title: Diagnostic I-131 scintigraphy in patients with differentiated thyroid cancer: no additional value of higher scan dose.
abstract: OBJECTIVE
  After initial treatment with total thyroidectomy and radioiodine ablation, most follow-up protocols for patients with differentiated thyroid carcinoma contain cyclic diagnostic I-131 imaging and serum thyroglobulin measurements. The applied diagnostic I-131 doses vary between 37 and 370 MBq. The aim of this study was to determine the yield of a diagnostic scan with 370 MBq I-131 in patients with a negative diagnostic scan with 74 MBq I-131.
  
  
  METHODS
  Retrospective evaluation of 158 patients who received a high-dose diagnostic scan with 370 MBq I-131 because of a negative low-dose diagnostic scan with 74 MBq I-131. Special attention was paid to the patients with positive high-dose diagnostic scanning and undetectable serum thyroglobulin levels after thyroid hormone withdrawal.
  
  
  RESULTS
  In 127 (80%) of patients the 370 MBq I-131 scan was negative, just like the preceding low-dose scan. In 31 (20%) of patients abnormal uptake was present on the 370 MBq diagnostic scan. In 19 of these 31 patients serum thyroglobulin was undetectable. In 15/19 the high-dose diagnostic scan proved either false positive or demonstrated clinically irrelevant minor ablation rests. In only four patients (2.5%) did the high-dose diagnostic scans reveal possibly relevant uptake caused by residual differentiated thyroid cancer.
  
  
  CONCLUSIONS
  In 98% of patients a 370 MBq dose of I-131 for diagnostic WBS had no additional value. The combination of a low-dose diagnostic I-131 scan using only 74 MBq combined with a serum Tg level measurement proved sufficient for correct clinical decision making regarding whether the patient requires additional I-131 therapy.
authors.affiliation: Department of Endocrinology, University Hospital Groningen, The Netherlands.
authors.forename: Thi T H
authors.initials: TT
authors.lastname: Phan
authors.forename: Karin M
authors.initials: KM
authors.lastname: van Tol
authors.forename: Thera P
authors.initials: TP
authors.lastname: Links
authors.forename: D Albertus
authors.initials: DA
authors.lastname: Piers
authors.forename: Elisabeth G E
authors.initials: EG
authors.lastname: de Vries
authors.forename: Robin P F
authors.initials: RP
authors.lastname: Dullaart
authors.forename: Pieter L
authors.initials: PL
authors.lastname: Jager
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood* / Q000000981:diagnostic imaging* / Q000517:prevention & control; D011379:Prognosis; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood* / Q000000981:diagnostic imaging* / Q000628:therapy
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013954:Thyroglobulin