From the Guidelines
There is no evidence to support a boost to gross tumor disease in cases of spinal Stereotactic Body Radiation Therapy (SBRT), as current practice already delivers high, ablative doses to the target volume. The use of SBRT in patients with spinal metastases is becoming more frequent, with the goal of achieving local tumor control 1. However, the risk of vertebral compression fractures (VCF) is significantly greater with SBRT, ranging from 11% to 39%, with median times to VCF ranging from 2 to 25 months 1.
Key Considerations
- The standard approach in spinal SBRT already delivers high doses, ranging from 16-24 Gy in a single fraction to 24-36 Gy in 3-5 fractions, depending on tumor location and proximity to critical structures 1.
- The concept of additional boost doses raises concerns about increased toxicity to adjacent critical structures, particularly the spinal cord, which has strict dose constraints to prevent radiation myelopathy.
- Some studies have reported a dose-complication relationship, with high rates of VCF (~40%) when using high single-fraction doses (24 Gy) compared to lower dose single-fraction doses (16-18 Gy) or fractionating with 24 Gy in 2 fractions 1.
Clinical Implications
- The primary focus in spinal SBRT planning remains delivering adequate dose to the target while respecting normal tissue constraints, particularly for the spinal cord.
- Baseline VCF is a risk factor for subsequent VCF following SBRT, and randomized trials are ongoing to evaluate the proposed benefits of SBRT as compared to external beam radiation therapy (EBRT) 1.
- In clinical practice, the use of boost doses to gross disease in spinal SBRT is not routinely recommended, and the standard approach should be individualized based on tumor characteristics, patient factors, and institutional protocols.
From the Research
Evidence of Boost to Gross Tumor Disease in Spinal SBRT
- There is no direct evidence in the provided studies to suggest a boost to gross tumor disease in cases of spinal Stereotactic Body Radiation Therapy (SBRT) 2, 3, 4, 5, 6.
- However, the studies do report on the effectiveness and safety of SBRT in treating spinal metastases, with some studies showing excellent local control rates and low toxicity 3, 4, 5.
- One study compared the fracture rates between SBRT and external-beam radiation therapy (EBRT) for metastatic spine tumors, and found that SBRT was associated with a higher rate of vertebral body fractures, but also higher rates of initial local control 6.
- Another study reported on the use of SBRT for reirradiation of recurrent epidural spinal metastases, and found that it was a feasible and effective treatment modality with minimal toxicity 4.
- The studies suggest that SBRT can be an effective treatment option for patients with metastatic spine tumors, but the optimal treatment characteristics and patient-specific factors necessary to achieve durable outcomes are still not well understood 2, 5.