To the Editor, We read with great interest the article “Application of diffusion-weighted magnetic resonance imaging to predict the intracranial metastatic tumor response to gamma knife radiosurgery” by Lee, Wintermark, Xu, Yen, Schlesinger and Sheehan (J Neurooncol. 2014 Jun; 118(2):351-61). Our group has recently undertaken investigation of DWI/ADC features in resected brain metastases in order to relate these to tissue characteristics and clinical outcomes. The authors present a series of mixed tumor types and add to the increasing evidence that DWI/ADC is a promising marker in these and other brain tumours, due to its ease of acquisition (both in terms of time on the scanner and cost) and robust, logical relation to tissue features such as cellularity.Brain metastasis studies of all varieties are made difficult by the variable behaviour of tumors depending on their primary cancer of origin. The authors suggest “further studies are required to assess whether DWI/ADC changes are infl ...