- Axial scan data reconstructed into other views or 3D images without re-scanning.
- Increased by: overuse, multi-detectors (faster scans), high resolution scans, larger area.
- More paediatric scans done as faster (~1s) scans now so less need for sedation.
- Average background radiation = 2.5-3mSv/yr (~25-30 CXRs)
Typical scan doses
|Modality||Body Area||Approx Ave Dose (mSv)||Chest X-ray Equivalent Dose||~Equivalent Period of Background Radiation|
|Pelvis or Abdomen||0.7||35||4mo|
|CT angiogram of aorta||24||1200||12yr|
|Trauma pan scan||34||1700||17yr|
Reducing radiation dose
- Is X-ray/CT really necessary
- Is there an alternative modality e.g. USS/MRI
- Focus scanning only on area of interest
- Adjust CT parameters (tube current and pitch) for body type & organ
- CT scans can be performed with lower exposure in children, if employed.
- Use of newer software that improves quality of low dose scan results
- Estimated lifetime cancer mortality risk attributable to a dose similar to an abdo CT: 1.1. 1yo child: ~0.05% (head) & 0.1% (abdominal), reducing to <0.01% & 0.02% in adults>35y. Overall ~1:1,000-1:10,000 CTs result in a cancer death.
- Risk F>M generally, sig (1.5-2.5x) if radiation of chest(breast) at all ages, or head <35y
- Additional risk is still low (1%) compared to background risk. (Lifetime risk of cancer in Aus ~25-33%, and lifetime cancer mortality ~10-15%).
- Survivors of atomic bombings @ Hiroshima and Nagasaki were exposed to ave 40mSv.