Spine Stereotactic Body Radiotherapy: Indications, Outcomes, and Points of Caution

Abstract

Study design: A broad narrative review.

Objectives: The objective of this article is to provide a technical review of spine stereotactic body radiotherapy (SBRT) planning and delivery, indications for treatment, outcomes, complications, and the challenges of response assessment. The surgical approach to spinal metastases is discussed with an overview of emerging minimally invasive techniques.

Methods: A comprehensive review of the literature was conducted on the techniques, outcomes, and developments in SBRT and surgery for spinal metastases.

Results: The optimal management of patients with spinal metastases is complex and requires multidisciplinary assessment from an oncologic team that is familiar with the shifting paradigm as a consequence of evolving techniques in surgery and stereotactic radiation, as well as new developments in systemic agents. The Spinal Instability Neoplastic Score and the epidural spinal cord compression (Bilsky) grading system are useful tools that facilitate communication among oncologic team members and can direct management by providing a baseline assessment of risks prior to therapy. The combined multimodality approach with "separation surgery" followed by postoperative spine SBRT achieves thecal sac decompression, improves tumor control, and avoids complications that may be associated with more extensive surgery.

Conclusion: Spine SBRT is a highly effective treatment that is capable of delivering ablative doses to the target while sparing the critical organs-at-risk, chiefly the critical neural tissues, within a short and manageable schedule. At the same time, surgery occupies an important role in select patients, particularly with the expanding availability and expertise in minimally invasive techniques. With rapid adoption of spine SBRT in centers outside of the academic setting, it is imperative for the practicing oncologist to understand the relevance and application of these evolving concepts.

Keywords: postoperative radiation; spinal cord compression; spine metastasis; spine radiosurgery; spine stereotactic body radiotherapy.

Figure 1.

An example of a spine SBRT immobilization device with a patient shown in the BodyFIX system (Elekta AB, Stockholm, Sweden). The device consists of a vacuum cushion, a clear plastic cover sheet, and a dual vacuum pump that maintains a vacuum seal over the top of the patient with the cover sheet molded to the body contours. Precise adjustments of the patient position may be made with the robotic couch, which permits both translational and rotational corrections (6 degrees of freedom).

Figure 2.

Schematic of the 6-point epidural spinal cord compression (ESCC) grading scale proposed by Bilsky et al. The grade represented by each figure is denoted in the upper left hand corner of the figure. Grade of 0 denotes bone-only disease; 1a, epidural impingement, without deformation of the thecal sac; 1b, deformation of the thecal sac, without spinal cord abutment; 1c, deformation of the thecal sac with spinal cord abutment, but without cord compression; 2, spinal cord compression, but with CSF visible around the cord; and 3, spinal cord compression, no CSF visible around the cord.

Figure 3.

Illustrative case of 61-year-old male patient with metastatic melanoma to T8 and L3 who was undergoing curative external beam radiation therapy for head and neck squamous cell carcinoma when he presented with mechanical back pain and right leg paresthesia along the L3 nerve root distribution. The diagnostic MRI shown in (A1-A2) demonstrated diffuse involvement of L3, a VCF with retropulsion, and extra osseous soft tissue extending into the anterior epidural space. The patient was treated with spine SBRT with minimal interruption to the head and neck cancer treatment with the target volume encompassing the entire vertebral body and bilateral posterior elements to a prescription dose of 24 Gy in 2 fractions, limiting the thecal sac to 18.7 Gy point max. Panel (B1-B2) illustrates the radiation plan in 2 planes, highlighting the tight isodose lines around the spinal canal with a rapid dose falloff gradient to limit exposure to normal tissues. Two and a half weeks after SBRT, the patient demonstrated fracture progression and underwent a posterior spinal decompression of circumferential disease, L3 vertebroplasty, and pedicle screw instrumentation L2 through L4, as shown in panel (C1-C2). Panel (D1-C2) indicates the hematoxylin and eosin stain and the SOX10 IHC, respectively, showing the tissue to be mostly reactive in nature with foamy histiocytes, hemorrhage, and multinucleated giant cells with only a few atypical nuclei in the background representing residual melanoma.