Glioblastoma is the most common malignant brain tumor in adults. The primary treatment consists of maximal tumor removal followed by radiotherapy (RT) with concomitant and adjuvant temozolomide. Tumor recurrence after chemoradiotherapy has previously been shown to be predominantly within or at the margin of the irradiated volume, but distant failure are not rare, especially in patients with MGMT methylation.Traditionally, RT has been planned based on on planning CT with co-registered postoperative MRI, with the addition of a clinical target volume margin of 2-3 cm to account for infiltrative odema.