Biological Effects of Radiation Used in Imaging (2): Stochastic Effect

Stochastic Effect of Radiation

• Effect of radiation that occurs by chance.
• Late effect such as cancer and genetic defects
• Probability (not severity) depends on dose. "As doses increase, the chance of cancer or genetic defect increases."
• No threshold dose
• Effects can occur even in human never been exposed to radiation above background level (remember normal background radiation from standing on Earth).
  

Effective Dose

• This term is used to determine probability of health effect from radiation (i.e. stochastic effects)
  
• Unit = Sv (sievert)
  
• Derived from calculation of i.e. entrance skin dose (based on dose indicator used in radiography), dose-area product (based on dose indicator in fluoroscopy), and CT dose index (based on dose indicator in CT)
• Good for dose optimization of procedures and balance radiation risks and information obtained from imaging
• Example: posteroanterior chest radiograph - <0.1>

Reference:
Verdun FR, et al. Radiation risk: what you should know to tell your patients. Radiographics 2008 (September)