Lecture 25 - Radiation Safety Flashcards
Ionising radiation
- radiation removes electrons from atoms to form ions
- can be carcinogenic, leukemogenci, mutagenic ot teratogenic
Non ionising radiation
- radiation energy cannot create ions but can have other effects such as thermal or photochemical
- not carcinogenic
Alpha particles
- nasty and dangerous
- not used except for some radioisotype therapy
Beta particles
- same as electrons
Nasty - used for therapy
Gamma rays
- electromagnetic radiation
- penetrating
- not as nasty as particles
- safe for imaging but at high intensities can also be used for therapy
X rays
- physicall identical to gamma rays but come from electron, not nucleus
- penetrating -> used for imaging
- relatively safe for imaging
- used for radiotherapy at high intensity
Appliation of ionising radiation
- radiology - x ray
- nucleuar medicine: radionuclides
- radiotherapy - X ray, particles and radionuclides
- dental
- radio-labelling techniques: radionuclide
- blood irradiation - gamma rays
Non ionising radiation appliation
- MRI
- UV therapy
- lasers” high and low power
Radiation dose units
- absorbed dose: gray Gy
- effective dose: Sievert SV
Physical effect of radiation
- energy absorption, ionisation
Physico-chemical effect of radiation
- interaction of ions with molecules, formation of free radicals
Chemical effect of radiation
- interaction of free radicals with molecules, cells and DNA
Biological effect of radiaiton
- cell death, change in genetic data in cell, mutations
3 types of radiation effect
- Stochastic: probability of effect related to dose
- DEterministic: threshold for effect: no effect below, above, certaintiy and severity increases with dose
- hereditary (genetic)
Eg of stochastic effect
- DNA effects, mainly repaired
- carcinogenesis, leukemogenesis
Eg of deterministic effect
- cell death not repaired
- epilation, radiation sickness, erythema
Time
- the longer the exposure, the higher the dose
Shielding
- high density, high atomic number and thickness are required for protection
- 0.3mm lead aprons for X ray staff
Distance
- radiation decreases with the square of distance
- twice the distance = 1/4 radiation level
- distance is the simplest and best protection
Structure of radiation protection
- internal body sets standards and philisophy, based on reviews and radiation effect
- Main recomendations are for dose limits to workers and public, and risk factors
- dose limits are reduced to 25% for medical workers in NSW
- equivalent to 2x annual background
Background radiation
- unavoilable and equivalent to 2 CXR per week in australia
- 2.3 mSv/yr in Sydney
- from radon/thoron in air mainly
- medical sources add about 15% average
Patient dose, indicated exposure
- doses for diagnostic procedures range from 20 year
- therapeutic procedures ranfe up to thousands of background years
- effects can be serious but rare
- CT scans largest source of exposure (50%)
Accident types
- wrong patient, wrong examination, wrong body part
- irradiation of uterus in unknown pregnancy
- overdose
- contamination
In utero irradiation
- before implantation: no risk
- 3-8 weeks: organ malformation
- 8-25 weeks: severe mental retardation
- organogenesis - cancer/leukemia in childhood or adult life
Risk for cancer/leukemia
- about 3 times that for pop as a whole
- 16%/SV
At most
Legal oblications
- regulatory body in NSW is the EPA
- radiologist and nuclear medicine physicians need a license
- non-radiologists want to use fluoroscopy need a licence
- radionuclide users ned a licence
- all examinations must be approved by a doctor
Other legal obligations
- radiation apparatus must be registered
- premises must be rgistered
- certain worker groups need a radiation monitor
- accidents must be reported
- research using radiaiton must be evaluated and approved
3 doctors rule
- limitation
- justification
- optimisation
