Radioiodine dosimetry in patients with end-stage renal disease receiving continuous ambulatory peritoneal dialysis therapy

In patients with end-stage renal disease (ESRD), Na131I dosages for thyroid cancer may have to be reduced to avoid excess radiation doses to red marrow, because radioiodine is primarily excreted by kidneys. In ESRD patients receiving continuous ambulatory peritoneal dialysis (CAPD) therapy (three to five 2-L exchanges daily) creatinine clearance rates are very low (mean, 7 mL/min), and radioiodine clearance rates may be proportionately reduced. Thus, radioiodine kinetic studies were performed in two hypothyroid CAPD patients with thyroid cancer, in eight euthyroid CAPD patients, and in eight thyroid cancer patients with normal renal function. All received Na131I or Na123I orally, with serial blood, urine, and/or dialysate sampling for 24-70 h. Dosimetry calculations were performed using the MIRDOSE3 computer program. In CAPD patients, serum radioiodine half-times were 5 times longer, and radioiodine clearance rates by urine plus dialysate were 20% of those in patients with normal renal function. Na131I dosages for the two CAPD patients with thyroid cancer were reduced from 150 mCi [5.6 gigabecquerels (GBq)] to 26.6 mCi (0.98 GBq) and 29.9 mCi (1.11 GBq), respectively, resulting in radiation doses to red marrow and total body comparable to those in patients with normal renal function who received a mean of 148 mCi (5.5 GBq) Na131I. Thus, in patients receiving continuous ambulatory peritoneal dialysis therapy, 5-fold reductions in radioiodine clearance rates require 5-fold decreases in Na131I dosages to avoid excessive radiation doses to total body and red marrow.