Evaluation of Dosimetric Parameters from Patients Based on Whole Body 131 I Bio-Kinetic Clearance in Thyroid Cancer Therapy
Keywords:
Thyroid cancer, Absorbed dose, I-131, Bio-kinetic clearance, Effective half-lifeAbstract
Objective: The study was designed to evaluate the bio-kinetic clearance of radioactive iodine (131l) in the well-differentiated thyroid carcinoma patients treated with 1.11 GBq and to calculate organs and whole body absorbed dose with MIRDOSE3.1 computer software.
Materials and Methods: The whole body retention/excretion of 131l in all patients was determined individually by using gamma camera with high-energy general all purpose (HEGP) at the specific time points after its administration.
Results: The effective half-live (T eff) was estimated from the generated time-activity curves. The mean for effective half-life from whole body clearance curve was 26.2 ± 10.8 hours. The calculated residence time (t) was 38.0 ± 15.6 hours. The retained activity of 131l at 4, 24, 48, 72 and 144 hours was 77.8 ± 11.4, 44.4 ± 13.9, 23.8 ± 12.4, 13.3 ± 9.1 and 2.7 ± 2.6%, respectively. The mean for absorbed doses to whole body was 0.10 (0.04 mGy/MBq). The highest organ dose was uterus (0.11 ± 0.05 mGy/MBq). The mean for effective dose was 0.11 ± 0.04 mSv/MBq.
Conclusion: Retention and clearance rates of 131l could be obtained by in vivo measurements in individual patients. Evaluations of the Teff are essential parameter for absorbed dose calculation to patient and minimize the risk of external radiation exposure to staffs of nuclear medicine, family member and the public. These parameters are essential for management in thyroid cancer therapy, for both in patients and outpatients. Additionally, our parameters could be a useful parameter to develop the guideline for occupational and public radiation protection.
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