Effects of Radiation and x-ray Hazards
Radiation or Radiant energy is energy emitted or transferred or propagated through the matter (space) that is cause biological effects of radiation on exposed person and these x-ray hazards should be minimized where ever possible.
Ionising Radiation is any type of energy or matter-energy combination capable of removing one or more orbital electrons from the atom after interaction. The process is called as Ionisation.
Once absorbed by tissue, all types of radiation produce changes within the living tissue. The X-ray beam while traversing the tissues forces the electron to be ejected from the atomic lattice. The atom is thus left with surplus positive electric charge. The cells within the tissue come to a state of high chemical reactivity, which can initiate biological effects.
The cellular injury causes pathological and physiological changes leading to “radiation sickness” and other manifestation of radiation damage to the body.
Biological Effects of radiation (Direct and Indirect effects)
After the transfer of radiant energy to the atoms and molecules in the form of excitation and ionisation, the resultant chemical changes in the molecules can be produced by direct and indirect effects of radiation. The direct effects appears due to absorption of energy by the molecules. Indirect effects are caused by the products of radiation decomposition (Radiolysis) of water and other solutes of the body.
After radiolysis of water in the cells, there is formation of free radicals with unpaired electrons. Hº and OHº are the free radicals and H2O2 formed by them are highly reactive and mutagenic.
The various types of damage produced by the radiation in a DNA molecule are change of base called Deamination, loss of base, H+ bond breakage between chains, single strand break, double strand break, cross linking with helix and cross linking with other DNA molecules and proteins.
Radiation Sensitivity of Different Body cells
All living tissues are susceptible to ionising radiation damage. Affected cells may be damaged or killed. Cells that are most sensitive to radiation are rapidly dividing cells i.e. gonadal cells, neoplastic cells, growth cells and metabolically active cells.
Therefore persons under the age of 18 years and pregnant women should not be involved in radiographic procedures.
Other tissues that are readily sensitive to radiation include bone, lymphatic, dermis, leukopoietic and haemopoietic (blood forming) and epithelial cells.
Radiation Hazards
Two types of biological damage can occur from over exposure to radiation-
- Somatic damage
- Genetic damage
The radiation effects may be somatic or genetic. The somatic effects are harmful to a person in his lifetime where as genetic effects affects after generations.
1. Somatic damage
Somatic damage is the term that describes damage to the body that become manifest within the lifetime of the recipient. Radiation can produce immediate changes in the cell. The damage may not be apparent for some time because body has ability to repair itself. Cell damage may never be appreciated or visible. Damage is more extensive when the body is exposed to a single massive dose of radiation than to smaller cumulatively equivalent repeated exposures.
Examples of Somatic damages are Cataract, Cancer, Aplastic anaemia, sterility, Leukaemia and Malignant tumour etc.
2. Genetic damage
Genetic damage from radiation occurs as a result of injury to the genes (DNA) of reproductive cells. Ionising radiation can damage chromosomal materials within any cell. The result of damage is determined by the cell type i.e. somatic cell or reproductive cell. Damage to reproductive cell can result in the effect known as gene mutation. Genetic damage is not detectable until future generations are produced. Their offspring of irradiated persons may be abnormally formed because of changes in the hereditary material resulting in alteration of individual phenotype (physical appearance). The mutation may be lethal / only may visible anomaly. The gene mutation may also lay latent or recessive until the second or third generation.
Mortality from radiation is caused by exposure to extremely high levels of radiation. Exposure to a large, single dose of radiation, as a form of hydrogen bomb is necessary to cause rapid death.
A single exposure to a dose of 300 rad (radiation absorbed dose) or more has been shown to lethal to humans. The exposure received by any individual should never exceed the maximum permissible dose (MPD)
The maximum permissible dose (MPD) is the maximum dose of radiation that a person may receive in a given period.
Measurement of radiation or Radiation Exposure units
Absorbed Dose
Absorbed Dose is the quantity of energy imparted by ionising radiation to matter per unit mass of matter. The unit of Absorbed Dose is gray (Gy) previously called as rad (1 Gy = 100 rad).
Dose Equivalent
Dose Equivalent is the quantity obtained by multiplying the absorbed dose in tissue by the quality factor. This equation accounts for the differing biological effectiveness of equal absorbed doses and other modifying factors. The unit of dose equivalent is Sivert (Sv) Recently called as Rem (Roentgen Equivalent Men) 1 Rem = rad X quality factor (ie. Biological effectiveness of given radiation. The Quality factor for X-ray and Gamma rays is one and for alpha particles 20).