Radiotherapy for Glioma: Number of Fractions
Radiotherapy for glioma is delivered in fractions over multiple weeks, not cycles—the specific fractionation schedule depends on glioma type, molecular markers, and patient characteristics, ranging from 15 to 33 fractions delivered over 3 to 6 weeks. 1
Standard Fractionation by Glioma Type
IDH-Wildtype Glioblastoma (Grade 4)
For newly diagnosed glioblastoma in patients under 70 years with good performance status:
- 30 fractions: 60 Gy delivered as 2 Gy per fraction, 5 fractions per week over 6 weeks 1, 2
- Concurrent temozolomide (75 mg/m² daily) is given throughout the 42-day radiation period 1, 2
- Followed by adjuvant temozolomide for up to 6 cycles (150-200 mg/m² for 5 days every 28 days) 1, 2
For elderly patients (≥70 years) or those with poor performance status:
- 15 fractions: 40-40.05 Gy delivered as 2.66-2.67 Gy per fraction over 3 weeks 1, 3
- Concurrent temozolomide (75 mg/m² daily for 21 days) can be added 1
- Followed by adjuvant temozolomide for up to 12 months 1
IDH-Mutant Lower Grade Gliomas
For IDH-mutant, 1p19q codeleted oligodendroglioma (Grade 2):
- 30 fractions: 54 Gy delivered as 1.8 Gy per fraction over 6 weeks 1
- Followed by 6 cycles of PCV chemotherapy (each cycle is 8 weeks) 1
For IDH-mutant, 1p19q codeleted anaplastic oligodendroglioma (Grade 3):
- 33 fractions: 59.4 Gy delivered as 1.8 Gy per fraction, 5 fractions per week 1
- Followed by 6 cycles of PCV or up to 12 months of temozolomide 1
For IDH-mutant, 1p19q non-codeleted astrocytoma (Grade 2 or 3):
- 30 fractions (Grade 2): 54 Gy as 1.8 Gy per fraction over 6 weeks 1
- 33 fractions (Grade 3): 59.4 Gy as 1.8 Gy per fraction 1
- Followed by adjuvant temozolomide for up to 12 months 1
Critical Distinctions: Fractions vs. Cycles
Radiotherapy is measured in fractions (daily treatments), not cycles. 3 The term "cycles" applies to chemotherapy regimens that follow radiation:
- PCV chemotherapy: 6 cycles total, each cycle lasting 8 weeks 1
- Temozolomide maintenance: 6-12 cycles, each cycle lasting 28 days 1, 2
Treatment Volume Considerations
All modern glioma radiotherapy uses partial brain (focal) irradiation, not whole brain radiation. 1, 3, 4
- Target volume includes tumor bed or resection site with 2-3 cm margin 1, 2
- Whole brain radiotherapy is no longer recommended due to increased toxicity without survival benefit 4
Common Pitfalls to Avoid
Do not confuse radiation fractions with chemotherapy cycles—patients often ask "how many cycles of radiation," but radiation is delivered as daily fractions over consecutive weeks, while chemotherapy follows in distinct cycles. 2, 3
Lower dose radiation (45-50.4 Gy) is NOT inferior to higher doses (59.4-64.8 Gy) for low-grade gliomas and reduces toxicity, making it an acceptable alternative. 5, 4
Hypofractionated regimens (15 fractions) are specifically designed for elderly or frail patients—they are not simply "abbreviated" standard treatment but represent evidence-based dose-equivalent schedules. 1, 3