Radiation Exposure

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