title: 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.
abstract: OBJECTIVE
  This study aimed to present a comparison of iodine-131 (I) 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 clearance and radiation doses for therapy procedures can be predicted by tracer activities.
  
  
  METHODS
  Eleven differentiated thyroid cancer patients were followed after receiving tracer and therapeutic I activity. Whole-body I clearance was estimated using radiation detectors and OLINDA/EXM software was used to calculate radiation doses to rm and wb.
  
  
  CONCLUSIONS
  Tracer I activity of 86 (±14) MBq and therapeutic activity of 8.04 (±1.18) GBq were administered to patients, thereby producing an average wb I 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 clearance, and up to 50% in radiation doses were observed when patients were analyzed individually, thus impacting on the total amount of I activity calculated to be safe for application in individual therapy.
  
  
  CONCLUSIONS
  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.
authors.affiliation: aCancer Institute of São Paulo State (ICESP), Clinical Hospital bNuclear Medicine Service, Department of Radiology, School of Medicine, University of São Paulo, São Paulo, Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Willegaignon
authors.forename: Rogério A
authors.initials: RA
authors.lastname: Pelissoni
authors.forename: Beatriz C G D
authors.initials: BC
authors.lastname: Lima
authors.forename: Marcelo T
authors.initials: MT
authors.lastname: Sapienza
authors.forename: George B
authors.initials: GB
authors.lastname: Coura-Filho
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Buchpiguel
mesh_terms: D000328:Adult; D001853:Bone Marrow / Q000528:radiation effects; D005260:Female; D006207:Half-Life; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D007700:Kinetics; D008875:Middle Aged; D009683:Nuclear Medicine; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000532:radiotherapy; D014916:Whole-Body Irradiation
chemical_list: D007457:Iodine Radioisotopes