Radiation Dose Flashcards
What are the units of radiation dose?
KERMA – dE/dm
Point interaction (a)
Kinetic Energy Released in the Material
What is the absorbed dose?
dE/dm
Energy dumped in unit mass of material
Distributed energy transfer (b) (eg. ~105 ionisations per 1-2cm)
J/kg or Gray
What is exposure?
Charge liberated per unit mass
Roentgen
What is the Linear Energy Transfer coefficient
Linear Energy Transfer coefficient = LET
dE/dx
How is radiobiology measured?
Survival fraction
Relative Biological Effectiveness
RBE
Q factor
What effect does ionisation have?
DNA damage
Direct or indirect mechanism
What are the stochastic effects?
probabilistic – no safe dose
What are the deterministic effects?
threshold – eg. cataract, burns etc.)
What can doses of radiation lead to?
lowish : variable effects, leukaemia, tumours ~1Gray ... Acute radiation sickness ~5 Gray ... LD50 ~20 Gray ... Death (days) ~100Gray ... Death (hours)
How is radiation damage quantified?
A bullet analogy – ‘lethality’? Energy (absorbed dose) Speed Nicked (dose equivalent) Increased damage Location (effective dose) Survival Systemic effect Absorbed dose; dose equivalent; effective dose
What is RBE?
Dose from standard radiation to produce given biological effect
/Dose from test radiation to produce given biological effect
Cellular reproduction
Reference radiation
200kVp X-rays
Survival fraction
What is the dose equivalent?
Sievert
Cellular reproduction
Dose Eq = Absorbed dose x Q(radiation weighting factor) x modifying factor
Q correlates with LET
What is an effective dose (Sievert)?
Any radiation insult can be normalised to an effective (whole body) dose that delivers the same ‘health detriment’
What bodies are associated with radiation dose?
ICRP – International Commission for Radiological Protection
NRPB – National Radiological Protection Board
ARSAC – Administration of Radioactive Substances Advisory Committee
What people are associated with radiation dose?
RPA – Radiation Protection Adviser
RPS – Radiation Protection Supervisor
