Shiro Watanabe1,2, Shozo Okamoto3, Kazumasa Akikawa4, Noriyuki Miyamoto3, Miyuki Okamura-Kawasaki5, Yuko Uchiyama6,7, Junki Takenaka6,7, Takuya Toyonaga8, Kenji Hirata6,7, Kohsuke Kudo6,9. 1. Department of Diagnostic Imaging, Hokkaido University Graduate School of Medicine, Kita 15 Nishi 7, Kita-Ku, Sapporo, Hokkaido, 060-8638, Japan. shirow@med.hokudai.ac.jp. 2. Department of Nuclear Medicine, Hokkaido University Hospital, Kita 14 Nishi 5, Kita-Ku, Sapporo, Hokkaido, 060-8648, Japan. shirow@med.hokudai.ac.jp. 3. Department of Radiology, Obihiro Kosei Hospital, Minami 10-1, Nishi 14, Obihiro City, Hokkaido, 080-0024, Japan. 4. Department of Internal Medicine, Hokkaido Medical Center of Rheumatic Diseases, 1-1-45, Kotoni 1-jo 3-chome, Nishi-ku, Sapporo, Hokkaido, 063-0811, Japan. 5. Department of Radiology, Tomakomai City Hospital, 1-5-20 Shimizu-cho, Tomakomai, 053-8567, Japan. 6. Department of Diagnostic Imaging, Hokkaido University Graduate School of Medicine, Kita 15 Nishi 7, Kita-Ku, Sapporo, Hokkaido, 060-8638, Japan. 7. Department of Nuclear Medicine, Hokkaido University Hospital, Kita 14 Nishi 5, Kita-Ku, Sapporo, Hokkaido, 060-8648, Japan. 8. Positron Emission Tomography (PET) Center, Radiology and Biomedical Imaging, Yale School of Medicine, 801 Howard Ave., P.O. Box 208048, New Haven, CT, 06520, USA. 9. Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Kita-14, Nishi-5, Kita-ku, Sapporo, Hokkaido, 060-8648, Japan.
Abstract
OBJECTIVE: Radioactive iodine (RAI) therapy is a useful treatment for Graves' disease (GD). Most RAI sessions administer ≤ 500 MBq of iodine (I)-131. Sometimes patients require repeated RAI, often for longer periods of remission. We investigated the characteristics of patients for whom high dose (mostly 1110 MBq of I-131) RAI was effective as RAI therapy for GD. METHODS: We retrospectively analyzed the cases of 79 patients who underwent RAI for GD in a multicenter setting. We divided the patients into two groups based on the I-131 dose administered: the low dose (LD) group who received ≤ 500 MBq (n = 44) and the high dose (HD) group who received > 500 MBq (n = 35). The therapeutic effect was defined as achieving remission and reaching the point of participating in thyroid hormone replacement therapy within 1 year after RAI. We compared the LD and HD groups' remission rates and conducted a multivariate logistic regression analysis of predictive factors for remission. In a simulation, using the formula for predicting the probability of remission obtained from the analysis results, we estimated how much the remission rate would change if the I-131 dose is increased from 500 to 1110 MBq. RESULTS: The mean ± standard deviation I-131 dose administered in the LD group was 480 ± 6 MBq, and that of the HD group was 1054 ± 265 MBq. Thirty-five patients (80%) in the LD group and 26 patients (74%) in the HD group achieved remission; this difference in the remission rate was not significant. The multivariate analysis results demonstrated that the absorbed dose and thyroid-stimulating antibody (TSAb) were independent predictors of remission. Seven patients (8.9%) showed an increased probability of remission from < 50% to > 50% when the higher RAI dose was applied (1110 MBq instead of 500 MBq). The thyroid volume and TSAb values in these patients were relatively large at 54.7 ± 34.2 mL and 1378.4 ± 586.3%, respectively. CONCLUSION: Although the overall remission rate was not significantly different between the patients who received high- or low-dose I-131, treatment with high-dose RAI may improve the probability of remission in patients with a massive thyroid volume and/or high-TSAb Graves' disease.
OBJECTIVE: Radioactive iodine (RAI) therapy is a useful treatment for Graves' disease (GD). Most RAI sessions administer ≤ 500 MBq of iodine (I)-131. Sometimes patients require repeated RAI, often for longer periods of remission. We investigated the characteristics of patients for whom high dose (mostly 1110 MBq of I-131) RAI was effective as RAI therapy for GD. METHODS: We retrospectively analyzed the cases of 79 patients who underwent RAI for GD in a multicenter setting. We divided the patients into two groups based on the I-131 dose administered: the low dose (LD) group who received ≤ 500 MBq (n = 44) and the high dose (HD) group who received > 500 MBq (n = 35). The therapeutic effect was defined as achieving remission and reaching the point of participating in thyroid hormone replacement therapy within 1 year after RAI. We compared the LD and HD groups' remission rates and conducted a multivariate logistic regression analysis of predictive factors for remission. In a simulation, using the formula for predicting the probability of remission obtained from the analysis results, we estimated how much the remission rate would change if the I-131 dose is increased from 500 to 1110 MBq. RESULTS: The mean ± standard deviation I-131 dose administered in the LD group was 480 ± 6 MBq, and that of the HD group was 1054 ± 265 MBq. Thirty-five patients (80%) in the LD group and 26 patients (74%) in the HD group achieved remission; this difference in the remission rate was not significant. The multivariate analysis results demonstrated that the absorbed dose and thyroid-stimulating antibody (TSAb) were independent predictors of remission. Seven patients (8.9%) showed an increased probability of remission from < 50% to > 50% when the higher RAI dose was applied (1110 MBq instead of 500 MBq). The thyroid volume and TSAb values in these patients were relatively large at 54.7 ± 34.2 mL and 1378.4 ± 586.3%, respectively. CONCLUSION: Although the overall remission rate was not significantly different between the patients who received high- or low-dose I-131, treatment with high-dose RAI may improve the probability of remission in patients with a massive thyroid volume and/or high-TSAb Graves' disease.