Describe the radiation hazards and their prevention.

Radiation Hazards

• Ionising radiation includes — X-rays and gamma rays (electromagnetic), and alpha, beta and neutron particles
• Their penetration differs greatly and determines the hazard — alpha particles are stopped by paper or skin and are dangerous only if inhaled or ingested; beta particles penetrate a few millimetres of tissue; and gamma and X-rays penetrate deeply and require dense shielding
• The sources:
• Natural (background), which accounts for the larger share of most people’s exposure — COSMIC rays, increasing with altitude; terrestrial radiation from soil and rock; radon gas, which accumulates indoors and is the largest single natural source and a recognised cause of lung cancer; and internal sources such as potassium-40
• Man-made — medical diagnostic and therapeutic use, which is much the largest man-made source; occupational exposure; nuclear power and fallout; and consumer products
• The units — the GRAY (Gy) for absorbed dose, and the sievert (Sv) for equivalent and effective dose, which weights the absorbed dose for the type of radiation and the sensitivity of the tissue
• The sievert is the unit used for protection purposes, precisely because it reflects biological effect rather than energy alone
• The biological effects divide into deterministic and stochastic, and this distinction is the single most important concept in the topic:
• Deterministic (tissue reaction) effects — have a threshold dose below which they do not occur, and above it the severity increases with dose
• They include — skin erythema and burns; epilation; cataract; sterility; bone marrow suppression; and acute radiation syndrome
• Stochastic (chance) effects — have NO threshold, so that any dose carries some risk; the probability increases with dose but the severity does not
• They include — cancer (leukaemia and solid tumours) and heritable genetic effects
• The practical consequence of the distinction — deterministic effects can be prevented entirely by keeping doses below the threshold, whereas stochastic effects can only be minimised, never eliminated
• This is why the guiding principle is ALARA — As Low As Reasonably Achievable, rather than merely staying below a limit
• Acute radiation syndrome follows a large whole-body dose, and presents in escalating forms with dose — haematopoietic, then gastrointestinal, then cerebrovascular, with a characteristic prodrome, latent period, and then manifest illness
• The most radiosensitive tissues are those with rapidly dividing cells — bone marrow, gonads, intestinal epithelium, lymphoid tissue and the fetus; while nerve, muscle and bone are relatively resistant
• The fetus is the most sensitive of all, with risks of death in the pre-implantation period, malformation during organogenesis, and intellectual impairment and later cancer thereafter
• The three cardinal principles of protection should be recited — time (minimise the duration of exposure); distance (dose falls with the inverse square of distance); and shielding (lead, concrete or water)
• The inverse square relationship is worth stating explicitly, since it means that doubling the distance reduces the dose to a quarter, which makes distance the cheapest and most effective single measure
• The practical measures in a health facility — justification of every examination, so that no radiograph is taken without a clinical reason; optimisation of technique and collimation to the area of interest; dose limits for workers and the public; lead aprons, gonad and thyroid shields; protective barriers and warning signs; film badges or thermoluminescent dosimeters for personnel monitoring; regular equipment quality assurance; and special care in pregnancy, with the "10-day rule" or, more usefully, asking every woman of reproductive age about the possibility of pregnancy before radiography
• The regulatory body in India is the atomic energy regulatory board (AERB), under the Atomic Energy Act
• Non-ionising radiation — ultraviolet, causing sunburn, photokeratitis, ageing of skin, skin cancer and cataract; infrared, causing cataract in glass and furnace workers; microwave and radiofrequency, causing tissue heating; and lasers, causing retinal and skin injury
• An honest note about mobile phones — the radiofrequency emitted is non-ionising and cannot damage DNA directly, and the evidence for a causal link with brain tumours remains inconclusive; the far larger and better-established health risk from a mobile phone is its use while driving
• Deterministic effects have a threshold and stochastic do not, which is the distinction that decides everything else
• Doubling the distance quarters the dose, which makes distance the cheapest protection available
• ALARA means as low as reasonably achievable, which goes beyond merely staying under a legal limit
• Alpha particles are dangerous only if internalised, being stopped by paper or by the skin
• Radon is the largest natural source and a recognised cause of lung cancer, accumulating indoors
• Medical use is the largest man-made source, which places the responsibility squarely on clinicians
• Justify every examination, since a radiograph without a clinical question is pure dose with no benefit
• Rapidly dividing tissues are most sensitive — marrow, gonads, intestine, lymphoid tissue and the fetus
• Ask every woman of reproductive age about possible pregnancy before radiography, which is more useful than the ten-day rule
• Ultraviolet causes cataract as well as skin cancer, which is the ocular effect most often forgotten
• Mobile phone radiation is non-ionising, and the larger established risk is using the phone while driving