Indian Journal of Radiology Indian Journal of Radiology  

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MAJOR PAPERS Table of Contents   
Year : 2002  |  Volume : 12  |  Issue : 1  |  Page : 21-32
A review of the current concepts of radiation measurement and its biological effects

Department of Radiology, Safdarjang Hospital, New Delhi-110029, India

Correspondence Address:
S B Grover
Department of Radiology, Safdarjang Hospital, New Delhi-110029
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Source of Support: None, Conflict of Interest: None

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Radiation measurement units have undergone a change from Rads and Rems to Grays and Sieverts. However, radiobiology literature uses both systems, resulting in confusion for Radiologists. Radiation exposure is quantified by the unit Kerma which is currently expressed in Grays and Sieverts. In this review, we attempt to explain both the earlier units and the present system of SI (System International) units. This review also appraises the reader that human beings live under significant doses of radiation from natural sources, such as the naturally occurring radioactive gas radon, besides that from man-made sources such as X-rays, radioactive medication and nuclear installations. The biological effects of radiation had been studied and documented within few years of the discovery of X-rays and further information has consequently been available from longitudinal studies on populations affected by the atomic bomb. Biological effects are classified as deterministic (or certainty effects) and stochastic effects. Both deterministic and stochastic effects may either result in changes in organs (somatic effects) or in the genes (genetic effects). Deterministic or certainty effects are directly related to a known dose of radiation and have a dose threshold and their severity is also dose related. Stochastic effects are random events which are not dose related but their probability increases with an increase in the radiation dose. Carcinogenesis and genetic mutations are stochastic effects. The radiosensitivity of organs varies, therefore the various doses at which the deterministic effects on different organs occur are reviewed. The doses likely to be associated with 'risks of cancer' are also enumerated and the doses related to genetic mutations are also discussed. The effects on the fetus are both somatic and genetic and the most radiosensitive period is 8-17 weeks of gestation. The safety of radiographic imaging is discussed with reference to doses delivered in common radiological studies. Radiation doses permissible during pregnancy in the general population and in radiation workers are also highlighted.

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