Subject(s)
Adenoma, Oxyphilic/metabolism , Carcinoma, Papillary/metabolism , Iodine Radioisotopes/pharmacokinetics , Models, Biological , Models, Statistical , Thyroid Neoplasms/metabolism , Adenoma, Oxyphilic/radiotherapy , Adenoma, Oxyphilic/secondary , Algorithms , Carcinoma, Papillary/radiotherapy , Carcinoma, Papillary/secondary , Electrons , Humans , Iodine Radioisotopes/administration & dosage , Iodine Radioisotopes/chemistry , Microspheres , Monte Carlo Method , Radiotherapy Planning, Computer-Assisted , Thyroid Neoplasms/radiotherapy , Tissue DistributionABSTRACT
UNLABELLED: We evaluated the effects on the absorbed dose to thyroid follicular cells of self-absorption of (131)I radiation (specifically, beta-rays) in the follicular colloid. METHODS: Thyroid follicles were modeled as colloid-filled spheres, containing a uniform concentration of (131)I and surrounded by a concentric monolayer of cells. Assuming close packing of identical follicles, we used Monte Carlo simulation to assess the absorbed dose to follicular cells. RESULTS: Because of beta-ray self-absorption in colloidal spheres with radii larger than 50 mum, the absorbed dose to follicular cells is less than the average thyroid absorbed dose. CONCLUSION: For the same thyroid mass, radioiodine thyroid uptake, and effective half-life, patients with follicles with colloidal sphere radii of 100, 200, 300, and 400 microm should be administered 9%, 15%, 21%, and 30% more (131)I, respectively, than patients with colloidal sphere radii of less than 50 microm, to yield the same absorbed dose to follicular cells.
