Stereotactic body radiotherapy: a new paradigm in the management of spinal metastases

Intensity-modulated radiation therapy administered to a previously irradiated spine is effective and well-tolerated

PURPOSE

This study sought to discern the clinical outcomes of intensity-modulated radiation therapy (IMRT) administered to the spine in patients who had undergone previous radiotherapy.

METHODS

A total of 81 sites of 74 patients who underwent previous radiotherapy administered to the spine or peri-spine and subsequently received IMRT for the spine were analyzed in this study. The prescribed dose of 80 Gy in a biologically effective dose (BED) of α/β = 10 (BED₁₀) was set as the planning target volume. The constraint for the spinal cord and cauda equine was D_0.1 cc ≤ 100 Gy and ≤ 150 Gy of BED for re-irradiation alone and the total irradiation dose, respectively.

RESULTS

The median follow-up period was 10.1 (0.9-92.1) months after re-irradiation, while the median interval from the last day of the previous radiotherapy to the time of re-irradiation was 15.6 (0.4-210.1) months. Separately, the median prescript dose of re-irradiation was 78.0 (28.0-104.9) of BED₁₀. The median survival time in this study was 13.9 months, with 1-, 3-, and 5-year overall survival rates of 53.7%, 29.3%, and 26.6%, respectively. The 1-, 3-, and 5-year local control rates were 90.8%, 84.0%, and 84.0%, respectively. Neurotoxicity was observed in two of 72 treatments (2.8%) assessed after re-irradiation.

CONCLUSION

Re-irradiation for the spine using IMRT seems well-tolerated. Definitive re-irradiation can be a feasible treatment option in patients with the potential for a good prognosis.

Technical Note: A custom-designed flexible MR coil array for spine radiotherapy treatment planning

PURPOSE

To assess the performance and optimize the MR image quality when using a custom-built flexible radiofrequency (RF) spine coil array fitted between the immobilization device and the patient for spine radiotherapy treatment planning.

METHODS

A 32 channel flexible custom-designed receive-only coil array has been developed for spine radiotherapy simulation for a 3 T Philips MR scanner. Coil signal-to-noise performance and interactions with standard vendor hardware were assessed. In four volunteers, immobilization molds were created with a dummy version of the array within the mold, and subjects were scanned using the custom array in the mold. Phantoms and normal volunteers were scanned with both the custom spine coil array and the vendor's FDA-approved in-table posterior coil array to compare performance.

RESULTS

The superior-inferior field of view for the custom spine array was ~30 cm encompassing at least 10 vertebrae. A noise correlation matrix showed at least 25 dB isolation between all coil elements. Signal-to-noise ratio (SNR) calculated on a phantom scan at the depth of the spinal cord was a factor of 3 higher with the form-fit spine array as compared to the vendor's posterior coil array. The body coil B₁ transmit map was equivalent with and without the spine array in place demonstrating that the elements are decoupled from the body coil. Volunteer imaging showed improved SNR as compared to the vendor's posterior coil array. The custom array permitted a high degree of acceleration making possible the acquisition of isotropic high-resolution 1.1 × 1.1 × 1.1 mm³ three-dimensional data set over a 30-cm section of the spine in less than 5 min.

CONCLUSION

The custom-designed form-fitting flexible spine coil array provided enhanced SNR and increased acceleration compared to the vendor's posterior array. Future studies will assess MR-based spinal cord imaging with the custom coil in comparison to CT myelogram.

Long-Term Update of Stereotactic Radiosurgery for Benign Spinal Tumors

BACKGROUND

Stereotactic radiosurgery (SRS) for benign intracranial tumors is an established standard of care. The widespread implementation of SRS for benign spinal tumors has been limited by lack of long-term data.

OBJECTIVE

To update our institutional experience of safety and efficacy outcomes after SRS for benign spinal tumors.

METHODS

We performed a retrospective cohort study of 120 patients with 149 benign spinal tumors (39 meningiomas, 26 neurofibromas, and 84 schwannomas) treated with SRS between 1999 and 2016, with follow-up magnetic resonance imaging available for review. The primary endpoint was the cumulative incidence of local failure (LF), with death as a competing risk. Secondary endpoints included tumor shrinkage, symptom response, toxicity, and secondary malignancy.

RESULTS

Median follow-up was 49 mo (interquartile range: 25-103 mo, range: 3-216 mo), including 61 courses with >5 yr and 24 courses with >10 yr of follow-up. We observed 9 LF for a cumulative incidence of LF of 2%, 5%, and 12% at 3, 5, and 10 yr, respectively. Excluding 10 tumors that were previously irradiated or that arose within a previously irradiated field, the 3-, 5-, and 10-yr cumulative incidence rates of LF were 1%, 2%, and 8%, respectively. At last follow-up, 35% of all lesions had decreased in size. With a total of 776 patient-years of follow-up, no SRS-related secondary malignancies were observed.

CONCLUSION

Comparable to SRS for benign intracranial tumors, SRS provides longer term local control of benign spinal tumors and is a standard-of-care alternative to surgical resection.

Modern approaches to the management of metastatic epidural spinal cord compression

Metastatic epidural spinal cord compression (MESCC) is an oncologic emergency requiring prompt treatment to maximize neurologic function, ambulatory function and local control. Traditionally, options for MESCC included external beam radiation therapy with or without surgery. Surgery has usually been reserved for the patient with optimal performance status, single level MESCC or mechanical instability. Advances in external beam radiation therapy such as the development of stereotactic body radiation therapy have allowed for the delivery of high-dose radiation, allowing for both long-term pain and local control. Surgical advances, such as separation surgery, minimal access spine surgery and percutaneous instrumentation, have decreased surgical morbidity. This review summarizes the latest advances and evidence in MESCC to enable modern management.

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

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.

Stereotactic spine radiosurgery: Review of safety and efficacy with respect to dose and fractionation

BACKGROUND

Stereotactic body radiotherapy (SBRT) is an emerging treatment option for spinal metastases with demonstrated efficacy in the upfront, postoperative, and re-treatment settings, as well as for tumor histologies considered radioresistant. Uncertainty exists regarding the optimal dose and fractionation schedule, with single and multifraction regimens commonly utilized.

METHODS

A literature search of the PubMed and Medline databases was conducted to identify papers specific to spine SBRT and the effect of varying dose/fractionation regimens on outcomes. Bibliographies of relevant papers were searched for further references, and international spine SBRT experts were consulted.

RESULTS

Local control rates generally exceed 80% at 1 year, while high rates of pain control have been attained. There is insufficient evidence to suggest superiority of either single or multiple fraction regimens with respect to local control and pain control. Low rates of toxicity have been reported, assuming strict dose constraints are respected. Radiation myelopathy may be the most morbid toxicity, although the rates are low. The risk of vertebral compression fracture appears to be associated with higher doses per fraction such as those used in single-fraction regimens. The Spinal Instability Neoplastic Score should be considered when evaluating patients for spine SBRT, and prophylactic stabilisation may be warranted. Pain flare is a relatively common toxicity which may be mediated with prophylactic dexamethasone. Because of the treatment complexity and potentially serious toxicities, strict quality assurance should occur at the organizational, planning, dosimetric, and treatment delivery levels.

CONCLUSION

Both single and multifraction regimens are safe and efficacious in spine SBRT for spinal metastases. There may be advantages to hypofractionated treatment over single-fraction regimens with respect to toxicity. Ongoing investigation is underway to define optimal dose and fractionation schedules.

Response assessment after stereotactic body radiotherapy for spinal metastasis: a report from the SPIne response assessment in Neuro-Oncology (SPINO) group

The SPine response assessment In Neuro-Oncology (SPINO) group is a committee of the Response Assessment in Neuro-Oncology working group and comprises a panel of international experts in spine stereotactic body radiotherapy (SBRT). Here, we present the group's first report on the challenges in standardising imaging-based assessment of local control and pain for spinal metastases. We review current imaging modalities used in SBRT treatment planning and tumour assessment and review the criteria for pain and local control in registered clinical trials specific to spine SBRT. We summarise the results of an international survey of the panel to establish the range of current practices in assessing tumour response to spine SBRT. The ultimate goal of the SPINO group is to report consensus criteria for tumour imaging, clinical assessment, and symptom-based response criteria to help standardise future clinical trials.

Salvage Stereotactic Body Radiotherapy (SBRT) Following In-Field Failure of Initial SBRT for Spinal Metastases

PURPOSE

We report our experience in salvaging spinal metastases initially irradiated with stereotactic body radiation therapy (SBRT), who subsequently progressed with imaging-confirmed local tumor progression, and were re-irradiated with a salvage second SBRT course to the same level.

METHODS AND MATERIALS

From a prospective database, 56 metastatic spinal segments in 40 patients were identified as having been irradiated with a salvage second SBRT course to the same level. In addition, 24 of 56 (42.9%) segments had initially been irradiated with conventional external beam radiation therapy before the first course of SBRT. Local control (LC) was defined as no progression on magnetic resonance imaging at the treated segment, and calculated according to the competing risk model. Overall survival (OS) was evaluated for each patient treated by use of the Kaplan-Meier method.

RESULTS

The median salvage second SBRT total dose and number of fractions was 30 Gy in 4 fractions (range, 20-35 Gy in 2-5 fractions), and for the first course of SBRT was 24 Gy in 2 fractions (range, 20-35 Gy in 1-5 fractions). The median follow-up time after salvage second SBRT was 6.8 months (range, 0.9-39 months), the median OS was 10.0 months, and the 1-year OS rate was 48%. A longer time interval between the first and second SBRT courses predicted for better OS (P=.02). The crude LC was 77% (43/56), the 1-year LC rate was 81%, and the median time to local failure was 3.0 months (range, 2.7-16.7 months). Of the 13 local failures, 85% (11/13) and 46% (6/13) showed progression within the epidural space and paraspinal soft tissues, respectively. Absence of baseline paraspinal disease predicted for better LC (P<.01). No radiation-induced vertebral compression fractures or cases of myelopathy were observed.

CONCLUSION

A second course of spine SBRT, most often with 30 Gy in 4 fractions, for spinal metastases that failed initial SBRT is a feasible and efficacious salvage treatment option.

Evaluating dosimetric differences in spine stereotactic body radiotherapy: An international multi-institutional treatment planning study

INTRODUCTION

Stereotactic body radiotherapy (SBRT) planning for spinal metastases is a challenging task that involves complex target shapes and steep dose gradients proximal to the spinal cord. The aim of the present study is to investigate dosimetric variability among delivery systems and institutions doing spine SBRT.Materials and Methods: Three institutions (in Japan, Canada, and the USA) participated in this retrospective treatment planning study. Computed tomography (CT) datasets for three patients including fully delineated targets and organs-at-risk (OAR) were distributed to all three institutions for planning. Delivery systems included the Clinac 21EX, Vero4DRT, Synergy S, and CyberKnife. All treatment plans were generated using a prescribed dose of 24 Gy in 2 fractions and met the following objectives: the evaluated planning target volume (PTV_evl, defined as the PTV minus spinal cord) should receive greater than 16.8 Gy in at least 95% of the volume (D₉₅ > 16.8 Gy) and a maximum dose to the less than 140% of the prescribed dose (D_max < 33.6 Gy). The maximum dose of planning risk volume (PRV) cord or thecal sac was limited to 0.035 cm³ receiving less than 17 Gy. Aside from minimum and maximum dose objectives for the PTV_evl, there were no criteria regarding the shape of the PTV_evl dose-volume histogram (DVH). For each completed treatment plan, the following DVH parameters were evaluated for the PTV_evl: D₉₅, D₈₀, D₅₀, D₂ and sigma-index (S-index, standard deviation of the differential DVH).

RESULTS

The PTV_evl and OAR dose volume constraints were satisfied in all treatment plans. For Case 1, the mean PTV_evl D₅₀ was 25.4 ± 1.5 Gy (range: 23.7 - 27.8 Gy), for Case 2 it was 26.7 ± 2.0 Gy (23.6 - 28.6 Gy), and for Case 3 it was 26.0 ± 1.3 Gy (24.1 - 27.3 Gy). The mean PTV_evl D₂ was 27.3 ± 2.2 Gy (24.4 - 30.2 Gy), 28.9 ± 3.0 Gy (24.5 - 31.4 Gy) and 28.7 ± 2.7 Gy (25.2 - 31.6 Gy) for Cases 1, 2, and 3, respectively. However, there were statistically significant variations in the DVH parameters of PTV_evl between apparatuses (CyberKnife versus non-CyberKnife) and among institutions (between 2 CyberKnife sites or between 2 conventional accelerator sites).

CONCLUSIONS

Although all institutions met the minimum prescribed objectives, inter-institutional and inter-apparatus target dose variations were observed. Further study is necessary to determine target dose constraints that may minimize inter-institutional variations and lead to plan standardization.