title: Higher administered activities of radioactive iodine are associated with less structural persistent response in older, but not younger, papillary thyroid cancer patients with lateral neck lymph node metastases.
abstract: BACKGROUND
  While radioactive iodine (RAI) adjuvant therapy is commonly recommended for most papillary thyroid cancer patients presenting with large volume nodal involvement, it remains unclear if such therapy impacts the disease-specific recurrence rate and overall survival. In this study, we compared the risk of achieving a structural persistent response after low administered activity (100 mCi), intermediate administered activity (150 mCi), and high administered activity (>200 mCi) RAI adjuvant therapy in patients presenting with pathologic N1b disease.
  
  
  METHODS
  This was a retrospective review of 181 papillary thyroid cancer patients with N1b disease treated with total thyroidectomy, neck dissection, and RAI remnant ablation. Dose-response relationships were determined between the administered activity of (131)I and the best response to initial therapy.
  
  
  RESULTS
  Out of the 181 patients, only 39% achieved no clinical evidence of disease (NED) after initial therapy. Young patients (Stage I) had a statistically nonsignificant trend toward higher rates of NED with increasing dose (34% low activity, 36% intermediate activity, 46% high activity), but there was no evidence of dose-response effect with regard to the likelihood of having a structural persistent response to initial therapy or the likelihood of having persistent biochemical evidence of disease. However, analysis of the older patients (Stage IVa) did reveal a trend toward statistically significant dose-response relationships with increasing administered activities being associated with lower rates of structural persistent response (46% low activity, 23% intermediate activity, 17% high dose). Unfortunately, the lower rate of structural persistent response only modestly increased the likelihood that patients would be NED but was instead associated with a higher proportion of patients being classified as having biochemical persistent disease at 12-18 months.
  
  
  CONCLUSIONS
  It appears that administering more than 100 mCi of RAI as adjuvant therapy in N1b disease is unlikely to improve the initial response to therapy. This is especially true for the younger (Stage I) patients. It is plausible that administered activities of 150-260 mCi may be associated with an improved response to initial therapy in older patients (Stage IVa) who are probably at highest risk of having poor outcomes, but the potential benefit from RAI should be balanced against potential adverse effects in those patients.
authors.affiliation: 1 Endocrinology Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center and Weill-Cornell College of Medicine , New York, New York.
authors.forename: Mona M
authors.initials: MM
authors.lastname: Sabra
authors.forename: Ravinder K
authors.initials: RK
authors.lastname: Grewal
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Ghossein
authors.forename: R Michael
authors.initials: RM
authors.lastname: Tuttle
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002291:Carcinoma, Papillary / Q000473:pathology / Q000532:radiotherapy / Q000556:secondary / Q000628:therapy*; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008207:Lymphatic Metastasis / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D037981:Neck Dissection; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery / Q000628:therapy*; D013965:Thyroidectomy; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes