TOPIC: RADIATION HAZARDS
🌟IMPORTANT POINTS TO REMEMBER
🔹Biological effects: Can be somatic (stochastic effect, deterministic effect) or genetic. The effect can be also acute or immediate effect and chronic or long-term effect.
🔹Immediate effects of radiation are dermatitis, brittleness of the fingernail, epilation and leukopenia.
🔹Chronic or long-term effect: Repeated low levels of radiation exposure lead to induction of carcinoma, leukaemia, necrosis and retardation of growth.
🔹Direct effect: When the energy of a photon or secondary electron ionises a biological macromolecule, the effect is termed as direct effect. There is formation of free radicals, dissociation and cross-linking, damage to DNA, radiation-induced malignancy and congenital abnormality.
🔹Indirect effect: Radiation incident on the tissue may ionise the cellular water releasing highly reactive radiolytic products, such as free radical and hydrate electrons which, in turn, react with cellular DNA.
🔹Radiolysis of water can cause formation of free radicals and hydroperoxyl free radicals.
🔹Effect of radiation on the body depends on a number of factors, including types of radiation, dose, dose rate, oxygen, LET, quality of beam, irradiation, cell and tissue sensitivity and age.
🔹Radiosensitivity of the cells: There are five types of radiosensitivity of cells: vegetative intermitotic cells, differentiating intermitotic cells, connective cells, reverting postmitotic cells and fixed postmitotic cells.
🔹Nucleic acids: Single-strand breakage, double-strand breakage and cross-linking of DNA strand.
🔹Proteins: Irradiation of proteins leads to changes in their secondary and tertiary structure by disruption of side chains or the breakage of hydrogen or disulphide bonds.
🔹Chromosomes: Chromatid aberration and chromosome aberration.
🔹Cytoplasm: Mitochondria demonstrate increased permeability.
🔹Cell kinetic: Mitotic delay and cell death.
🔹OMM: Mucositis, pseudomembrane formation, infection and loss of taste.
🔹Salivary gland: Loss of salivary secretion, xerostomia and increase in bacterial count.
🔹Radiation caries: Widespread superficial lesion, circumferential caries and pigmentation of crown.
🔹Bone: Due to irradiation normal marrow is replaced by fatty marrow and endosteum becomes atrophic.
🔹Osteoradionecrosis: Bone infection occurs due to radiation-induced breakdown of the OMM, mechanical damage to the weakened OMM, periodontal lesion or radiation caries.
🔹Acute radiation syndrome: Prodromal period after exposure of 1.5 Gy.
🔹Haematopoietic syndrome: Whole-body exposure of 2–7 Gy causes injury to the haematopoietic stem cells of the bone marrow.
🔹Gastrointestinal syndrome: Exposure of the whole body in the range of 7–15 Gy causes extensive damage to the gastrointestinal system.
🔹Cardiovascular and central nervous system syndrome: Exposure in excess of 50 Gy can cause death in 1–2 days.
🔹Effect on unborn (fetus): There can be congenital abnormalities and death associated with large dose of radiation.
🔹Occupational exposure: MPD for an individual during occupational exposure is 0.05 Sv (5 rem) per year.
🔹Age proportional formula is given as follows🙁 1 N − × 8) 0.05 Sv where N is the actual age of a person.
🔹Skin dose: It is the measure of intensity of radiation at the surface of the patient’s skin surface in coulombs per kilogram.
🔹Gonadal dose: Radiation to abdomen results in the highest dose to gonads, and radiation to head, neck and extremities results in the lowest dose to gonads.
🔹Mean active bone marrow dose: The mean active bone marrow dose is derived as specific tissue dose relevant to particular somatic effect. It is the average dose of radiation in entire active bone marrow.
🔹Thyroid dose: Average dose to the thyroid gland is 6 mrad or 1/1000 of the dose necessary to induce thyroid cancer.
🔹Eye dose: Radiation of more than 2 Gy is necessary to induce cataract formation.
🔹Parotid dose: Parotid gland tumour can occur with dental X-ray exposure of 50 rad.
🔹Carcinogenesis: Radiation causes cancer by modifying DNA. Most common types of cancers after radiation exposure are thyroid cancer, oesophageal cancer, brain and nervous system cancer, salivary gland cancer and leukaemia.
🔹Other effects are on growth and development, mental retardation and sterility.