Abstract—The amount of 131I necessary for successful ablation
in patients with differentiated thyroid cancer (DTC) is still subject
to debate. This study investigates the relationship of the
absorbed dose of radiation to the blood while administering
131I activity with several other parameters in DTC patients.
This prospective study included 90 DTC patients who were
classified into three groups according to their level of dosage:
3.7 GBq (38.9%), 5.55 GBq (55.6%), and 7.4 GBq (5.5%).
Blood dosimetry of treated patients was performed using external
whole-body counting with a Geiger Muller dosimeter
located 2 m away from the patients. Dose rate was measured
at 2, 4, 5, 24, and 48 h after the administration of radioiodine.
Based on the results of whole-body dose rate measurements,
48 h after administration of 3.7, 5.55, and 7.4 GBq of radioiodine,
absorbed doses to patients’ blood were estimated at 0.49 ±
0.12, 0.71 ± 0.21, and 0.76 ± 0.11 Gy, respectively. Increasing radioiodine
dosage from 3.7 GBq to 5.55 GBq significantly increased
blood dose, while there was no significant difference in blood dose
between radioiodine dosages of 5.55 GBq and 7.4 GBq. The absorbed
dose to the blood was significantly correlated to the patients’
gender and the presence of lymph node metastases, but
it was not significantly correlated to the type of pathology and
regional or distant metastases. Ablation activities exceeding
5.55 GBq produce no further increase in the accumulated activity
per volume of blood. The literature regarding this issue is
scarce, and further studies are required to verify these preliminary
results.
Health Phys. 108(1):53–58; 201
