Chemoradiation in elderly patients with glioblastoma from the multi-institutional GBM-molRPA cohort: is short-course radiotherapy enough or is it a matter of selection?

Background: The optimal radiotherapy regimen in elderly patients with glioblastoma treated by chemoradiation needs to be addressed. We provide the results of a comparison between conventionally fractionated standard radiotherapy (CRT) and short-course radiotherapy (SRT) in those patients treated by temozolomide-based chemoradiation. Methods: Patients aged 65 years or older from the GBM-molRPA cohort were included. Patients who were planned for a ≥ 6-week or ≤ 4-week radiotherapy were regarded as being treated by CRT or SRT, respectively. The median RT dose in the CRT and SRT group was 60 Gy in 30 fractions and 45 Gy in 15 fractions, respectively. Results: A total of 260 and 134 patients aged older than 65 and 70 years were identified, respectively. CRT- and SRT-based chemoradiation was applied for 192 (73.8%) and 68 (26.2%) patients, respectively. Compared to SRT, CRT significantly improved MS from 13.2 to 17.6 months and 13.3 to 16.4 months in patients older than 65 years (P < 0.001) and 70 years (P = 0.002), respectively. Statistical significance remained after adjusting for age, performance status, surgical extent, and MGMT promoter methylation in both age groups. The benefit was clear in all subgroup analyses for patients with Karnofsky performance score 70–100, Karnofsky performance score ≤ 60, gross total resection, biopsy, methylated MGMT promoter, and unmethylated MGMT promoter (all P < 0.05). Conclusion: CRT significantly improved survival compared to SRT in elderly glioblastoma patients treated with chemoradiation in selected patients amenable for chemoradiation. This study is hypothesis-generating and a prospective randomized trial is urgently warranted.