Stereotactic Body Radiotherapy in the Treatment of Spinal Metastases

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Patients with metastatic disease including polymetastatic, oligometastatic, and oligorecurrent spinal lesions have extended life expectancy secondary to improvements in systemic agents, and thus require durable local control of spine metastases. Stereotactic body radiotherapy (SBRT), which uses highly conformal treatment planning techniques coupled with image-guided technology, has enabled the safe delivery of tumor-ablative doses of radiotherapy. The NOMS decision framework has been developed as a tool to aid in the determination of the optimal treatment of spinal metastases, incorporating radiosurgery, separation surgery, stabilization techniques, and conventional radiation. Tumor radiosensitivity is critical in determining appropriateness of radiosurgery. In general, higher radiation doses provide significant, more durable tumor control, whether single-fraction or hypofractionated regimens are used. Spine SBRT can provide a high likelihood of durable tumor control with very low rates of serious toxicity, and careful attention should be given to dose constraints of organs at risk. Here, we review the indications for spine SBRT via the NOMS decision framework and provide practical information to the radiation oncologist regarding spine radiosurgery.

Section snippets

Spinal Metastases

The prevalence of spinal metastases in North America is high with more than 180,000 cases each year. A large portion of patients with cancer, more than 40%, will develop metastatic extradural spinal disease.1 Patients with metastatic disease are living longer, and the incidence of spinal metastases is expected to rise. With improvements in disease-specific survival in patients with stage IV cancer, an increasingly important aspect of spine metastasis treatment is the durability of treatment, as

NOMS Framework

The NOMS (neurologic, oncologic, mechanical, and systemic) decision framework, shown in Figure 1, is an excellent tool to determine the optimal multidisciplinary management of spinal lesions.5 It incorporates radiosurgery, conventional external beam radiation, and minimally invasive and open surgical treatment options.

Primary (De Novo) Irradiation: Single-Fraction Radiosurgery

The ideal candidate for high-dose single-session SBRT (radiosurgery) is a patient who on neurologic assessment has limited spinal cord compromise (Bilsky criteria grade of 0-1b), an oncologically radioresistant histology without mechanical instability and with limited metastatic disease, or a good prognosis that exceeds at least 6 months.

Single-fraction, high-dose radiosurgery has been proven to be highly effective in both pain and radiographic control, irrespective of tumor histology. Pain

Primary (De Novo) Radiation: Hypofractionated Radiosurgery

Hypofractionated treatment schedules may still offer the benefits of high dose per fraction treatment while allowing a higher total dose to critical normal tissues because of the opportunity for normal tissue repair of radiation effects between fractions of radiation. This may be a useful strategy when the proximity of tumor to critical structures demands dose reduction to the target volumes to such an extent that single-fraction radiation would not be able to deliver a meaningful dose of

Adjuvant Postoperative SBRT After Separation Surgery

In the NOMS framework, there may be several reasons to consider surgical intervention. In the neurologic realm, potentially reversible myelopathy should be surgically decompressed. In the setting of high-grade epidural disease, particularly with radioresistant disease, separation surgery to provide adequate space between epidural disease and spinal cord as a neoadjuvant to radiosurgery may be an appropriate treatment option. Separation surgery employs spinal instrumentation and circumferential

Salvage Hypofractionated Radiosurgery: Reirradiation

Tumor recurrence after conventional radiation is common for long-term survivors and is in the range of 50%-80% at 2 years.8 In addition, recurrent tumor is likely increasingly radioresistant as tumors develop an adaptive response and epigenetic changes resulting in acquired therapy resistance. In the recurrent setting, a robust radiation dose schedule to tumor while minimizing the dose to previously irradiated tissues is necessary for successful salvage.

There are no prospective randomized

Conclusions

Spine SBRT is proof of the principle that the accurate delivery of tumoricidal doses of radiation is feasible with the judicious use of image-guided technology and highly conformal treatment planning in de novo, postsurgical and reirradiation settings, and is able to provide durable tumor control with limited toxicity. The NOMS framework, which incorporates spine SBRT, is a useful way to approach the management of spinal metastases in a multidisciplinary fashion.

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    Conflicts of interest: Yoshiya Yamada is a member of the Speakers Bureau of the Institute for Medical Education and has served as a consultant for Varian Medical Systems. Ilya Laufer is a consultant for DePuy/Synthes, Globus, Medtronic, and SpineWave.

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