Suwinski R, Lee S P, Withers H R
Center of Oncology, M. Sklodowska-Curie Memorial Institute, Branch Gliwice, Poland.
Int J Radiat Oncol Biol Phys. 1998 Mar 1;40(4):797-806. doi: 10.1016/s0360-3016(97)00856-0.
To determine the dose-response relationship for prophylactic cranial irradiation (PCI) in small cell lung cancer, to quantify the growth kinetics of subclinical metastases, and to determine the influence of time-delay in initiating PCI on its utility.
Published reports of brain relapse rates in small cell lung cancer with and without PCI were collected. The reduction in brain relapse rate as a function of radiation dose was analyzed. The time interval between treatment of the primary tumor and the initiation of PCI was analyzed as a factor potentially influencing dose-response.
A shallow dose-response curve without any threshold in the dose intercept was demonstrated for control of subclinical brain metastases in "early PCI" (delay between initiation of treatment for primary tumor and PCI less than 60 days). By contrast "late PCI" (delay over 60 days) was associated with a significant displacement of the dose intercept. Doses over 30-35 Gy in 2-Gy fractions did not result in a further reduction in brain relapse rate, but there were too few high-dose studies to draw any definite conclusion.
The nearly linear dose-response relationship for reduction in brain relapses demonstrated for "early PCI" in the range of doses from zero up to 35 Gy given in 2-Gy fractions supports the model of a fairly logarithmically uniform distribution of metastatic cell number within a series of patients. When PCI is delayed, a significant threshold in dose-response was observed, consistent with a fast growth rate of untreated subclinical brain metastases from small cell lung cancer. The exact shape and locations of dose-response curves is not well established by this retrospective analysis of diverse data. A high probability of eliminating brain relapses following PCI requires a dose of about 30-35 Gy in 2-Gy fractions. Control rates in brain can be enhanced if PCI is applied early.
确定小细胞肺癌预防性颅脑照射（PCI）的剂量反应关系，量化亚临床转移灶的生长动力学，并确定开始PCI的时间延迟对其效用的影响。
收集了有或无PCI的小细胞肺癌脑复发率的已发表报告。分析了脑复发率随辐射剂量的降低情况。分析了原发性肿瘤治疗与开始PCI之间的时间间隔，将其作为可能影响剂量反应的一个因素。
对于“早期PCI”（原发性肿瘤治疗开始与PCI之间的延迟小于60天），在控制亚临床脑转移方面显示出一条浅剂量反应曲线，在剂量截距处无任何阈值。相比之下，“晚期PCI”（延迟超过60天）与剂量截距的显著位移相关。以2 Gy分割给予超过30 - 35 Gy的剂量并未导致脑复发率进一步降低，但高剂量研究数量过少，无法得出任何明确结论。
对于“早期PCI”，在以2 Gy分割给予从零到35 Gy的剂量范围内，脑复发率降低呈现出近乎线性的剂量反应关系，这支持了一系列患者中亚临床转移细胞数呈相当对数均匀分布的模型。当PCI延迟时，观察到剂量反应中有显著阈值，这与小细胞肺癌未经治疗的亚临床脑转移灶的快速生长率一致。通过对不同数据的回顾性分析，剂量反应曲线的确切形状和位置尚未明确确立。PCI后消除脑复发的高概率需要以2 Gy分割给予约30 - 35 Gy的剂量。如果早期应用PCI，可提高脑控制率。
