Pre-therapeutic 124I PET(/CT) dosimetry confirms low average absorbed doses per administered 131I activity to the salivary glands in radioiodine therapy of differentiated thyroid cancer

Walter Jentzen, Robert F. Hobbs, Alexander Stahl, Jochen Knust, George Sgouros, Andreas Bockisch

Research output: Contribution to journalArticle

Abstract

Purpose: Salivary gland impairment following high activity radioiodine therapy of differentiated thyroid cancer (DTC) is a severe side effect. Dosimetric calculations using planar gamma camera scintigraphy (GCS) with 131I and ultrasonography (US) provided evidence that the average organ dose per administered 131I activity (ODpA) is too low to account for observed radiation damages to the salivary glands. The objective of this work was to re-estimate the ODpA using 124I PET(/CT) as a more reliable approach than 131I GCS/US. Methods: Ten DTC patients underwent a series of six (or seven) PET scans and one PET/CT scan after administration of ∼23 MBq 124I-iodide. Volumes of interest (VOIs) drawn on the CT and serial PET images were used to determine the glandular volumes and the imaged 124I activities. To enable identical VOIs to be drawn on serial PET images, each PET was co-registered with the CT image. To correct for partial volume effect and for the artificial bias in the activity concentration due to cascading gamma coincidences occurring in 124I decay, the imaged activity was effectively corrected using isovolume recovery coefficients (RCs) based on recovery phantom measurements. A head-neck phantom, which contained 124I-filled spheres, was manufactured to validate the isovolume recovery correction method with a realistic patient-based phantom geometry and for a range of activity concentration regimes. The mean±standard deviation (range) ODpA projected for 131I was calculated using the absorbed dose fraction method. Results: The ODpAs (in Gy/GBq) for the submandibular and parotid glands were 0.32±0.13 (0.18-0.55) and 0.31±0.10 (0.13-0.46), respectively. No significant differences (p>0.2) in the mean ODpA between 124I PET(/CT) and 131I GCS/US dosimetry was found. The validation experiment showed that the percentage deviations between RC-corrected and true activity concentrations were <10%. Conclusion: 124I PET(/CT) dosimetry also corroborates the low ODpAs to the salivary glands. A voxel-based calculation taking into account the nonuniform activity distributions in the glands is necessary to possibly explain the radiation-induced salivary gland damage.

Original languageEnglish (US)
Pages (from-to)884-895
Number of pages12
JournalEuropean Journal of Nuclear Medicine and Molecular Imaging
Volume37
Issue number5
DOIs
StatePublished - May 2010

Keywords

  • Differentiated thyroid cancer
  • Dosimetry
  • I
  • Radioiodine therapy
  • Salivary gland

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

Fingerprint Dive into the research topics of 'Pre-therapeutic <sup>124</sup>I PET(/CT) dosimetry confirms low average absorbed doses per administered <sup>131</sup>I activity to the salivary glands in radioiodine therapy of differentiated thyroid cancer'. Together they form a unique fingerprint.

  • Cite this