OHS Lecture #02 PDF

# OHS Lecture # 02 ## Introduction - Radiation is increasingly used for diagnostic and therapeutic purposes. - Hazardous to both patient and operator, especially during major therapeutic procedures. - Appropriate education -> about radiation safety - Concern of radiation safety increased in recen...

# OHS Lecture # 02 ## Introduction - Radiation is increasingly used for diagnostic and therapeutic purposes. - Hazardous to both patient and operator, especially during major therapeutic procedures. - Appropriate education -> about radiation safety - Concern of radiation safety increased in recent times because of evolution of endovascular techniques with our speciality over the past decade. ## Hazards of Radiation An image of a brain, a doctor, a thyroid, breasts, and an eye are displayed, all with areas highlighted in red to indicate points of potential radiation hazard. ## Types of Radiation - Radiation is a form of energy emitted as electromagnetic waves or particles. - **Non Ionizing:** - US, MRI, Laser and microwaves - Doesn't possess energy to ionize atoms of absorbing matter - **Ionizing:** - X-rays, Gamma rays and beta rays - Contain sufficient energy to interact with atoms and produce biologic injury ## Measurement - **Amount of ionization that radiation produces in air:** - Measured as roentgen - Won't accurately reflect potential to cause biologic injury - **Biologic effect depends:** - Total energy of radiation absorbed per unit mass - Sensitivity of organ - Actual strength of radiation An image showing a chain of DNA splitting apart due to radiation exposure is displayed. ## Quantification of Radiation - **Absorbed dose:** - Measure of amount of energy deposited in medium by ionizing radiation per unit mass of matter and is equal to amount of heat generated by radiation per tissue weight in specified material - **SI unit of absorbed dose:** - Gy (Gray) - 1Gy = 1 Joule of energy absorbed / kilogram (J/kg) - **Older term = Radiation absorbed dose (Rad):** - 1Gy = 100 Rad - 1 Rad = 0.01 J/Kg - **Equivalent dose:** - Measure of radiation dose to tissue and takes into account different degrees of damage by different types of radiation by introducing a radiation weighing factor (Wr) - **SI unit of Equivalent dose:** - Sv (Sievert) - Equivalent dose = absorbed dose x Wr (Sv = Gy x Wr) - **Old Term → Roentgen equivalent man (REM):** - REM = Rad x Wr - 1Sv = 100 REM - **Wr→ calculated by type of radiation (1: gamma & X-rays, 3-10: protons and neutrons)** - For vascular surgical interventions -> Sievert & Gray are roughly equal (Absorbed = equivalent dose) - **Effective dose:** - Different tissues and organs have different sensitivity to radiation - Takes into account part of body irradiated and volume & type of radiation exposed - **Done by Weighting equivalent dose by tissue weighting factor (Wt)** - **Often to avoid confusion Wr and Wt grouped as W (single weighting factor)** - In medical field, commonly milli grays (mGy) or milli sieverts (mSv) is used ## Biologic Effects of Radiation - **Ionizing radiation damages living cells:** - Repair themselves - Die - Undergo mutation - **Effects on biologic tissue:** - Deterministic effect - Stochastic effect ## Deterministic Effect (DE) - **Dose dependent:** - Cell death - Impairs hair follicles, skin, subcutaneous tissues and lens. - **Higher dose = Greater injury** - **Threshold exists**, but varies amongst individuals. Often large doses causes DE (1-2 Sv) - Symptoms start when significant cells are killed and subsequent inflammation or fibrosis begins. - **Whole body exposure → 10-20 Gy high energy radiation at single time is fatal.** - **0.5-1 Sv → light radiation sickness** - **1 Sv → slight blood changes** - **2-3 Sv→ nausea, hair loss, hemorrhage** - **Acute dose of 3 Sv → death in 50% within 30 days.** ## Stochastic Effect - Probabilistic effect. - DNA damage to cells -> mutations -> cancer & genetic defects. - All or none phenomenon. - No threshold levels. Probability increases as cumulative radiation exposure increases, but severity is independent of the dose. - Theoretically, with doses <100 mSv/year, probabilistic effect is very low. - **Type of cancer produced is independent of type of radiation -> Leukemia and other cancers (lungs, breast, thyroid, skin, GIT)** - **Latent period between exposure and cancer:** - 2-5 years -> leukemia - 5 yrs -> thyroid - >10 years -> other cancers - **Probability of fatal cancer -> 4% per 1 Sv of lifetime dose equivalent** ## Background Exposure - Humans are constantly exposed to naturally occurring radiation: - Radioactive materials - Cosmic radiation - **Average annual radiation in US -> 3mSv/ year.** - **Dose increases with higher altitudes.** - **Greatest source of domestic radiation:** - Radon gas from decay of radium (2nd most frequent cause of lung cancer after cigarette smoking) - Building materials, fuels, televisions, smoke detectors An image depicting a house with a radioactive signal emanating from the ground is shown. ## Principles of Radiation Protection - **ICRP system of protection in medical practice:** - Stresses the fundamental principles of justification - Optimization of protection - Dose and risk limits - **Use of radiation in medicine must be Justified -> produce more benefit than harm** - **Responsibility of the hospital:** - Ensure that the radiation equipment is properly maintained to deliver the lowest possible dose of radiation - Safety instructions and protective measures are available and adopted - System of reporting and remedial measures be in place when recommended limit is exceeded - Special operating procedures available for high-risk paediatric and pregnant workers ## Safety in Diagnostic Procedures - **Alternative imaging modality without ionizing radiation -> US and MRI, preferred whenever possible.** - **Routine X-rays as skull (for minor head injuries)and chest (done after hospital admission) -> avoided.** - **CT:** - Commonly used due to wide availability and faster results - Spiral CT and Multidetector CT -> 10-30% more dosage - Less essential cases -> low dose exam, wider pitch and partial rotation ## Practical Safety Points - Fluoroscopy should be intermittent - Never use unless operator sees monitor - Allow only essential persons inside room - Display ample warning signs at entrances - Regularly service and calibrate equipment's - Newer machines and fixed systems are better -> less dosing, better image intensifier, pulsed fluoroscopy, better quality images in less time - Use radio opaque catheters whenever feasible ## Radiation and Pregnancy - **Recommended -> an occupationally exposed pregnant women declare pregnancy for purpose of reducing risk to unborn child.** - **Risk highest during organogenesis -> first trimester and least in third trimester** - **Diagnostic tests or procedures that involve radiation exposure -> deferred or adequately informed and performed.** - **Major adverse events to foetus -> abortion, teratogenicity, mental retardation, intrauterine growth retardation and induction of cancer.** ## General Recommendations - **In European Union:** - 20mSv/year, averaged over defined period of 5 years - May not exceed 50 mSv in one year - **Germany:** - 400mSv life time dose limit - **US:** - <50mSv/year, lifetime limit - 10mSv multiplied by patient age in years