Prediction of iodine-131 biokinetics and radiation doses from therapy on the basis of tracer studies: an important question for therapy planning in nuclear medicine

摘要

ObjectivesThis study aimed to present a comparison of iodine-131 (I-131) biokinetics and radiation doses to red-marrow (rm) and whole-body (wb), following the administration of tracer and therapeutic activities, as a means of confirming whether I-131 clearance and radiation doses for therapy procedures can be predicted by tracer activities.MethodsEleven differentiated thyroid cancer patients were followed after receiving tracer and therapeutic I-131 activity. Whole-body I-131 clearance was estimated using radiation detectors and OLINDA/EXM software was used to calculate radiation doses to rm and wb.Results and discussionTracer I-131 activity of 86 (14)MBq and therapeutic activity of 8.04 (+/- 1.18)GBq were administered to patients, thereby producing an average wb I-131 effective half-time and residence time of, respectively, 13.51 (+/- 4.05) and 23.13 (+/- 5.98)h for tracer activities and 13.32 (+/- 3.38) and 19.63 (+/- 4.77)h for therapy. Radiation doses to rm and wb were, respectively, 0.0467 (+/- 0.0208) and 0.0589 (+/- 0.0207)mGy/MBq in tracer studies and 0.0396 (+/- 0.0169) and 0.0500 (+/- 0.0163)mGy/MBq in therapy. Although the differences were not considered statistically significant between averages, those between the values of effective half-times (P=0.906), residence times (P=0.145), and radiation doses to rm (P=0.393) and to wb (P=0.272), from tracer and therapy procedures, large differences of up to 80% in wb I-131 clearance, and up to 50% in radiation doses were observed when patients were analyzed individually, thus impacting on the total amount of I-131 activity calculated to be safe for application in individual therapy.Conclusion(131)I biokinetics and radiation doses to rm and wb in therapy procedures are well predicted by diagnostic activities when average values of a group of patients are compared. Nonetheless, when patients are analyzed individually, significant differences may be encountered, thus implying that nuclear medicine therapy-planning requires due consideration of changes in individual patient-body status from initial tracer to final therapy procedures to thus provide appropriate adjustments in therapeutic activities. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.