Is a reduction of radiation dose feasible in patients affected by glioblastoma undergoing radio-chemotherapy according to MGMT promoter methylation status without jeopardizing survival?

Objective: To explore therapeutic results of different radiotherapy (RT) dose schedules combined to Temozolomide (TMZ)-RT treatment in newly diagnosed glioblastoma (GB), according to the O (6)-methylguanine-DNA methyltransferase (MGMT) methylation status. Patients and methods: Patients with newly diagnosed GB received either standard (60-59.4 Gy) or reduced (54-52 Gy) dose radiation therapy (RT) with concurrent and adjuvant TMZ between June 2010 and October 2016. We retrospectively evaluated the therapeutic effectiveness of the RT ranges schedules in terms of overall survival (OS) with univariate and multivariate analysis, after analyzing the MGMT methylation status. Results: One hundred and seventeen patients were selected for the present analysis out of 146 total treated patients accrued. Seventy-two out of the selected cases received the standard RT-TMZ course (SDRT-TMZ) whereas the remaining 45 underwent the reduced dose schedule (RDRT-TMZ). The analysis according to the MGMT promoter methylation status showed that, in methylated-MGMT GB patients, SDRT-TMZ and RDRT-TMZ groups did not show different median OS (p = ns) according to the two RT schedules, independently by the extent of surgical resection. Instead, a difference in survival outcomes was confirmed in unmethylated-MGMT GB patients with better survival for patients undergoing to SDRT, particularly in sub-total resection. Conclusion: In our experience, a reduction of radiation dose schedule does not seem to jeopardize survival in methylated-MGMT patients independently by the extent of resection. A therapeutic approach to a standard reduction of RT dose for the methylated subset of patients may be feasible and could deserve prospective trials for validation.