Stereotactic body radiotherapy for spinal metastases: current status, with a focus on its application in the postoperative patient

Quantification of MRI Artifacts in Carbon Fiber Reinforced Polyetheretherketone Thoracolumbar Pedicle Screw Constructs prior to Spinal Stereotactic Radiosurgery

PURPOSE

Carbon fiber reinforced polyetheretherketone (CFRP) is a nonmetallic material that is a subject of growing interest in the field of spinal instrumentation manufacturing. The radiolucency and low magnetic susceptibility of CFRP has potential to create less interference with diagnostic imaging compared with titanium implants. However, an objective comparison of the image artifact produced by titanium and CFRP implants has not been described. Spinal oncology, particularly after resection of spinal tumors and at the time of spinal stereotactic radiosurgery planning, relies heavily on imaging interpretation for evaluating resection, adjuvant treatment planning, and surveillance. We present a study comparing measurements of postoperative magnetic resonance imaging artifacts between titanium and CFRP pedicle screw constructs in the setting of separation surgery for metastatic disease.

METHODS AND MATERIALS

The diameter of the signal drop around the screws (pedicle screw artifact) and the diameter of the spinal canal free from artifacts (canal visualization) were measured in consecutive patients who had spinal instrumentation followed by spinal stereotactic radiosurgery in the June 2019 to May 2022 timeframe. The spinal cord presented a shift at the screw level in sagittal images which was also measured (Sagittal Distortion, SagD).

RESULTS

Fifty patients, corresponding to 356 screws and 183 vertebral levels, were evaluated overall. CFRP produced less artifacts in all the 3 parameters compared with titanium: mean pedicle screw artifact (CFRP = 5.8 mm, Ti = 13.2 mm), canal visualization (CFRP = 19.2 mm, Ti = 15.5 mm), and SagD (CFRP = .5 mm, Ti = 1.9 mm), all P < .001. In practice, these findings translate into better-quality magnetic resonance imaging.

CONCLUSIONS

The initial perceived advantages are easier evaluation of postoperative imaging, facilitating radiation treatment planning, recurrence detection, and avoidance in repeating a suboptimal computed tomography myelogram. Further clinical studies analyzing long-term outcomes of patients treated with CFRP implants are necessary.

Practice and principles of stereotactic body radiation therapy for spine and non-spine bone metastases

Radiotherapy is the dominant treatment modality for painful spine and non-spine bone metastases (NSBM). Historically, this was achieved with conventional low dose external beam radiotherapy, however, stereotactic body radiotherapy (SBRT) is increasingly applied for these indications. Meta-analyses and randomized clinical trials have demonstrated improved pain response and more durable tumor control with SBRT for spine metastases. However, in the setting of NSBM, there is limited evidence supporting global adoption and large scale randomized clinical trials are in need. SBRT is technically demanding requiring careful consideration of organ at risk tolerance, and strict adherence to technical requirements including immobilization, simulation, contouring and image-guidance procedures. Additional considerations include follow up practices after SBRT, with appropriate imaging playing a critical role in response assessment. Finally, there is renewed research into promising new technologies that may further refine the use of SBRT in both spinal and NSBM in the years to come.

MRI feature-based radiomics models to predict treatment outcome after stereotactic body radiotherapy for spinal metastases

OBJECTIVE

This study aimed to extract radiomics features from MRI using machine learning (ML) algorithms and integrate them with clinical features to build response prediction models for patients with spinal metastases undergoing stereotactic body radiotherapy (SBRT).

METHODS

Patients with spinal metastases who were treated using SBRT at our hospital between July 2018 and April 2023 were recruited. We assessed their response to treatment using the revised Response Evaluation Criteria in Solid Tumors (version 1.1). The lesions were categorized into progressive disease (PD) and non-PD groups. Radiomics features were extracted from T1-weighted image (T1WI), T2-weighted image (T2WI), and fat-suppression T2WI sequences. Feature selection involved intraclass correlation coefficients, minimal-redundancy-maximal-relevance, and least absolute shrinkage and selection operator methods. Thirteen ML algorithms were employed to construct the radiomics prediction models. Clinical, conventional imaging, and radiomics features were integrated to develop combined models. Model performance was evaluated using receiver operating characteristic (ROC) curve analysis, and the clinical value was assessed using decision curve analysis.

RESULTS

We included 194 patients with 142 (73.2%) lesions in the non-PD group and 52 (26.8%) in the PD group. Each region of interest generated 2264 features. The clinical model exhibited a moderate predictive value (area under the ROC curve, AUC = 0.733), while the radiomics models demonstrated better performance (AUC = 0.745-0.825). The combined model achieved the best performance (AUC = 0.828).

CONCLUSION

The MRI-based radiomics models exhibited valuable predictive capability for treatment outcomes in patients with spinal metastases undergoing SBRT.

CRITICAL RELEVANCE STATEMENT

Radiomics prediction models have the potential to contribute to clinical decision-making and improve the prognosis of patients with spinal metastases undergoing SBRT.

KEY POINTS

• Stereotactic body radiotherapy effectively delivers high doses of radiation to treat spinal metastases. • Accurate prediction of treatment outcomes has crucial clinical significance. • MRI-based radiomics models demonstrated good performance to predict treatment outcomes.

Monte Carlo Dosimetric Study of Percutaneous Vertebroplasty and Brachytherapy for the Treatment of Spinal Metastases

Background

Percutaneous vertebroplasty employs bone cement for injecting into the fractured vertebral body (VB) caused by spinal metastases. Radioactive bone cement and also brachytherapy seeds have been utilized to suppress the tumor growth in the VB.

Objective

This study aims to investigate the dose distributions of low-energy brachytherapy seeds, and to compare them to those of radioactive bone cement, by Monte Carlo simulation.

Material and Methods

In this simulation study, nine CT scan images were imported in Geant4. For the simulation of brachytherapy, I-125, Cs-131, or Pd-103 seeds were positioned in the VB, and for the simulation of vertebroplasty, the VB was filled by a radioactive cement loaded by P-32, Ho-166, Y-90, or Sm-153 radioisotopes. The dose-volume histograms of the VB, and the spinal cord (SC) were obtained after segmentation, considering that the reference dose is the minimum dose covered 95% of the VB.

Results

The SC sparing was improved by using beta-emitting cement because of their steep gradient dose distribution. I-125 seeds and Y-90 radioisotope showed better VB coverage for brachytherapy and vertebroplasty techniques, respectively. Pd-103 seeds and P-32 radioisotope showed better SC sparing for brachytherapy and vertebroplasty, respectively. The minimum mean doses that covered 100% of the VB were 62.0%, 56.5%, and 45.0% for I-125, Cs-131, and Pd-103 seeds, and 28.3%, 28.6%, 32.9%, and 17.7%, for P-32, Ho-166, Y-90, and Sm-153 sources, respectively.

Conclusion

I-125 and Cs-131 seeds may be useful for large tumors filling the entire VB, and also for the extended tumors invading multiple vertebrae. Beta-emitting bone cement is recommended for tumors located near the SC.

Spinal Cord Delineation Based on Computed Tomography Myelogram Versus T2 Magnetic Resonance Imaging in Spinal Stereotactic Body Radiation Therapy

Purpose

Spinal cord delineation is critical to the delivery of stereotactic body radiation therapy (SBRT). Although underestimating the spinal cord can lead to irreversible myelopathy, overestimating the spinal cord may compromise the planning target volume coverage. We compare spinal cord contours based on computed tomography (CT) simulation with a myelogram to spinal cord contours based on fused axial T2 magnetic resonance imaging (MRI).

Methods and Materials

Eight patients with 9 spinal metastases treated with spinal SBRT were contoured by 8 radiation oncologists, neurosurgeons, and physicists, with spinal cord definition based on (1) fused axial T2 MRI and (2) CT-myelogram simulation images, yielding 72 sets of spinal cord contours. The spinal cord volume was contoured at the target vertebral body volume based on both images. The mixed-effect model assessed comparisons of T2 MRI- to myelogram-defined spinal cord in centroid deviations (deviations in the center point of the cord) through the vertebral body target volume, spinal cord volumes, and maximum doses (0.035 cc point) to the spinal cord applying the patient's SBRT treatment plan, in addition to in-between and within-subject variabilities.

Results

The estimate for the fixed effect from the mixed model showed that the mean difference between 72 CT volumes and 72 MRI volumes was 0.06 cc and was not statistically significant (95% confidence interval, -0.034, 0.153; P = .1832). The mixed model showed that the mean dose at 0.035 cc for CT-defined spinal cord contours was 1.24 Gy lower than that of MRI-defined spinal cord contours and was statistically significant (95% confidence interval, -2.292, -0.180; P = .0271). Also, the mixed model indicated no statistical significance for deviations in any of the axes between MRI-defined spinal cord contours and CT-defined spinal cord contours.

Conclusions

CT myelogram may not be required when MRI imaging is feasible, although uncertainty at the cord-to-treatment volume interface may result in overcontouring and hence higher estimated cord dose-maximums with axial T2 MRI-based cord definition.

The efficacy of laser interstitial thermal therapy in the management of spinal metastases: a systematic review of the literature

BACKGROUND

In the last years, laser interstitial thermal therapy (LITT) has started to be used also in neurosurgical setting. Its efficacy for intracranial pathologies, namely, tumors and epilepsy, has been widely demonstrated. However, the literature evidences about the use of LITT for spinal lesions are recent, and it is still a topic of discussion regarding its efficacy. Here, the authors sought to present a systematic review of the literature investigating the utility of LITT for spinal lesions.

METHODS

Using PubMed, Scopus, and the Cochrane Library, the authors performed a systematic review of the literature focused on the use of spinal laser interstitial thermal therapy (sLITT). Included in the search were randomized controlled trials, cohort studies, and clinical series. Two independent reviewers conducted the study appraisal, data abstraction, and quality assessments of the studies.

RESULTS

Out of the initial 134 studies, 6 met the inclusion criteria for the systematic review, resulting in a total of 206 patients. All the patients have been treated with sLITT for compressive spinal metastases. Most of the lesions were thoracic (88.8%). All the studies reported an effective local control of the disease with a reduction of epidural compression at 30 days. Complication rate was 12.6%, but most of them were transient conditions, and only 3.4% patients needed a revision surgery.

CONCLUSION

sLITT is safe and provides effective local control for epidural compression from metastases, particularly in the thoracic spine. The authors propose considering sLITT as an alternative to open surgery in selected patients with spinal metastases.

Implementation of triggered kilovoltage imaging for stereotactic radiotherapy of the spine for patients with spinal fixation hardware

Background and purpose

Mitigation of intrafraction motion (IM) is valuable in stereotactic radiotherapy (SRT) radiotherapy where submillimeter accuracy is desired. The purpose of this study was to investigate the application of triggered kilovoltage (kV) imaging for spine SRT patients with hardware by correlating kV imaging with patient motion and summarizing implications of tolerance for IM based on calculated dose.

Materials and methods

Ten plans (33 fractions) were studied, correlating kV imaging during treatment with pre- and post-treatment cone beam computed tomography (CBCT). Images were taken at 20-degree gantry angle intervals during the arc-based treatment. The contour of the hardware with a 1 mm expansion was displayed at the treatment console to manually pause treatment delivery if the hardware was visually detected outside the contour. The treatment CBCTs were compared using retrospective image registration to assess the validity of contour-based method for pausing treatment. Finally, plans were generated to estimate dose volume objective differences in case of 1 mm deviation.

Results

When kV imaging during treatment was used with the 1 mm contour, 100 % of the post-treatment CBCTs reported consistent results. One patient in the cohort exhibited motion greater than 1 mm during treatment which allowed intervention and re-setup during treatment. The average translational motion was 0.35 mm. Treatment plan comparison at 1 mm deviation showed little differences in calculated dose for the target and cord.

Conclusions

Utilizing kV imaging during treatment is an effective method of assessing IM for SRT spine patients with hardware without increasing treatment time.

Evaluation of a proprietary software application for motion monitoring during stereotactic paraspinal treatment

PURPOSE

Stereotactic paraspinal treatment has become increasingly popular due to its favorable clinical outcome. An often-overlooked factor that compromises the effectiveness of such treatment is the patients' involuntary intrafractional motion. This work introduces and validates a proprietary software application that quantifies such motion for accurate patient monitoring during treatment.

METHODS

The software uses a separate full-trajectory cone-beam computed tomography (CBCT) after daily patient setup to establish reference projections. Once treatment starts, the software grabs the intrafraction motion review (IMR) image acquired by TrueBeam via the Varian iTools Capture software and compares it against the corresponding reference projection to instantly determine the 2D shifts of the vertebrae being monitored using the classical downhill simplex optimization method. To evaluate its performance, an anthropomorphic phantom was shifted 0, 0.6, 1.2, 1.8, 2.4, 3.0, and 5 mm in three orthogonal directions, immediately after the full-trajectory CBCT but prior to treatment. Depending on the scenario of shift, a nine-field fixed gantry intensity-modulated radiation therapy (IMRT) plan and/or a four partial-posterior-arcs volume-modulated radiation therapy (VMAT) plan were delivered. For the IMRT plan, three IMR images were acquired sequentially every 200 monitor units (MU) at each treatment angle. For the VMAT plan, one IMR image was acquired every 15° of each arc. For each IMR image, the software-reported 2D shift was compared with the ground truth. Certain tests were repeated with 1°, 2°, and 3° of rotation, pitch, and roll, respectively. Some of these tests were also repeated independently on separate days.

RESULTS

Based on the group of tests that involved only the IMRT delivery, the maximum standard deviation of the software-reported shifts for each set of three IMR images was 0.16 mm, with 95th percentile at 0.02 mm. For translational shift, the maximum registration error was 0.44 mm, with 95th percentile at 0.23 mm. Left unaccounted for, rotation and pitch degraded the registration accuracy mainly in the longitudinal direction, while roll degraded it mainly in the lateral direction. The degradation of registration accuracy is positively related to the degree of rotation, pitch, and roll. The maximum registration errors under 3° rotation, pitch, and roll were 2.97, 1.44, 2.72 mm, respectively. Based on the group of tests that compared IMRT delivery with VMAT delivery, the registration errors slightly increased as magnitude of shifts increased; however, they were well under the 0.5-mm threshold. No significant differences in registration errors were observed between IMRT and VMAT deliveries. In addition, the variation in registration errors among different days was limited for both IMRT and VMAT deliveries.

CONCLUSIONS

Our proprietary software has high repeatability, both intrafractionally and interfractionally, and high accuracy in registering IMR images with the reference projections for motion monitoring, regardless of the magnitude of shifts or treatment delivery technique. Rotation, pitch, and roll degrade registration accuracy and need to be accounted for in the future work.

Radiomic modeling to predict risk of vertebral compression fracture after stereotactic body radiation therapy for spinal metastases

OBJECTIVE

In the treatment of spinal metastases with stereotactic body radiation therapy (SBRT), vertebral compression fracture (VCF) is a common and potentially morbid complication. Better methods to identify patients at high risk of radiation-induced VCF are needed to evaluate prophylactic measures. Radiomic features from pretreatment imaging may be employed to more accurately predict VCF. The objective of this study was to develop and evaluate a machine learning model based on clinical characteristics and radiomic features from pretreatment imaging to predict the risk of VCF after SBRT for spinal metastases.

METHODS

Vertebral levels C2 through L5 containing metastases treated with SBRT were included if they were naive to prior surgery or radiation therapy, target delineation was based on consensus guidelines, and 1-year follow-up data were available. Clinical features, including characteristics of the patient, disease, and treatment, were obtained from chart review. Radiomic features were extracted from the planning target volume (PTV) on pretreatment CT and T1-weighted MRI. Clinical and radiomic features selected by least absolute shrinkage and selection operator (LASSO) regression were included in random forest classification models, which were trained to predict VCF within 1 year after SBRT. Model performance was assessed with leave-one-out cross-validation.

RESULTS

Within 1 year after SBRT, 15 of 95 vertebral levels included in the analysis demonstrated new or progressive VCF. Selected clinical features included BMI, performance status, total prescription dose, dose to 99% of the PTV, lumbar location, and 2 components of the Spine Instability Neoplastic Score (SINS): lytic tumor character and spinal misalignment. Selected radiomic features included 5 features from CT and 3 features from MRI. The best-performing classification model, derived from a combination of selected clinical and radiomic features, demonstrated a sensitivity of 0.844, specificity of 0.800, and area under the receiver operating characteristic (ROC) curve (AUC) of 0.878. This model was significantly more accurate than alternative models derived from only selected clinical features (AUC = 0.795, p = 0.048) or only components of the SINS (AUC = 0.579, p < 0.0001).

CONCLUSIONS

In the treatment of spinal metastases with SBRT, a machine learning model incorporating both clinical features and radiomic features from pretreatment imaging predicted VCF at 1 year after SBRT with excellent sensitivity and specificity, outperforming models developed from clinical features or components of the SINS alone. If validated, these findings may allow more judicious selection of patients for prophylactic interventions.

Anterior Corpectomy and Plating with Carbon-PEEK Instrumentation for Cervical Spinal Metastases: Clinical and Radiological Outcomes

Background: Anterior cervical corpectomy and plating has been recognized as a valuable approach for the surgical treatment of cervical spinal metastases. This study aimed to report the surgical, clinical and radiological outcomes of anterior carbon-PEEK instrumentations for cervical spinal metastases. Methods: Demographical, clinical, surgical and radiological data were collected from 2017 to 2020. The Neck Disability Index (NDI) questionnaire for neck pain, EORTC QLQ-C30 questionnaire for quality of life, Nurick scale for myelopathy and radiological parameters (segmental Cobb angle and cervical lordosis) were collected before surgery, at 6 weeks postoperatively and follow-up. Results: Seventeen patients met inclusion criteria. Mean age was 60.9 ± 7.6 years and mean follow-up was 12.9 ± 4.0 months. The NDI (55.4 ± 11.7 to 25.1 ± 5.4, p < 0.001) scores and the EORTC QLQ-C30 global health/QoL significantly improved postoperatively and at the last follow-up. The segmental Cobb angle (10.7° ± 5.6 to 3.1° ± 2.2, p < 0.001) and cervical lordosis (0.9° ± 6.7 to −6.2 ± 7.8, p = 0.002) significantly improved postoperatively. Only one minor complication (5.9%) was recorded. Conclusions: Carbon/PEEK implants represent a safe alternative to commonly used titanium ones and should be considered in cervical spinal metastases management due to their lower artifacts in postoperative imaging and radiation planning. Further larger comparative and cost-effectiveness studies are needed to confirm these results.

Fundamentals of Radiation Oncology for Treatment of Vertebral Metastases

The fields of both radiology and radiation oncology have evolved considerably in the past few decades, resulting in an increased ability to delineate between tumor and normal tissue to precisely target and treat vertebral metastases with radiation therapy. These scientific advances have also led to improvements in assessing treatment response and diagnosing toxic effects related to radiation treatment. However, despite technological innovations yielding greatly improved rates of palliative relief and local control of osseous spinal metastases, radiation therapy can still lead to a number of acute and delayed posttreatment complications. Treatment-related adverse effects may include pain flare, esophageal toxic effects, dermatitis, vertebral compression fracture, radiation myelopathy, and myositis, among others. The authors provide an overview of the multidisciplinary approach to the treatment of spinal metastases, indications for surgical management versus radiation therapy, various radiation technologies and techniques (along with their applications for spinal metastases), and current principles of treatment planning for conventional and stereotactic radiation treatment. Different radiologic criteria for assessment of treatment response, recent advances in radiologic imaging, and both common and rare complications related to spinal irradiation are also discussed, along with the imaging characteristics of various adverse effects. Familiarity with these topics will not only assist the diagnostic radiologist in assessing treatment response and diagnosing treatment-related complications but will also allow more effective collaboration between diagnostic radiologists and radiation oncologists to guide management decisions and ensure high-quality patient care. ^©RSNA, 2021.

Reduction of inter-observer differences in the delineation of the target in spinal metastases SBRT using an automatic contouring dedicated system

BACKGROUND

Approximately one third of cancer patients will develop spinal metastases, that can be associated with back pain, neurological symptoms and deterioration in performance status. Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) have been offered in clinical practice mainly for the management of oligometastatic and oligoprogressive patients, allowing the prescription of high total dose delivered in one or few sessions to small target volumes, minimizing the dose exposure of normal tissues. Due to the high delivered doses and the proximity of critical organs at risk (OAR) such as the spinal cord, the correct definition of the treatment volume becomes even more important in SBRT treatment, thus making it necessary to standardize the method of target definition and contouring, through the adoption of specific guidelines and specific automatic contouring tools. An automatic target contouring system for spine SBRT is useful to reduce inter-observer differences in target definition. In this study, an automatic contouring tool was evaluated.

METHODS

Simulation CT scans and MRI data of 20 patients with spinal metastases were evaluated. To evaluate the advantage of the automatic target contouring tool (Elements SmartBrush Spine), which uses the identification of different densities within the target vertebra, we evaluated the agreement of the contours of 20 spinal target (2 cervical, 9 dorsal and 9 lumbar column), outlined by three independent observers using the automatic tool compared to the contours obtained manually, and measured by DICE similarity coefficient.

RESULTS

The agreement of GTV contours outlined by independent operators was superior with the use of the automatic contour tool compared to manually outlined contours (mean DICE coefficient 0.75 vs 0.57, p = 0.048).

CONCLUSIONS

The dedicated contouring tool allows greater precision and reduction of inter-observer differences in the delineation of the target in SBRT spines. Thus, the evaluated system could be useful in the setting of spinal SBRT to reduce uncertainties of contouring increasing the level of precision on target delivered doses.

Utility of carbon fiber instrumentation in spinal oncology

Spinal oncology has had many advancements often necessitating serial imaging for post-surgical treatment planning and close follow up. Traditional spinal instrumentation introduces artifact into MRI and CT imaging, which can reduce the efficacy of follow up imaging and treatment. Newly created carbon-fiber instrumentation can offer many advantages compared to traditional instrumentation while typically maintaining biomechanical stability. The utility of this new instrumentation continues to evolve as more surgeons utilize these materials, which can improve patient outcomes. We illustrate the utility of this new hardware technology through various patient examples.

Postoperative Stereotactic Body Radiotherapy for Spinal Metastasis and Predictors of Local Control

BACKGROUND

Spine surgery is indicated for select patients with mechanical instability, pain, and/or malignant epidural spinal cord compression, with or without neurological compromise. Stereotactic body radiotherapy (SBRT) is an option for durable local control (LC) for metastatic spine disease.

OBJECTIVE

To determine factors associated with LC and progression-free survival (PFS) for patients receiving postoperative stereotactic spine radiosurgery.

METHODS

We analyzed consecutive patients from 2013 to 2019 treated with surgical intervention followed by SBRT. Surgical interventions included laminectomy and vertebrectomy. SBRT included patients treated with 1 to 5 fractions of radiosurgery. We analyzed LC, PFS, overall survival (OS), and toxicity. Univariate and multivariate analyses were performed.

RESULTS

A total of 63 patients were treated with a median follow-up of 12.5 mo. Approximately 75% of patients underwent vertebrectomy and 25% underwent laminectomy. One-year cumulative incidence of local failure was 19%. LC was significantly improved for patients receiving radiosurgery ≤40 d from surgery compared to that for patients receiving radiosurgery ≥40 d from surgery, 94% vs 75%, respectively, at 1 yr (P = .03). Patients who received preoperative embolization had improved LC with 1-yr LC of 88% vs 76% for those who did not receive preoperative embolization (P = .037). Significant predictors for LC on multivariate analysis were time from surgery to radiosurgery, higher radiotherapy dose, and preoperative embolization. The 1-yr PFS and OS was 56% and 60%, respectively.

CONCLUSION

Postoperative radiosurgery has excellent and durable LC for spine metastasis. An important consideration when planning postoperative radiosurgery is minimizing delay from surgery to radiosurgery. Preoperative embolization and higher radiotherapy dose were associated with improved LC warranting further study.

Vertebral compression fracture rate following stereotactic ablative body radiotherapy for spine oligometastases: a UK experience

Aim:

Stereotactic ablative body radiotherapy (SABR) for spine metastases is associated with a risk of vertebral compression fracture (VCF). The aim of this study was to determine the rate of VCF at one UK institution and evaluate the use of the Spinal Instability Neoplastic Score (SINS) to predict these.

Materials and methods:

A retrospective analysis of all patients who underwent SABR for spinal metastases between 2014 and 2018 at one UK institution was performed. Basic demographic data were collected, and SINS prior to SABR was calculated. The primary outcome was VCF rate. Secondary outcomes included time to VCF and need for surgical intervention following VCF.

Results:

A total of 48 oligometastases were treated with a median follow-up of 20·5 months. A maximum of two vertebral bodies were treated. The median baseline SINS was calculated as 3. The median dose was 26 Gy in three fractions. Two patients were reported to have VCF and both were successfully conservatively managed.

Findings:

SABR for spine oligometastases is being performed safely with low VCF rates which are comparable with those in international publications. This may be as a result of strict adherence to criteria for delivery of SABR with low pre-treatment SINS.

Stereotactic Body Radiation Therapy for Spinal Metastases: Tumor Control Probability Analyses and Recommended Reporting Standards

PURPOSE

We sought to investigate the tumor control probability (TCP) of spinal metastases treated with stereotactic body radiation therapy (SBRT) in 1 to 5 fractions.

METHODS AND MATERIALS

PubMed-indexed articles from 1995 to 2018 were eligible for data extraction if they contained SBRT dosimetric details correlated with actuarial 2-year local tumor control rates. Logistic dose-response models of collected data were compared in terms of physical dose and 3-fraction equivalent dose.

RESULTS

Data were extracted from 24 articles with 2619 spinal metastases. Physical dose TCP modeling of 2-year local tumor control from the single-fraction data were compared with data from 2 to 5 fractions, resulting in an estimated α/β = 6 Gy, and this was used to pool data. Acknowledging the uncertainty intrinsic to the data extraction and modeling process, the 90% TCP corresponded to 20 Gy in 1 fraction, 28 Gy in 2 fractions, 33 Gy in 3 fractions, and (with extrapolation) 40 Gy in 5 fractions. The estimated TCP for common fractionation schemes was 82% at 18 Gy, 90% for 20 Gy, and 96% for 24 Gy in a single fraction, 82% for 24 Gy in 2 fractions, and 78% for 27 Gy in 3 fractions.

CONCLUSIONS

Spinal SBRT with the most common fractionation schemes yields 2-year estimates of local control of 82% to 96%. Given the heterogeneity in the tumor control estimates extracted from the literature, with variability in reporting of dosimetry data and the definition of and statistical methods of reporting tumor control, care should be taken interpreting the resultant model-based estimates. Depending on the clinical intent, the improved TCP with higher dose regimens should be weighed against the potential risks for greater toxicity. We encourage future reports to provide full dosimetric data correlated with tumor local control to allow future efforts of modeling pooled data.

Stereotactic Ablative Radiotherapy for the Management of Spinal Metastases: A Review

Importance

Rising cancer incidence combined with improvements in systemic and local therapies extending life expectancy are translating into more patients with spinal metastases. This makes the multidisciplinary management of spinal metastases and development of new therapies increasingly important. Spinal metastases may cause significant pain and reduced quality of life and lead to permanent neurological disability if compression of the spinal cord and/or nerve root occurs. Until recently, treatments for spinal metastases were not optimal and provided temporary local control and pain relief. Spinal stereotactic ablative radiotherapy (SABR) is an effective approach associated with an improved therapeutic ratio, with evolving clinical application.

Objective

To review the literature of spinal SABR for spinal metastases, discuss a multidisciplinary approach to appropriate patient selection and technical considerations, and summarize current efforts to combine spinal SABR with systemic therapies.

Evidence Review

The MEDLINE database was searched to identify articles reporting on spinal SABR to September 30, 2018. Articles including clinical trials, prospective and retrospective studies, systematic reviews, and consensus recommendations were selected for relevance to multidisciplinary management of spinal metastases.

Results

Fifty-nine unique publications with 5655 patients who underwent SABR for spinal metastases were included. Four comprehensive frameworks for patient selection were discussed. Spinal SABR was associated with 1-year local control rates of approximately 80% to 90% in the de novo setting, greater than 80% in the postoperative setting, and greater than 65% in the reirradiation setting. The most commonly discussed adverse effect was development of a vertebral compression fracture with variable rates, most commonly reported as approximately 10% to 15%. High-level data on the combination of SABR with modern therapies are still lacking. At present, 19 clinical trials are ongoing, mainly focusing on combined modality therapies, radiotherapy prescription dose, and oligometastic disease.

Conclusions and Relevance

These findings suggest that spinal SABR may be an effective treatment option for well-selected patients with spinal metastases, achieving high rates of local tumor control with moderate rates of adverse effects. Optimal management should include review by a multidisciplinary care team.

Evaluation of multi-institutional end-to-end testing for post-operative spine stereotactic body radiation therapy

BACKGROUND AND PURPOSE

Post-operative spine stereotactic body radiation therapy (SBRT) represents a significant challenge as there are many restrictions on beam geometry to avoid metal hardware as it surrounds the target volume. In this study, an international multi-institutional end-to-end test using an in-house spine phantom was developed and executed. The aim was to evaluate the impact of titanium spine hardware on planned and delivered dose for post-operative spine SBRT.

MATERIALS AND METHODS

Five centers performed simulation, planning and irradiation of the spine phantom, with/without titanium metal hardware (MB/B), following our pre-specified protocol. The doses were calculated using the centers' treatment planning system (TPS) and measured with radiophotoluminescent glass dosimeters (RPLDs) embedded within each phantom.

RESULTS

The dose differences between the RPLD measured and calculated doses in the target region were within ± 5% for both phantoms studied. Differences greater than 5% were observed for the spinal cord and the out-of-the target regions due to steeper dose gradient regions that are created in these plans. Dose measurements within ± 3% were observed between RPLDs that were embedded in MB and B inserts. For the spinal cord and the out-of-target regions surrounded by metal hardware, the dose measured using RPLDs was within 3% different near the titanium screws compared to the dose measured near only the metal rods.

CONCLUSION

We have successfully performed the first multi-institutional end-to-end dose analysis using an in-house phantom built specifically for post-operative spine SBRT. The differences observed between the measured and planned doses in the presence of metal hardware were clinically insignificant.

Mature Imaging-Based Outcomes Supporting Local Control for Complex Reirradiation Salvage Spine Stereotactic Body Radiotherapy

BACKGROUND

Upon progression after upfront radiotherapy to spinal metastases, low-dose re-irradiation conventional external beam radiation (cEBRT) provides limited clinical benefit. Spine stereotactic body radiotherapy (SBRT) allows for dose escalation in the salvage setting with the potential for improved local control.

OBJECTIVE

To report mature clinical and imaging-based outcomes for salvage SBRT.

METHODS

A retrospective review was undertaken of consecutive patients with spinal metastases treated with re-irradiation spine SBRT having failed either cEBRT (n = 60 with 1 prior course and n = 17 with 2 or more prior cEBRT courses), or prior SBRT (n = 6) to the same spinal segment. The primary outcome was local failure (LF), and secondary outcomes included overall survival (OS) and the rate of vertebral compression fracture (VCF).

RESULTS

A total of 43 patients with 83 spinal segments treated with salvage SBRT were reviewed. The crude risk of LF was 18%, and actuarial LF rates at 6, 12, and 24 mo were 7%, 14%, and 19%, respectively. The presence of extensive paraspinal disease (hazard ratio [HR] = 7.1, 95% CI 1.5-34) significantly predicted for LF. The median OS was 13.2 (95% CI 6.1-16.3) mo, and the presence of neurological deficits (HR = 4.7, 95% CI 1.8-12.1) and brain metastases (HR = 2.6, 95% CI 1.1-6.3) were significant prognostic factors. The crude risk of VCF was 4%, and radiation myelopathy was not observed.

CONCLUSION

These data support the safety and efficacy of spinal re-irradiation with SBRT including patients with prior SBRT and multiple courses of prior cEBRT.

Clinical effectiveness of percutaneous vertebroplasty in conjunction with postoperative radiotherapy in the treatment of spinal metastases

PURPOSE

This study aimed to evaluate the clinical effects of percutaneous vertebroplasty (PVP) combined with postoperative radiotherapy (RT) in the treatment of spinal metastases.

METHODS

Nine patients (4 males and 5 females, mean age 59.56 years) with painful pathologic compression vertebral fractures caused by metastatic cancers of the spine (5 thoracic levels, 8 lumbar levels) were admitted to our hospital between July 17, 2016 and September 25, 2018. All patients were treated with PVP via bilateral pedicle approach combined with postoperative RT to treat metastatic lesions of the centrum. The clinical records of the patients were retrospectively analyzed. Patients' demographic features and medical conditions including the Visual Analogue Scale (VAS), Oswestry Disability Index (ODI) and Imageology data were observed.

RESULTS

Patients' mean VAS scores decreased from 8.67 ± 0.50 preoperatively to 1.78 ± 0.83 at 6 months after PVP. Moreover, the mean ODI score decreased from 74.07 ± 13.15 preoperatively to 31.87 ± 10.00 at 6 months after PVP. Significant improvement in the degree of pain and dysfunction among the enrolled patients were observed. Furthermore, the metastatic carcinoma lesion within the vertebral body was well controlled according to imaging.

CONCLUSION

PVP in conjunction with postoperative RT is a good treatment strategy for vertebral compression fractures caused by 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.

Imaging response assessment following stereotactic body radiotherapy for solid tumour metastases of the spine: Current challenges and future directions

Patients with metastatic disease are routinely serially imaged to assess disease burden and response to systemic and local therapies, which places ever-expanding demands on our healthcare resources. Image interpretation following stereotactic body radiotherapy (SBRT) for spine metastases can be challenging; however, appropriate and accurate assessment is critical to ensure patients are managed correctly and resources are optimised. Here, we take a critical review of the merits and pitfalls of various imaging modalities, current response assessment guidelines, and explore novel imaging approaches and the potential for radiomics to add value in imaging assessment.

Minimally invasive lateral approaches for the treatment of spinal tumors: single-position surgery without the "flip"

Although primary tumors of the spine and neural elements are rare, metastatic disease to the spine is quite common. Traditionally, surgical treatment for spinal tumor patients involves open decompression with or without stabilization. The single-position minimally invasive (MIS) lateral approach, which has been recently described over the recent decade, allows simultaneous access to the anterior and posterior columns with the patient positioned in the lateral decubitus position. Herein, we review the application of single-position MIS lateral surgery for the treatment of spinal neoplasm. The aim was to review the evolution, operative technique, outcomes, and complications associated with MIS lateral approaches for spinal tumors. The history of spinal tumor diagnosis and management are reviewed and discussed as well as the author's experience and literature regarding spinal tumor treatment outcome and surgical complications, with particular attention to single-position, MIS lateral approaches. In addition, the author's surgical technique is outlined in detail for thoracic, thoracolumbar and lumbar tumors. Furthermore, there are specific indications and complications associated with the surgical treatment of spinal tumors, and the MIS, single-position lateral approach, when applied appropriately, allows for concurrent access to the anterior and posterior column while mitigating the complications associated with traditional, open posterior-based approaches. In the treatment of spinal neoplasms, the goals of surgery are dictated by a number of tumor-specific and patient-specific factors. Therefore, operative treatment of tumors in the future may be a consolidation of historical surgical techniques and MIS, single-position lateral approaches. Regardless, multidisciplinary management is imperative for the individualized treatment of the patient and optimization of outcome.

Intrafractional motion in stereotactic body radiotherapy of spinal metastases utilizing cone beam computed tomography image guidance

Background and purpose

Spine stereotactic body radiotherapy (SBRT) requires a high degree of accuracy due to steep dose gradients close to the spinal cord. This study aimed to (1) evaluate intrafractional motion in spine SBRT utilizing flattening filter free (FFF) beam delivery and cone beam computed tomography (CBCT) image guidance and (2) evaluate if adding another CBCT acquisition and corrections prior to treatment improves the overall position accuracy.

Materials and methods

Intrafractional motion was retrospectively analyzed for 78 fractions in 54 patients. All patients were immobilized with an evacuated cushion. Before treatment, a CBCT was acquired, a bony fusion with the planning CT was performed and translational and rotational errors were corrected. For 30 of the patients (39 fractions) acquisition of another CBCT and corrections were performed before treatment. A post treatment CBCT was acquired for all patients, and translational and rotational errors measured by fusion of the post treatment CBCT with the planning CT were recorded to calculate means and standard deviations (SDs).

Results

The positional errors were significantly smaller in 4 out of 6 error values in the patient group treated with verification CBCT. In this group, translational and rotational SDs ranged from 0.5 to 0.6 mm and 0.3°, respectively. Corresponding values in the group treated without verification CBCT were 0.7-1.0 mm and 0.4-0.7°.

Conclusion

With proper CBCT image guidance, patient immobilization and FFF-beam delivery, one can obtain very high patient position accuracy in spine SBRT. Inclusion of a verification CBCT prior to treatment increases the overall position accuracy.

Feasibility and preliminary clinical results of linac-based Stereotactic Body Radiotherapy for spinal metastases using a dedicated contouring and planning system

Background

Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) are well established local treatment approaches in several cancer settings. Although SBRT is still under investigation for spinal metastases, promising results in terms of a high effectiveness and optimal tolerability have been recently published on this topic. For spinal SBRT, one of the most relevant issues is represented by the inter-observer variability in target definition. Recently, several technological innovations, including specific tools such as multimodality-imaging (computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET-CT), automated volumes contouring and planning, could allow clinicians to minimize the uncertainties related to spinal SBRT workflow. Aim of this study is to report the feasibility of the clinical application of a dedicated software (Element®, Brainlab™ Germany) for spinal metastases SBRT.

Material and method

The patient selection criteria for SBRT in spinal metastases were the following: age > 18 years, diagnosis of spinal metastases (n ≤ 3), life expectancy > 3 months, controlled primary tumor or synchronous diagnosis and Spinal Instability Neoplastic Score (SINS) ≤ 12 points. All radiation target volumes were defined and planned with the support of the dedicated software Elements® (Brainlab™ Germany). Different dose prescription have been used: 12 Gy in single fraction, 12 Gy, 18 Gy, 21 Gy and 24 Gy in 3 fractions. Toxicity was assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.0. SPSS version 20 was used for statistical analysis.

Results

From April 2018 to April 2019, 54 spinal metastases in 32 recruited patients were treated with Linac-based SBRT. With a median follow-up of 6 months (range 3–12), local control rates at 6 months and 9 months were 86 and 86%, respectively. No adverse events ≥3 grade were observed.

Conclusions

This preliminary experience shows that with respect to acute toxicity and early clinical response, linac-based using Elements® Spine SRS is a feasible and effective approach.

Postoperative Stereotactic Body Radiotherapy for Spinal Metastases and the Impact of Epidural Disease Grade

BACKGROUND

Postoperative stereotactic body radiotherapy (pSBRT) is an emerging indication for spinal metastases (SM).

OBJECTIVE

To report our experience with pSBRT for SM.

METHODS

A retrospective chart review was performed for prospectively collected data of patients treated between September 2008 to December 2015 with pSBRT and followed with serial spinal MRIs every 2 to 3 mo until death or last follow-up. Univariate and multivariable analyses were performed to identify predictive factors.

RESULTS

A total of 83 spinal segments in 47 patients treated with a median dose of 24 Gy in 2 fractions were included, with mostly lung and breast primaries. A total of 59.3% had preoperative high-grade epidural disease (ED) and 39.7% were unstable. The 12-mo cumulative incidence of local failure was 17% for all segments, and 33.3%, 21.8%, and 0% in segments with postoperative high-grade, low-grade, and no ED, respectively. Downgrading preoperative ED was predictive of better local control (P = .03). The grade of postoperative ED was also predictive for local control (P < .0001), as was a longer interval between prior radiotherapy and pSBRT in those previously irradiated (P = .004). The 12-mo overall survival rate was 55%. One case of radiculopathy, 3 vertebral compression fractures, and no cases of myelopathy, hardware failure, or skin breakdown were observed.

CONCLUSION

pSBRT is an effective and safe treatment. The association between downgrading preoperative ED and better local control following pSBRT is confirmed and supports the concept of separation surgery.

Thermal-ablation of vertebral metastases prevents adverse events in patients with differentiated thyroid carcinoma

PURPOSE

To evaluate a strategy that used thermal-ablation of vertebral metastases (VM) to prevent vertebral related events (VRE) in patients with differentiated thyroid cancer (DTC).

METHODS

This single center study retrospectively reviewed records and post-operative imaging of all DTC patients treated with thermal-ablation for asymptomatic VMs. Rate of local tumor control at first post-operative imaging, 12 and 24 months after thermal-ablation and rate of VREs at 12 and 24 months among the treated VMs were reported. New VMs that occurred during the follow-up and were not considered for additional thermal-ablation were moniroted and VREs were reported.

RESULTS

Thermal-ablation was used to achieve local control of 41 VMs in 28 patients. Median post-treatment follow-up was 22 months [range: 12-80] and the mean delay for first post-operative imaging was 2 months [range: 0.6-7.5]. Local control at first post-operative imaging, 12 and 24 months was achieved in 87.8%, 82.9% and 75.6%, respectively. Among the treated VMs the rates of VRE was 7.3% at 2 years, significantly lower if local control was achieved at first post-operative imaging than if it was not (0% vs 30%, p = 0.011, OR = 0.184 [95%CI = 0.094-0.360]). After thermal-ablation procedures, 19 news VMs occurred in 11 patients (39.2%) with a median interval of 8 months [range 1-26] and remained untreated. Among these untreated VMs, the rate of VREs at 2 years was significantly higher compared to the treated VMs: (36.8% vs. 7.3%, p = 0.008, OR = 0.135, [95%CI = 0.030-0.607]).

CONCLUSION

local tumor control of VMs using thermal-ablation decreases the risk of VREs in DTC patients.

Dosimetric comparison of two treatment planning systems for spine SBRT

Two commonly used treatment planning systems (TPS) are compared for the planning of spine stereotactic body radiotherapy (SBRT). The main purpose is to highlight relative advantages and disadvantages of each system and propose a methodologic approach for comparisons. Twenty clinical plans were inversely planned with step-and-shoot intensity-modulated radiotherapy (IMRT) each using 9 to 11 beams, referred to as IMRT_P. The prescription dose was 24 Gy in 2 fractions, and the plans were generated following our institutional protocol using the Pinnacle³ v9.2. Each case was replanned using a 2-arc volumetric modulated arc therapy (VMAT) approach, referred as VMAT_P. CT and structure sets were DICOM exported to Monaco v5.10 and planned in 2 different ways: IMRT (IMRT_M) and VMAT (VMAT_M) using the same prescription dose. Dose volume histograms (DVH) and other dose statistics of planning target volumes (PTV) and organ-at-risk (OAR) were analyzed and compared between plans. The gradient index (GI = ratio of 50% isodose volume to prescribed isodose volume) was used to measure dose fall-off outside of the PTV. Another metric - Gradient Index Inner (GI_inner = the rate (in Gy/mm) - at which the dose changes from the level of the spinal cord/thecal sac toward the prescription dose) was developed and compared. All plans were considered clinically acceptable by institutional guidelines and achieved all of the OAR dose constraints. VMAT_M and IMRT_M showed comparable dose statistics for the PTV when compared to VMAT_P and IMRT_P, respectively. For IMRT plans, the median GI_inner was 1.88 Gy/mm vs 1.52 Gy/mm for IMRT_M and IMRT_P respectively (p< 0.001). All other IMRT metrics were statistically similar except for the PTV maximum dose (D_max), which was higher for IMRT_M than IMRT_P (median 30.7 Gy vs 29.0 Gy, p< 0.001). For VMAT plans, only PTV D_min showed a statistical different between VMAT_M and VMAT_P of median 12.7 Gy vs 9.7 Gy (p< 0.001). In terms of beam sequencing parameters, the number of monitor units was statistically higher for VMAT_P compared to VMAT_M (median = 6764 vs 5376) whereas the number of segments for IMRT_M was statistically greater than IMRT_P (median = 155 vs 73). We were able to generate clinically acceptable plans for different types of spine SBRT using 2 different TPS. We used an evaluation strategy involving coverage, conformity, and dose gradient that can compared between TPS.

Image guidance in spine tumor surgery

Beginning with basic stereotactic operative methods in neurosurgery, intraoperative navigation and image guidance systems have since become the norm in that field. Following the introduction of image guidance into spinal surgery, there has been a dramatic increase in its utilization across disciplines and pathologies. Spine tumor surgery encompasses a wide range of complex surgical techniques and treatment strategies. Similarly to deformity correction and trauma surgery, spine navigation holds potential to improve outcomes and optimize surgical technique for spinal tumors. Recent data demonstrate the applicability of neuro-navigation in the field of spinal oncology, particularly for spinal stabilization, maximizing extent of resection and integration of minimally invasive therapies. The rapid introduction of new, less invasive, and ablative surgical techniques in spine oncology coupled with the rising incidence of spinal metastatic disease make it imperative for spine surgeons to be familiar with the indications for and limitations of imaging guidance. Herein, we provide a practical, current concepts narrative review on the use of spinal navigation in three areas of spinal oncology: (a) extent of tumor resection, (b) spinal column stabilization, and (c) focal ablation techniques.

Neuroimaging and Stereotactic Body Radiation Therapy (SBRT) for Spine Metastasis

Historically, management options for spinal metastases include surgery for stabilization and decompression and/or external beam radiation therapy (EBRT). EBRT is palliative in nature, as it lacks accurate targeting such that the prescribed radiation doses must be limited in order to maintain safety. Modern advancement in imaging and radiotherapy technology have facilitated the development of stereotactic body radiation therapy (SBRT), which provides increased targeted precision for radiation delivery to tumors resulting in lower overall toxicity, particularly to regional structures such as the spinal cord and esophagus, while delivering higher, more effective, and radically ablative radiation doses.Over the past decade, SBRT has been increasingly utilized as a method of treating spinal metastases either as the primary modality or following surgical intervention in both de novo and reirradiation setting. Numerous studies suggest that SBRT is associated with an 80% to 90% rate of 1-year local control across clinical scenarios. For example, studies of SBRT as the primary treatment modality suggest long-term local control rate of 80% to 95% for spinal metastases. Similarly, SBRT in the adjuvant setting following surgery is associated with local control rates ranging from 70% to 100%. Furthermore, because SBRT allows for lower dose to the spinal cord, it has also been used in patients who have had prior radiation therapy, with studies showing 66% to 93% local control in this scenario.

Instability and impending instability in patients with vertebral metastatic disease

Metastatic disease commonly involves the spine with an increasing incidence due to a worldwide rise of cancer incidence and a longer survival of patients with osseous metastases. Metastases compromise the mechanical integrity of the vertebra and make it susceptible to fracture. Patients with pathological vertebral fracture often become symptomatic, with mechanical pain generally due to intervertebral instability, and may develop spinal cord compression and neurological deficits. Advances in imaging, radiotherapy, as well as in spinal surgery techniques, have allowed the evolution from conventional palliative external beam radiotherapy to modern stereotactic radiosurgery and from traditional open surgery to less-invasive, and sometimes prophylactic stabilization surgical treatments. It is therefore clear that fracture risk prediction, and maintenance or restoration of intervertebral stability, are important objectives in the management of these patients. Correlation between imaging findings and clinical manifestations is crucial, and a common knowledge base for treatment team members rather than a compartmentalized view is very important. This article reviews the literature on the imaging and clinical diagnosis of intervertebral instability and impending instability in the setting of spine metastatic disease, including the spinal instability neoplastic score, which is a reliable tool for diagnosing unstable or potentially unstable metastatic spinal lesions, and on the different elements considered for treatment.

Stereotactic Body Radiation Therapy for Spinal Malignancies

Stereotactic body radiation therapy and stereotactic radiosurgery have become important treatment options for the treatment of spinal malignancies. A better understanding of dose tolerances with more conformal technology have allowed administration of higher and more ablative doses. In this review, the framework for approaching a patient with spinal metastases and primary tumors will be discussed as well as details on the delivery of this treatment.

Local response and pathologic fractures following stereotactic body radiotherapy versus three-dimensional conformal radiotherapy for spinal metastases - a randomized controlled trial

BACKGROUND

This was a prespecified secondary analysis of a randomized trial, which analyzed bone density following stereotactic body radiotherapy (SBRT) versus conventional three-dimensional conformal radiotherapy (3DCRT) as part of palliative management of painful spinal metastases.

METHODS

Fifty-five patients were enrolled in this single-institutional randomized exploratory trial (NCT02358720). Participants were randomly assigned to receive SBRT (single-fraction 24 Gy) or 3DCRT (30 Gy/10 fractions). Quantitative bone density was evaluated at baseline, 3 and 6 months in both irradiated and unirradiated spinal bodies, along with rates of pathologic fractures and vertebral compression fractures.

RESULTS

As compared to baseline, bone density became significantly higher at 3 and 6 months following SBRT by a median of 33.8% and 72.1%, respectively (p < 0.01 for both). These figures in the 3DCRT cohort were 32.9% and 41.2%, respectively (p < 0.01 for both). There were no statistical differences in bone density between SBRT and 3DCRT at 3 (p = 0.629) or 6 months (p = 0.327). Subgroup analysis of osteolytic metastases showed an increase in bone density relative to baseline in the SBRT (but not 3DCRT) arm. Bone density in unaffected vertebrae did not show substantial changes in either group. The 3-month incidence of new pathological fractures was 8.7% in the SBRT arm vs. 4.3% in the 3DCRT arm.

CONCLUSIONS

Despite high ablative doses in the SBRT arm, the significant increase in bone density after 3 and 6 months was similar to that of 3DCRT. Our trial demonstrated a moderate rate of subsequent pathological fracture after SBRT. Future randomized investigations with larger sample sizes are recommended.

TRIAL REGISTRATION

www.clinicaltrials.gov : NCT02358720 on 9nd of February 2015.

Phase I/II trial of combined kyphoplasty and intraoperative radiotherapy in spinal metastases

BACKGROUND CONTEXT

Spinal metastases occur in 30%-50% of patients with systemic cancer. The primary goals of palliation are pain control and prevention of local recurrence.

PURPOSE

This study aimed to test the safety and efficacy of a combined modality approach consisting of kyphoplasty and intraoperative radiotherapy (Kypho-IORT).

STUDY DESIGN/SETTING

Kyphoplasty and intraoperative radiotherapy was a prospective, single-center phase I/II trial. Patients were enrolled in a classical 3+3 scheme within the initial phase I, where Kypho-IORT was applied using a needle-shaped 50 kV X-ray source at three radiation dose levels (8 Gy in 8-mm, 8 Gy in 11-mm, and 8 Gy in 13-mm depth). Thereafter, cohort expansion was performed as phase II of the trial. The trial is registered with clinicaltrials.gov, number NCT01280032.

PATIENT SAMPLE

Patients aged 50 years and older with a Karnofsky Performance Status of at least 60% and with one to three painful vertebral metastases confined to the vertebral body were eligible to participate.

OUTCOME MEASURES

The primary end point was safety as per the occurrence of dose-limiting toxicities. The secondary end points were pain reduction, local progression-free survival (L-PFS), and overall survival (OS).

METHODS

Pain was measured using the visual analog scale (VAS) and local control was assessed in serial computed tomography or magnetic resonance imaging scans.

RESULTS

None of the nine patients enrolled in the phase I showed dose-limiting toxicities at any level and thus, 52 patients were subsequently enrolled into a phase II, where Kypho-IORT was performed at various dose levels. The median pain score significantly dropped from 5 preoperatively to 2 at the first postoperative day (p<.001). Of 43 patients who reported a pre-interventional pain level of 3 or more, 30 (69.8%) reported a reduction of ≥3 points on the first postoperative day. A persistent pain reduction beyond the first postoperative day of ≥3 points was seen in 34 (79.1%) patients. The 3, 6, and 12 month L-PFS was excellent with 97.5%, 93.8%, and 93.8%. The 3, 6, and 12 months OS was 76.9%, 64.0%, and 48.4%.

CONCLUSION

Kyphoplasty and intraoperative radiotherapy is safe and immediately provided sustained pain relief with excellent local control rates in patients with painful vertebral metastases.

Treatment for Malignant Pheochromocytomas and Paragangliomas: 5 Years of Progress

PURPOSE OF REVIEW

The purpose of this manuscript is to review the progress in the field of therapeutics for malignant pheochromocytomas and sympathetic paraganglioma (MPPG) over the past 5 years.

RECENT FINDINGS

The manuscript will describe the clinical predictors of survivorship and their influence on the first TNM staging classification for pheochromocytomas and sympathetic paragangliomas, the treatment of hormonal complications, and the rationale that supports the resection of the primary tumor and metastases in patients with otherwise incurable disease. Therapeutic options for patients with bone metastasis to the spine will be presented. The manuscript will also review chemotherapy and propose a maintenance regimen with dacarbazine for patients initially treated with cyclophosphamide, vincristine, and dacarbazine. Finally, the manuscript will review preliminary results of several phase 2 clinical trials of novel radiopharmaceutical agents and tyrosine kinase inhibitors. MPPGs are very rare neuroendocrine tumors. MPPGs are usually characterized by a large tumor burden, excessive secretion of catecholamines, and decreased overall survival. Recent discoveries have enhanced our knowledge of the pathogenesis and phenotypes of MPPG. This knowledge is leading to a better understanding of the indications and limitations of the currently available localized and systemic therapies as well as the development of phase 2 clinical trials for novel medications.

Stereotactic body radiotherapy for de novo spinal metastases: systematic review

OBJECTIVE

The aim of this systematic review was to provide an objective summary of the published literature pertaining to the use of stereotactic body radiation therapy (SBRT) specific to previously untreated spinal metastases.

METHODS

The authors performed a systematic review, using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, of the literature found in a search of Medline, PubMed, Embase, and the Cochrane Library up to March 2015. The search strategy was limited to publications in the English language.

RESULTS

A total of 14 full-text articles were included in the analysis. All studies were retrospective except for 2 studies, which were prospective. A total of 1024 treated spinal lesions were analyzed. The median follow-up time ranged from 9 to 49 months. A range of dose-fractionation schemes was used, the most common of which were 16–24 Gy/1 fraction (fx), 24 Gy/2 fx, 24–27 Gy/3 fx, and 30–35 Gy/5 fx. In studies that reported crude results regarding in-field local tumor control, 346 (85%) of 407 lesions remained controlled. For studies that reported actuarial values, the weighted average revealed a 90% 1-year local control rate. Only 3 studies reported data on complete pain response, and the weighted average of these results yielded a complete pain response rate of 54%. The most common toxicity was new or progressing vertebral compression fracture, which was observed in 9.4% of cases; 2 cases (0.2%) of neurologic injury were reported.

CONCLUSION

There is a paucity of prospective data specific to SBRT in patients with spinal metastases not otherwise irradiated. This systematic review found that SBRT is associated with favorable rates of local control (approximately 90% at 1 year) and complete pain response (approximately 50%), and low rates of serious adverse events were found. Practice guidelines are summarized based on these data and International Stereotactic Radiosurgery Society consensus.

Stereotactic ablative body radiotherapy for spinal metastasis from hepatocellular carcinoma: its oncologic outcomes and risk of vertebral compression fracture

Spinal metastases from hepatocellular carcinoma (HCC) require high-dose irradiation for durable pain and tumor control. Stereotactic ablative body radiotherapy (SABR) enables the delivery of high-dose radiation. However, but vertebral compression fracture (VCF) can be problematic. The aim of his study is to evaluate the outcome and risk of VCF after SABR for spinal metastasis from HCC. We retrospectively reviewed 33 lesions in 42 spinal segments from 29 patients who received SABR with 1 fraction (16-20 Gy), or 3 fractions (18-45 Gy) from September 2009 to January 2015. The 1-year local control (LC) rate was 68.3%. Radiographic grade of cord compression (RGCC) was the only independent prognostic factor associated with LC (P = 0.007). The 1-year ultimate LC rate including the outcome of salvage re-irradiation was 87.2%. The pain response rate was 73.3% according to the categories of the International Bone Metastases Consensus Group. The 1-year VCF-free rate was 71.5%. Pre-existing VCF (P < 0.001) and only-lytic change (P = 0.017) were associated with a higher post-SABR VCF rate. One-third of post-SABR VCFs required interventions. SABR for spinal metastases from HCC provided efficacious LC, especially for lesions with RGCC ≤ II, and showed effective and durable pain relief. As VCF after SABR occurred frequently for vertebral segments with pre-existing VCF and only-lytic change, early preventive vertebroplasty is considerable for those high-risk vertebral segments.

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.

Optimization of the dosimetric leaf gap for use in planning VMAT treatments of spine SABR cases

The dosimetric leaf gap (DLG) is a beam configuration parameter used in the Varian Eclipse treatment planning system, to model the effects of rounded MLC leaf ends. Measuring the DLG using the conventional sliding‐slit technique has been shown to be produce questionable results for some volumetric modulated arc therapy (VMAT) treatments. This study therefore investigated the use of radiochromic film measurements to optimize the DLG specifically for the purpose of producing accurate VMAT plans using a flattening‐filter‐free (FFF) beam, for use in treating vertebral targets using a stereotactic (SABR, also known as SBRT) fractionation schedule. Four test treatments were planned using a VMAT technique, to deliver a prescription of 24 Gy in 3 fractions to four different spine SABR treatment sites. Measurements of the doses delivered by these treatments were acquired using an ionization chamber and radiographic film. These measurements were compared with the doses calculated by the treatment planning system using a range of DLG values, including a DLG identified using the conventional sliding‐slit method (1.1 mm). An optimal DLG value was identified, as the value that produced the closest agreement between the planned and measured doses (1.9 mm). The accuracy of the dose calculations produced using the optimized DLG value was verified using additional radiochromic film measurements in a heterogeneous phantom. This study provided a specific initial DLG (1.9 mm) as well as a film‐based optimization method, which may be used by radiotherapy centers when attempting to commission or improve an FFF VMAT‐based SABR treatment programme.

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.