Radiation Units
Exposure
- is a measure of quantity of ionisation, produced in air, by x-ray, or gamma radiation per unit mass
- SI unit is the Coulomb per kg (C/kg)
Absorbed dose
- is a measure of the amount of energy imparted to matter by ionising radiation per unit mass of irradiated material
- SI unit is the Gray(Gy)
Dose equivalent
- is a quantity introduced for radiation protection purposes
- correlates better with the harmful effects caused by exposure to the various types of ionising radiation
- SI unit is the Sievert (Sv)
- the subunit, millisievert (mSv), one thousandth of a Sv, is used more often because of the large size of a Sievert
- Dose equivalent = Absorbed dose X quantity factor X modifying factor
- for xrays, dose equivalent and absorbed dose are the same in magnitude
Background radiation
Depends on where you live
- 2 mSv / yr = 5 micro SV/day
- flying = 3-4 micro Sv/hr
Xray Doses
AP CXR 20microSv (4 days)
Lat CXR 50microSv
AXR 100microSv (20 days)
Lumbar Spine
- AP&Lat 500microSv (100 days)
- 5 view series 1milliSv
Pelvic XR 100 microSv
Wrist XR 4 microSv
Bone Scan
6mSV = 200 CXR = 2.5 years
CT
CT Chest/Abdo/ Pelvis
- 8-12 mSV each (5 years)
- whole series is 30 mSV (15 years)
CT Spine 8-10 milliSv
CT Head 20 milliSv (10 years)
CT Hand 4 milliSv
Ratios of exposure
CXR = 20 microSV (4d)
Pelvis XR = 5 CXR
Spine XR (AP/L) = 25 CXR
NMBS = 200 CXR
CT chest / abdo / pelvis = 400 CXR
CT head = 800 CXR
Exposure
Dose
- directly related to trauma load
- use of Image Intensifier
Average Orthopaedic Trainee
- exposed to 1.6 mSv per year on outside lead gown
- normal background radiation 2.5 milliSieverts / yr
- thyroid shield can reduce radiation by X13
- most commonly with NOF pin and plate / IM Nailing / MUA
- highest dose during IM Nail Femur
(Long procedure, increased scatter, close proximity during distal locking)
Exposure reduced by
- increased distance from source > 50 cm
- wearing lead apron
- minimise screening times
- with lead apron, maximum exposure to head & neck & hands
Effects
Lymphatic depression > 100mSv
Radiation sickness & increased solid neoplasia ~ 1000mSv
NHMRC Recommended Maximum Dose in addition to background radiation
- Occupational < 5mSv over 3/12
- General population < 0.25mSv over 3/12
- Average orthopedic trainee 0.4 mSv over 3/12
Primary concern is malignancy
- minimum safe dose unknown
- ? > 25 Gy
Areas in question are
- Eyes / Thyroid / RES / Gonads / Hands (Skin)
Absolute risk from low-dose radiation not determined
Protection
Wear protective lead apron at all times
- check regularly for cracks in lead
- thyroid protector & lead-lined glasses
Safety Procedures
- minimise exposure time
- use sparingly
- avoid live screening
- avoid cavalier operating
- do not handle tube
- do not place hand in tube
- don't operate II without radiographer
"HINTS TO MINIMISE EXPOSURE"
As low as reasonably achievable (ALARA)
- Operative planning
- Inform all staff
- Consider set-up and positioning of equipment
- Operating surgeon to set the example
- Lead gown - 0.5mm / thyroid protector / lead glasses
- Gloves in high exposure procedure
- Advise all staff to wear appropriate protection
- Wear a radiation monitor (beneath lead gown)
- Never stand behind someone for protection
- Sign on door - ionizing radiating in use
- Maintain distance from beam
- Lead shield if possible
- Don't use II as table
- Single exposure (not continuous)
- Minimise exposure time
- Clear warning when to be used
- Consider altering surgical technique to avoid excess exposure
- Minimise II distance from pt
- Minimise field size
- Exposure tube side > II side
- Don't use saline bags