Stereotactic body radiosurgery for spinal metastatic disease: an evidence-based review

Management of Metastatic Spinal Disease - A Practical Approach

STUDY DESIGN

Narrative review.

OBJECTIVE

This review presents a comprehensive approach to the management of spinal metastases.

METHODS

N/A.

RESULTS

The wide spectrum of clinical presentation in spinal metastases necessitates a personalized approach to treatment planning. This includes a comprehensive diagnostic workup, oncological management, palliation of symptoms, and surgical intervention if appropriate. A systematic and multidisciplinary approach allows optimal shared decision making to reach an evidence-informed and value-congruent treatment plan for the patient. We highlight how advances in stereotactic body radiotherapy (SBRT) and separation surgery may be incorporated into clinical management from a spine surgeon's perspective.

CONCLUSION

This review summarizes the approach and management of spinal metastases, its outcomes and complications.

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.

The Importance of Radiation Planning Guidelines in Spinal Stereotactic Body Radiotherapy

Introduction

Stereotactic body radiotherapy (SBRT) is a well-established treatment for spinal metastases. Official guidelines for radiation planning were published and revised by several groups. Here, we present real-world data about the importance of adhering to those guidelines.

Case Report

A 42-year-old metastatic colon cancer patient presented with oligometastatic disease to L3 vertebra and underwent SBRT treatment. Due to lack of adhering to official guidelines both in dose regiment and in volume definition, he progressed locally and required re-treatment.

Conclusions

SBRT is a well-known established choice for oligometastatic spinal lesions. Thorough evaluation of imaging and adherence to clinical guidelines are crucial for achieving a high local control rate and reducing the likelihood of re-irradiation and associated complications.

Markerless motion tracking with simultaneous MV and kV imaging in spine SBRT treatment-a feasibility study

Objective. Motion tracking with simultaneous MV-kV imaging has distinct advantages over single kV systems. This research is a feasibility study of utilizing this technique for spine stereotactic body radiotherapy (SBRT) through phantom and patient studies.Approach. A clinical spine SBRT plan was developed using 6xFFF beams and nine sliding-window IMRT fields. The plan was delivered to a chest phantom on a linear accelerator. Simultaneous MV-kV image pairs were acquired during beam delivery. KV images were triggered at predefined intervals, and synthetic MV images showing enlarged MLC apertures were created by combining multiple raw MV frames with corrections for scattering and intensity variation. Digitally reconstructed radiograph (DRR) templates were generated using high-resolution CBCT reconstructions (isotropic voxel size (0.243 mm)3) as the reference for 2D-2D matching. 3D shifts were calculated from triangulation of kV-to-DRR and MV-to-DRR registrations. To evaluate tracking accuracy, detected shifts were compared to known phantom shifts as introduced before treatment. The patient study included a T-spine patient and an L-spine patient. Patient datasets were retrospectively analyzed to demonstrate the performance in clinical settings.Main results. The treatment plan was delivered to the phantom in five scenarios: no shift, 2 mm shift in one of the longitudinal, lateral and vertical directions, and 2 mm shift in all the three directions. The calculated 3D shifts agreed well with the actual couch shifts, and overall, the uncertainty of 3D detection is estimated to be 0.3 mm. The patient study revealed that with clinical patient image quality, the calculated 3D motion agreed with the post-treatment cone beam CT. It is feasible to automate both kV-to-DRR and MV-to-DRR registrations using a mutual information-based method, and the difference from manual registration is generally less than 0.3 mm.Significance. The MV-kV imaging-based markerless motion tracking technique was validated through a feasibility study. It is a step forward toward effective motion tracking and accurate delivery for spinal SBRT.

Optimized workflow to minimise intra-fractional motion during stereotactic body radiotherapy of spinal metastases

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More frequent mid-treatment image guidance improved accuracy of treatment delivery

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97 % of treatment fractions showed an intra-fraction motion of less than 1 mm /1° using mid-arc image guidance

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Treatment delivery was optimized within a standard treatment timeslot without applying substantial additional radiation dose

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ExacTrac portal verifications during and between arcs to monitor and correct patient position, limits additional dose to the patient and OAR

Background and purpose

This study evaluated translational and rotational intra-fractional patient movement during spinal stereotactic body radiotherapy (SBRT) using 6D positioning based on 3D cone beam computerized tomography (CBCT) and stereoscopic kilovoltage imaging (ExacTrac). The aim was to determine whether additional intra-fractional image verification reduced intra-fractional motion without significantly prolonging treatment time, whilst maintaining acceptable imaging related dose.

Materials and methods

A retrospective analysis of 38 patients with 41 primary tumour volumes treated with SBRT between September 2018 and May 2021 was performed. Three different image-guided radiotherapy (IGRT) workflows were assessed. The translational and rotational positioning errors for the different imaging workflows, 3D translational vectors and estimates of imaging dose delivered for the different imaging workflows were evaluated.

Results

As the frequency of intra-fractional imaging increased from workflow 1 to 3, the mean intra-fraction 3D translational vector improved from 0.91 mm (±0.52 mm), to 0.64 (±0.34 mm). 85 %, 83 % and 97 % of images were within a tolerance of 1 mm/1° for workflows 1, 2 and 3 respectively, based on post treatment CBCT images. The average treatment time for workflow 3 was 13 min, as compared to 12 min for workflows 1 and 2. The effective dose per treatment for IGRT workflows 1, 2 and 3 measured 0.6 mSv, 0.95 mSv and 1.8 mSv respectively.

Conclusion

The study demonstrated that the use of additional intra-fractional stereoscopic kilovoltage image-guidance during spinal SBRT, reduced the number of measurements deemed “out of tolerance” and treatment delivery could be optimized within a standard treatment timeslot without applying substantial additional radiation dose.

Radiation myelopathy following stereotactic body radiation therapy for spine metastases

PURPOSE

Stereotactic body radiation therapy (SBRT) is now considered a standard of care treatment option in the management of spine metastases. One of the most feared complications of spine SBRT is radiation myelopathy (RM).

METHODS

We provided a narrative review of RM following spine SBRT based on review of the published literature, including data on spinal cord dose constraints associated with the risk of RM, strategies to mitigate the risk, and management options for RM.

RESULTS

There are limited published data of cases of RM following spine SBRT with detailed spinal cord dosimetry. The HyTEC report provided recommendations for the point maximal dose (Dmax) for the spinal cord that is associated with a < 5% risk of RM for 1-5 fractions spine SBRT. In the setting of spine SBRT reirradiation after previous conventional external beam radiation therapy (cEBRT), factors associated with RM are: SBRT spinal cord Dmax, cumulative spinal cord Dmax, and the time interval between previous RT and SBRT reirradiation. There are various strategies to mitigate the risk of RM, including accurate delineation of the spinal cord (or thecal sac), strict adherence to the recommended spinal cord dose constraints, and robust treatment immobilisation set-up and delivery. Limited effective treatment options are available for patients who develop RM, and these include corticosteroids, hyperbaric oxygen, and bevacizumab; however, none have been supported by high quality evidence.

CONCLUSION

RM is a rare but devastating complication following SBRT for spine metastases. There are strategies to minimise the risk of RM to ensure safe delivery of spine SBRT.

Stereotactic radiotherapy (SRT) for differentiated thyroid cancer (DTC) oligometastases: an AIRO (Italian association of radiotherapy and clinical oncology) systematic review

PURPOSE

The aim of this systematic review was to examine efficacy of stereotactic radiotherapy (SRT) in patients with oligometastatic thyroid cancer.

MATERIALS AND METHODS

A systematic search was conducted by means of PubMed, Scopus, and Cochrane library.

CLINICALTRIALS

gov was searched for ongoing or recently completed trials, and PROSPERO was searched for ongoing or recently completed systematic reviews. We analyzed only clinical studies as full text carried out on patients with oligometastatic thyroid cancer treated with SRT. Conference papers, surveys, letters, editorials, book chapters, and reviews were excluded. Time of publication was restricted to the years 1990-2021.

RESULTS

The number of evaluated patients was 146 (267 lesions), and the median age was 58 years. The median 1-year local control (LC) was 82% (range 67.0%-97.1%); the median disease-free survival (DFS) was 12 months (range 4-53); the median 1-year overall survival was 72% (range 66.6%-85.0%); the 3-year cancer-specific survival was 75.0%; and the 4-year cancer-specific survival was 37.5%. No grade 3-5 acute toxicity was reported. No late effects were recorded.

CONCLUSIONS

SRT for oligometastases from thyroid cancer as salvage therapy is well tolerated and yields high rates of LC and prolonged DFS.

Defining the role of high-dose radiation in oligometastatic & oligorecurrent cervical cancer

Around 5-8 per cent of women diagnosed with cervical cancer present with metastatic disease at presentation and 16-25 per cent of patients fail at either within irradiated fields or at distant sites post-curative therapy in advanced cervical cancers. Conventionally, chemotherapy with palliative intent constituted the mainstay of treatment with modest survival outcomes and radiation therapy was reserved for symptomatic benefit only. While targeted therapies and immunotherapy have been added in therapeutic armamentarium, the impact on the outcomes is modest. In limited metastatic disease, radiation therapy to metastatic sites from different primary cancers has shown survival benefits; however, the data are scarce in cervical cancer. With a better understanding of the molecular biology of the metastases and recurrence pattern, emphasis is laid upon total eradication of the disease rather than offering relief from symptoms. This article summarizes the role of radiation therapy in limited metastatic disease and recurrent cervical cancer.

Study protocol of the LARK (TROG 17.03) clinical trial: a phase II trial investigating the dosimetric impact of Liver Ablative Radiotherapy using Kilovoltage intrafraction monitoring

BACKGROUND

Stereotactic Ablative Body Radiotherapy (SABR) is a non-invasive treatment which allows delivery of an ablative radiation dose with high accuracy and precision. SABR is an established treatment for both primary and secondary liver malignancies, and technological advances have improved its efficacy and safety. Respiratory motion management to reduce tumour motion and image guidance to achieve targeting accuracy are crucial elements of liver SABR. This phase II multi-institutional TROG 17.03 study, Liver Ablative Radiotherapy using Kilovoltage intrafraction monitoring (LARK), aims to investigate and assess the dosimetric impact of the KIM real-time image guidance technology. KIM utilises standard linear accelerator equipment and therefore has the potential to be a widely available real-time image guidance technology for liver SABR.

METHODS

Forty-six patients with either hepatocellular carcinoma or oligometastatic disease to the liver suitable for and treated with SABR using Kilovoltage Intrafraction Monitoring (KIM) guidance will be included in the study. The dosimetric impact will be assessed by quantifying accumulated patient dose distribution with or without the KIM intervention. The patient treatment outcomes of local control, toxicity and quality of life will be measured.

DISCUSSION

Liver SABR is a highly effective treatment, but precise dose delivery is challenging due to organ motion. Currently, there is a lack of widely available options for performing real-time tumour localisation to assist with accurate delivery of liver SABR. This study will provide an assessment of the impact of KIM as a potential solution for real-time image guidance in liver SABR.

TRIAL REGISTRATION

This trial was registered on December 7th 2016 on ClinicalTrials.gov under the trial-ID NCT02984566 .

Early response assessment after CyberKnife stereotactic radiosurgery for symptomatic vertebral hemangioma by quantitative parameters from dynamic contrast-enhanced MRI

PURPOSE

The present study aimed to explore the value of DCE-MRI to evaluate the early efficacy of CyberKnife stereotactic radiosurgery in patients with symptomatic vertebral hemangioma (SVH).

METHODS

A retrospective analysis of patients with spinal SVH who underwent CyberKnife stereotactic radiosurgery from January 2017 to August 2019 was performed. All patients underwent DCE-MRI before treatment and three months after treatment. The parameters included volume transfer constant (K^trans), transfer rate constant (K_ep), and extravascular extracellular space volume fraction (V_e).

RESULTS

A total of 11 patients (11 lesions) were included. After treatment, six patients (54.5%) had a partial response, five patients (45.4%) had stable disease, and three patients (27.3%) presented with reossification. K^trans and K_ep decreased significantly in the third month after treatment (p = 0.003 and p = 0.026, respectively). ΔK^trans was -46.23% (range, -87.37 to -23.78%), and ΔK_ep was -36.18% (range, -85.62 to 94.40%). The change in V_e was not statistically significant (p = 0.213), and ΔV_e was -28.01% (range, -58.24 to 54.76%).

CONCLUSION

DCE-MRI parameters K^trans and K_ep change significantly after CyberKnife stereotactic radiosurgery for SVH. Thus, DCE-MRI may be of value in determining the early efficacy of CyberKnife stereotactic radiosurgery.

Full automation of spinal stereotactic radiosurgery and stereotactic body radiation therapy treatment planning using Varian Eclipse scripting

The purpose of this feasibility study is to develop a fully automated procedure capable of generating treatment plans with multiple fractionation schemes to improve speed, robustness, and standardization of plan quality. A fully automated script was implemented for spinal stereotactic radiosurgery/stereotactic body radiation therapy (SRS/SBRT) plan generation using Eclipse v15.6 API. The script interface allows multiple dose/fractionation plan requests, planning target volume (PTV) expansions, as well as information regarding distance/overlap between spinal cord and targets to drive decision‐making. For each requested plan, the script creates the course, plans, field arrangements, and automatically optimizes and calculates dose. The script was retrospectively applied to ten computed tomography (CT) scans of previous cervical, thoracic, and lumbar spine SBRT patients. Three plans were generated for each patient — simultaneous integrated boost (SIB) 1800/1600 cGy to gross tumor volume (GTV)/PTV in one fraction; SIB 2700/2100 cGy to GTV/PTV in three fractions; and 3000 cGy to PTV in five fractions. Plan complexity and deliverability patient‐specific quality assurance (QA) was performed using ArcCHECK with an Exradin A16 chamber inserted. Dose objectives were met for all organs at risk (OARs) for each treatment plan. Median target coverage was GTV V100% = 87.3%, clinical target volume (CTV) V100% = 95.7% and PTV V100% = 88.0% for single fraction plans; GTV V100% = 95.6, CTV V100% = 99.6% and PTV V100% = 97.2% for three fraction plans; and GTV V100% = 99.6%, CTV V100% = 99.1% and PTV V100% = 97.2% for five fraction plans. All plans (n = 30) passed patient‐specific QA (>90%) at 2%/2 mm global gamma. A16 chamber dose measured at isocenter agreed with planned dose within 3% for all cases. Automatic planning for spine SRS/SBRT through scripting increases efficiency, standardizes plan quality and approach, and provides a tool for target coverage comparison of different fractionation schemes without the need for additional resources.

Efficacy Analysis of Separation Surgery Combined with SBRT for Spinal Metastases-A Long-Term Follow-Up Study Based on Patients with Spinal Metastatic Tumor in a Single-Center

Objective

Follow‐up data of patients with spinal metastatic tumors were analyzed to investigate the effect of separation surgery combined with SBRT on clinical outcomes.

Methods

The clinical data of 52 patients with spinal metastatic tumors admitted to our hospital from January 2015 to December 2018 were retrospectively analyzed. There were 24 males and 28 females, aged 25–77 years, with an average of 56.7 ± 7.4 years. The separation surgery of all patients was successfully completed and followed up. Frankel neurological function grading, Karnofsky performance scores, VAS scores, Epidural spinal cord compression (ESCC) grading and muscle strength grading were used to assess the patients’ condition. Kaplan‐Meier analysis and the Log⁃rank test were used to calculate the hazard ratio (HR) and the 95% feasible interval for patients with different ages, genders, and treatments. The multivariate Cox regression model was used to calculate the risk value HR and the 95% feasible interval in patients undergoing only separation surgery or separation surgery combined with SBRT.

Results

After separation surgery, 46 patients had pain relief (88.5%), and the average VAS score decreased to 2.17 ± 0.52 points, which was significantly improved compared with preoperative score (P < 0.01). Muscle strength grading decreased in seven cases, showed no change in two cases, and recovered in 19 cases. Postoperative Frankel neurological function grading and Karnofsky performance scores were also significantly improved compared with preoperative scores (P < 0.01). The patients who accepted separation surgery were followed up for 9–47 months (26.3 ± 18.1 months), and 15 patients died due to the deterioration of the primary tumor. Thirteen patients received SBRT after surgery, including 12 cases of pain relief. The average VAS score of these 13 patients decreased to 1.64±0.41 points, which was significantly improved compared with preoperative and postoperative (P < 0.01), and muscle strength recovered in eight cases. Frankel neurological function grading and Karnofsky performance scores of these patients were also significantly improved compared with preoperative and postoperative Frankel neurological function grading and Karnofsky performance scores (P < 0.01). The patients who accepted separation surgery combined with SBRT were followed up for 11–38 months (mean 22.5 ± 10.2 months), and five cases died of primary tumor. Univariate and multivariate analysis showed that separation surgery combined with SBRT was an independent predictor of overall survival rate (OS).

Conclusions

Separation surgery combined with SBRT is an effective way to treat spinal metastatic tumors as it not only has smaller surgical trauma, but can also significantly relieve pain, improve nerve function, and relieve spinal cord compression.

Stereotactic Body Radiotherapy (SBRT) for Oligometastatic Spine Metastases: An Overview

The oligometastatic state is hypothesized to represent an intermediary state of cancer between widely metastatic disease and curable, localized disease. Advancements in radiotherapy have allowed for delivery of high precision, dose escalated treatment known as stereotactic body radiotherapy (SBRT) to targets throughout the body with excellent rates of local control. Recently, the first phase II randomized trial comparing conventional radiotherapy to comprehensive SBRT of oligometastatic disease demonstrated an overall survival and progression free survival advantage. The spine is a common site of metastasis, and a complex site for SBRT given the adjacent spinal cord and the tumor embedded within the bone tissue putting the patient at risk of fracture. Although there are expert spine SBRT guidelines for practice, there are as yet no reported randomized trials that proves superiority as compared to conventional radiation. The use of SBRT in patients with oligometastatic disease and spinal metastases is the focus of this review.

A dosimetric analysis of a spine SBRT specific treatment planning system

PURPOSE

The Brainlab Elements treatment planning system utilizes distinct modules for treatment planning specific to stereotactic treatment sites including single or multiple brain lesions as well as spine. This work investigates the hypothesis that an optimization tailored specifically to spine can in fact create dosimetrically superior plans to those created in more general use treatment planning systems (TPS).

METHODS

Ten spine patients at our institution were replanned in Brainlab Elements, Phillips Pinnacle3 , and Elekta Monaco. The planning target volume (PTV) included the vertebral body (in either the thoracic or lumbar spine), pedicles, and transverse processes. In all plans, the target was prescribed 20 Gy to 95% of the PTV. Objectives for the study included D5%<25 Gy and spinal cord D0.035cc < 14 Gy. Plans were evaluated by the satisfaction of the objectives as well total monitor units (MU), gradient index (GI), conformity index (CI), and dose gradient (distance between 100% and 50% isodose lines) in a selected slice between the vertebral body and spinal cord.

RESULTS

All TPS produced clinically acceptable plans. The sharpest dose gradient was achieved with Elements (mean 3.3 ± 0.2 mm). This resulted in lowest spinal cord maximum point doses (6.6 ± 1.0 Gy). Gradient indices were also the smallest for Elements (3.6 ± 0.5). Further improvement in gradient index and spinal cord sparing were not performed due to the subsequent violation of the PTV D5% < 25 Gy constraint or the loss of conformity due to the loss of coverage at the PTV-spinal canal interface.

CONCLUSIONS

Brainlab Elements planning which relies on arc duplication to specifically optimize for spine anatomy did result in dosimetrically superior plans while holding prescription levels constant. While any planning system can improve upon specific dosimetric objectives, the simultaneous satisfaction of all constraints was best achieved with Brainlab Elements.

Thermal effect of percutaneous radiofrequency ablation with a clustered electrode for vertebral tumors: In vitro and vivo experiments and clinical application

Purpose

To investigate effects and heat distribution of radiofrequency ablation (RFA) on vertebral tumors in vitro and in vivo swine experiments and its clinical application.

Materials and methods

RFA was performed on the swine spine in vitro and in vivo for 20 min at 90 °C at the electrode tip, and the temperature at the electrode tip and surrounding tissues were recorded. Clinical application of ablation combined with vertebroplasty was subsequently performed in 4 patients with spinal tumors.

Results

In the in vitro study, the mean temperature at the front and ventral wall of the spinal canal was 50.8 °C and 43.6 °C, respectively, at 20 mm significantly greater than 37.7 °C and 33.7 ± 1.7 °C, respectively, at 10 mm ablation depth. The coagulative necrosis area was significantly (P < 0.0001) greater at 20 mm depth than at 10 mm depth (mean 17.0 × 20.7 mm² vs. 14.2 × 16.6 mm²). In the in vivo experiment, the local temperature increased significantly (P < 0.05) from around 36 °C before ablation to over 41 °C at 20 min after ablation, with the temperature at the electrode tip (90.4 °C) and within the vertebral body (67.0 °C) significantly (P < 0.05) greater than at the posterior (41.9 °C) and lateral wall (41.8 °C). From 2 to 5 weeks, bone remodeling began. Clinically, all four patients had successful RFA and vertebroplasty, with no neurological deficits. The pain scores were significanlty (P < 0.05) improved before (4.5–10, mean 8.0) compared with at four weeks (0–1.8, mean 1.8).

Conclusion

The clustered electrode can be efficiently and safely applied in the treatment of spinal tumors without damaging the spinal cord and adjacent nerves by heat distribution.

Dose escalation by image-guided intensity-modulated radiotherapy leads to an increase in pain relief for spinal metastases: a comparison study with a regimen of 30 Gy in 10 fractions

PURPOSE

Under the existing condition that the optimum radiotherapy regimen for spinal metastases is controversial, this study investigates the benefits of dose escalation by image-guided intensity-modulated radiotherapy (IG-IMRT) with 60-66 Gy in 20-30 fractions for spinal metastases.

RESULTS

In the dose-escalation group, each D50 of planning gross tumor volume (PGTV) was above 60 Gy and each Dmax of spinal cord planning organ at risk volume (PRV) was below 48 Gy. The median biological effective dose (BED) of Dmax of spinal cord was lower in the dose-escalation group compared with that in the 30-Gy group (69.70 Gy vs. 83.16 Gy, p < 0.001). After one month and three months of the radiotherapy, pain responses were better in the dose-escalation group than those in the 30-Gy group (p = 0.005 and p = 0.024), and the complete pain relief rates were respectively 73.69% and 34.29% (p = 0.006), 73.69% and 41.38% (p = 0.028) in two compared groups. In the dose-escalation group, there is a trend of a longer duration of pain relief, a longer overall survival and a lower incidence of acute radiation toxicities. No late radiation toxicities were observed in both groups.

MATERIALS AND METHODS

Dosimetric parameters and clinical outcomes, including pain response, duration of pain relief, radiation toxicities and overall survival, were compared among twenty-five metastatic spinal lesions irradiated with the dose-escalation regimen and among forty-four lesions treated with the 30-Gy regimen.

CONCLUSIONS

Conventionally-fractionated IG-IMRT for spinal metastases could escalate dose to the vertebral lesions while sparing the spinal cord, achieving a better pain relief without increasing radiation complications.

Considerations for Quality Improvement in Radiation Oncology Therapy for Patients with Uncomplicated Painful Bone Metastases

Background: There is an increasing need for evidence-based efficiency in providing a growing amount of cancer care. One example of a quality gap is the use of multiple-fraction palliative radiation for patients with advanced cancer who have uncomplicated bone metastases; evidence suggests similar pain outcomes for treatment regimens with a lower burden of treatments. Methods: During the first phase of quality improvement work, we used RAND/UCLA appropriateness methodology to understand how radiation oncologists at one academic medical center rate the appropriateness of different treatment regimens for painful uncomplicated bone metastases. We compared radiation oncologist appropriateness ratings for radiation treatments with radiation therapy provided by these oncologists to patients with painful bone metastases between July 2012 and June 2013. Results: Appropriateness ratings showed that single-fraction (8 Gy) treatment (a low burden treatment) was consistently considered an appropriate option to treat a variety of uncomplicated bone metastases. The use of >10 fractions was consistently rated as inappropriate regardless of other factors. Eighty-one patients receiving radiation therapy for painful bone metastases during the study period had an available medical record for chart abstraction. Almost one-third of metastases were considered complicated because of a concern of spinal cord compression, a history of prior irradiation, or an associated pathological fracture. Among uncomplicated bone metastases, 25% were treated with stereotactic body radiation treatment (SBRT). Among the 54 uncomplicated bone metastases treated with conformal radiation, only one was treated with single-fraction treatment and 32% were treated with greater than 10 fractions. Conclusions: Treatment at the study site demonstrates room for improvement in providing low-burden radiation oncology treatments for patients with painful bone metastases. Choosing a radiation treatment schedule for patients with advanced cancer and painful bone metastases requires consideration of many medical and patient-centered factors. Our experience suggests that it will take more than the existence of guidelines to change practice in this area.

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.

Timely stereotactic body radiotherapy (SBRT) for spine metastases using a rapidly deployable automated planning algorithm

Purpose/objectives

The complex planning and quality assurance required for spine SBRT are a barrier to implementation in time-sensitive or limited resource clinical situations. We developed and validated an automated inverse planning algorithm designed to streamline planning and allow rapid delivery of conformal single fraction spine SBRT using widely available technology.

Materials/methods

The Rapid Spine (RaSp) automated script successfully generated single fraction SBRT plans for fourteen complex spinal lesions previously treated at a single high-volume institution. Automated RaSp plans were limited to 5 beams with a total of 15 segments (allowing calculation-based verification) and optimized based on RTOG 0631 objectives. Standard single fraction (16 Gy) stereotactic IMRT plans were generated for the same set of complex spinal lesions and used for comparison. A conservative 2 mm posterior isocenter shift was used to simulate minor set-up error.

Results

Automated plans were generated in under 5 min from target definition and had a mean dose to the PTV of 1663 cGy (SD 131.5), a dose to 90 % of PTV (D90) of 1358 cGy (SD 111.0), and a maximum point dose (Dmax) to the PTV of 2055 cGy (SD 195.2) on average. IMRT plans took longer to generate but yielded more favorable dose escalation with a mean dose to the PTV of 1891 cGy (SD 117.6), D90 of 1731 cGy (SD 126.5), and Dmax of 2218 cGy (SD 195.7). A 2 mm posterior shift resulted in a 20 % (SD 10.5 %) increase in cord dose for IMRT plans and a 10 % (SD 5.3 %) increase for RaSp plans. The 2 mm perturbation caused 3 cord dose violations for the IMRT plans and 1 violation for corresponding RaSp plans.

Conclusion

The Rapid Spine plan method yields timely and dosimetrically reasonable SBRT plans which meet RTOG 0631 objectives and are suitable for rapid yet robust pretreatment quality assurance followed by expedited treatment delivery. RaSp plans reduce the tradeoff between rapid treatment and optimal dosimetry in urgent cases and limited resource situations.

Radiographic Local Control of Spinal Metastases with Percutaneous Radiofrequency Ablation and Vertebral Augmentation

BACKGROUND AND PURPOSE

Combination radiofrequency ablation and vertebral augmentation is an emerging minimally invasive therapy for patients with metastatic spine disease who have not responded to or have contraindications to radiation therapy. The purpose of this study was to evaluate the rate of radiographic local control of spinal metastases treated with combination radiofrequency ablation and vertebral augmentation.

MATERIALS AND METHODS

We retrospectively reviewed our tumor ablation database for all patients who underwent radiofrequency ablation and vertebral augmentation of spinal metastases between April 2012 and July 2014. Tumors treated in conjunction with radiation therapy were excluded. Tumor characteristics, procedural details, and complications were recorded. Posttreatment imaging was reviewed for radiographic evidence of tumor progression.

RESULTS

Fifty-five tumors met study inclusion criteria. Radiographic local tumor control rates were 89% (41/46) at 3 months, 74% (26/35) at 6 months, and 70% (21/30) at 1 year after treatment. Clinical follow-up was available in 93% (51/55) of cases. The median duration of clinical follow-up was 34 weeks (interquartile range, 15-89 weeks), during which no complications were reported and no patients had clinical evidence of metastatic spinal cord compression at the treated levels.

CONCLUSIONS

Combination radiofrequency ablation and vertebral augmentation appears to be an effective treatment for achieving local control of spinal metastases. A prospective clinical trial is now needed to replicate these results.

Volumetric Modulated Arc Therapy for Spine Radiosurgery: Superior Treatment Planning and Delivery Compared to Static Beam Intensity Modulated Radiotherapy

PURPOSE

Spine stereotactic radiosurgery (SRS) delivers an accurate and efficient high radiation dose to vertebral metastases in 1-5 fractions. We aimed to compare volumetric modulated arc therapy (VMAT) to static beam intensity modulated radiotherapy (IMRT) for spine SRS.

METHODS AND MATERIALS

Ten spine lesions of previously treated SRS patients were planned retrospectively using both IMRT and VMAT with a prescribed dose of 16 Gy to 100% of the planning target volume (PTV). The plans were compared for conformity, homogeneity, treatment delivery time, and safety (spinal cord dose).

RESULTS

All evaluated parameters favored the VMAT plan over the IMRT plans. D min in the IMRT was significantly lower than in the VMAT plan (7.65 Gy/10.88 Gy, p < 0.001), the Dice Similarity Coefficient (DSC) was found to be significantly better for the VMAT plans compared to the IMRT plans (0.77/0.58, resp., p  value < 0.01), and an almost 50% reduction in the net treatment time was calculated for the VMAT compared to the IMRT plans (6.73 min/12.96 min, p < 0.001).

CONCLUSIONS

In our report, VMAT provides better conformity, homogeneity, and safety profile. The shorter treatment time is a major advantage and not only provides convenience to the painful patient but also contributes to the precision of this high dose radiation therapy.

Dosimetric analysis of varying cord planning organ at risk volume in spine stereotactic body radiation therapy

Background

Spine stereotactic body radiation therapy (SBRT) is becoming widely accepted as first-line treatment of oligometastatic spine disease as well as in the postoperative setting. The reported incidence of myelopathy is very low and guidelines vary widely on the maximum tolerable dose of the spinal cord and thecal sac.

Methods and materials

Between April 2008 and December 2010, radiation parameters were exported for 46 patients treated with spine SBRT at the Mayo Clinic. Using an in-house data mining program, dose-volume histogram constraints were extracted, including dose prescription, dose fractionation, planning target volume, planning target volume coverage, maximum dose to the cord, D2cc thecal sac, and D2cc spinal cord. Diagnostic magnetic resonance imaging scans and/or computed tomography myelograms were fused with the planning set to delineate the cord and thecal sac for receiver operating characteristic analysis of cord and thecal sac subvolume doses. A high-resolution planning at-risk volume was created in 1-mm increments for cord (1-7 mm) and the thecal sac (1-2 mm) to examine dose gradients that might be correlated with toxicity.

Results

No patients experienced myelopathy with a median follow-up of 14 months. The most common toxicities were pain and nausea. Median values of D2cc maximum dose (maximum dose received by 2 cc of the organ at risk; biologically equivalent 2-Gy dose maximum [EQD2]) for cord and thecal sac were 38.5 Gy (range, 7.5-67.9 Gy) and 67.7 Gy (range, 15.5-155.8 Gy), respectively. Median values for high-dose subvolumes for cord and thecal sac were 2 times higher than the doses for 5% predicted grade 3 cord toxicity as recommended in the current literature. Cord D0.1cc[EQD2] ≥23.8 Gy was correlated with pain flare (n = 5). Thecal sac D2cc [EQD2] ≥29.3 Gy was a significant indicator of nausea.

Conclusion

Current guidelines may overestimate the risk of myelopathy from spine SBRT. The current study's population included both radiation-naïve and retreatment cases, but no myelopathy was observed despite exceeding recommended spine limits.

Spinal metastases: From conventional fractionated radiotherapy to single-dose SBRT

AIM

To review the recent evolution of spine SBRT with emphasis on single dose treatments.

BACKGROUND

Radiation treatment of spine metastases represents a challenging problem in clinical oncology, because of the high risk of inflicting damage to the spinal cord. While conventional fractionated radiation therapy still constitutes the most commonly used modality for palliative treatment, notwithstanding its efficacy in terms of palliation of pain, local tumor control has been approximately 60%. This limited effectiveness is due to previous lack of technology to precisely target the tumor while avoiding the radiosensitive spinal cord, which constitutes a dose-limiting barrier to tumor cure.

MATERIALS AND METHODS

A thorough review of the available literature on spine SBRT has been carried out and critically assessed.

RESULTS

Stereotactic body radiotherapy (SBRT) emerges as an alternative, non-invasive high-precision approach, which allows escalation of tumor dose, while effectively sparing adjacent uninvolved organs at risk. Engaging technological advances, such as on-line Cone Beam Computed Tomography (CBCT), coupled with Dynamic Multi-Leaf Collimation (DMLC) and rapid intensity-modulated (IMRT) beam delivery, have promoted an interactive image-guided (IGRT) approach that precisely conforms treatment onto a defined target volume with a rapid dose fall-off to collateral non-target tissues, such as the spinal cord. Recent technological developments allow the use of the high-dose per fraction mode of hypofractionated SBRT for spinal oligometastatic cancer, even if only a few millimeters away from the tumor.

CONCLUSION

Single-dose spine SBRT, now increasingly implemented, yields unprecedented outcomes of local tumor ablation and safety, provided that advanced technology is employed.

Successful treatment of infantile fibrosarcoma spinal metastasis by chemotherapy and stereotactic hypofractionated radiotherapy

We report a case of infantile fibrosarcoma in an 8-month-old boy manifested as a right-sided lower leg mass. Repeated local recurrence and distant metastasis were noted during the following three-year period. Whole body fluoro-deoxyglucose positron emission tomography scan revealed an asymptomatic metastasis involving the fourth lumbar vertebrae. The patient received chemotherapy (VAC regimen) with Cyberknife® stereotactic hypofractionated radiotherapy (26 Gy; 4 fractions). This treatment reduced tumor size by 23% without acute radiation toxicity even after 33 months. This case suggests that combining chemotherapy and this form of radiotherapy may be safe and effective against childhood spinal metastasis.