Table 2 Results of the univariable Cox regression analysis. For variables with missing values, only known values were considered for model building

RT-protocol NFRT vs HFRT

1.381

0.906

2.106

0.133

Age (continuous)

1.023

1.007

1.039

0.0052

Gender: Female vs. Male

0.700

0.481

1.019

0.062

Subtotal vs. complete resection

1.253

0.797

1.969

0.329

Debulking vs. complete resection

1.152

0.557

2.385

0.703

Biopsy vs. complete resection

2.813

1.752

4.516

1.87 × 10⁻⁵

Mental status: Impaired vs. Normal

0.809

0.421

1.554

0.524

Neurological function: Impaired vs. Normal

1.008

0.671

1.514

0.969

MGMT methylation: Yes vs. No

0.232

0.133

0.403

2.23 × 10⁻⁷

IDH mutation: Yes vs. No

0.167

0.023

1.211

0.0766

Secondary GBM: Yes vs. No

0.311

0.143

0.676

0.0032

PTV: >  269 ccm vs. ≤269 ccm

1.750

1.168

2.622

0.00668

Temozolomide: Yes vs. No

0.523

0.355

0.769

0.000984

Steroids: Yes vs. No

2.205

1.471

3.307

0.00013

Salvage: Yes vs. No

0.268

0.180

0.400

1.24 × 10⁻¹⁰

70–80 vs. < 70

90–100 vs. < 70

0.786

0.706

0.426

0.386

1.447

1.292

0.440

0.259

2008–2013 vs. 2004-2008

11.55

0.032

2014–2018 vs. 2004-2008

11.98

0.032

Tumor treating fields: Yes vs. No

0.836

0.386

1.809

0.649