Efficacy of dosimetric versus empiric prescribed activity of 131I for therapy of differentiated thyroid cancer

J Clin Endocrinol Metab. 2011 Oct;96(10):3217-25. doi: 10.1210/jc.2011-0494. Epub 2011 Aug 17.


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).

Aim: 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.

Conclusion: 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.

MeSH terms

  • Aged
  • Carcinoma, Papillary / pathology
  • Carcinoma, Papillary / radiotherapy*
  • Carcinoma, Papillary / therapy
  • Combined Modality Therapy
  • Disease-Free Survival
  • Female
  • Humans
  • Iodine Radioisotopes / administration & dosage*
  • Iodine Radioisotopes / adverse effects
  • Iodine Radioisotopes / therapeutic use*
  • Kaplan-Meier Estimate
  • Magnetic Resonance Imaging
  • Male
  • Middle Aged
  • Neoplasm Metastasis
  • Positron-Emission Tomography
  • Radiometry
  • Retrospective Studies
  • Survival Analysis
  • Thyroid Neoplasms / pathology
  • Thyroid Neoplasms / radiotherapy*
  • Thyroid Neoplasms / therapy
  • Thyroidectomy
  • Tomography, X-Ray Computed


  • Iodine Radioisotopes