title: Clinical significance of diffuse intrathoracic uptake on post-therapy I-131 scans in thyroid cancer patients.
abstract: OBJECTIVE
  The purpose of this study was to identify the frequency and possible cause of diffuse intrathoracic uptake on post-therapy I-131 scans in thyroid cancer patients.
  
  
  METHODS
  We retrospectively reviewed 781 post-therapy scans of 755 thyroid cancer patients who underwent total thyroidectomy and radioactive iodine therapy between January and December 2010. Diffuse intrathoracic uptake on post-therapy scans was examined, and clinical patient characteristics including sex, age, regimen for thyroid-stimulating hormone (TSH) stimulation (thyroid hormone withdrawal or recombinant human TSH injection), TSH, thyroglobulin (Tg) and anti-thyroglobulin antibody (anti-Tg Ab) levels, therapeutic dose of radioactive iodine therapy and prior history of radioactive iodine therapy were recorded.Scan findings were correlated with chest CT, chest radiographs, laboratory tests and/or clinical status. Diffuse intrathoracic uptake without evidence of pathologic condition was categorized as indeterminate. The association between clinical characteristics and intrathoracic uptake were analyzed for negative intrathoracic uptake and indeterminate uptake groups.
  
  
  RESULTS
  Diffuse intrathoracic uptake on post-therapy scans was demonstrated in 39 out of 755 (5.2 %) patients, among which 3 were confirmed as lung metastasis. The 14 patients that showed high Tg or anti-Tg Ab levels were considered to be at risk of having undetected micrometastasis on other imaging modalities. The remaining 22 were indeterminate (2.9 %).Upon comparison of negative intrathoracic uptake and indeterminate uptake groups, TSH stimulation by thyroid hormone withdrawal was shown to be significantly correlated with diffuse intrathoracic uptake (p < 0.05).
  
  
  CONCLUSIONS
  The frequency of diffuse intrathoracic uptake on post-therapy scans was 5.2 % and could be seen in thyroid cancer patients with underlying lung metastasis as well as those without definite pathologic condition. In the latter, there was a higher frequency for diffusely increased intrathoracic uptake in those who underwent thyroid hormone withdrawal rather than recombinant human TSH injection.
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, 137-701 Republic of Korea.
authors.forename: Hyun Su
authors.initials: HS
authors.lastname: Choi
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, 137-701 Republic of Korea.
authors.forename: Sung Hoon
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, 137-701 Republic of Korea.
authors.forename: Sonya Youngju
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, 137-701 Republic of Korea.
authors.forename: Hye Lim
authors.initials: HL
authors.lastname: Park
authors.affiliation: Department of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 505 Banpo-dong Seocho-gu, Seoul, 137-701 Republic of Korea.
authors.forename: Ye Young
authors.initials: YY
authors.lastname: Seo
authors.affiliation: Department of Radiology, St. Vincent's Hospital, College of Medicine, The Catholic University of Korea, 93 Ji-Dong Paldal-gu, Suwon, Gyeonggi-do 442-723 Republic of Korea.
authors.forename: Woo Hee
authors.initials: WH
authors.lastname: Choi
keywords: Post-therapy scan; Radioactive iodine therapy; Thyroid cancer