The subventricular zone concept: ready for therapeutic implications?

For more than 10 years, with reaffirmation of the key role of radiation therapy (RT) in the postoperative management of most gliomas,¹ it has been a frustrating fact that no significant progress can be claimed in our specialty. Neither the "dose-escalation" nor the "dose-painting" concept, even when guided by "high-tech" imaging, permits significantly better local control that translates into longer survival. What we define as the CTV (clinical target volume), which should reflect the microscopic extension of glioma cells, is still a rather rough isotropic expansion of the GTV (gross tumor volume), usually 1.5–2 cm beyond.² Exploring new areas of potential progress in RT, several publications focused on glioblastoma (GBM) suggested that the subventricular zone (SVZ) could be the "niche" of glioma stem cells, which explains at least in part the inevitable recurrence of most gliomas: We would regularly miss the target, ignoring this key zone where the more radioresistant cells would hide.^3,4