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KMID : 1143620140180010098
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Korean Journal of Nuclear Medicine Technology
2014 Volume.18 No. 1 p.98 ~ p.103
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Measurement of Effective Half-life Using Dual Time I-131 Whole Body Scan in Patients with Differentiated Thyroid Cancer Treated by High Dose Therapy
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Yoon Jae-Sik
Lee Jae-Gon
Lee Ki-Hyun
Lim Kwang-Seok
Choi Hak-Ki
Lee Sang-Mi
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Abstract
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Purpose: The effective half life of I-131 is useful to calculate radiation dose, period of hospitalization, and exposure dose of surrounding people from patient. However, it is difficult to measure. This study estimates the effective half life in whole body and thyroid in using of value of residual radioactivity obtained from the early and delay images of Dual time I-131 whole body scan. Also, the correlations between the effective half life and serum creatinine, GFR, and administration dose were investigated in this study.
Materials and Methods: The targets were 50 patients administration high dose of I-131 from February to August in 2013, having normal range of serum creatinine and over 30 μIU/mL of TSH levels. After administration radioactive I-131, the early scan in the 3rd day and the delay scan in the 5-6th days were performed. To measure the residual radioactivity in the whole body and thyroid, ROI was set and then background radioactivity was corrected to estimate. The effective half life was estimated by calculating the ratio of measured values between the early and delay images. To compare the effective half lives of the whole body and thyroid, it was analyzed by Independent t-test, and each correlation of the effective half life, GFR, serum creatinine, and the dose of administration were analyzed by calculating the pearson’s correlation coefficient. All of the analysis were determined to be statistically significant when P<0.05.
Results: The effective half life of the whole body was 17.06±5.50 hours and of the thyroid was 17.22±5.41 hours. The two effective half life did not show significant difference (P=0.887). As the value of GFR was increased, the effective half life of whole body (r=-0.407, P=0.003) and of thyroid (r=-0.473, P=0.001) were significantly decreased; as the value of serum creatinine was increased, the effective half life of whole body (r=0.309, P=0.029) and of thyroid (r=0.371, P=0.008) were significantly increased. In the administration dose, effective half life did not have correlations.
Conclusion: The effective half life of I-131 of patients treated for their thyroids were estimated only by using the images of Dual time I-131 whole body scan. Also, the correlations with the effective life, GFR, and serum creatinine were examined. This study might be utilized for a study on optimization for the period of hospitalization of patients treated by high dose of I-131 and on evaluation for internal absorbed dose of MIRD schema in application of the effective half life.
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KEYWORD
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Thyroid cancer, Effective half life, I-131, Dual time I-131 whole body scan
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