The effects of dialysis on 131I kinetics and dosimetry in thyroid cancer patients--a pharmacokinetic model.
Currently, an accepted post-surgical treatment of patients with thyroid carcinoma is administration of an ablative dose of I. This treatment is well established based on extensive experience and modeling. However, for patients with renal disease, reduced iodine removal rates result in controversial thyroid doses and potentially excessive red bone marrow doses. There are differences of opinion regarding I dose recommendations ranging from a reduction in dose to an increase in dose compared with conventional amounts. Determination of suitable doses must take into account varying dialysis protocols and absorbed dose considerations to the thyroid and sensitive tissues such as red bone marrow. The specific aim of this study was to develop a simple yet comprehensive compartmental model for I kinetics in patients with thyroid carcinoma and end stage renal disease, which accounts for dialysis and provides absorbed dose estimates for the thyroid as well as the red bone marrow. STELLA, a compartmental modeling software program, was used to develop a kinetic model that includes the blood pool, thyroid, gastrointestinal tract, kidneys, bladder, and a conventional dialysis machine. Benchmarking was performed to demonstrate the validity of the model with data obtained from ICRP 30 and MIRD Dose Estimate Report No. 5. Iodine kinetics were simulated for normal patients, thyroid cancer patients, and patients with thyroid cancer and renal failure undergoing two standard types of dialysis, hemodialysis and continuous ambulatory peritoneal dialysis (CAPD). Results in this work show that thyroid doses to patients with thyroid cancer and renal failure on hemodialysis or CAPD are slightly higher than doses to patients with thyroid cancer and normal renal function. These results further indicate that red bone marrow doses to patients with thyroid cancer and renal failure on dialysis can be significantly higher than red bone marrow doses to patients with thyroid cancer and normal renal function, and thus these patients could benefit from a reduction in administered activity. Thyroid doses and red bone marrow doses to patients on standard hemodialysis depend on both dialysis frequency and the time interval between administration and first dialysis. The results in this study provide guidelines on how much activity a patient on dialysis should receive based on thyroid and red bone marrow absorbed dose (Gy MBq) considerations. This study should help to clarify some of the contradictory recommendations regarding I dose for thyroid carcinoma patients with renal failure.
Pahlka
Raymond B
RB
INP-606 Everett Tower, University of Oklahoma Health Sciences Center, Oklahoma, OK 73190, USA.
Sonnad
Jagadeesh R
JR
D001853:Bone Marrow / Q000528:radiation effects; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use*; D007676:Kidney Failure, Chronic / Q000150:complications*; D008954:Models, Biological; D011879:Radiotherapy Dosage; D006435:Renal Dialysis; D012984:Software; D013961:Thyroid Gland / Q000378:metabolism / Q000528:radiation effects; D013964:Thyroid Neoplasms / Q000150:complications / Q000532:radiotherapy*
D007457:Iodine Radioisotopes