Spine Stereotactic Body Radiotherapy Research Articles

International consensus recommendations for target volume delineation specific to sacral metastases and spinal stereotactic body radiation therapy (SBRT)

Background and purposeTo interrogate inter-observer variability in gross tumour volume (GTV) and clinical target volume (CTV) delineation specific to the treatment of sacral metastases with spinal stereotactic body radiation therapy (SBRT) and develop CTV consensus contouring recommendations. Materials and methodsNine specialists with spinal SBRT expertise representing 9 international centres independently contoured the GTV and CTV for 10 clinical cases of metastatic disease within the sacrum. Agreement between physicians was calculated with an expectation minimisation algorithm using simultaneous truth and performance level estimation (STAPLE) and with kappa statistics. Optimised confidence level consensus contours were obtained using a voxel-wise maximum likelihood approach and the STAPLE contours for GTV and CTV were based on an 80% confidence level. ResultsMean GTV STAPLE agreement sensitivity and specificity was 0.70 (range, 0.54–0.87) and 1.00, respectively, and 0.55 (range, 0.44–0.64) and 1.00 for the CTV, respectively. Mean GTV and CTV kappa agreement was 0.73 (range, 0.59–0.83) and 0.59 (range, 0.41–0.70), respectively. Optimised confidence level consensus contours were identified by STAPLE analysis. Consensus recommendations for the CTV include treating the entire segment containing the disease in addition to the immediate adjacent bony anatomic segment at risk of microscopic extension. ConclusionConsensus recommendations for CTV target delineation specific to sacral metastases treated with SBRT were established using expert contours. This is a critical first step to achieving standardisation of target delineation practice in the sacrum and will serve as a baseline for meaningful pattern of failure analyses going forward.

Dosimetric Feasibility of Utilizing the ViewRay Magnetic Resonance Guided Linac System for Image-guided Spine Stereotactic Body Radiation Therapy

Introduction: Spine stereotactic body radiation therapy (SBRT) achieves favorable outcomes compared to conventional radiotherapy doses/fractionation. The spinal cord is the principal dose-limiting organ-at-risk (OAR), and safe treatment requires precise immobilization/localization. Therefore, image guidance is paramount to successful spine SBRT. Conventional X-ray imaging and alignment to surrogate bony anatomy may be inadequate, whereas magnetic resonance imaging (MRI) directly visualizes the dose-limiting cord. This work assessed the dosimetric capability of the ViewRay (ViewRay Inc. Oakwood Village, OH) magnetic resonance (MR) guided linac (MR-Linac) for spine SBRT.Methods: Eight spine SBRT patients without orthopedic hardware who were previously treated on a TrueBeam using volumetric modulated arc therapy (VMAT) were re-planned using MR-Linac fixed-field intensity-modulated radiation therapy (IMRT). Phantom measurements using film, ionization chamber, and a commercial diode-array assessed feasibility. Plans included a variety of prescriptions (30-50 Gy in 3-10 fractions).Results: MR-Linac plans satisfied all clinical goals. Compared to VMAT plans, both entrance dose and heterogeneity increased (Dmax: 134±3% vs. 120±2%, p=0.0270), while conformality decreased (conformity index: 1.28±0.06 vs. 1.06±0.06, p=0.0005), and heterogeneity increased. However, while not statistically significant, MR-linac cord sparing improved (cord Dmax: 16.1±2.7Gy vs. 19.5±1.6Gy, p=0.2066; cord planning organ at risk volume (cord PRV) Dmax: 20.0±2.6Gy vs. 24.5±2.0Gy, p=0.0996). Delivery time increased but was acceptable (14.39±1.26min vs. 9.57±1.19min). Ionization chamber measurements agreed with planned dose to within 2.5%. Film and diode measurements demonstrated accurate/precise delivery of dose gradients between the target and the cord.Conclusion: Spine SBRT with the MR-Linac is feasible as verified via re-planning eight clinical cases followed by delivery verification in phantoms using film, diodes, and an ionization chamber. Real-time visualization of the dose-limiting cord during spine SBRT may enable cord-based gating, reduced margins, alternate dose schemas, and/or adaptive therapy.

Strategies to Mitigate Toxicities From Stereotactic Body Radiation Therapy for Spine Metastases.

Improvements in systemic therapy are translating into more patients living longer with metastatic disease. Bone is the most common site of metastasis, where spinal lesions can result in significant pain impacting quality of life and possible neurological dysfunction resulting in a decline in performance status. Stereotactic body radiation therapy (SBRT) of the spine has emerged as a promising technique to provide durable local control, palliation of symptoms, control of oligoprogressive sites of disease, and possibly augment the immune response. SBRT achieves this by delivering highly conformal radiation therapy to allow for dose escalation due to a steep dose gradient from the planning target volume to nearby critical organs at risk. In our review, we provide an in-depth review and expert commentary regarding seminal literature that defined clinically meaningful toxicity endpoints with actionable dosimetric limits and/or clinical management strategies to mitigate toxicity potentially attributable to SBRT of the spine. We placed a spotlight on radiation myelopathy (de novo, reirradiation after conventional external beam radiation therapy or salvage after an initial course of spinal SBRT), plexopathy, vertebral compression fracture, pain flare, esophageal toxicity, myositis, and safety regarding combination with concurrent targeted or immune therapies.

Stereotactic Body Radiotherapy for Spinal Metastases at the Extreme Ends of the Spine: Imaging-Based Outcomes for Cervical and Sacral Metastases.

The unique anatomy and biomechanical features of the cervical spine and sacrum may impact treatment outcomes following spine stereotactic body radiotherapy (SBRT). Current data for spine metastases are not specific for these locations. To report imaging-based SBRT outcomes to cervical and sacral metastases. We retrospectively reviewed our prospective spine SBRT database for cervical and sacral metastases. Patients were followed at 2- to 3-mo intervals with a clinical visit and full spine magnetic resonance imaging (MRI) and we report overall survival (OS), vertebral compression fracture (VCF), and MR imaging-based local control (LC) rates. Fifty-two patients and 93 treated spinal segments were identified. Fifty-six segments were within the cervical spine and 37 within the sacrum, the median follow-up was 14.4 and 19.5 mo, and the median total dose/number of fractions was 24 Gy/2, respectively. Cumulative LC at 1 and 2 yr were 94.5% and 92.7% for the cervical cohort, and 86.5% and 78.7% in the sacral cohort, respectively. Lack of posterior spinal element involvement in the cervical spine (P<.0001) and absence of epidural disease (hazard ratio 0.275, 95% confidence interval 0.076-0.989, P=.048) in the sacral cohort predicted LC. Median OS was 16.3 and 28.5 mo in the cervical spine and sacrum cohorts, respectively. Two cases of sacral VCF, 1 brachial plexopathy, and 1 lumbar-sacral plexopathy were observed. Although high rates of LC were observed, strategies specific to the sacrum may require further optimization.

A prospective multicentre feasibility study of stereotactic body radiotherapy in Japanese patients with spinal metastases.

Stereotactic body radiotherapy has emerged as an attractive alternative to conventional radiotherapy for spinal metastases. However, it has limitations, including the need for advanced techniques and specific adverse effects. The present trial aimed to validate the feasibility and safety of stereotactic body radiotherapy in Japanese patients with spinal metastases. Patients with one or two spinal metastases received stereotactic body radiotherapy of 24Gy in two fractions. The primary endpoint was the proportion of severe adverse effects (≥ grade 3) in patients within 6months after spine stereotactic body radiotherapy. Adverse effects were evaluated according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4. The treatment protocol was considered feasible and tolerable if the proportion of severe adverse effects was 10% or less. Overall, 20 spinal segments in 20 patients who registered between March 2014 and October 2015 were included. Minor and major deviations were observed in the planning of 2 and 0 cases, respectively. The treatment completion rate was 100%. The median follow-up after registration was 24.5 (range: 1-61) months. Although four patients experienced acute grade 2 adverse effects, no grade 3 or higher adverse effects were observed within 6months after spine stereotactic body radiotherapy. Vertebral compression fractures were observed in two patients (14 and 16months after stereotactic body radiotherapy). The local control and pain response rates at 6months were 100 and 83%, respectively. This study demonstrated the feasibility and safety of spine stereotactic body radiotherapy in Japanese patients with spinal metastases.

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

BackgroundStereotactic 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 methodThe 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.ResultsFrom 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.ConclusionsThis 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.

A Phase 2 Study of Post-Operative Stereotactic Body Radiation Therapy (SBRT) for Solid Tumor Spine Metastases

In patients with spinal instability, cord compression, or neurologic deficits, the standard of care is surgery followed by radiation therapy (RT). Recurrence rates after conventional RT remain high. The purpose of this study is to prospectively examine the efficacy of postoperative stereotactic body RT (SBRT) in patients who have undergone surgical intervention for spine metastases. We hypothesize that postoperative SBRT to the spine would be associated with higher local control than historical rates after conventional RT. Thirty-five adult patients with a Karnofsky Performance Status score ≥40 and spine metastases from solid tumors with no prior overlapping RT and target volumes ≤3 consecutive vertebral levels were enrolled. Thirty-three patients were treated. Two patients underwent treatment to 2 target volumes for a total of 35 target volumes. All patients received SBRT 30 Gy in 5 fractions. Patients were followed with neurological examinations and computed tomography and/or magnetic resonance imaging every 3 months. Neurologic function was assessed at the same time points using the American Spinal Injury Association (ASIA) impairment score. Pain was rated according to the 10-point visual analogue scale and MD Anderson Cancer Center brief pain index. Toxicity was recorded according to National Cancer Institute Common Toxicity Criteria for Adverse Events Version 4. The primary objective was the rate of radiographic local recurrence at 12 months after completion of SBRT. Patient characteristics were as follows: 34.3% had radioresistant primaries; 71.4% were ASIA E and the remainder ASIA D; and the median baseline Karnofsky Performance Status score was 70 (range, 50-100). Radiographic and symptomatic local control at 1 year were 90% (95% confidence interval, 76%-98%). The median time to recurrence in these 3 patients was 3.5 months (range, 3.4-5.8 months), all had radiosensitive tumors, and all recurrences were epidural. No patients experienced wound dehiscence, hardware failure, or spinal cord myelopathy. The median time to return to systemic therapy was 0.5 months (range, 0-9.4 months). This prospective study of postoperative spine SBRT demonstrates excellent local control with low toxicity. These data suggest superior rates of local control compared with conventional RT; however, a formal comparative study is warranted.

Spinal Cord Dose Tolerance to Stereotactic Body Radiation Therapy

Spinal cord tolerance data for stereotactic body radiation therapy (SBRT) were extracted from published reports, reviewed, and modelled. For de novo SBRT delivered in 1 to 5 fractions, the following spinal cord point maximum doses (Dmax) are estimated to be associated with a 1% to 5% risk of radiation myelopathy (RM): 12.4 to 14.0 Gy in 1 fraction, 17.0 Gy in 2 fractions, 20.3 Gy in 3 fractions, 23.0 Gy in 4 fractions, and 25.3 Gy in 5 fractions. For reirradiation SBRT delivered in 1 to 5 fractions, reported factors associated with a lower risk of RM include cumulative thecal sac equivalent dose in 2 Gy fractions with an alpha/beta of 2 (EQD22) Dmax ≤70 Gy; SBRT thecal sac EQD22 Dmax ≤25 Gy, thecal sac SBRT EQD22 Dmax to cumulative EQD22 Dmax ratio ≤0.5, and a minimum time interval to reirradiation of ≥5 months. Larger studies containing complete institutional cohorts with dosimetric data of patients treated with spine SBRT, with and without RM, are required to refine RM risk estimates.

129 Features of Patients Living Less than 3 Months Following Spine Stereotactic Body Radiotherapy

129 Features of Patients Living Less than 3 Months Following Spine Stereotactic Body Radiotherapy

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

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. 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). 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°. 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.

Dosimetric study for spine stereotactic body radiation therapy: magnetic resonance guided linear accelerator versus volumetric modulated arc therapy.

BackgroundStereotactic body radiation therapy (SBRT) given in 1-5 fractions is an effective treatment for vertebral metastases. Real-time magnetic resonance-guided radiotherapy (MRgRT) improves soft tissue contrast, which translates into accurate delivery of spine SBRT. Here we report on clinical implementation of MRgRT for spine SBRT, the quality of MRgRT plans compared to TrueBeam based volumetric modulated arc therapy (VMAT) plans in the treatment of spine metastases and benefits of MRgRT MR scan.Patients and methodsTen metastatic lesions were included in this study for plan comparison. Lesions were spread across thoracic spine and lumbosacral spine. Three fraction spine SBRT plans: 27Gy to planning target volume (PTV) and 30Gy to gross tumor volume (GTV) were generated on the ViewRay MRIdian Linac system and compared to TrueBeamTM STx based VMAT plans. Plans were compared using metrics such as minimum dose, maximum dose, mean dose, ratio of the dose to 50% of the volume (R50), conformity index, homogeneity index and dose to the spinal cord.ResultsMRIdian plans achieved equivalent target coverage and spinal cord dose compared to VMAT plans. The maximum and minimum PTV doses and homogeneity index were equivalent for both planning systems. R50 was lower for MRIdian plans compared to VMAT plans, indicating a lower spread of intermediate doses with MRIdian system (5.16 vs. 6.11, p = 0.03).ConclusionsMRgRT can deliver high-quality spine SBRT plans comparable to TrueBeam volumetric modulated arc therapy (VMAT) plans.

Risk factors for vertebral compression fracture after spine stereotactic body radiation therapy: Long-term results of a prospective phase 2 study

PurposeTo identify frequency, clinical relevance and risk factors for vertebral compression fracture (VCF) after spine stereotactic body radiation therapy (SBRT) with long-term follow up (FU). MethodsFrom 2012 to 2015, 61 lesions (56 patients) were treated within a prospective multicenter phase 2 study (NCT01594892) of SBRT for painful vertebral metastases. Post-SBRT VCF were identified. Anatomical segments, normal and tumor tissue of treated vertebrae were segmented for volumetric analyses. Predictive factors for VCF were identified by logistic regression. ResultsMedian clinical and radiological FU for all patients was 16.2 months (range, 0–68.2) and 7.8 months (range, 0–66.9), respectively. Local metastasis control was observed in 82% of lesions at last imaging FU. Post-SBRT VCF occurred in 21 lesions (34.4%): 16.4% showed a progressive VCF, while a new VCF occurred in 18.0%. 3/56 (5.4%) patients developed painful VCF defined as pain increase by ≥2 on the visual analogue scale (VAS) and 2 (3.6%) patients required surgical stabilization. Pre-SBRT VCF, localization in the thoracic spine, Bilsky score >0, SINS score, pre-SBRT osteolytic volume and metastatic vertebral body (VB) involvement were predictive factors for VCF on univariate analysis. Relative VB involvement, osteolytic volume and pre-SBRT VCF remained in the multivariate logistic regression model that had AUC = 0.930, 83.3% sensitivity and 96.6% specificity. ConclusionSpine SBRT resulted in favorable long-term pain and local metastasis control. Despite post-SBRT VCF being observed after one third of treatments, this was symptomatic in only 5% of patients. Predictive factors for developing VCF were identified which could contribute to better selection of patients for spine SBRT.

Risk of Vertebral Fracture and Local Recurrence after Palliative Spine Stereotactic Body Radiotherapy (SBRT)

Bony metastases to the spinal column are a common manifestation of cancer that can lead to significant morbidity. Although stereotactic body radiotherapy (SBRT) has been increasingly employed as an effective treatment for spinal column metastases, the optimal dosimetric parameters to maximize disease control and minimize toxicity remain unclear. Thus, we sought to understand the dosimetric factors associated with pain palliation, local control, and toxicity with spinal column SBRT for bone metastases. Patients from a single institution treated with spine SBRT between 2010 and 2017 for metastatic disease had electronic records retrospectively reviewed. Baseline patient characteristics, treatment parameters including spinal cord dose, and follow-up data were collected. Treatment-related outcomes including freedom from fracture rate (FFFR), myelitis, and freedom from local recurrence (FFLR) were assessed. Statistical analysis of categorical variables was done with Fischer’s exact test and continuous variables with Wilcoxon rank sum, with the threshold for significance of all tests at a p-value <0.05. During the study period 96 patients were treated with SBRT to 137 sites in the cervical, thoracic, and lumbar spine, with a median clinical follow up of 15 months per lesion (IQR: 4-33). There were 79, 19, and 39 treatments with 1, 3, and 5 fractions, with dose ranges of 14-20 Gy, 24-27 Gy, and 30-40 Gy, respectively. Eight lesions were treated post-operatively, 19 lesions were treated with SBRT as re-irradiation, with the rest of the lesions undergoing SBRT as the first treatment of choice. Pain was a presenting symptom at 104 of treated sites, and the median pain score was 3/10 (IQR: 1-7). On post treatment clinical follow up approximately 2-4 weeks after treatment, 89% of patients noted improved pain, with a median decrease in score of 3 points. FFFR at 12 and 24 months was 91% (CI: 86-97) and 86% (CI: 78-94) respectively without significant association with fractionation, dose, SINS score, or pre-existing compression fracture. The median D0.035cc of the true spinal cord for 1, 3, and 5 fraction treatments were 12.9 Gy (IQR:10.4-14.4), 18.5 Gy (IQR: 17.2-20.8), and 25.2 Gy (IQR: 21.8-28.4), with only one case of asymptomatic radiographic myelitis noted. FFLR at 12 and 24 months was 84% (CI: 77-92) and 78% (CI: 69-87) respectively, with no significant association between histology, dose, or fractionation and local recurrence. Spine SBRT demonstrated high rates of pain relief with acceptable toxicity profile over a range of relatively conservative dose-fractionation schema. Treatments typically exceeded TG101 guideline spinal cord “threshold doses,” while respecting maximum point doses, for the spinal cord without evidence of symptomatic myelitis. These results show superior FFFR and FFLR than prior reported studies and supports increasing use of SBRT in a wide range of patients.

Recursive Partitioning Analysis of Patients with Spine Metastases Treated with Stereotactic Body Radiotherapy

Uncertainty exits regarding the outcomes of patients receiving stereotactic body radiotherapy (SBRT) for spinal metastases. We sought to create a prognostic index using recursive partitioning analysis (RPA) for overall survival (OS). After institutional review board (IRB) approval, we performed a retrospective review on 334 patients treated with SBRT between 2005 and 2017. The cohort was split 2:1 into modelling and validation datasets. RPA was performed in the modeling cohort of patients to identify any association of the following variables with OS after spine SBRT: tumor histology, gender, age, race, performance status (KPS), controlled primary, extraosseous metastases, previous surgery, previous radiation therapy, time from primary diagnosis to treatment with SBRT, extent of spinal disease (single or multiple), spine disease type (bone only, epidural only, or bone plus epidural), paraspinal extension, equivalent dose in 2-Gy fractions (EQD2) for a/b ratio of 2, and EQD2 a/b ratio of 10. Median OS for the entire cohort was 9.8 months (95% CI 7.8-11.8). RPA analysis identified two prognostic groups (p<0.001). RPA1 included patients with bone only disease or extraosseous metastases and controlled primary from breast/prostate primary; RPA2 included extraosseous metastases from non-breast/prostate primary or uncontrolled breast/prostate primary. Median OS was 18.0 months (IQR: 6.9-29.0) and 5.4 months (IQR: 4.1-6.8) for RPA1 and RPA2, respectively. Multivariate Cox regression including the RPA and all other factors found to be significant initially in univariate analysis confirmed the RPA as the most significant variable predicting survival after spine SBRT in the validation data set. Patients treated for spine metastases with SBRT have variability in OS. An RPA classification system was developed with plans to further refine OS outcomes with additional variables. The RPA1 classification can successfully identify patients with sufficiently long expected OS that prospective analysis for late effects could be feasible in this cohort.

Dosimetric Effect of Calculation Grid Size on Epidural Space in Spine Stereotactic Body Radiotherapy Using Volumetric Modulated Arc Therapy

To perform spine stereotactic body radiotherapy (SBRT), it is important to spare the dose to the spinal cord to prevent radiation myelopathy. Conversely, we should keep sufficient dose to the target volume in the epidural space neighboring the spinal cord because the epidural space is reported as the most common site of recurrence after spine SBRT. Especially for re-irradiation, the dose constraint of the spinal cord is severer than first time radiation and it is more difficult to keep the dose in epidural space high. With the development of computer technology in recent year, a finer calculation grid size (CGS) has come to be used in dose optimization of volumetric modulated arc therapy (VMAT). However, in the spinal SBRT using VMAT, the effect of CGS on the dose to the epidural space has not been elucidated. The aim of this study was to determine the dosimetric effect on the target in the epidural space and spinal cord of the CGS in dose optimization of VMAT. This study was a single center retrospective dosimetric study of 9 patients previously treated for the spinal metastasis at our institution. Planning target volume (PTV) and planning organ at risk volume (PRV) for spinal cord were defined by adding isotropic margins of 2 mm for clinical target volume (CTV) and of 1.5 mm for the spinal cord, respectively. In addition, kidneys, trachea, and esophagus around the PTV were defined as the organ at risks. The prescribed dose was 24 Gy in 2 fractions for the volume obtained by subtracting the PRV of the spinal cord from the PTV. The dose tolerance for PRV of the spinal cord was 12.2 Gy. The following dose parameters were compared between the CGSs of 1 mm and 2 mm in dose optimization of VMAT: D99%, D98%, D95%, D50% for the PTV in the epidural space, and D0.035cc for the PRV of the spinal cord. The dose parameters for the CGS of 2 mm were evaluated after resampling to 1 mm without the change of fluence per delivery angle. Regarding the CGSs of 1 mm and 2 mm, D99%, D98%, D95%, D50% for the PTV in the epidural space were 10.1±1.3 Gy, 10.7±1.3 Gy, 11.7±1.5 Gy, 18.6±4.6 Gy and 9.6±1.1 Gy, 10.1±1.1 Gy, 11.0±1.3 Gy, 17.8±4.8 Gy, respectively. The CGS of 2 mm showed dose decrease of approximately 0.7 Gy for all parameters (p ˂0.01). The values of D0.035cc for the PRV of the spinal cord were 12.1±0.0 Gy and 11.4±0.2 Gy, respectively. The value obtained by the CGS of 2 mm decreased approximately 0.7 Gy (p <0.001) compared to that of 1 mm. In addition, visual evaluation of the difference image obtained by subtracting the dose distribution of the CGS of 1 mm from that of 2 mm showed the decrease of the PTV dose in the epidural space. For the epidural space where the most frequent recurrence occurs in the spinal SBRT, the dosimetric effect of the CGS in dose optimization of VMAT were investigated. In our analysis, the CGS of 2 mm underestimates the dose to the target in the epidural space, while the CGS of 1 mm would be more accurate for calculation of the target in the epidural space.

Magnetic Resonance Image-Guided Treatment: An Innovative Approach for Spine Stereotactic Body Radiation Therapy

Magnetic Resonance Image-Guided Treatment: An Innovative Approach for Spine Stereotactic Body Radiation Therapy

Re-Irradiation with Spine Stereotactic Body Radiotherapy in a Heavily Pre-Treated Cohort

Re-Irradiation with Spine Stereotactic Body Radiotherapy in a Heavily Pre-Treated Cohort

Features of Patients Living Less Than 3 Months Following Spine Stereotactic Body Radiotherapy

Features of Patients Living Less Than 3 Months Following Spine Stereotactic Body Radiotherapy

Fractionated Spine Stereotactic Body Radiotherapy for Treatment of Primary and Metastatic Sarcoma

Sarcomas are biologically characterized by aggressive local spread and a relative insensitivity to radiotherapy. Our group previously reported that single fraction spine stereotactic radiosurgery (sSRS) for sarcomas was associated with suboptimal local control. This study analyzes whether fractionated sSRS is associated with improved radiographic control and reduced risk for pain flare as compared to single fraction sSRS. We conducted a retrospective review of patients with metastatic or primary spine sarcoma treated with sSRS at a single tertiary care institution over a decade. Patient, treatment and dosimetric variables and clinical outcomes were retrospectively reviewed using an IRB-approved prospective database. Rates of radiographic failure and pain flare were compared with the chi squared test. A total of 76 patients underwent sSRS for primary or metastatic sarcoma between 2006 and 2016 with a mean follow up was 16 months. Of these, 18 patients were treated with fractionated sSRS. Patients treated with fractionated sSRS tended to be younger (42.4±22.9 vs. 53.9±14.3; p=0.01), have a lower KPS (71.8±12.4 vs. 80.2±11.5; p=0.01), and were more likely to have oligometastatic disease (77.8% vs. 44.8%; p=0.05). All other patient characteristics were similar. Patients treated with single fraction sSRS received an average dose of 15Gy (range 10-18Gy). Patients treated with fractionated sSRS received a mean dose of 30 Gy (range, 24-40 Gy) in 3-5 fractions. In single fraction patients 24/58 (41.4%) experienced radiographic progression as compared to 4/18 (22.2%) in fractionated sSRS patients (p=0.14). Univariable competing risk regression with death as a competing risk showed that fractionated sSRS was associated with a decreased risk of radiographic progression (HR=0.52, 0.17-1.59; p=0.25), although this finding was not significant. Additionally, in single fraction patients, 10/58 (17.2%) experienced pain flare as compared to 1/18 (5.6%) in fractionated sSRS patients (p=0.22). Similarly, univariable competing risks analysis showed that fractionated sSRS was associated with a decreased risk of pain flare (HR=0.30, 0.04-2.15; p=0.23), although this was not statistically significant. Treatment of primary and metastatic sarcoma with sSRS has demonstrated a trend towards superior radiographic control and decreased pain flares. In our experience from a small sample, we have seen a two-fold decrease in radiographic failure and three-fold decrease in pain flare among patients treated with fractionated sSRS. Although patients treated with fractionated sSRS tended to be younger, they had a lower functional status and were more likely to have oligometastatic disease. Further research with larger sample sizes is warranted to establish the role of fractionated sSRS in this population.

Frequency of Large Intrafractional Target Motions During Spine Stereotactic Body Radiation Therapy

Spine stereotactic body radiation therapy frequently involves the delivery of high doses to targets in proximity to the spinal cord; thus, the radiation must be delivered with great spatial accuracy. Monitoring for large shifts in target and cord position that might occur during dose delivery is a challenge for clinics equipped with a conventional C-arm Linac. Treatment must be halted, then imaging and registration must be done to determine whether a significant shift has occurred. In this retrospective study of 1019 spine SBRT treatments, we investigated the number of target shifts >2 mm in any direction that occurred in carefully immobilized patients. Orthogonal kV images were acquired 3 to 5 times during each session using in an in-room imaging system. Although the likelihood of large intrafractional shifts was found to be very low, they did occur in 6 treatment sessions. Intrafractional monitoring was found to be an important safety component of treatment delivery.