Goddu S M, Howell R W, Rao D V
Department of Radiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark 07103, USA.
J Nucl Med. 1995 Oct;36(10):1923-7.
Tumor absorbed dose calculations in radionuclide therapy are presently based on the assumption of static tumor mass. This work examines the effect of dynamic tumor mass (growth and/or shrinkage) on the absorbed dose.
Tumor mass kinetic characteristics were modeled with the Gompertz equation to simulate tumor growth and an additional exponential term to accommodate tumor shrinkage that may result as a consequence of therapy.
Correction factors, defined as the ratio of the absorbed dose, which was calculated by considering tumor mass dynamics, to the absorbed dose, which was calculated by assuming static mass, are presented for 1- and 100-g tumors with different tumor mass kinetics. The dependence of the correction factor on the effective half-life Te of the radioactivity in the tumor and the tumor shrinkage half-time Ts was examined. The correction factors for the 1-g tumor were > 1 for short Ts and Te. In contrast, the correction factor was less than 1 for long Ts ( > 9 days). The dose correction factors for the 100-g tumor were > 1 for all Ts and Te. Finally, the dosimetric method for dynamic masses is illustrated with experimental data on Chinese hamster V79 multicellular spheroids that were treated with 3H.
Correction factors as high as about 10 are likely when Te and Ts are short. As Ts increases beyond 20 days, the importance of dynamic mass diminishes because most of the activity decays before the mass changes appreciably. In some cases, mass dynamics should be taken into account when the absorbed dose to tumors is estimated.
放射性核素治疗中肿瘤吸收剂量的计算目前基于肿瘤质量恒定的假设。本研究探讨动态肿瘤质量（生长和/或缩小）对吸收剂量的影响。
用Gompertz方程对肿瘤质量动力学特征进行建模以模拟肿瘤生长，并增加一个指数项以适应治疗可能导致的肿瘤缩小。
给出了1克和100克肿瘤在不同肿瘤质量动力学情况下的校正因子，校正因子定义为考虑肿瘤质量动态计算得到的吸收剂量与假设质量恒定计算得到的吸收剂量之比。研究了校正因子对肿瘤内放射性有效半衰期Te和肿瘤缩小半衰期Ts的依赖性。1克肿瘤在Ts和Te较短时校正因子>1。相反，Ts较长（>9天）时校正因子小于1。100克肿瘤的剂量校正因子在所有Ts和Te情况下均>1。最后，用3H处理的中国仓鼠V79多细胞球体的实验数据说明了动态质量的剂量学方法。
当Te和Ts较短时，校正因子可能高达约10。当Ts增加超过20天时，动态质量的重要性降低，因为大部分活度在质量有明显变化之前就已衰变。在某些情况下，估计肿瘤吸收剂量时应考虑质量动态。
