title: Efficacy of dosimetric versus empiric prescribed activity of 131I for therapy of differentiated thyroid cancer.
abstract: BACKGROUND
  The optimal management of high-risk patients with differentiated thyroid cancer (DTC) consists of thyroidectomy followed by radioiodine ((131)I) therapy. The prescribed activity of (131)I can be determined using two approaches: 1) empiric prescribed activity of (131)I (E-Rx); and 2) dosimetry-based prescribed activity of (131)I (D-Rx).
  
  
  OBJECTIVE
  The aim of the study was to compare the relative treatment efficacy and side effects of D-Rx vs. E-Rx.
  
  
  METHODS
  A retrospective analysis was performed of patients with distant metastases and/or locoregionally advanced radioiodine-avid DTC who were treated with either D-Rx or E-Rx. Response to treatment was based on RECIST (Response Evaluation Criteria in Solid Tumors) 1.1 criteria.
  
  
  RESULTS
  The study group consisted of 87 patients followed for 51 ± 35 months, of whom 43 were treated with D-Rx and 44 with E-Rx. Multivariate analysis, controlling for age, gender, and status of metastases revealed that the D-Rx group tended to be 70% less likely to progress (odds ratio, 0.29; 95% confidence interval, 0.087-1.02; P = 0.052) and more likely to obtain complete response (CR) compared to the E-Rx group (odds ratio, 8.2; 95% confidence interval, 1.2-53.5; P = 0.029). There was an association in the D-Rx group between the observed CR and percentage of maximum tolerable activity given as a first treatment of (131)I (P = 0.030). The advantage of D-Rx was specifically apparent in the locoregionally advanced group because CR was significantly higher in D-Rx vs. E-Rx in this group of patients (35.7 vs. 3.3%; P = 0.009). The rates of partial response, stable disease, and progression-free survival, as well as the frequency of side effects, were not significantly different between the two groups.
  
  
  CONCLUSIONS
  Higher efficacy of D-Rx with a similar safety profile compared to E-Rx supports the rationale for employing individually prescribed activity in high-risk patients with DTC.
authors.affiliation: Division of Nuclear Medicine, Washington Hospital Center, Washington, DC 20010-2910, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: Klubo-Gwiezdzinska
authors.forename: Douglas
authors.initials: D
authors.lastname: Van Nostrand
authors.forename: Frank
authors.initials: F
authors.lastname: Atkins
authors.forename: Kenneth
authors.initials: K
authors.lastname: Burman
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Jonklaas
authors.forename: Mihriye
authors.initials: M
authors.lastname: Mete
authors.forename: Leonard
authors.initials: L
authors.lastname: Wartofsky
mesh_terms: D000368:Aged; D002291:Carcinoma, Papillary / Q000473:pathology / Q000532:radiotherapy* / Q000628:therapy; D003131:Combined Modality Therapy; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage* / Q000009:adverse effects / Q000627:therapeutic use*; D053208:Kaplan-Meier Estimate; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D049268:Positron-Emission Tomography; D011874:Radiometry; D012189:Retrospective Studies; D016019:Survival Analysis; D013964:Thyroid Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000628:therapy; D013965:Thyroidectomy; D014057:Tomography, X-Ray Computed
chemical_list: D007457:Iodine Radioisotopes