Random DR/RP Flashcards
Who is responsible for implementing regulations and how is this usually done
Employer has responsibility, usually delegated to radiation protection committee
Who is RPA
Radiation protection adviser - individual or body appointed by radiation employer and meeting criteria of competence specified by HSE.
Advice on compliance that RPA might give
Radiation risk assessment
Designation of controlled and supervised areas
Handling of investigations
Contingency plans
Dose assessment and recording
What must RPAs be consulted on
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
HSE graded approach
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
Designated area
Work area where special procedures are needed to restrict dose (access, training, work practice). Person working here likely to receive dose over threshold.
Values for dose rate
Instantaneous dose rate
Dose rate (DR) - over 1 minute
Time-averaged dose rate (TADR) - over 8 hours
TADR2000 (same over 2000 hours)
Requirements for designated areas
Warning signs
Systems of work to restrict exposures
Environmental monitoring
Assessment of dose (personal and environmental) to ensure dose limits not exceeded
What should local rules contain
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
RPS
Should be appointed when local rules are needed, preferably full time and sufficiently senior.
Classified workers
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
What does classification involve
Regular medical surveillance, personal monitoring performed by an approved lab and person dose record kept on CIDI
Pregnant staff
Dose to foetus should be ALARP and unlikely to exceed 1mSv - equivalent to 2mSv on abdomen
Diagnostic reference levels
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
Stochastic vs tissue reactions
Stochastic: probability of effect occurring increases with dose, no threshold
Tissue reactions: no effect below threshold, above threshold severity increases with dose
Classified worker limits
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
TADR2000 each area
Controlled: >3
Supervised: > 0.5
Unsupervised: <0.15
microsievert/hr
3 types of personal dosimeter
TLD (thermoluminescent dosimeter)
OSL (optically stimulated luminescence)
EPD (electronic personal dosimeter)
TLD material and details
Lithium Fluoride
1microGy - 10Gy
Reusable
OSL material and details
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
EPD
Direct read of dose and dose-rate. Audible alarms
Dose for estimating skin, eye, effective
Whole body: Hp(10)
Extremity: Hp(0.07)
Lens of eye: Hp(3)
How do we decrease noise
- Increase no of photons to increase SNR
- Use smoothing filters
- Can use iterative reconstruction in CT
Principles of radiation protection
Justification
Optimisation
Limitation
Justification
Is there enough benefit to justify the procedure: benefit must outweigh risk
Optimisation
Is the dose ALARP
Limitation
Set exposure limits for doses
General principles of IRMER
Should only be carried out if necessary
Alternative non-ionising measures should be considered
All exposures must be justified
Exposure should be ALARP
Duty holders and what legislation do they come under
IRMER
Referrer
Practitioner
Operator
MPE
Role of referrer
Refer patient
Must identify paitent, give info to justify and information about breast feeding etc
Role of practitioner
Justifies exposure
Confirms justification, authorises request
Need ARSAC license for radionucides
Role of operator
Anyone carrying out a practical aspect of the exposure
Accidental vs unintended exposur
Accidental: patient shouldn’t have been exposed at all
Unintended: get higher dose or wrong area
Types of noise
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
KERMA
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
What does RBE change with
Dose
Dose rate
Fractionation
Physiological conditions
Biological species
What makes a good detector
Can detect radiation
Appropriate accuracy and precision
Gives relevant dose quantity
Appropriate range (E,D)
Linear response with dose
Pros and cons of ionisation chamber
+ 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
Pros and cons of Geiger counter
+ 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
How does Geiger counter work
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
Detriment
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
What does bit depth govern
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
Pre-processing examples
DR: flat fielding, correcting for dead pixels
CR: corret for variations in senstivity of light collecting guide
Post processing examples
Window width and level
Noise reduction
Edge enhancement
Cause of electronic noise
Readout electronics
Thermal effects
What affects spatial resolution
Characteristics of detector (pixel size, spread of signal)
Focal spot size
Magnification (image intensifier)
When do risk assessment
Prior to starting a new activity but must also be reviewed regularly
Risk assessment considerations
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?
Who optimises exposure?
Operator
How do we use the k-edge
Match the materials of the detector with the x-ray spectrum so it is absorbed
Use contrast material
What are operational quantities
Ambient dose equivalent
Personal dose equivalent
Operational quantity for area monitoring
Ambient dose equivalent H*(10)
Operational quantity for personal dose
Personal dose equivalent Hp(d)
Physical quantities
KERMA, exposure, absorbed dose
Protection quanitities
Equivalent organ dose
Effective dose
Employers procedures
Identify duty holders
Use and review of DRLs
Deal with incidents
Non-medical exposures
Carers and comforters
