Pathways to consensus.

Recommendations for radiation for glioblastoma multiforme (GBM) are pretty uniform. Too bad radiation volumes aren’t, as made painfully clear by central review of recent NRG trials. Most people know low- and high-risk volumes include T2/FLAIR and T1-contrasted lesions, respectively, with generous 2 cm clinical target volume (CTV) expansions. The major variation arises with showers over- and underestimating anatomic pathways of tumor spread. To help address this, the NRG now offers up the first consensus guidelines on contouring for GBM. Common pitfalls include failing to trim CTV expansions sup-inf at the tentorium and left-right at the falx—two large anatomic barriers that deserve respect. Or, conversely, trimming too tight at the corpus callosum, anterior/posterior commissures, and cerebellar peduncles connecting thalamus to mid-brainstem—all providing tumor-accessible highways across midline. TBL: The NRG recommends showing your anatomy skilz by judicious cropping of large CTV volumes for GBM. | Kruser, J Neurooncol 2019