Dosimetry of renal radiopharmaceuticals: the importance of bladder radioactivity and a simple aid for its estimation

The contribution from radioactivity in bladder contents to dose commitments to the embryo, ovaries, red marrow, kidney, bladder wall and total body has been estimated for various renal radiopharmaceuticals, assuming a bladder-voiding period of 3.5 h. For hippuran and GFR agents this contribution is 70-97% of the embryo dose and 50-93% of the ovary dose. The embryo dose exceeds the ovary dose by a factor of two or more. For the radiopharmaceuticals with no significant kidney retention, the surface dose to the bladder wall is higher, by more than an order of magnitude, than doses to other organs and is largely responsible for the effective dose equivalent exceeding the estimated whole-body dose by factors of up to 25. Since the estimation of cumulated activity in bladder contents is necessary for bladder dosimetry, a nomogram based on a 3.5 h voiding period is presented as a convenient aid for this purpose. (author)