Department of Nuclear Medicine, Instituto Nacional de Cancerologia E.S.E., Bogotá, Colombia.
Department of Physics, Universidad Nacional de Colombia, Bogotá, Colombia.
Cancer Biother Radiopharm. 2023 Sep;38(7):445-449. doi: 10.1089/cbr.2022.0094. Epub 2023 Jun 26.
In I therapies internal dosimetry is crucial for determining the mean absorbed dose to organs at risk, particularly the bone marrow, which has a dose constraint of 2 Gy. Traditionally, multicompartmental models have been used for bone marrow dosimetry, necessitating whole-body absorbed-dose assessments. However, noninvasive techniques, such as γ-camera scans or ceiling-mounted Geiger-Müller (GM) counters, can estimate the aforementioned. This study was aimed to evaluate the agreement between whole-body mean absorbed dose using γ-camera scans and ceiling-mounted GM in patients with thyroid carcinoma undergoing I therapy. This study included 31 patients with thyroid cancer who were treated with I. The whole-body time-integrated activity (TIA) and mean absorbed dose were estimated using the elimination curves obtained with γ-camera scans and ceiling-mounted GM. In addition, statistical analysis was performed on the data to determine the Coefficient Correlation Coefficient and the Bland-Altman limits of agreement for both parameters, as well as for the elimination curves' effective half-life. The study revealed correlations of 0.562 and 0.586 between whole-body TIA and mean absorbed dose, respectively. The Bland-Altman limits of agreement were found to be below -3.75% and within 12.75% of the bone marrow dose constraint of 2 Gy. The nonparametric evaluation revealed that whole-body TIA and mean absorbed dose medians from GM were lower than those from γ-camera scans ( < 0.001). Effective half-life estimation mean was significantly lower in the GM than in the γ-camera of 13 and 23 h. Although GM calculates the whole-body absorbed dose with margins of error within clinical acceptance, underestimation of the effective half-life makes it an unacceptable substitute method for γ-cameras in clinical practice. Further research should be conducted to evaluate single-point GM measurement substitutions in time-activity curves.
在 I 疗法中，内部剂量学对于确定风险器官（尤其是骨髓）的平均吸收剂量至关重要，骨髓的剂量约束为 2 Gy。传统上，骨髓剂量学采用多室模型，需要进行全身吸收剂量评估。然而，γ相机扫描或天花板安装的盖革-弥勒（GM）计数器等非侵入性技术可以估计上述剂量。本研究旨在评估接受 I 治疗的甲状腺癌患者中，使用γ相机扫描和天花板安装 GM 估算全身平均吸收剂量的一致性。
这项研究包括 31 名接受 I 治疗的甲状腺癌患者。使用γ相机扫描和天花板安装 GM 获得的消除曲线来估算全身时间积分活度（TIA）和平均吸收剂量。此外，还对数据进行了统计分析，以确定这两个参数以及消除曲线有效半衰期的相关系数、Bland-Altman 一致性界限。
研究结果显示，全身 TIA 与平均吸收剂量之间的相关性分别为 0.562 和 0.586。Bland-Altman 一致性界限发现低于 -3.75%，并且在骨髓剂量约束 2 Gy 的 12.75% 以内。非参数评估显示，GM 获得的全身 TIA 和平均吸收剂量中位数低于γ相机扫描（<0.001）。GM 获得的有效半衰期估计平均值明显低于γ相机的 13 和 23 h。
虽然 GM 以临床可接受的误差幅度计算全身吸收剂量，但有效半衰期的低估使得 GM 成为临床实践中不可接受的γ相机替代方法。应该进行进一步的研究来评估时间-活度曲线中 GM 单点测量的替代。
