title: Extremity Radioactive Iodine Uptake on Post-therapeutic Whole Body Scan in Patients with Differentiated Thyroid Cancer.
abstract: OBJECTIVE
  We investigated a frequency of lower extremity uptake on the radioactive iodine (RAI) whole body scan (WBS) after RAI treatment in patients with differentiated thyroid cancer, in order to retrospectively examine whether or not the frequency was pathological.
  
  
  METHODS
  This retrospective study included 170 patients with thyroid cancer, undergoing RAI treatment. Overall, 99(58%) and 71(42%) patients received single and multiple RAI treatments, respectively. Post-therapeutic WBS was acquired after 3 days of RAI administration. For patients with multiple RAI treatments, the WBS of their last RAI treatment was evaluated. Lower extremity uptake on post-therapeutic WBS was classified into 3 categories: bilateral femoral uptake (type A), bilateral femoral and tibia uptake (type B), and uptake in bilateral upper and lower extremities (type C). Then, the patients with RAI uptake in the lower extremities on WBS were analyzed with clinical parameters.
  
  
  RESULTS
  Overall, 99 patients (58%) had the extremity uptake on their posttherapeutic RAI WBS. As the results indicated, 42, 53, and 4 patients had type A, type B, and type C uptakes, respectively. Lower extremity uptake was significantly associated with younger age, not only in subjects with multiple RAI treatments but also in all the patients (P<0.05). Accumulation in patients with multiple RAI treatments was more frequent than patients with single RAI treatment (P<0.05). Lower extremity uptake was not associated with counts of the white blood cell count, hemoglobin level, platelet count, estimated glomerular filtration rate, effective half-time of RAI, serum TSH level, and anti-Tg concentration.
  
  
  CONCLUSIONS
  About half of the patients had lower extremity uptake on the posttherapeutic RAI WBS, especially younger patients and those with multiple courses of RAI treatment. Bilateral lower extremity's RAI uptake on the posttherapeutic WBS should be considered as physiological RAI distribution in bone marrow.
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Wakabayashi
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Taki
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Anri
authors.initials: A
authors.lastname: Inaki
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Ayane
authors.initials: A
authors.lastname: Toratani
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Kayano
authors.affiliation: Department of Nuclear Medicine, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Seigo
authors.initials: S
authors.lastname: Kinuya
keywords: Lower Extremity; Physiological Uptake; Radioactive Iodine; Thyroid Cancer; Whole Body Scan