title: Maximum dose rate is a determinant of hypothyroidism after 131I therapy of Graves' disease but the total thyroid absorbed dose is not.
abstract: BACKGROUND
  The determinants of successful (131)I therapy of Graves' disease (GD) are unclear.
  
  
  OBJECTIVE
  To relate dosimetry parameters to outcome of therapy to identify significant determinants eu- and/or hypothyroidism after (131)I therapy in patients with GD.
  
  
  METHODS
  A retrospective study in which 206 Patients with GD treated in University Hospital between November 1999 and January 2011. All received (131)I therapy aiming at a total absorbed dose to the thyroid of 250 Gy based on pre-therapeutic dosimetry. Post-therapy dosimetric thyroid measurements were performed twice daily until discharge. From these measurements, thyroid (131)I half-life, the total thyroid absorbed dose, and the maximum dose rate after (131)I administration were calculated.
  
  
  RESULTS
  In all, 48.5% of patients were hypothyroid and 28.6% of patients were euthyroid after (131)I therapy. In univariate analysis, nonhyperthyroid and hyperthyroid patients only differed by sex. A lower thyroid mass, a higher activity per gram thyroid tissue, a shorter effective thyroidal (131)I half-life, and a higher maximum dose rate, but not the total thyroid absorbed dose, were significantly associated with hypothyroidism. In multivariate analysis, the maximum dose rate remained the only significant determinant of hypothyroidism (P < .001). Maximum dose rates of 2.2 Gy/h and higher were associated with a 100% hypothyroidism rate.
  
  
  CONCLUSIONS
  Not the total thyroid absorbed dose, but the maximum dose rate is a determinant of successfully achieving hypothyroidism in Graves' disease. Dosimetric concepts aiming at a specific total thyroid absorbed dose will therefore require reconsideration if our data are confirmed prospectively.
authors.affiliation: Department of Nuclear Medicine (T.K., B.M., F.B., A.H., F.M.M., F.A.V.), RWTH Aachen University Hospital, 52074 Aachen, Germany; Department of Nuclear Medicine (H.H.), University of Würzburg, 97080 Würzburg, Germany; and Department of Nuclear Medicine (F.M.M., F.A.V.), Maastricht University Medical Center, 6229 HX Maastricht, The Netherlands.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krohn
authors.forename: Heribert
authors.initials: H
authors.lastname: Hänscheid
authors.forename: Berthold
authors.initials: B
authors.lastname: Müller
authors.forename: Florian F
authors.initials: FF
authors.lastname: Behrendt
authors.forename: Alexander
authors.initials: A
authors.lastname: Heinzel
authors.forename: Felix M
authors.initials: FM
authors.lastname: Mottaghy
authors.forename: Frederik A
authors.initials: FA
authors.lastname: Verburg
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006111:Graves Disease / Q000188:drug therapy*; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis*; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D013961:Thyroid Gland; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals