Value of normalization analysis of thyroid scans on 131I treatment planning for Graves' disease

Objective To explore the value of normalization analysis of thyroid scans on 131 I treatment planning for Graves' disease.Methods Patients with hyperthyroidism treated by 131I were retrospectively analyzed.Sixty cases with thyroid glands less than 35 g and without thyroid nodules were enrolled.Raw data of thyroid scans were re-processed using a software for normalization and magnification.Correlation between total dose,the number of treatments and other factors,such as area ratios of bilateral lobes,bilateral radioactive counts,bilateral gray scales and multifocal uptake patterns,were analyzed using step-bystep regression analysis.Correlations between normal thyroid function,hypothyroidism and the abovementioned factors were analyzed using multiple linear regression analysis.Results Fifty percent (30/60) of cases were cured after a single-dose treatment,and the remaining 50％ required multiple treatments.In addition to thyroid mass and radioactive iodine uptake,total dose correlated with gender ( F =4.23,P =0.050 ),area ratio of bilateral lobes ( F =6.20,P =0.020) and multifocal uptake pattern ( F =5.12,P =0.033 ).The number of treatments correlated with ratio of bilateral gray scales ( F =8.89,P =0.006) and multifocal uptake pattern (F =4.98,P =0.034).According to outcomes,patients were divided into a normal thyroid function group and a hypothyroidism group.131 I dose correlated with the area ratio of bilateral lobes ( F =10.42,P =0.018 ) and ratio of bilateral gray scales in the normal thyroid function group ( F =10.66,P =0.017 ) ; whereas in the hypothyroidism group,the clinical outcome correlated with thyroid mass (F=7.65,P=0.013) and multifocal uptake pattern (F=8.01,P=0.011 ).Conclusions Computeraided normalization analysis is useful for 131I dose calculation in the treatment of hyperthyroidism.For patients with significantly unbalanced bilateral radiotracer distribution,increasing the dose and the number of treatments should be suggested.For patients with homogeneous radiotracer distribution,a linear method of dose increment according to the thyroid mass should be avoided to reduce the rate of hypothvroidism. Key words: Graves' disease;  Iodine radioisotopes;  Radiotherapy;  Radionuclide imaging; Normalize analysis