Figure 1.

Top: Example of spontaneous velocity of radius expansion of a left temporo‐insular diffuse low‐grade glioma through the evolution of its mean tumour radius on MRI over time. Each point represents an MR examination. Before treatment by radiotherapy (a), the tumour grew spontaneously and continuously. Duration of radiotherapy is indicated by joined arrows. Following radiotherapy, tumour volume measured on follow‐up MRIs decreased for more than 5 years. Then, tumour progression was observed on MRI with a tumour regrowth. Bottom: MRI images corresponding to the times indicated by letters on the radius‐versus‐time curve.