2015 年 1 巻 p. 26-32
Magnetic resonance imaging (MRI) is usually carried out in follow-up evaluation after Gamma Knife surgery (GKS) for metastatic brain tumors. The purpose of this study is to assess the utility of serial measurements of the apparent diffusion coefficient (ADC) values in differentiating radiation effects from tumor recurrence. We enrolled 57 metastatic brain tumors (>10mm in maximum diameter) from 51 patients treated with GKS in our institution from February 2011 to September 2012. Diffusion weighted imaging was added to conventional MRI, and the ADC values were measured every three months at least. The ADC index was defined as the ratio of normalized minimum ADC value in the latest observation to that of the former observation and was used for chronological evaluation. During follow-up, four lesions were diagnosed as tumor recurrence. In these lesions, the ADC indices were lower than 1.00 when the tumors were diagnosed as recurrences. In the cases of good outcome, the ADC indices were higher than 1.00. Based on these results, a reduction of the ADC indices between two consecutive exams strongly suggests tumor recurrence. The serial ADC analysis can be one of the reasonable diagnostic tools to distinguish tumor recurrence from radiation necrosis in follow-up imaging after GKS.
