Radiation Safety in Medical Applications Radiation Types • Ionising: radiation removes electron from atoms to make ions. Carcinogenic, leukaemogenic, mutagenic, teratogenic • Non-ionising: can’t make ions but can have thermal or photochemical effects Applications • Ionising o In vivo diagnosis and treatment  Radiology: including CT, x-ray  Nuclear medicine: radionucleotides Radiotherapy: x-rays, particles and radionucleotides   Dental: intra-oral, OPG, CT, x-ray o In vitro:  Radiolabelling techniques  Blood irradiation (gamma rays) • Non-ionising o MRI o UV-therapy o Lasers o Radiofrequency techniques: TUNA Absorbed Dose: Gray (Gy) Effectuve Dose: Sievert (Sv) • Takes into account that some tissues are more sensitive to radiation than others • CXR: ~5µSv • Annual background radiation in Sydney: ~2.3mSv • CT of chest/abdo/pelvis: 20mSV • Whole body acute lethal dose: 5-7Sv Stage Process Duration Physical Energy absorption, ionisation 10-16S Physicochemical Ions interact with molecules  ROS 10-6S Chemical ROS interact with cells, DNA Seconds Biological Cell death, change in genetics, mutations Minutes to Years Radiation Effect: • Stochastic: probability of effect related to dose down to zero • Tissue: threshold for effect to appear  Hereditary Stochastic Effects • E.g. carcinogenesis, leukaemogenesis  Probabilities: o Cancer: 5.5%/Sv o Hereditary effects: 0.2%/Sv o Total: 5.7%/Sv Tissue Deterministic Effect • Epilation, radiation sickness, erythema Radiation Protection Procedures • Time: length of exposure  Shielding: o High density and thickness of barrier needed o 0.3mm Pb for staff o Gyprock for mammography room walls o 2mm Pb walls for radiology rooms o 25mm Pb or 200mm concrete for PET o 2500mm (2.5m) concrete for radiotherapy • Distance: radiation dose is inversely proportional to distance squared i.e. 2x away = quarter of dose o 𝐷𝑜𝑠𝑒 = 1 2 𝑑 ICRP International Body sets rules for doses, risk, etc. • Background radiation = ~2.3mSv/year = 2 CXR/week o Radon, thoron in air, cosmic rays, ingesting natural radioisotopes, etc. o On average medical sources add ~15% Note: Regulatory body in NSW is EPA