| Purpose: There are three methods for iodine 131 radionuclide in the treatment of differentiated thyroid cancer?DTC?: empirical fixed value,bone marrow and systemic dose threshold?maximum tolerated dose?,and tumor tissue absorbed dose.How to accurately assess the maximum tolerated dose of bone marrow in patients is of great significance in guiding the individual treatment of iodine 131.The purpose of this article is to determine the absorbed dose of bone marrow in patients with DTC treated with iodine 131 using SPECT/CT imaging,and explore its method and feasibility to guide the individualized treatment of DTC.Methods: A total of 56 patients with DTC undergone thyroid ectomy were randomly selected.All patients required iodine 131 treatment according to the 2015 ATA guidelines.SPECT/ CT imaging was used to determine the absorbed dose of bone marrow in patients.All patients received oral diagnostic dose of 131 185 MBq,and performed 5 whole-body planes + 1?4 h?SPECT/CT tomography in 2 beds.In order to obtain the optimal imaging scheme,29 patients were subjected to 7 consecutive systemic.For planar imaging,three combinations of acquisition time points?2h,4h,6h,8h,24 h or 0.5,1,2,4,24 h or 1,2,4,6,24h?were used to analyze the image data.Bone marrow absorbed dose was measured using OLINDA / EXM software?version 1.1?.To calculate the maximum tolerated dose of iodine 131 for each patient,2Gy was used as the threshold of maximum absorbed dose of bone marrow.Based on the determination of the maximum tolerated dose of bone marrow,patients with DTC were individually adjusted for the iodine 131 treatment dose,and their hematological toxicity was analyzed individually.Results: Fifty-six patients were all papillary thyroid carcinoma.Among them,there were 16 males and 40 females,aged 24 to 70 years,with an average age of 46.02±11.58 years.54 patients were with total resection or subtotal thyroidectomy and 2 cases were thyroid lobectomy plus isthmus resection.131I bone marrow absorbed dose per unit dose was 2.07E-04± 1.21E-04Gy/ MBq?0.58E-045.94E-04Gy/MBq?.The maximum tolerated dose of oral iodine 131 was 13.07±7.03GBq?3.3734.56GBq?.There were no statistically significant differences between the three methods of measuring bone marrow absorbed dose at five different time points?P = 0.48?.According to 2015 ATA guidelines,17 patients were adjusted for the iodine 131 treatment dose based on the maximum tolerated dose of bone marrow.Six patients received a 20% reduction in the dose,and eleven patients received an increase dose of 59.09%.Among 11 patients with increased dosage,all patients had successful removal for the first time.Among the 6 patients with decreased dosage,2 patients had incomplete removal of residual thyroid for the first time and successfully treated with iodine-131 for the second time.Of all 56 patients,the white blood cells,red blood cells,platelet counts were all in normal reference at 1 month and 4 months after 131 I treatment.There were no bone marrow suppression occurred.The white blood cell counts at 1 month and 4 months after 131 I treatment were lower than pre-therapy?Z=-4.495,P=0.000;Z=-3.573,P=0.000?.While the red blood cell counts and platelet counts at 1 month and 4 months after 131 I treatment were higher?t=-1.751,P=0.085;t=-1.170,P=0.247?and lower?t=6.342,P=0.000;t=4.865,P=0.000?.Conclusions:SPECT/CT imaging method can be used to estimate the maximum tolerated dose of iodine 131 in bone marrow and guide the individualized iodine 131 treatment in patients with DTC.It is relatively simple and feasible for widely clinical use to estimate the maximum tolerated dose of bone marrow using 0.5,1,2,4,24 hours SPECT/CT imaging. |
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