Physical & biological aspects of radiation dosimetry in nuclear medicine

Increasing the use of ionising radiation in nuclear medicine application has raised the concern among society. This is because of associated risk of low dose ionising radiation in nuclear medicine procedures. Radiation risk mainly associated with biological effects such as indirect effects which may take place due to formation of free radicals in water and sometime direct effects to DNA. Nuclear medicine uses small amount of radioactivity for the functional imaging and treatment of various diseases. It is still unclear the dose response relationship for different short lived tracers being used in nuclear medicine. The another method of estimation of absorbed dose of ionising radiation is biological dosimetry, which is an established method to assess the radiation dose following radiation exposure. If physical dosimetry is not feasible, biological dosimetry can also be used as an alternative and reliable method. Biological dosimetry consists of different methods i e. Comet assay, Gamma H2AX assay, sister chromatid exchange, chromosomal breaks, fluorescence in situ hybridization (FISH) or micronucleus (MN) which are used to define the frequency of micronucleated cells in lymphocytes. Recent studies have clearly shown strong correlation between frequency of radiation-induced MN and radiation dose. Apart from this, the dicentric chromosome (DC) is known as one of the most sensitive and reliable biomarker in acute radiation exposure. DC in the FISH images can be estimated using fluorescence imaging software. In order to use the biological dosimetry for dose assessment, the first step is to determine the frequency of DNA damage, MN, aberrations in the peripheral blood lymphocytes of exposed human being. Thereafter, the radiation dose may be estimated using dose response curve