Cuban typical doses for 99mTc-DMSA renal gammagraphy studies: a methodology for the establishment of reference levels

Since a handful of years ago, international rules on Radiological Protection include the principle of optimization of given dose to patients, if this procedure doesn't lessen diagnosis quality, and the establishment of reference levels of activity. For these reasons, the Radiological Protection staff of Cuban Institute of Nephrology's Nuclear Medicine Service, where morpho functional renal studies are carried out, 70% on infants and young children, started a research on that way. Thus, because their biggest incidence, 99mTc -DMSA renal gammagraphy studies were chosen, using a General Electric 400 AT Planar Gamma Camera. Studied sample was randomly selected, including adults (12 peoples) and children (23); divided into 4 groups, lessen given dose step by step. Other items were kept in mind in the research, such age, weight, time delayed between administrations and image getting, getting time of each view and total time of the study, as well as radiopharmaceuticals quality and Gamma Camera performance. Image quality was evaluated for each case, using both, objective and subjective criteria. Objective evaluation was done by using contrast/noise ratios and variance of the random noise. They were used to develop clustering and discriminant analysis over the independent variables to detect groups with differentiated image quality from the physical and mathematical point of view. Subjective evaluation was performed using the criteria of two expert observers who had no information about the activity levels used. They evaluated image quality separately, giving a good, regular or bad evaluation for each image. As a conclusion, we found that it is possible to reduce the given activities in 50% and thus, indirectly, to reduce doses for workers and for the public. Additionally, we propose a methodology for the establishment of reference levels for 99mTc -DMSA renal gammagraphy studies in Cuba, both, for adults and paediatric patients. (author)