Recent Advances in Stereotactic Body Radiation Therapy for Spinal Malignancies

Dear Colleagues,

Bone is among the most common metastatic sites in cancer patients, and the spine is the most involved region for bony metastases. Spinal metastases are often painful, and patients are at high risk of vertebral fracture and neurological disabilities.

Bone metastases are classified as lytic (destructive), sclerotic (bone forming), or mixed, depending on the bone remodeling mechanisms. Lytic metastases are caused by the stimulation of osteoclasts via tumor cells in the bone microenvironment, which result in bone matrix destruction. On the other hand, sclerotic lesions are the result of osteoblast stimulation and uncontrolled new bone formation. Osteolytic metastases are mostly associated with lung, breast, thyroid, colorectal, and renal cancer. Osteoblastic lesions predominantly have prostate and breast cancer as the primary origin.

The treatments of such lesions consist of surgery, chemotherapy, radiation therapy (RT), or a combination of these modalities. Conventional RT is the cornerstone for the palliative management of spinal metastases; however, it is unable to apply an ablative dose to the affected vertebra due to technical limitations and, therefore, the local control (LC) remains poor. The life expectancy and overall survival of cancer patients have shown significant improvement in recent years. This is in part due to innovative surgical skills, advanced RT techniques, and novel systemic therapies such as immunotherapy. As these patients live longer, there is an increasing need to achieve a better LC and improve the quality of life (QOL).  In recent years, SBRT has become a preferred method for treating spinal metastases, especially in patients with few metastases (oligometastatic) and radio-resistant tumors, and good performance status. SBRT delivers high-radiation doses in few fractions to a relatively small target volume, while respecting the organs at risk (OARs) constraints. Numerous retrospective and some prospective studies have shown excellent LC after spine SBRT. Besides LC, pain relief is another important goal of SBRT for spinal metastasis. We can hypothesize that excellent LC might result in better pain response after SBRT, which has been previously shown in two prospective randomized trials. However, three other prospective randomized studies showed negative results for pain relief after SBRT, as compared to conventional RT with a palliative dose.

As spine SBRT requires highly precise planning, pre-SBRT imaging is essential in order to delineate target volumes and OARs. According to the literature, MRI is currently the best imaging modality available in the detection of spine metastases and is recommended for pre-SBRT planning by the International Spine Radiosurgery Consortium, as well as the SPINO group. The sensitivity, specificity, and accuracy of MRI in diagnosing bone metastases and differentiating them from benign and inflammatory lesions are very high.

Following SBRT and—especially in patients who still present with oligo-metastatic/progressive disease—radiological response assessment is crucial to ensure that patients are managed correctly. This management is a spectrum, from an observation in the case of a locally controlled tumor or pseudo-progression to active salvage therapy in the case of evidence of tumor persistence/recurrence being found.

Response assessment after SBRT or radiosurgery is a highly challenging topic in different organs, as we are already aware from intracranial malignancies. For spinal metastases, there are some further aspects to consider in the interpretation of radiological changes after SBRT, including pseudo-progression, vertebral compression fracture (VCF), epidural progression, changes in bone density depending on the nature of metastasis, and altered vascularization.

VCF is the most important complication after spinal SBRT. A review from Faruqi et al. showed a crude VCF rate of 13.9%, with lytic lesion, baseline VCF, and higher dose per fraction as relevant risk factors in multivariate analysis. In this regard, several studies have demonstrated the clinical usefulness of multimodal MRI, including functional sequences. While CT provides information on bone density and fracture margins, MRI is the modality of choice, including multiple distinguishing parameters to characterize the nature of a fracture. 

In view of the information presented above, we aim to produce a Special Issue for the Current Oncology journal with the following title: “Recent Advances in Stereotactic Body Radiation Therapy for Spinal Malignancies”. As such, we invite authors interested in this field to contribute to the Special Issue. Submissions on the following topics are especially welcomed:

• modern techniques for spine SBRT;
• different target volume delineations;
• different SBRT dose and fractionation;
• response assessment using different imaging modalities (PET/CT, MRI, CT, etc.).

Dr. Hossein Hemmatazad
Guest Editor

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• spinal metastases
• Stereotactic Body Radiation Therapy
• dose and fractionation