Simulation of renal function by tumor and its effect on the calculated glomerular filtration rate.

A patient with a retroperitoneal sarcoma near the left kidney was to undergo radiotherapy. Renal assessment with Tc-99m DTPA to determine renal function before radiotherapy resulted in what was thought to be a low glomerular filtration rate based on the Gates computer method and the Russell two-blood-sample method. Most likely this resulted from the observed significant accumulation of DTPA in the tumor for the first few minutes with washout for the rest of the imaging time, simulating renal function.