Impact of Postoperative Changes in Brain Anatomy on Target Volume Delineation for High-Grade Glioma.

High-grade glioma has a poor prognosis, and radiation therapy plays a crucial role in its management. Every step of treatment planning should thus be optimised to maximise survival chances and minimise radiation-induced toxicity. Here, we compare structures needed for target volume delineation between an immediate postoperative magnetic resonance imaging (MRI) and a radiation treatment planning MRI to establish the need for the latter. Twenty-eight patients were included, with a median interval between MRIs (range) of 19.5 (8-50) days. There was a mean change in resection cavity position (range) of 3.04 ± 3.90 (0-22.1) mm, with greater positional changes in skull-distant (>25 mm) resection cavity borders when compared to skull-near (≤25 mm) counterparts ( p < 0.001). The mean differences in resection cavity and surrounding oedema and FLAIR hyperintensity volumes were -32.0 ± 29.6% and -38.0 ± 25.0%, respectively, whereas the mean difference in midline shift (range) was -2.64 ± 2.73 (0-11) mm. These data indicate marked short-term volumetric changes and support the role of an MRI to aid in target volume delineation as close to radiation treatment start as possible. Planning adapted to the actual anatomy at the time of radiation limits the risk of geographic miss and might thus improve outcomes in patients undergoing adjuvant radiation for high-grade glioma.