title: SPECT/CT localization of oral radioiodine activity: a retrospective study and in-vitro assessment.
abstract: OBJECTIVE
  We sought to further localize radioiodine activity in the mouth on post-thyroid cancer therapy imaging using single-photon emission computed tomography/computed tomography (SPECT/CT).
  
  
  METHODS
  We retrospectively reviewed all patients (58) who underwent thyroid cancer therapy with iodine-131 (131I) at our institution from August 2009 to March 2011 whose post-therapy radioiodine imaging included neck SPECT/CT. A small group (six) of diagnostic 131I scans including SPECT/CT was also reviewed. Separately, we performed in-vitro 131I (sodium iodide) binding assays with amalgam and Argenco HP 77 (77% dental gold alloy) as proof of principle for these interactions.
  
  
  RESULTS
  Of the 58 post-therapy patients, 45 (78%) had undergone metallic dental restorations, and of them 41 (91%) demonstrated oral 131I activity localizing preferentially to those restorations. It was observed that radioiodine also localized to other dental restorations and to orthodontic hardware. Gum-line activity in edentulous patients suggests radioiodine interaction with denture adhesive. In vitro, dental amalgam and Argenco HP 77 bound 131I in a time-dependent manner over 1-16 days of exposure. Despite subsequent washings with normal saline, significant 131I activity (maximally 12% for amalgam and 68% for Argenco HP 77) was retained by these metals. Subsequent soaking in a saturated solution of potassium iodide partially displaced 131I from amalgam, with near-total displacement of I from Argenco HP 77.
  
  
  CONCLUSIONS
  SPECT/CT shows that radioiodine in the oral cavity localizes to metallic dental restorations. Furthermore, in-vitro studies demonstrate partially reversible binding of 131I to common dental metals.
authors.affiliation: aDepartment of Radiology, University of New Mexico bPrivate Practice, Albuquerque, New Mexico cDepartment of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, USA.
authors.forename: Jared S
authors.initials: JS
authors.lastname: Burlison
authors.forename: Michael F
authors.initials: MF
authors.lastname: Hartshorne
authors.forename: Alan M
authors.initials: AM
authors.lastname: Voda
authors.forename: Franklin H
authors.initials: FH
authors.lastname: Cocks
authors.forename: Joanna R
authors.initials: JR
authors.lastname: Fair
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes