Surgery plays an important role in the treatment of spinal metastases. A prospective randomized study showed that patients with spinal cord compression secondary to solid metastatic tumors benefit from surgical decompression prior to undergoing radiation therapy. Surgery provides spinal cord decompression and spinal stabilization, allowing patients to safely proceed to radiation treatment.
Historically, conventional external-beam radiation therapy (cEBRT) has been used as the postoperative adjuvant in order to achieve tumor control. Unfortunately, most of the solid tumor histologies are resistant to cEBRT and recurrence rates after adjuvant cEBRT have been high, with up to 69 percent recurrence rates at one year documented. Spinal stereotactic radiosurgery (SRS) has consistently shown excellent tumor control rates, regardless of tumor histology, tumor resistance to cEBRT, previous radiation treatments, and size.
Based on the tumor control provided by SRS in the treatment of spinal metastases that do not require surgery, our team increasingly has been implementing its use in the postoperative setting. Furthermore, the fact that SRS provides tumor control independent of tumor size allows us to alter the goal of surgery. We no longer need to perform extensive operations in order to maximize the volume of the tumor removed. Currently, we perform “separation surgery” with the purpose of providing a separation between the tumor and the spinal cord to allow safe delivery of optimal radiation dose to the entire tumor volume. This procedure allows us to focus the resection on the epidural tumor rather than on the vertebral body and decreases the operative time and the extent of required vertebral column reconstruction.
We analyzed local tumor control results in 186 patients who underwent SRS after surgery, with a median follow-up of 7.6 months. All patients underwent separation surgery followed by SRS administered either as single-fraction treatment (24 Gy) or as hypofractionated treatment.
The hypofractionated treatment was either administered in five to six low-dose fractions of 3 to 6 Gy or in three high-dose fractions of 8 to 10 Gy. The patients were stratified according to radiosensitivity of the tumor histology, previous radiation, postoperative radiation dosing and fractionation, and the degree of postoperative and preoperative epidural tumor extension. All patients were followed with serial MRI and CT scans every three to four months to monitor for recurrence.
The majority of the tumors were located in the thoracic spine and had high-grade epidural extension. Eighty percent of the tumors had radioresistant histology, and nearly 50 percent were previously irradiated. One hundred and nine patients received low-dose hypofractionated therapy, 37 patients received high-dose hypofractionated, and 40 received single-fraction treatments. At last follow-up, 70 percent had no evidence of local recurrence, and 54 patients were alive. None of the patients developed a neurologic deficit secondary to surgery or radiation and only four patients required reoperation.
The estimated incidence of local recurrence at one year after SRS was 16 percent. Postoperative radiation dose was the only stratification variable that was significantly associated with recurrence risk. Radioresistance of the tumor, prior radiation history, and degree of epidural extension were not associated with local recurrence. When stratified by postoperative radiation, the one-year incidence of local recurrence was 22.6 percent for the low-dose hypofractionated group, 9 percent for the SRS group, and 4.1 percent for the high-dose hypofractionated group. All of these recurrence rates are much lower than the previously reported results after cEBRT.
SRS has become an important component of spinal oncology. In the postoperative setting, it provides durable local control regardless of tumor histology, previous radiation, and size. The high-dose per fraction treatment strategies provide better control compared with low-dose hypofractionated treatment. The efficacy and safety of postoperative SRS allows the surgeon to significantly decrease the extent of tumor resection, nearly eliminating the need for complex and extended approaches and circumferential spinal reconstruction. By decreasing the extent of operative intervention, we facilitate postoperative recovery and allow patients to more quickly proceed to systemic and radiation therapy.