title: Pretherapeutic dosimetry before 131I therapy of benign thyroid disease. A clinical practice assessment of dosimetric parameters.
abstract: OBJECTIVE
  To compare uptake measurements and different methods for the pretherapeutic determination of the effective thyroidal ¹³¹I half life (Teff) to the results of posttherapeutic dosimetric measurements.
  
  
  METHODS
  Retrospective study of 1538 patients who received their first RIT in our department for autonomous thyroid nodules (ATN), autonomous multinodular goiter (AMG) or Graves' disease (GD) between November 1999 and January 2011. Pretherapeutic measurements were performed at any combination of 24 h, 48 h and 6 days after 131I administration. Post-therapy dosimetric measurements were performed in 12 h intervals until discharge. Teff was determined through monoexponential curve fitting.
  
  
  RESULTS
  Pretherapeutic Teff values based on measurements at 24 h and 48 h, 24 h and 6 d, 48 h and 6 d as well as on day 24 h, 48 h and 6 d yielded implausible (< 2 d or > 8 d) values for Teff, in 60.4%, 25.7%, 29.1 and 21.4% of available calculations, respectively. The plausible results showed significant, clinically relevant and sometimes considerable overestimations of Teff. Using empirically determined fixed disease specific Teff values resulted in a better congruence between the pre- and posttherapeutic dosimetry results. 24 h measurements were marginally more accurate than 48 h ones in AMG and GD whereas 48 h measurements were marginally more accurate in ATN; these differences are however not clinically relevant. 6 d measurements are clearly less accurate than those after 24 h or 48 h.
  
  
  CONCLUSIONS
  In ATN, AMG and GD, pretherapeutic dosimetry can be performed by a single uptake measurement at 24 h or 48 h using a fixed, disease specific value for Teff. Additional later measurements do not yield a further clinically relevant contribution to accuracy of pretherapeutic dosimetry.
authors.affiliation: Thomas Krohn, MD, University Hospital Aachen, Department of Nuclear Medicine, Pauwelsstr. 3, 52074 Aachen, Germany, Tel. +49/(0)241/803 57 89, Fax +49/(0)241/808 25 20.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krohn
authors.forename: F F
authors.initials: FF
authors.lastname: Behrendt
authors.forename: A
authors.initials: A
authors.lastname: Heinzel
authors.forename: B
authors.initials: B
authors.lastname: Müller
authors.forename: F M
authors.initials: FM
authors.lastname: Mottaghy
authors.forename: F A
authors.initials: FA
authors.lastname: Verburg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000032:analysis / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011874:Radiometry / Q000379:methods*; D019275:Radiopharmaceuticals / Q000032:analysis / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013959:Thyroid Diseases / Q000175:diagnosis* / Q000532:radiotherapy*; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals
keywords: 131I therapy; benign thyroid disease; dosimetry