Pretherapeutic dosimetry in patients affected by metastatic thyroid cancer using 124I PET/CT sequential scans for 131I treatment planning

Clin Nucl Med. 2014 Aug;39(8):e367-74. doi: 10.1097/RLU.0000000000000490.


Purpose: This study evaluates the use of sequential I PET/CT for predicting absorbed doses to metastatic lesions in patients with differentiated thyroid cancer undergoing I therapy.

Methods: From July 2011 until July 2013, 30 patients with metastatic differentiated thyroid cancer were enrolled. Each participant underwent PET/CT at 4, 24, 48, and 72 hours with 74 MBq of I. Blood samples and whole-body exposure measurements were obtained to calculate blood and red marrow doses. Activity concentrations and lesion volumes obtained from PET/CT were used to evaluate tumor doses with medical internal radiation dose formalism and spheres modeling. Mean administered I therapeutic dose was 5994 MBq (range, 1953-11,455 MBq).

Results: I PET/CT demonstrated all lesions detected by posttherapy I whole-body scans. Mean dose rates for blood, red marrow, and lesions were as follows: 0.07 ± 0.02 mGy/MBq, 0.05 ± 0.02 mGy/MBq, and 46.5 ± 117 mGy/MBq, respectively. Despite the high level of thyroid-stimulating hormone and CT detectable lesions, 15 of 30 patients did not show any abnormal I uptake.

Conclusions: The quantitative value of I PET/CT allows simple and accurate evaluation of lesion dosimetry following medical internal radiation dose formalism. Negative I PET/CT predicts absence of iodine avidity, potentially allowing avoidance of therapeutically ineffective I administration.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Female
  • Humans
  • Iodine Radioisotopes* / therapeutic use
  • Male
  • Middle Aged
  • Multimodal Imaging*
  • Neoplasm Metastasis / diagnostic imaging
  • Neoplasm Metastasis / radiotherapy
  • Positron-Emission Tomography*
  • Radiopharmaceuticals* / therapeutic use
  • Radiotherapy Dosage*
  • Thyroid Neoplasms / diagnostic imaging*
  • Thyroid Neoplasms / pathology
  • Thyroid Neoplasms / radiotherapy
  • Tomography, X-Ray Computed*


  • Iodine Radioisotopes
  • Radiopharmaceuticals