Radiation therapy has a major role in the treatment of patients with high-grade gliomas. A systematic review and meta-analysis of five randomized trials (plus one trial with allocation by birth date) comparing postoperative radiation therapy (PORT) with no radiation therapy showed a statistically significant survival advantage with radiation (risk ratio (RR) = 0.81; 95% CI, 0.74–0.88).[Level of evidence: 1iiA] Based on a randomized trial comparing 60 Gy (in 30 fractions over 6 weeks) with 45 Gy (in 25 fractions over 4 weeks) that showed superior survival in the first group (12 months vs. 9 months median survival; hazard ratio [HR] = 0.81; 95% CI, 0.66–0.99), 60 Gy is the accepted standard dose of EBRT for malignant gliomas.[Level of evidence: 1iiA]
EBRT using either 3-dimensional conformal radiation therapy or intensity-modulated radiation therapy is considered an acceptable technique in radiation therapy delivery. Typically 2- to 3-cm margins on the MRI-based volumes (T1-weighted and FLAIR [fluid-attentuated inversion recovery]) to create the planning target volume are used. Dose escalation using radiosurgery has not improved outcomes.
A randomized trial tested radiosurgery as a boost added to standard EBRT, but the trial found no improvement in survival, quality of life, or patterns of relapse compared with EBRT without the boost.[14,15]
For the same theoretical reasons, brachytherapy has been used to deliver high doses of radiation locally to the tumor while sparing normal brain tissue. However, this approach is technically demanding and has fallen out of favor with the advent of the above-mentioned techniques.
The role of immediate PORT for low-grade gliomas (i.e., low-grade astrocytoma, oligodendroglioma, mixed oligoastrocytomas) is not as clear as in the case of high-grade tumors. The European Organisation for Research and Treatment of Cancer (EORTC) randomly assigned 311 patients with low-grade gliomas to radiation versus observation in the EORTC-22845 and MRC BR04 trials.[16,17] (On central pathology review, about 25% of the patients on the trial were reported to actually have high-grade tumors.) Most of the control patients received radiation at the time of progression. After a median follow-up of 93 months, median progression-free survival was 5.3 years in the radiation arm versus 3.4 years in the control arm (HR = 0.59; 95% CI, 0.45–0.77).[16,17][Level of evidence: 1iiDiii] However, there was no difference in the overall survival (OS) rate (median survival = 7.4 years vs. 7.2 years; HR = 0.97; 95% CI, 0.71–1.34; P = .87).[16,17][Level of evidence: 1iiA] This was caused by a longer survival after progression in the control arm (3.4 years) than in the radiation arm (1.0 years) (P < .0001). The investigators did not collect reliable quality-of-life measurements, so it is not clear whether the delay in initial relapse in the radiation therapy arm translated into improved function or quality of life.