ESTRO/EANO recommendation on reirradiation of glioblastoma

<b>Background and Purpose: </b> Although reirradiation of glioblastoma has a long history of clinical practice, guidance on how to perform it in the context of recent technological advances, modern imaging modalities or systemic therapy is scarce. This joint ESTRO/EANO guideline aims to collect the existing evidence to produce recommendations for safe reirradiation of glioblastoma. <b>Methods: </b> The basis of this ESTRO/EANO clinical practice guideline are nine key questions (KQ) which were formulated by a consortium of radiation-oncologists, radiologists, medical oncologists, neurooncologists, medical physicists and radiation therapists. A systematic review was conducted and the KQ were addressed based on this evidence and expert opinion to draft recommendations and statements which were then voted on in a modified DELPHI process. <b>Results: </b> The DELPHI consensus process resulted in 18 recommendations and nine statements of which all achieved group consensus. Thirteen (48%) were based on available prospective evidence and 14 (52%) on expert opinion. Level of evidence did not exceed “moderate”, reflecting the scarcity of prospective randomized evidence for most aspects of reirradiation. Consensus recommendations and statements reflected aspects of patient selection, imaging for recurrence assessment, target volume delineation, treatment planning, combined modality treatment, and follow-up. <b>Conclusions: </b> Currently, based on the ESTRO/EANO consensus, reirradiation may be considered in selected patients with glioblastoma. GTV definition is based on T1-weighted MR-sequences, while a GTV to CTV margin is not mandatory. A PTV margin of maximum 3 mm is recommended based on the individual mask system and IGRT procedures. A biological effective dose greater than 36 Gy in 2 Gy fractions is recommended. A careful assessment of prognostic factors on survival such as age, interval from initial radiation, large treatment volumes, poor KPS, and poor neurologic/neurocognitive status is essential for making a clinical recommendation. <p/>