Details

Autor(en) / Beteiligte

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

Titel

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.