurable dose quantities (ESD, CTDI, DAP)
Should be reviewed and investigated if regularly exceeded

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15
Q

Stochastic vs tissue reactions

A

Stochastic: probability of effect occurring increases with dose, no threshold
Tissue reactions: no effect below threshold, above threshold severity increases with dose

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16
Q

Classified worker limits

A

Effective dose > 20mSv in short period of time or equivalent dose > dose limit very quickly
Likely o get annual effective dose > 6mSv or 3/10ths another dose limit

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17
Q

TADR2000 each area

A

Controlled: >3
Supervised: > 0.5
Unsupervised: <0.15
microsievert/hr

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18
Q

3 types of personal dosimeter

A

TLD (thermoluminescent dosimeter)
OSL (optically stimulated luminescence)
EPD (electronic personal dosimeter)

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19
Q

TLD material and details

A

Lithium Fluoride
1microGy - 10Gy
Reusable

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20
Q

OSL material and details

A

Aluminium oxide Al2O3:C
10microGy - 100Gy
Irradiated electrons trapped in valence band in structure
Laser light used to read results - less signal loss than TLD, can be reread

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21
Q

EPD

A

Direct read of dose and dose-rate. Audible alarms

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22
Q

Dose for estimating skin, eye, effective

A

Whole body: Hp(10)
Extremity: Hp(0.07)
Lens of eye: Hp(3)

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23
Q

How do we decrease noise

A
  1. Increase no of photons to increase SNR
  2. Use smoothing filters
  3. Can use iterative reconstruction in CT
24
Q

Principles of radiation protection

A

Justification
Optimisation
Limitation

25
Q

Justification

A

Is there enough benefit to justify the procedure: benefit must outweigh risk

26
Q

Optimisation

A

Is the dose ALARP

27
Q

Limitation

A

Set exposure limits for doses

28
Q

General principles of IRMER

A

Should only be carried out if necessary
Alternative non-ionising measures should be considered
All exposures must be justified
Exposure should be ALARP

29
Q

Duty holders and what legislation do they come under

A

IRMER
Referrer
Practitioner
Operator
MPE

30
Q

Role of referrer

A

Refer patient
Must identify paitent, give info to justify and information about breast feeding etc

31
Q

Role of practitioner

A

Justifies exposure
Confirms justification, authorises request
Need ARSAC license for radionucides

32
Q

Role of operator

A

Anyone carrying out a practical aspect of the exposure

33
Q

Accidental vs unintended exposur

A

Accidental: patient shouldn’t have been exposed at all
Unintended: get higher dose or wrong area

34
Q

Types of noise

A

Quantum noise: should dominate
Electronic noise: can be significant at low doses
Fixed pattern noise: pixel to pixel variations, should be low in DR because of flat fielding

35
Q

KERMA

A

Kinetic energy released per unit mass
Not necessarily dose in air because energy lost from beam is not necessarily same as energy absorbed
To good approximation this is correct though: negligable Brem. and short range of electrons

36
Q

What does RBE change with

A

Dose
Dose rate
Fractionation
Physiological conditions
Biological species

37
Q

What makes a good detector

A

Can detect radiation
Appropriate accuracy and precision
Gives relevant dose quantity
Appropriate range (E,D)
Linear response with dose

38
Q

Pros and cons of ionisation chamber

A

+ gives air KERMA
+ comes in a range of sizes - good for sensitivity and resolutiosn
+ linear response
+ stable over time
-needs electrometer for read out
-T/P corrections
-requires careful calibration

39
Q

Pros and cons of Geiger counter

A

+ can detect all types of radiation
+ increased sensitivity over ion chamber
+ low dose measurements
+ cheap
-poor at high doserates due to dead time
- poor energy response output

40
Q

How does Geiger counter work

A

Sealed chamber contains gas at low P
Two electrodes with high V between them
Radiation creates ion pairs
Electron accelerated by a high voltage causes further ionization of gas molecules therefore large number of electrons
Chain reaction - pulse detected

41
Q

Detriment

A

Measure of whole body harm
-probability of fatal cancer
-probability of severe genetic effects
-relative length of life lost
-weighted probability of non-fatal cancer

42
Q

What does bit depth govern

A

Range of grey scales
Each pixel stores discrete number related to shade of grey
4bit is 2^4 levels, 16. Numbered 0 (black) to 15 (white)
Typically 12 bit

43
Q

Pre-processing examples

A

DR: flat fielding, correcting for dead pixels
CR: corret for variations in senstivity of light collecting guide

44
Q

Post processing examples

A

Window width and level
Noise reduction
Edge enhancement

45
Q

Cause of electronic noise

A

Readout electronics
Thermal effects

46
Q

What affects spatial resolution

A

Characteristics of detector (pixel size, spread of signal)
Focal spot size
Magnification (image intensifier)

47
Q

When do risk assessment

A

Prior to starting a new activity but must also be reviewed regularly

48
Q

Risk assessment considerations

A

Routine work:
What radiation dose might people get?
What control measures are in place/needed?

Accidents:
What might go wrong?
What doses might people get then?
What control measures are needed?
What contingency plans are needed?

49
Q

Who optimises exposure?

A

Operator

50
Q

How do we use the k-edge

A

Match the materials of the detector with the x-ray spectrum so it is absorbed
Use contrast material

51
Q

What are operational quantities

A

Ambient dose equivalent
Personal dose equivalent

52
Q

Operational quantity for area monitoring

A

Ambient dose equivalent H*(10)

53
Q

Operational quantity for personal dose

A

Personal dose equivalent Hp(d)

54
Q

Physical quantities

A

KERMA, exposure, absorbed dose

55
Q

Protection quanitities

A

Equivalent organ dose
Effective dose

56
Q

Employers procedures

A

Identify duty holders
Use and review of DRLs
Deal with incidents
Non-medical exposures
Carers and comforters

Medical Physics (16 decks)

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