Canzi Cristina, Zito Felicia, Voltini Franco, Reschini Eugenio, Gerundini Paolo
Department of Nuclear Medicine and Health Physics, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy.
Med Phys. 2006 Aug;33(8):2860-7. doi: 10.1118/1.2210564.
The aim of this study was to verify the capability of an MIRD formula-based dosimetric method to predict radioiodine kinetics (fraction of administered iodine transferred to the thyroid, U0, and effective clearance rate, lambda(eff)) and absorbed dose after oral therapeutic 131I administration. The method is based on 123I intravenous administration and five subsequent gamma camera measured uptake values determined separately on different structures within the thyroid. Another dosimetric method based on only the 123I 24-h uptake and a fixed lambda(eff) value was also considered. Eighty-nine hyperthyroid patients (10 with Graves' disease and 79 with autonomously functioning nodules) were studied and 132 thyroidal structures were evaluated. The mean time interval between dosimetry and therapy was 20 +/- 10d. Uptake values were measured at 2, 4, 24, 48, and 120 h during dosimetry and at 2, 4, 24, 48, 96, and 168 h during therapy. The value 0.125d(-1) was chosen in the fixed-lambda(eff) method. The planned doses to the target ranged from 120 to 250 Gy depending on the type and severity of hyperthyroidism. The following significant correlations between therapeutic and dosimetric parameters were found: U0(ther)=0.88U0(dos) (r=0.97,p<0.01), lambda(eff)ther = 1.01 lambda(eff)dos (r=0.85,p<0.01), and D(estimated)= 0.85D(planned) (r=0.88, p<0.01). The percent difference between U0(ther) and U0(dos) ranged from -44 to 32% and between lambda(eff)ther and lambda(eff)dos from -32 to 48%. U0(ther) was lower than U0(dos) in 74% of cases: this can be explained by the self-stunning effect of 131I therapeutic activity that produced a dose of about 20 Gy with a maximum dose rate of 0.6 Gy/h over the initial 24-48 h. The differences, deltaD, between the estimated and the planned doses ranged from -42% (-87 Gy) to 32% (59 Gy); in 73% of cases the difference was within +/- 35 Gy. Greater discrepancies were found with the fixed-lambda(eff) method, in which deltaD ranged from -69 to 95% (-202 to 88 Gy, respectively). In hyperthyroid patients, the five uptake value dosimetric method is able to predict with a good agreement the radioiodine kinetics and the dose after the therapeutic administration in about 73% of the analyzed thyroid structures. The fixed-lambda(eff) method is less reliable.
本研究的目的是验证基于MIRD公式的剂量测定方法预测口服治疗性131I给药后放射性碘动力学（给药碘转移至甲状腺的分数U0和有效清除率lambda(eff)）及吸收剂量的能力。该方法基于静脉注射123I以及随后通过γ相机分别测定甲状腺内不同结构上的5个摄取值。还考虑了另一种仅基于123I 24小时摄取量和固定lambda(eff)值的剂量测定方法。研究了89例甲状腺功能亢进患者（10例患有格雷夫斯病，79例患有自主功能性结节），并评估了132个甲状腺结构。剂量测定与治疗之间的平均时间间隔为20±10天。在剂量测定期间于2、4、24、48和120小时测量摄取值，在治疗期间于2、4、24、48、96和168小时测量摄取值。在固定lambda(eff)方法中选择的值为0.125d(-1)。根据甲状腺功能亢进的类型和严重程度，计划给予靶区的剂量范围为120至250 Gy。发现治疗参数与剂量测定参数之间存在以下显著相关性：U0(ther)=0.88U0(dos)（r = 0.97，p<0.01），lambda(eff)ther = 1.01 lambda(eff)dos（r = 0.85，p<0.01），以及D(estimated)= 0.85D(planned)（r = 0.88，p<0.01）。U0(ther)与U0(dos)之间的百分比差异范围为-44%至32%，lambda(eff)ther与lambda(eff)dos之间的百分比差异范围为-32%至48%。在74%的病例中，U0(ther)低于U0(dos)：这可以通过131I治疗活性的自我抑制效应来解释，该效应在最初的24至48小时内产生约20 Gy的剂量，最大剂量率为0.6 Gy/h。估计剂量与计划剂量之间的差异deltaD范围为-42%（-87 Gy）至32%（59 Gy）；在73%的病例中，差异在±35 Gy以内。在固定lambda(eff)方法中发现了更大的差异，其中deltaD范围为-69%至95%（分别为-202至88 Gy）。在甲状腺功能亢进患者中，对于约73%的分析甲状腺结构，五次摄取值剂量测定方法能够很好地预测放射性碘动力学和治疗给药后的剂量。固定lambda(eff)方法不太可靠。
