SN5 SHORT NOTE 5M ★ High-yield

Describe radiation injuries and their medicolegal importance.

Forensic Medicine · 2nd Professional — Para-Clinical

Types and Mechanism

Type	Nature and penetration
Alpha particles	Helium nuclei; heavy and highly ionising but with minimal penetration — stopped by paper or the outer layer of skin. Harmless externally but extremely dangerous if inhaled or ingested, since all the energy is deposited in a small volume of tissue (polonium-210 is the notorious example)
Beta particles	Electrons; penetrate a few millimetres of tissue; cause skin burns and are dangerous internally
Gamma rays and X-rays	Electromagnetic; highly penetrating, passing through the whole body; the principal external hazard
Neutrons	Highly penetrating and highly damaging; and they can render the irradiated material itself radioactive
Non-ionising	Ultraviolet (sunburn, cataract, skin cancer), infrared, microwave and laser — causing thermal rather than ionising damage

The mechanism of ionising damage — ionisation of water generating free radicals, which damage DNA; and direct damage to DNA. Rapidly dividing cells are most sensitive — which is why the bone marrow, the gonads, the intestinal mucosa, the skin and the lymphoid tissue are affected first, and why the fetus is exceptionally vulnerable
Units — the GRAY (Gy) measures absorbed dose, and the sievert (Sv) the equivalent dose weighted for the biological effect of the radiation type

Acute Radiation Syndrome

Dose (whole body)	Syndrome and outcome
Below 1 Gy	Usually asymptomatic; a transient fall in the lymphocyte count
1 to 2 Gy	Nausea and vomiting; mild haematopoietic effects; recovery expected
2 to 6 Gy — haematopoietic syndrome	Bone marrow failure, with the nadir at 2 to 4 weeks; infection and haemorrhage. Survival depends on supportive care and transfusion; the LD50 is about 4 Gy without treatment
6 to 10 Gy — gastrointestinal syndrome	Destruction of the intestinal mucosa, with intractable diarrhoea, fluid loss and sepsis; death in 1 to 2 weeks, and survival is unusual
Above 10 to 20 Gy — cerebrovascular (neurovascular) syndrome	Cerebral oedema, convulsions, coma and shock; death within hours to a few days, and is invariable

The course has a characteristic pattern — a prodromal phase of nausea, vomiting and malaise within hours, whose speed of onset indicates the dose and is the best early guide; a latent phase of apparent recovery lasting days to weeks, which is deceptive; the manifest illness; and recovery or death
The absolute lymphocyte count at 48 hours is the most useful early indicator of dose; and chromosomal aberration (dicentric) analysis of lymphocytes is the reference method of biological dosimetry

CLINICAL PEARL

The latent phase is what makes radiation injury dangerous to manage. After the initial vomiting settles, the patient feels well for days or weeks while the marrow is dying, and may be discharged. The speed of onset of the prodrome and the lymphocyte count at 48 hours are therefore the findings that matter — they estimate the dose while the patient still looks healthy.

Late Effects and Applied Aspects

Late (stochastic) effects, which have no threshold dose and whose probability rather than severity increases with dose — malignancy, particularly leukaemia (appearing after about 5 to 7 years) and solid tumours of the thyroid, breast and lung (after 10 to 20 years or more); and genetic effects in offspring
Deterministic effects, which have a threshold and whose severity increases with dose — skin erythema and necrosis, cataract, sterility, marrow depression, and radiation fibrosis
Effects on the fetus — the greatest risk is in the period of organogenesis (weeks 2 to 8), and of mental retardation between weeks 8 and 15; producing microcephaly, growth retardation, malformation and childhood malignancy. This is why radiography of the abdomen in a woman of reproductive age requires the exclusion of pregnancy
Medicolegal contexts — occupational exposure and compensation claims; nuclear and industrial accidents; therapeutic overdose and negligence in radiotherapy; radiation from lost or stolen industrial sources, of which India has had notable incidents; deliberate poisoning with a radionuclide; and medical exposure from unnecessary imaging
Protection rests on time, distance and shielding — minimise the time of exposure, maximise the distance (the dose falls with the inverse square of distance, so doubling the distance quarters the dose), and interpose shielding; together with dosimeter badges, designated controlled areas, and the ALARA principle (as low as reasonably achievable)
In a contaminated casualty, decontaminate by removing the clothing, which removes the great majority of external contamination, and wash the skin; treat life-threatening injuries first, since radiation exposure is never the immediate threat to life; and protect staff without withholding treatment
Take an early lymphocyte count and repeat it; it is the most practical estimate of dose available, and blood should be sent for cytogenetic dosimetry

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