ESTRO/EANO recommendation on reirradiation of glioblastoma

Background and Purpose: 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. Methods: 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. Results: 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 se- lection, imaging for recurrence assessment, target volume delineation, treatment planning, combined modality treatment, and follow-up. Conclusions: Currently, based on the ESTRO/EANO consensus, reirradiation may be considered in selected pa- tients 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.