Radiation dose estimates in Indian adults in normal and pathological conditions due to 99Tcm-labelled radiopharmaceuticals.

ICRP Publications 53, 62 and 80 give organ dose coefficients and effective doses to ICRP Reference Man and Child from established nuclear medicine procedures. However, an average Indian adult differs significantly from the ICRP Reference Man as regards anatomical, physiological and metabolic characteristics, and is also considered to have different tissue weighting factors (called here risk factors). The masses of total body and most organs are significantly lower for the Indian adult than for his ICRP counterpart (e.g. body mass 52 and 70 kg respectively). Similarly, the risk factors are lower by 20-30% for 8 out of the 13 organs and 30-60% higher for 3 organs. In the present study, available anatomical data of Indians and their risk factors have been utilised to estimate the radiation doses from administration of commonly used 99Tcm-labelled radiopharmaceuticals under normal and certain pathological conditions. The following pathological conditions have been considered for phosphates/phosphonates--high bone uptake and severely impaired kidney function; IDA--parenchymal liver disease, occlusion of cystic duct, and occlusion of bile duct; DTPA--abnormal renal function; large colloids--early to intermediate diffuse parenchymal liver disease, intermediate to advanced parenchymal liver disease; small colloids--early to intermediate parenchymal liver disease, intermediate to advanced parenchymal liver disease; and MAG3--abnormal renal function, acute unilateral renal blockage. The estimated 'effective doses' to Indian adults are 14-21% greater than the ICRP value from administration of the same activity of radiopharmaceutical under normal physiological conditions based on anatomical considerations alone, because of the smaller organ masses for the Indian; for some pathological conditions the effective doses are 11-22% more. When tissue risk factors are considered in addition to anatomical considerations, the estimated effective doses are still found to be generally somewhat higher for the Indian, for both normal and pathological states (but lower than the values based on anatomical considerations alone). However, when the radiopharmaceutical is administered in quantities proportional to the body mass, the effective doses are 11-28% lower for the Indian under both normal and pathological conditions. It may be concluded that Indians are at a lower risk of radiation health detriment in comparison with the ICRP adult on administration of the various 99Tcm-labelled radiopharmaceuticals considered in this study.