Lecture 1a - Radiation Risk in Perspective

What is particulate radiation

• Fast moving matter with mass such as alpha and beta particles

• Ionising

What is electromagnetic radiation

• Massless energy packers or waves such was light, x-ray and gamma rays

• Can be non-ionising or ionising

Where is radiation used in the hospital?

• Diagnostic imaging

• Radiation therapy

• Interventional procedures

• Guiding surgery

What are the phases of the biological effects of radiation

Absorption of radiation → Excitation/ionisation → Chemical lesion → Enzyme repair or development of lesion

What happens during the excitation/ionisation phase

• The stable atoms in the body get excited by the radiation

• Electron is pushed to a higher energy/out of atom

• Excited atoms become free radicals

What happens during the chemical lesion phase

Free radicals/charged particles start causing damage

What happens during the enzymatic repair phase

• Cells are able to repair the damaged caused by low levels of radiation

• May cause probabilistic (stochastic) effects

What happens during the development of lesion phase

• Dose is too high for cell to repair

• Double strand break

• Deterministic effects will occur

• Apoptosis (cell death)

Biological effects depend on:

• Acute vs chronic radiation exposure

• Type of radiation

• Energy of radiation

• Dose

• Dose rate

Define somatic effects

Effects that occur to the specific person who gets exposed

Define genetic effects

Inheritable changes in the DNA that can be passed onto the next generation

What happens during an acute exposure to radiation

• Dose delivered quickly over a short time

• Large dose

• Effects appear quickly (days or weeks)

What happens during a chronic exposure to radiation

• Dose delivered in small increments over a long time

• Low incremental doses

• Effects appear over time (years)

Define deterministic effects

• Severity of effects increase with increasing radiation dose

• Threshold exists

Define stochastic effects

• The probability of an effect occurring increases with dose

• No safe threshold

• Cancer/genetic mutation

What is absorbed dose

• Amount of energy deposited per unit of mass

• Milligrays (mGy)

What is equivalent dose

• The absorbed dose to an organ, adjusted to account for the type of radiation

• Millisieverts (mSv)

What is effective dose

• Sum of all individual organ equivalent doses multiplied by tissue weighting factor to account for more radiosensitive organs

• Millisieverts (mSv)

What is effective dose used for

• Prospective dose assessment for planning and optimisation in radiation protection

• Demonstration of compliance with dose limits for regulation

Describe the linear no threshold model

• There is no safe level of radiation exposure

• Assumed that effects at high doses can be extrapolated to low doses