title: Impact of patient age on the iodine/FDG "flip-flop" phenomenon in lung metastasis from thyroid cancer.
abstract: OBJECTIVE
  Radioiodine therapy is an effective treatment for lung metastasis from thyroid cancer. However, cases of lung metastasis without iodine uptake are often encountered. In such cases, FDG accumulation in lung lesions is often observed. There is a reverse relationship between iodine and FDG accumulation in thyroid cancer lesions, the so-called "flip-flop" phenomenon. The aim of this study was to assess the relationship between patient age and the occurrence of the flip-flop phenomenon.
  
  
  METHODS
  Eighty-six patients who underwent radioiodine therapy for lung metastasis were studied retrospectively (age 17-73 years; median 60 years; males:females 22:64). We compared the clinical data and imaging findings (size and FDG uptake of lung nodules) between patients with (n = 44) and without (n = 42) iodine uptake in lung metastasis.
  
  
  RESULTS
  Significantly more young patients showed iodine accumulation in lung metastasis than old patients (p = 0.0025). Lung metastases with larger size or greater FDG uptake showed no iodine uptake more frequently with significant difference (p = 0.015 and <0.001, respectively). Among patients with FDG uptake in the lung metastasis, 57.1 % of young patients (<60 years) and 24.3 % of the old patients (≥60 years) showed iodine uptake (p = 0.0029).
  
  
  CONCLUSIONS
  Higher patient age and lung nodules with large size or FDG accumulation are negative factors for iodine accumulation in lung metastases from thyroid cancer. In addition, our results show that young patients have a greater likelihood of iodine uptake even when FDG accumulates in lung metastasis, in contrast to old patients.
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan. taisoda@radiol.med.kyushu-u.ac.jp.
authors.forename: Takuro
authors.initials: T
authors.lastname: Isoda
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: BaBa
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Maruoka
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kitamura
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Tahara
authors.affiliation: Department of Health Sciences, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Sasaki
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-Ku Fukuoka, Fukuoka, 812-8582, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Honda
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001692:Biological Transport; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000556:secondary*; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology* / Q000532:radiotherapy*; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019788:Fluorodeoxyglucose F18
keywords: FDG-PET; Flip-flop phenomenon; Radioiodine therapy; Thyroid cancer