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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
Ist Teil von
European journal of nuclear medicine and molecular imaging, 2010-05, Vol.37 (5), p.884-895
Ort / Verlag
Berlin/Heidelberg: Springer-Verlag
Erscheinungsjahr
2010
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
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
131
I and ultrasonography (US) provided evidence that the average organ dose per administered
131
I 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
124
I PET(/CT) as a more reliable approach than
131
I 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
124
I-iodide. Volumes of interest (VOIs) drawn on the CT and serial PET images were used to determine the glandular volumes and the imaged
124
I 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
124
I decay, the imaged activity was effectively corrected using isovolume recovery coefficients (RCs) based on recovery phantom measurements. A head-neck phantom, which contained
124
I-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
131
I 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
124
I PET(/CT) and
131
I GCS/US dosimetry was found. The validation experiment showed that the percentage deviations between RC-corrected and true activity concentrations were <10%.
Conclusion
124
I 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.