Abstract
BACKGROUND: A post-operative MRI (MRI(post-op)) performed within 72 h is routinely used for radiation treatment planning in glioblastoma (GBM) patients, with radiotherapy starting about 4-6 weeks after surgery. Some patients undergo an additional pre-radiotherapy MRI (MRI(pre-RT)) about 2-6 weeks after surgery. We sought to analyze the incidence of rapid early progression (REP) between surgery and initiation of radiotherapy seen on MRI(pre-RT) and the impact on radiation target volumes. METHODS: Patients with GBM diagnosed between 2018 and 2020 who had an MRI(post-op) and MRI(pre-RT) were retrospectively identified. Criteria for REP was based on Modified RANO criteria. Radiation target volumes were created and compared using the MRI(post-op) and MRI(pre-RT). RESULTS: Fifty patients met inclusion criteria. The median time between MRI(post-op) and MRI(pre-RT) was 26 days. Indications for MRI(pre-RT) included clinical trial enrollment in 41/50 (82%), new symptoms in 5/50 (10%), and unspecified in 4/50 (8%). REP was identified in 35/50 (70%) of patients; 9/35 (26%) had disease progression outside of the MRI(post-op)-based high dose treatment volumes. Treatment planning with MRI(post-op) yielded a median undertreatment of 27.1% of enhancing disease and 11.2% of surrounding subclinical disease seen on MRI(pre-RT). Patients without REP had a 38% median volume reduction of uninvolved brain if target volumes were planned with MRI(pre-RT). CONCLUSION: Given the incidence of REP and its impact on treatment volumes, we recommend using MRI(pre-RT) for radiation treatment planning to improve coverage of gross and subclinical disease, allow for early identification of REP, and decrease radiation treatment volumes in patients without REP.