Relationship between cumulative radiation dose and salivary gland uptake associated with radioiodine therapy of thyroid cancer.
OBJECTIVE
To estimate the individual absorbed dose to the parotid and submandibular salivary glands in radioiodine therapy and its dependence from the previous cumulative therapy.


METHODS
Fifty-five patients with differentiated thyroid carcinoma after thyroidectomy received 1-21 GBq (131)I using single activities of 1-6 GBq. The patients were stratified according to the cumulative activities into low-activity (1-2 GBq), middle-activity (3-7 GBq), and high-activity groups (9-21 GBq). The time-activity curves over the respective salivary glands were derived from multiple static calibrated images measured for each patient up to 48 h after ingestion of the radioiodine therapy capsule with a gamma camera. Manually drawn regions of interests were used to determine the background activities and the activities arising from the salivary glands. The gland volumes were determined by ultrasonography using appropriate volume models.


RESULTS
The median absorbed dose per administered activity of each single parotid and submandibular gland was about 0.15 Gy.GBq (range, 0.1-0.3 Gy.GBq(-1)) and 0.48 Gy.GBq(-1) (range, 0.2-1.2 Gy.GBq(-1)), respectively. The maximum uptake of both gland types was significantly lower for the high-activity than for the low-activity groups and correlated with the mean cumulative administered activity of the activity groups.


CONCLUSIONS
The iodine uptake of salivary glands is significantly reduced, whereas the absorbed dose per administered (131)I activity was not significantly decreased during the course of therapy. Comparing the well-known dose-effect relationships in external radiation therapy, the absorbed dose per administered (131)I activity is too low to induce comparable radiation damage, suggesting an inhomogeneous distribution of (131)I in human salivary glands.
Jentzen
Walter
W
Clinic for Nuclear Medicine, University of Duisburg/Essen, Germany. walter.jentzen@uni-essen.de
Schneider
Elke
E
Freudenberg
Lutz
L
Eising
Ernst G
EG
Görges
Rainer
R
Müller
Stefan P
SP
Brandau
Wofgang
W
Bockisch
Andreas
A
D000328:Adult; D000368:Aged; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control; D011874:Radiometry; D011877:Radionuclide Imaging; D012062:Relative Biological Effectiveness; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012469:Salivary Glands / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000528:radiation effects; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000532:radiotherapy*
D007457:Iodine Radioisotopes