title: The impact of iodinated contrast agent administered during preoperative computed tomography scan on body iodine pool in patients with differentiated thyroid cancer preparing for radioactive iodine treatment.
abstract: BACKGROUND
  Iodine in iodinated contrast agents (ICAs) interferes with radioactive iodine treatment (RAIT) and diagnostic scans in patients with differentiated thyroid carcinoma (DTC) because it can compete with ¹³¹I. Published guidelines recommend delaying RAIT for three to four months in patients who have been exposed to ICA. Spot urinary iodine concentration is a useful marker to reflect the body iodine pool. We investigated the impact of ICAs administered at preoperative computed tomography (CT) scan on the body iodine pool to determine the proper time interval between preoperative CT and RAIT in DTC patients.
  
  
  METHODS
  We performed a retrospective review of 1023 patients with DTC who underwent a preoperative CT scan with ICA, total thyroidectomy, and one week of low-iodine diet in preparation for RAIT. Urine iodine excretion (UIE) was measured in spot urine by inductively coupled plasma mass spectrometry and reported both in simple concentration (μg/L) and divided by gram creatinine (μg/gCr). Patients were divided into five groups by time interval in days between preoperative CT scan and spot urine iodine measurement (A, 31-60 [n=29]; B, 61-90 [n=155]; C, 91-120 [n=546]; D, 121-150 [n=226]; E, 151-180 [n=67]).
  
  
  RESULTS
  The median (interquartile range) of UIE (μg/gCr) in each group was 44.4 (27.7-73.2) in group A, 33.3 (22.8-64.7) in group B, 32.7 (20.8-63.0) in group C, 32.0 (20.6-67.0) in group D, and 30.4 (19.6-70.8) in group E. There was no significant difference between group A and the remaining groups (p>0.05) Also, the proportion of patients who achieved the appropriate UIE for RAIT according to our hospital's cutoff (≤66.2 μg/gCr) was not different between groups (A, 72.4%; B, 76.1%; C, 77.5%; D, 74.8%; E, 74.6%) (p=0.78).
  
  
  CONCLUSIONS
  This study shows that a UIE of one month after preoperative CT scan with ICA was not higher than that of six months after CT scan in patients who underwent total thyroidectomy for DTC. Thus, current guidelines that recommend delay of RAIT for three to four months after CT scan with ICA should be revisited and future studies to clarify the appropriate time interval between CT scan with ICA and RAIT are warranted.
authors.affiliation: 1 Division of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine , Seoul, Republic of Korea.
authors.forename: Seo Young
authors.initials: SY
authors.lastname: Sohn
authors.forename: Ji Hun
authors.initials: JH
authors.lastname: Choi
authors.forename: Na Kyung
authors.initials: NK
authors.lastname: Kim
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Joung
authors.forename: Yoon Young
authors.initials: YY
authors.lastname: Cho
authors.forename: Sun Mi
authors.initials: SM
authors.lastname: Park
authors.forename: Tae Hun
authors.initials: TH
authors.lastname: Kim
authors.forename: Sang Man
authors.initials: SM
authors.lastname: Jin
authors.forename: Ji Cheol
authors.initials: JC
authors.lastname: Bae
authors.forename: Soo Youn
authors.initials: SY
authors.lastname: Lee
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Chung
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000652:urine; D002277:Carcinoma / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery / Q000652:urine; D002291:Carcinoma, Papillary; D003287:Contrast Media / Q000009:adverse effects* / Q000032:analysis / Q000493:pharmacokinetics; D004347:Drug Interactions; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007455:Iodine / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000652:urine; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D011300:Preoperative Care / Q000009:adverse effects*; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D018714:Radiotherapy, Adjuvant; D065667:Renal Elimination; D056910:Republic of Korea; D012189:Retrospective Studies; D062606:Tertiary Care Centers; D000077273:Thyroid Cancer, Papillary; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery / Q000652:urine; D013965:Thyroidectomy; D014057:Tomography, X-Ray Computed
chemical_list: D015415:Biomarkers; D003287:Contrast Media; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D007455:Iodine