Recommended HSRT Dose for Brain Metastases
For hypofractionated stereotactic radiotherapy (HSRT) of brain metastases, the optimal regimen is 27 Gy in 3 fractions or 30 Gy in 5 fractions, which provides superior local control with minimal radiation necrosis risk compared to single-fraction SRS. 1
Dose Selection Algorithm by Clinical Scenario
For Intact Brain Metastases
Lesions ≤3 cm:
- Primary recommendation: 30 Gy in 5 daily fractions 2
- This dose achieves 12-month local control of 81% with acceptable toxicity 2
- Doses <30 Gy result in significantly worse local control (33% failure at 12 months vs 19% with ≥30 Gy) 2
- Alternative: 27 Gy in 3 fractions provides 91% 1-year local control with only 8% radiation necrosis 1
Lesions >3 cm:
- Preferred: 30 Gy in 5 fractions 1
- Alternative regimens for larger volumes (>15 cm³): 40 Gy in 10 fractions (4 Gy per fraction) shows excellent tolerability with no side effects 3
- Avoid 5 × 6-7 Gy or 7 × 5 Gy for lesions >15 cm³ due to 22% toxicity rate 3
For Post-Resection Cavities
Cavities 2-3 cm (4.2-14.1 cm³):
- Recommended: 27-30 Gy in 3 fractions 4
- 33 Gy in 3 fractions is safe for cavities <3 cm but provides marginal benefit 4
- 1-year local progression rate: 10% 4
Cavities 3-4 cm (14.2-33.5 cm³):
- Recommended: 27 Gy in 3 fractions 4
- 30 Gy shows 33% grade 3-4 necrosis risk 4
- 33 Gy results in 83% any-grade necrosis in larger volumes 4
General cavity dosing:
- Median effective dose: 38.4 Gy EQD2 (α/β=10) 5
- Higher equivalent doses improve local control (HR 0.79 per 10 Gy increase) 5
- Most common regimen: 24 Gy in 3 fractions 5
Critical Dosing Principles
Dose-Response Relationship
- Multisession HSRT demonstrates superior outcomes compared to single-fraction SRS 1
- 1-year local control: 91% with multisession vs 77% with single-session (P=0.01) 1
- Radiation necrosis: 8% with multisession vs 20% with single-session (P=0.004) 1
Volume-Dependent Toxicity
- For lesions >3 cm, surgical resection should be considered first 1
- Radiation necrosis risk increases with volume, particularly at higher doses 4, 3
- PTV >15 cm³ requires dose de-escalation to maintain acceptable toxicity 3
Common Pitfalls to Avoid
Underdosing:
- Doses of 15-18 Gy result in <50% 1-year local control 1
- 24 Gy single fraction achieves only 85% 1-year local control 1
- Doses <30 Gy in 5-fraction regimens increase local failure risk by 62% 2
Overdosing Large Volumes:
- 33 Gy in 3 fractions for cavities 3-4 cm causes 83% any-grade necrosis 4
- 5 × 6-7 Gy for lesions >15 cm³ results in 22% symptomatic toxicity 3
Ignoring Histology:
- Dose-response effect is independent of histology, including breast cancer subtypes 2
- Do not reduce dose based on presumed radiosensitivity 2
Treatment Delivery Specifications
- Prescription isodose line: typically 50% (range 20-90%) 1
- Daily fractionation preferred for 5-fraction regimens 2
- Consecutive-day treatment acceptable for 3-fraction regimens 4
- Non-invasive skull fixation adequate for HSRT delivery 3
Expected Outcomes with Optimal Dosing
Local Control:
Toxicity:
- Grade 3-4 toxicity: 4-8% 5, 4
- Symptomatic radiation necrosis: 9.5-13% 5, 2
- Any-grade necrosis: 15-29% depending on dose/volume 4, 2
Survival: