title: Effects of low-dose and high-dose postoperative radioiodine therapy on the clinical outcome in patients with small differentiated thyroid cancer having microscopic extrathyroidal extension.
abstract: BACKGROUND
  It is unclear whether differentiated thyroid cancer (DTC) patients classified as intermediate risk based on the presence of microscopic extrathyroidal extension (ETE) should be treated with low or high doses of radioiodine (RAI) after surgery. We evaluated success rates and long-term clinical outcomes of patients with DTC of small tumor size, microscopic ETE, and no cervical lymph node (LN) metastasis treated either with a low (1.1 GBq) or high RAI dose (5.5 GBq).
  
  
  METHODS
  This is a retrospective analysis of a historical cohort from 2000 to 2010 in a tertiary referral hospital. A total of 176 patients with small (≤2 cm) DTC, microscopic ETE, and no cervical LN metastasis were included. Ninety-six patients were treated with 1.1 GBq (LO group) and 80 patients with 5.5 GBq (HI group). Successful RAI therapy was defined as (i) negative stimulated thyroglobulin (Tg) in the absence of Tg antibodies, and (ii) absence of remnant thyroid tissue and of abnormal cervical LNs on ultrasonography. Clinical recurrence was defined as the reappearance of disease after ablation, which was confirmed by cytologically or pathologically proven malignant tissue or of distant metastatic lesions.
  
  
  RESULTS
  There was no significant difference in the rate of successful RAI therapy between the LO and HI groups (p=0.75). In a subgroup analysis based on tumor size, success rates were not different between the LO group (34/35, 97%) and the HI group (50/56, 89%) in patients with a tumor size of 1-2 cm (p=0.24). In patients with smaller tumor size (≤1 cm), there was no significant difference in success rates between the LO (59/61, 97%) and HI groups (22/24, 92%; p=0.30). No patient had clinical recurrences in either group during the median 7.2 years of follow-up.
  
  
  CONCLUSIONS
  Low-dose RAI therapy is sufficient to treat DTC patients classified as intermediate risk just by the presence of microscopic ETE.
authors: 1 Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine , Seoul, South Korea .
authors: Ji Min
authors: JM
authors: Han
authors: Won Gu
authors: WG
authors: Kim
authors: Tae Yong
authors: TY
authors: Kim
authors: Min Ji
authors: MJ
authors: Jeon
authors: Jin-Sook
authors: JS
authors: Ryu
authors: Dong Eun
authors: DE
authors: Song
authors: Suck Joon
authors: SJ
authors: Hong
authors: Young Kee
authors: YK
authors: Shong
authors: Won Bae
authors: WB
authors: Kim
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000517:prevention & control* / Q000556:secondary; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects / Q000601:surgery; D037981:Neck Dissection; D009364:Neoplasm Recurrence, Local / Q000453:epidemiology / Q000517:prevention & control*; D009367:Neoplasm Staging; D019275:Radiopharmaceuticals / Q000008:administration & dosage* / Q000627:therapeutic use; D018714:Radiotherapy, Adjuvant; D056910:Republic of Korea / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013964:Thyroid Neoplasms / Q000473:pathology / Q000517:prevention & control / Q000532:radiotherapy* / Q000601:surgery; D013965:Thyroidectomy; D047368:Tumor Burden / Q000528:radiation effects; D014463:Ultrasonography
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals