ASTRO Guidelines for Metastatic Spine Lesions
Stereotactic body radiation therapy (SBRT) is the recommended treatment for metastatic spine lesions, achieving approximately 90% local control at 1 year and 54% complete pain response, with superior outcomes compared to conventional external beam radiotherapy. 1, 2
Primary Treatment Recommendations
Dose and Fractionation Schemes
The most commonly used and effective SBRT regimens include 1, 3:
- 16-24 Gy in 1 fraction
- 24 Gy in 2 fractions
- 24-27 Gy in 3 fractions
- 30-35 Gy in 5 fractions
All of these regimens achieve a biologically effective dose (BED₁₀) of at least 100 Gy, which is the minimum threshold for optimal outcomes 3. Do not use BED₁₀ <100 Gy for curative intent, as it is associated with poor outcomes 3.
Patient Selection Criteria
SBRT should be prioritized for patients with 1:
- Radioresistant histologies (melanoma, renal cell carcinoma, sarcoma) - these achieve 90% 2-year local control with SBRT versus <50% at 1 year with conventional radiotherapy 1, 3
- Oligometastatic disease or bone-only metastases indicating longer survival potential 1
- Bulky "mass-type" tumors with extraosseous extension - conventional radiotherapy achieves <50% control at 1 year in these cases 1
- Expected survival >3-6 months - median survival after SBRT is 15-17 months 1
Mandatory Pre-Treatment Surgical Consultation
For patients with any of the following features, obtain spine surgery consultation BEFORE initiating SBRT 1:
- Malignant epidural spinal cord compression
- Mechanical instability
- Baseline vertebral body compression fracture
- Spinal Instability Neoplasia Score ≥12 2
Reirradiation Guidelines
When Prior Conventional Radiotherapy Was Given
SBRT is the recommended retreatment option following conventional external beam radiotherapy, achieving 76% local control at 1 year and 65-81% pain control 1. Common reirradiation regimens include 1:
- 24 Gy in 3 fractions
- 30 Gy in 5 fractions
- 27 Gy in 3 fractions
- 20 Gy in 2 fractions
When Prior SBRT Was Given
Retreatment with SBRT following prior SBRT is a treatment option based on multidisciplinary assessment 1. Median survival after reirradiation SBRT ranges from 10-22.5 months, justifying aggressive local therapy 1.
Critical Caveat for Reirradiation
Prior radiation at the same site is the strongest predictor of persistent pain after SBRT 4. Epidural disease is the most common site of failure after reirradiation (38-63% of failures) 1.
Safety and Toxicity Profile
Expected Adverse Events
- Vertebral compression fracture: 9.4-12% - most common toxicity 1
- Radiation myelopathy: 0.2% - extremely rare with proper technique 1
High-Risk Features for Vertebral Fracture
Patients with the following require heightened surveillance 1:
- Significant lytic disease
- Baseline compression fracture
- Treatment with >19 Gy per fraction
- High Spinal Instability Neoplasia Score
Critical Dose Constraints
Paramount to any SBRT plan is careful delineation of the spinal cord and strict adherence to safe dose limits 1. Use daily image guidance and planning organ at risk volume margins for critical structures 3.
Comparative Effectiveness Evidence
The landmark randomized trial demonstrated SBRT (24 Gy in 2 fractions) achieved 35% complete pain response at 3 months versus 14% with conventional radiotherapy (20 Gy in 5 fractions), with risk ratio 1.33 (p=0.0002) 2. This superiority was maintained in multivariable analysis with odds ratio 3.47 (p=0.0003) 2.
Timing of Pain Response
Significant pain reduction occurs as early as 3 months after SBRT, with continued improvement at 6 and 12 months 4. Pain palliation is limited in patients with epidural extension deforming the spinal cord (Bilsky grade ≥1c) 4.
Common Pitfalls to Avoid
- Do not use conventional low-BED palliative radiation (8 Gy in 1 fraction) for patients with adequate life expectancy - this increases spinal adverse events 3
- Do not use BED₁₀ >146 Gy - very high doses show paradoxically worse survival outcomes 3
- Do not proceed with SBRT without surgical evaluation in patients with instability or high-grade epidural disease - this is a Level II recommendation 1