Incidence and extent of disease progression on MRI between surgery and initiation of radiotherapy in glioblastoma patients.

BACKGROUND

A post-operative MRI (MRI) 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) 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 and the impact on radiation target volumes.

METHODS

Patients with GBM diagnosed between 2018 and 2020 who had an MRI and MRI were retrospectively identified. Criteria for REP was based on Modified RANO criteria. Radiation target volumes were created and compared using the MRI and MRI.

RESULTS

Fifty patients met inclusion criteria. The median time between MRI and MRI was 26 days. Indications for MRI 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-based high dose treatment volumes. Treatment planning with MRI yielded a median undertreatment of 27.1% of enhancing disease and 11.2% of surrounding subclinical disease seen on MRI. Patients without REP had a 38% median volume reduction of uninvolved brain if target volumes were planned with MRI.

CONCLUSION

Given the incidence of REP and its impact on treatment volumes, we recommend using MRI 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.