Image-guided Stereotactic Radiosurgery Research Articles

369 Successful Image-Guided Stereotactic Radiosurgery for Treatment of Spasticity

INTRODUCTION: Close to 100 million people worldwide suffer the sequelae of severe trauma to the brain or spinal cord. Spasticity and related pain are a common and debilitating long-term complication in survivors. Conventional surgical treatments such as baclofen pumps & cordotomy are effective but offered to a very limited number of patients. METHODS: Four patients with refractory spasticity and related pain due to traumatic brain and/or spinal cord injury, brain and/or spinal cord surgery, and stroke underwent stereotactic irradiation of selected cervical or lumbar roots. The treatment was delivered to the post-ganglionic sensory segment of cervical roots or to the dorsolateral sensory region of lumbar roots. Selection of the irradiated roots was based on somatotopic distribution of spasticity and related pain as well as EMG findings. Modified Ashworth Scale (MAS) and Visual Analogue Score (VAS) have been used to assess spasticity and related pain levels before and after the procedure. RESULTS: The treatment was well tolerated. Marked symptomatic relief on spasticity and pain was found in all the patients. After 2 years, the median reduction of MAS score was 50%. The mean reduction of MAS and VAS was, respectively, 43,7% and 64.3%. CONCLUSIONS: SRS of spinal nerve roots appears to be a safe and effective noninvasive treatment for patients with spasticity and pain caused by brain or spinal cord injury. This technique provides a useful option for the treatment of a wide variety of patients suffering from the long-term sequelae of neurological injury and can broadly expand the ability to treat patients currently orphan of treatment. A randomized, sham-controlled prospective study is underway to provide further insight.

Image-Guided Stereotactic Radiosurgery for the Treatment of Spasticity and Pain: A Preliminary Experience.

BackgroundSpasticity is a major health problem worldwide. Response to current medical and rehabilitation treatments is often poor. Surgical treatment is available only for a very limited number of patients.AimWe recently reported the application of stereotactic radiosurgery as a treatment option for spasticity and related pain. This paper describes a larger experience using image-guided stereotactic radiosurgery targeting the cervical or lumbar spinal roots to relieve spasticity and pain in four patients.MethodsAll the patients had refractory spasticity and related pain, one patient had additional paroxystic neuralgic pain. The cause of spasticity and pain was a traumatic brain and/or spinal cord injury, brain and/or spinal cord surgery, and stroke. Symptoms affected the right superior limb in one patient, and the inferior limbs in three patients (unilaterally in two, bilaterally in one). According to the symptoms, one patient was treated at the cervical level (C7 right sensory root) and three patients at lumbar level (right L4, left S1, and L2 roots bilaterally). The target was selected on constructive interference in steady-state (CISS) MR, focusing the irradiation on the postganglionic sensory segment of the cervical root or the intra-foraminal dorsolateral sensory portion of the lumbar roots. Appropriate spasticity and pain scales were used to assess the patient’s status after the treatment.ResultsThe treatments were tolerated well. Marked symptomatic relief was found in all the treated patients. Improvements in spasticity and pain scales were observed up to the latest follow-up. After 2 years, the mean reduction of the visual analog scale (VAS) and Modified Ashworth Scale (MAS) was 64.3% and 43.7%, respectively, while the median reduction of MAS score was 50%.ConclusionsExcept for a previous case report, this is the first study describing a novel noninvasive technique based on image-guided radiosurgery to treat severe spasticity and pain due to brain and spinal cord injury. This novel technique appears to be safe and effective and deserves to be studied further.

Five-Fraction Stereotactic Radiosurgery (SRS) For Resected Brain Metastases

Randomized trials have demonstrated improved rates of local control (LC) in patients who undergo postoperative stereotactic radiosurgery (SRS) compared to observation following resection of brain metastases. However, for larger tumors, dose reduction is commonly required for single-fraction SRS in order to minimize toxicity, potentially compromising LC. Hypofractionated SRS (HF-SRS) may improve LC with minimal toxicity, in particular radionecrosis (RN). In this IRB-approved retrospective study, patients who received 5-fraction HF-SRS at Duke University Medical Center from 2008 to 2018 were identified. GTVs were contoured per consensus guidelines; PTV expansions were 2mm. Patients were treated with 5 or 5.5 Gy per fraction, the latter typically utilized for tumor histologies considered to be radioresistant. Treatment consisted of linear-accelerator-based image-guided SRS with HD-MLC. Data collected included demographics, primary disease characteristics and treatment details. For patients with sufficient radiographic follow up, rates of LC, distant brain failure (DBF), RN, overall survival (OS), and leptomeningeal disease (LMD) were calculated. 250 patients were identified. Lung was the most common primary site (43%), followed by breast (16%) and GI (13%). 69% had evidence of active systemic disease at time of treatment. Of 144 patients with recorded Karnofsky performance status (KPS), 90% had a KPS of 70 or greater. Median age at time of craniotomy was 63 years. Median time interval between craniotomy and start of SRS was 4 weeks (range 1-16). 86% of patients had at least 1 subsequent brain MRI post SRS. 3-year LC was 84% and median OS was 12.8 months (95% CI 10.9-15.5). 24-month incidence of DBF was 50% (95% CI 44%-56%). 24-month incidence of RN was 4% (95% CI 2% to 7%). 14% of patients developed LMD. On univariate analysis (UVA), a dose of 5.5 Gy/fraction was associated with improved LC, HR 0.25 (0.08, 0.82), as was no prior treatment, HR 0.40 (0.20, 0.82). Location, receipt of immunotherapy or small molecule inhibitor, dural contact, and cavity volume were not significant for LC on UVA. Compared to historical standards of single fraction SRS, post-operative, five-fraction HF-SRS results in low rates of LC and RN. The use of 5.5 Gy per fraction and the absence of prior treatment were associated with improved LC. Rates of LMD in this patient population are comparable to other studies in the postoperative setting.

Image-Guided Robotic Radiosurgery for Treatment of Recurrent Grade II and III Meningiomas. A Single-Center Study

Stereotactic radiosurgery (SRS) has been increasingly applied for malignant meningiomas as an alternative to conventionally fractioned radiation therapy. We performed a retrospective analysis of an institutional patient cohort with malignant meningiomas treated by image-guided SRS. All patients with atypical or anaplastic meningiomas who were treated by SRS using CyberKnife (CK) were identified. Local failure and regional and/or distant recurrences were evaluated together with toxicity and overall survival. We identified 127 treated lesions (105 atypical and 22 anaplastic) in 35 patients. The mean time interval between the last surgery and subsequent CK-SRS was 30.8 ± 24.5 months. Most lesions (83.5%) were treated using single-fraction CK-SRS. The median planning target volume of all 127 lesions was 1.71 cm3 (range, 0.06-22.5 cm3). The median follow-up period was 23 months (range, 2.1-60.3 months). The estimated local control rates were 97%, 77%, and 67% at 12, 36, and 60 months, respectively, in atypical meningiomas and 66% each at 12 and 24 months in anaplastic meningiomas. The regional progression-free survival was 93%, 73%, and 59% at 12, 36, and 60 months, respectively, in atypical lesions and 93% and 46% at 12 and 24 months in anaplastic lesions. The estimated distant tumor progression-free interval in atypical lesions was 80%, 44%, and 44% at 12, 36, and 60 months, respectively, and 49% and 24% at 12 and 24 months, respectively, in anaplastic lesions. Age was identified as a risk factor for local failure. Although the real boundaries of efficacy of SRS have to be further evaluated in a prospective trial, it seems that aggressive treatment by high-dose single or multisession SRS of recurring malignant meningiomas provides satisfactory local control rates.

Impact of 68Ga-DOTATOC PET/MRI on robotic radiosurgery treatment planning in meningioma patients: first experiences in a single institution.

OBJECTIVEFor stereotactic radiosurgery (SRS) planning, precise contouring of tumor boundaries and organs at risk is of utmost importance. Correct interpretation of standard neuroimaging (i.e., CT and MRI) can be challenging after previous surgeries or in cases of skull base lesions with complex shapes. The aim of this study was to evaluate the impact of 68Ga-DOTATOC PET/MRI on treatment planning for image-guided SRS by CyberKnife.METHODSThe authors retrospectively identified 11 meningioma treatments in 10 patients who received a 68Ga-DOTATOC PET/MRI prior to SRS. The planning target volume (PTV) used for the patients' treatment was defined as the reference standard. This was contoured by a treating radiosurgeon (RS0) using fused planning CT and PET/MRI data sets. The same tumors were then contoured by another experienced radiosurgeon (RS1) and by a less-experienced radiosurgeon (RS2), both blinded to PET data sets. A comparison of target volumes with focus on volume-based metrics and distance to critical structures was performed. RS1 and RS2 also filled in a questionnaire analyzing the confidence level and the subjective need for the implementation of PET data sets for contouring.RESULTSAnalysis showed a subjective personal preference for PET/MRI in all cases for both radiosurgeons, particularly in proximity to critical structures. The analysis of the planning volumes per physician showed significantly smaller RS2-PTV in comparison to RS1-PTV and to RS0-PTV, whereas the median volumes were comparable between RS1-PTV and RS2-PTV (median: RS0: 4.3 cm3 [IQR 3.4-6.5 cm3] and RS1: 4.5 cm3 [IQR 2.7-6 cm3] vs RS2: 2.6 cm3 [IQR 2-5 cm3]; p = 0.003). This was also reflected in the best spatial congruency between the 2 experienced physicians (RS0 and RS1). The percentage of the left-out volume contoured by RS1 and RS2 compared to RS0 with PET/MRI demonstrated a relevant left-out-volume portion in both cases with greater extent for the less-experienced radiosurgeon (RS2) (RS1: 19.1% [IQR 8.5%-22%] vs RS2: 40.2% [IQR 34.2%-53%]). No significant differences were detected regarding investigated critical structures.CONCLUSIONSThis study demonstrated a relevant impact of PET/MRI on target volume delineation of meningiomas. The extent was highly dependent on the experience of the treating physician. This preliminary study supports the relevance of 68Ga-DOTATOC PET/MRI as a tool for radiosurgical treatment planning of meningiomas.

Long-term Outcomes and Imaging Response for Image-Guided Stereotactic Radiosurgery (IG-SRS) of Brain Arteriovenous Malformations (AVM)

Long-term Outcomes and Imaging Response for Image-Guided Stereotactic Radiosurgery (IG-SRS) of Brain Arteriovenous Malformations (AVM)

Stereotactic Shifts During Frame-Based Image-Guided Stereotactic Radiosurgery: Clinical Measurements

To determine the magnitude and reason for discrepancies between frame- and cone beam computed tomography (CBCT)-determined stereotactic coordinates, we reviewed frame-based Gamma Knife radiosurgery procedures in which CBCT was performed before treatment. Clinical and treatment documentation was reviewed for 150 frame placements for which stereotactic coordinates were defined via both frame and fiducials on computed tomography imaging and CBCT. Treatment planning system-reported rotational and translational differences and standard deviations (SDs) between frame-based and CBCT-based stereotactic coordinates were recorded. Potential clinical predictors for increased differences were collected. Multiple linear regressions were performed to evaluate for associations with increased translations and rotations. The absolute mean of the measured pitch, yaw, and roll shifts was 0.14 degrees (range -0.71-0.63 degrees, SD 0.19 degrees), 0.16 degrees (range -0.50 to 0.83 degrees, SD 0.21 degrees), and 0.12 degrees (range 0.37-0.51 degrees, SD 0.15 degrees), respectively. The absolute mean of the measured shifts in the left-right, anteroposterior, and superior-inferior direction was 0.29mm (range -1.29 to 0.82mm, SD 0.35mm), 0.24mm (range -0.59 to 0.33mm, SD 0.19mm), and 0.24mm (range -0.69 to 0.91mm, SD 0.27mm), respectively. Three cases (2.0%) exceeded 1mm in translational difference, all in the left-right direction (1.05, 1.13, and 1.29mm). Lower Karnofsky Performance Scale status was associated with greater translational differences (vector magnitude, P=.023) and rotation (pitch, P=.044; yaw, P=.002). Usage of longer total pin length (sum of all 4 fixation pin lengths) was associated with increased rotation but not with translation (P<.001 and P=.56, respectively). CBCT imaging in this cohort of frame-based cases suggests that the discrepancy in stereotactic coordinates is less than 1mm or degree in most cases. Low Karnofsky Performance Scale status and longer total pin length correlate with larger differences between frame-defined and CBCT-defined stereotactic coordinates.

A Study of Six-Dimensional Intrafractional Shifts During Frameless Image-Guided Radiosurgery and Pain Outcome for Trigeminal Neuralgia

Precision targeting is essential to successful stereotactic radiosurgery (SRS) for trigeminal neuralgia (TGN). We investigate the impact of intra-fractional 6-dimensional shifts during frameless image-guided stereotactic radiosurgery (IGRS) on pain relief outcome for TGN patients. A total of 41 sets of intra-fractional shifts from 35 patients with idiopathic TGN treated by a dedicated Linac-based radiosurgery unit from 2009 to 2013 were retrospectively studied. All patients were immobilized by facemask and received 90 Gy point dose via a 4 mm cone from an average of 6 non-coplanar arcs to the affected trigeminal nerve. The in-room kV X-ray imaging system with 6-degree of freedom robotic couch was utilized for image-guided positioning corrections. During each frameless IGRS, translational shifts in lateral, longitudinal and vertical directions, as well as rotational shifts in pitch, roll and yaw were conducted at each couch angle. These 6-dimentional shifts and the average calculated distance derived from translational shifts were analyzed and correlated with clinical pain outcome. Clinical pain outcome was assessed by patient interviews according the 5-point Barrow Neurological Institute (BNI) pain scale. Student’s t test was used to detect significance between values. The absolute mean lateral, longitudinal and vertical translational were 0.46 ± 0.15, 0.36 ± 0.16 and 0.21 ± 0.08 mm, respectively. The absolute mean pitch, roll and yaw rotational shifts were 0.33 ± 0.24, 0.18 ± 0.09 and 0.27 ± 0.15 degrees, respectively. For patients with less than 2 points of pain relief, the absolute mean lateral, longitudinal and vertical translational shifts were 0.09 ± 0.01, 0.14 ± 0.01 and 0.09 ± 0.01 mm, respectively. The average calculated distance shift for patients with less than 2 points of pain relief was 0.23 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.15 ± 0.01, 0.10 ± 0.00 and 0.09 ± 0.01 degrees, respectively. For patients with at least 2 points of pain relief, the average absolute lateral, longitudinal and vertical translational shifts were 0.12 ± 0.00, 0.16 ± 0.01 and 0.09 ± 0.00 mm, respectively. The average calculated distance shift for these patients was 0.26 ± 0.01 mm. The average absolute pitch, roll and yaw rotational shifts for these patients were 0.14 ± 0.01, 0.10 ± 0.00 and 0.13 ± 0.00 degrees, respectively. The two patient groups demonstrate no statistically significant difference in the translational or rotational intra-fractional shifts. Our analysis revealed no correlation between pain relief outcome and the amount of intra-fractional shift in all six dimensions during frameless IGRS. Our results indicate the less than 0.5 mm nominal mechanical deviation during frameless IGRS does not impact on TGN pain outcome.

Peripheral nervous system injury after high-dose single-fraction image-guided stereotactic radiosurgery for spine tumors.

OBJECTIVE The object of this study was to determine the percentage of high-dose (1800-2600 cGy) single-fraction stereotactic radiosurgery (SF-SRS) treatments to the spine that result in peripheral nervous system (PNS) injury. METHODS All patients treated with SF-SRS for primary or metastatic spine tumors between January 2004 and May 2013 and referred to the Rehabilitation Medicine Service for evaluation and treatment of neuromuscular, musculoskeletal, or functional impairments or pain were retrospectively identified. RESULTS Five hundred fifty-seven SF-SRS treatments in 447 patients resulted in 14 PNS injuries in 13 patients. All injures resulted from SF-SRS delivered to the cervical or lumbosacral spine at 2400 cGy. The overall percentage of SF-SRS treatments resulting in PNS injury was 2.5%, increasing to 4.5% when the thoracic spine was excluded from analysis. The median time to symptom onset following SF-SRS was 10 months (range 4-32 months). The plexus (cervical, brachial, and/or lumbosacral) was affected clinically and/or electrophysiologically in 12 (86%) of 14 cases, the nerve root in 2 (14%) of 14, and both in 6 (43%) of 14 cases. All patients experienced pain and most (93%) developed weakness. Peripheral nervous system injuries were CTCAE Grade 1 in 14% of cases, 2 in 64%, and 3 in 21%. No dose relationship between SF-SRS dose and PNS injury was detected. CONCLUSIONS Single-fraction SRS to the spine can result in PNS injury with major implications for function and quality of life.

On the use of volumetric-modulated arc therapy for single-fraction thoracic vertebral metastases stereotactic body radiosurgery

To retrospectively evaluate quality, efficiency, and delivery accuracy of volumetric-modulated arc therapy (VMAT) plans for single-fraction treatment of thoracic vertebral metastases using image-guided stereotactic body radiosurgery (SBRS) after RTOG 0631 dosimetric compliance criteria. After obtaining credentialing for MD Anderson spine phantom irradiation validation, 10 previously treated patients with thoracic vertebral metastases with noncoplanar hybrid arcs using 1 to 2 3D-conformal partial arcs plus 7 to 9 intensity-modulated radiation therapy beams were retrospectively re-optimized with VMAT using 3 full coplanar arcs. Tumors were located between T2 and T12. Contrast-enhanced T1/T2-weighted magnetic resonance images were coregistered with planning computed tomography and planning target volumes (PTV) were between 14.4 and 230.1cc (median = 38.0cc). Prescription dose was 16Gy in 1 fraction with 6MV beams at Novalis-TX linear accelerator consisting of micro multileaf collimators. Each plan was assessed for target coverage using conformality index, the conformation number, the ratio of the volume receiving 50% of the prescription dose over PTV, R50%, homogeneity index (HI), and PTV_1600 coverage per RTOG 0631 requirements. Organs-at-risk doses were evaluated for maximum doses to spinal cord (D0.03cc, D0.35cc), partial spinal cord (D10%), esophagus (D0.03cc and D5cc), heart (D0.03cc and D15cc), and lung (V5, V10, and maximum dose to 1000cc of lung). Dose delivery efficiency and accuracy of each VMAT-SBRS plan were assessed using quality assurance (QA) plan on MapCHECK device. Total beam-on time was recorded during QA procedure, and a clinical gamma index (2%/2mm and 3%/3mm) was used to compare agreement between planned and measured doses. All 10 VMAT-SBRS plans met RTOG 0631 dosimetric requirements for PTV coverage. The plans demonstrated highly conformal and homogenous coverage of the vertebral PTV with mean HI, conformality index, conformation number, and R50% values of 0.13 ± 0.03 (range: 0.09 to 0.18), 1.03 ± 0.04 (range: 0.98 to 1.09), 0.81 ± 0.06 (range: 0.72 to 0.89), and 4.2 ± 0.94 (range: 2.7 to 5.4), respectively. All 10 patients met protocol guidelines with maximum dose to spinal cord (average: 8.83 ± 1.9Gy, range: 5.9 to 10.9Gy); dose to 0.35cc of spinal cord (average: 7.62 ± 1.7Gy, range: 5.4 to 9.6Gy); and dose to 10% of partial spinal cord (average 6.31 ± 1.5Gy, range: 3.5 to 8.5Gy) less than 14, 10, and 10Gy, respectively. For all 10 patients, the maximum dose to esophagus (average: 9.41 ± 4.3Gy, range: 1.5 to 14.9Gy) and dose to 5cc of esophagus (average: 7.43 ± 3.8Gy, range: 1.1 to 11.8Gy) were kept less than protocol requirements 16Gy and 11.9Gy, respectively. In a similar manner, all 10 patients met protocol compliance criteria with maximum dose to heart (average: 4.62 ± 3.5Gy, range: 1.3 to 10.2Gy) and dose to 15cc of heart (average: 2.23 ± 1.8Gy, range: 0.3 to 5.6Gy) less than 22 and 16Gy, respectively. The dose to the lung was retained much lower than protocol guidelines for all 10 patients. The total number of monitor units was, on average, 6919 ± 1187. The average beam-on time was 11.5 ± 2.0 minutes. The VMAT plans demonstrated dose delivery accuracy of 95.8 ± 0.7%, on average, for clinical gamma passing rate with 2%/2mm criteria and 98.3 ± 0.8%, on average, with 3%/3mm criteria. All VMAT-SBRS plans were considered clinically acceptable per RTOG 0631 dosimetric compliance criteria. VMAT planning provided highly conformal and homogenous dose distributions for the lower-dose vertebral PTV and the spinal cord as well as organs-at-risk such as esophagus, heart, and lung. Higher QA pass rates and shorter beam-on time suggest that VMAT-SBRS is a clinically feasible, fast, and effective treatment option for patients with thoracic vertebral metastases.

Image-guided stereotactic radiosurgery for treatment of spinal hemangioblastoma.

OBJECTIVE Stereotactic radiosurgery (SRS) has been an attractive treatment option for hemangioblastomas, especially for lesions that are surgically inaccessible and in patients with von Hippel-Lindau (VHL) disease and multiple lesions. Although there has been a multitude of studies examining the utility of SRS in intracranial hemangioblastomas, SRS has only recently been used for spinal hemangioblastomas due to technical limitations. The purpose of this study is to provide a long-term evaluation of the effectiveness of image-guided radiosurgery in halting tumor progression and providing symptomatic relief for spinal hemangioblastomas. METHODS Between 2001 and 2011, 46 spinal hemangioblastomas in 28 patients were treated using the CyberKnife image-guided radiosurgery system at the authors' institution. Fourteen of these patients also had VHL disease. The median age at treatment was 43.5 years (range 19-85 years). The mean prescription radiation dose to the tumor periphery was 21.6 Gy (range 15-35 Gy). The median tumor volume was 0.264 cm3 (range 0.025-70.9 cm3). Tumor response was evaluated on serial, contrast-enhanced CT and MR images. Clinical response was evaluated by clinical and imaging evaluation. RESULTS The mean follow-up for the cohort was 54.3 months. Radiographic follow-up was available for 19 patients with 34 tumors; 32 (94.1%) tumors were radiographically stable or displayed signs of regression. Actuarial control rates at 1, 3, and 5 years were 96.1%, 92.3%, and 92.3%, respectively. Clinical evaluation on follow-up was available for 13 patients with 16 tumors; 13 (81.2%) tumors in 10 patients had symptomatic improvement. No patient developed any complications related to radiosurgery. CONCLUSIONS Image-guided SRS is safe and effective for the primary treatment of spinal hemangioblastomas and is an attractive alternative to resection, especially for those with VHL disease.

A Systematic Analysis of Errors in Target Localization and Treatment Delivery for Stereotactic Radiosurgery Using 2D/3D Image Registration.

To determine the localization uncertainties associated with 2-dimensional/3-dimensional image registration in comparison to 3-dimensional/3-dimensional image registration in 6 dimensions on a Varian Edge Linac under various imaging conditions. The systematic errors in 6 dimensions were assessed by comparing automatic 2-dimensional/3-dimensional (kV/MV vs computed tomography) with 3-dimensional/3-dimensional (cone beam computed tomography vs computed tomography) image registrations under various conditions encountered in clinical applications. The 2-dimensional/3-dimensional image registration uncertainties for 88 patients with different treatment sites including intracranial and extracranial were evaluated by statistically analyzing 2-dimensional/3-dimensional pretreatment verification shifts of 192 fractions in stereotactic radiosurgery and stereotactic body radiotherapy. The systematic errors of 2-dimensional/3-dimensional image registration using kV-kV, MV-kV, and MV-MV image pairs were within 0.3 mm and 0.3° for the translational and rotational directions within a 95% confidence interval. No significant difference ( P > .05) in target localization was observed with various computed tomography slice thicknesses (0.8, 1, 2, and 3 mm). Two-dimensional/3-dimensional registration had the best accuracy when pattern intensity and content filter were used. For intracranial sites, means ± standard deviations of translational errors were -0.20 ± 0.70 mm, 0.04 ± 0.50 mm, and 0.10 ± 0.40 mm for the longitudinal, lateral, and vertical directions, respectively. For extracranial sites, means ± standard deviations of translational errors were -0.04 ± 1.00 mm, 0.2 ± 1.0 mm, and 0.1 ± 1.0 mm for the longitudinal, lateral, and vertical directions, respectively. Two-dimensional/3-dimensional image registration for intracranial and extracranial sites had comparable systematic errors that were approximately 0.2 mm in the translational direction and 0.08° in the rotational direction. The standard 2-dimensional/3-dimensional image registration tool available on the Varian Edge radiosurgery device, a state-of-the-art system, is helpful for robust and accurate target positioning for image-guided stereotactic radiosurgery.

The Mathematics of Three N-Localizers Used Together for Stereotactic Neurosurgery.

The N-localizer enjoys widespread use in image-guided stereotactic neurosurgery and radiosurgery. This article derives the mathematical equations that are used with three N-localizers and provides analogies, explanations, and appendices in order to promote a deeper understanding of the mathematical principles that govern the N-localizer.

Characteristics of a novel treatment system for linear accelerator-based stereotactic radiosurgery.

The purpose of this study is to characterize the dosimetric properties and accuracy of a novel treatment platform (Edge radiosurgery system) for localizing and treating patients with frameless, image‐guided stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Initial measurements of various components of the system, such as a comprehensive assessment of the dosimetric properties of the flattening filter‐free (FFF) beams for both high definition (HD120) MLC and conical cone‐based treatment, positioning accuracy and beam attenuation of a six degree of freedom (6DoF) couch, treatment head leakage test, and integrated end‐to‐end accuracy tests, have been performed. The end‐to‐end test of the system was performed by CT imaging a phantom and registering hidden targets on the treatment couch to determine the localization accuracy of the optical surface monitoring system (OSMS), cone‐beam CT (CBCT), and MV imaging systems, as well as the radiation isocenter targeting accuracy. The deviations between the percent depth‐dose curves acquired on the new linac‐based system (Edge), and the previously published machine with FFF beams (TrueBeam) beyond Dmax were within 1.0% for both energies. The maximum deviation of output factors between the Edge and TrueBeam was 1.6%. The optimized dosimetric leaf gap values, which were fitted using Eclipse dose calculations and measurements based on representative spine radiosurgery plans, were 0.700 mm and 1.000 mm, respectively. For the conical cones, 6X FFF has sharper penumbra ranging from 1.2−1.8 mm (80%‐20%) and 1.9−3.8 mm (90%‐10%) relative to 10X FFF, which has 1.2−2.2 mm and 2.3−5.1 mm, respectively. The relative attenuation measurements of the couch for PA, PA (rails‐in), oblique, oblique (rails‐out), oblique (rails‐in) were: −2.0%, −2.5%, −15.6%, −2.5%, −5.0% for 6X FFF and −1.4%, −1.5%, −12.2%, −2.5%, −5.0% for 10X FFF, respectively, with a slight decrease in attenuation versus field size. The systematic deviation between the OSMS and CBCT was −0.4±0.2 mm, 0.1±0.3 mm, and 0.0±0.1 mm in the vertical, longitudinal, and lateral directions. The mean values and standard deviations of the average deviation and maximum deviation of the daily Winston‐Lutz tests over three months are 0.20±0.03 mm and 0.66±0.18 mm, respectively. Initial testing of this novel system demonstrates the technology to be highly accurate and suitable for frameless, linac‐based SRS and SBRT treatment.PACS number: 87.56.J‐

PCN13 - Clinical Effectiveness of Robotic Image-Guided Stereotactic Radiosurgery (CyberKnife) in Selected Primary and Secondary Soft Tissue Neoplasms: A Systematic Review

PCN13 - Clinical Effectiveness of Robotic Image-Guided Stereotactic Radiosurgery (CyberKnife) in Selected Primary and Secondary Soft Tissue Neoplasms: A Systematic Review

Defining the Optimal Planning Target Volume in Image-Guided Stereotactic Radiosurgery of Brain Metastases: Results of a Randomized Trial

To identify an optimal margin about the gross target volume (GTV) for stereotactic radiosurgery (SRS) of brain metastases, minimizing toxicity and local recurrence. Adult patients with 1 to 3 brain metastases less than 4 cm in greatest dimension, no previous brain radiation therapy, and Karnofsky performance status (KPS) above 70 were eligible for this institutional review board-approved trial. Individual lesions were randomized to 1- or 3- mm uniform expansion of the GTV defined on contrast-enhanced magnetic resonance imaging (MRI). The resulting planning target volume (PTV) was treated to 24, 18, or 15 Gy marginal dose for maximum PTV diameters less than 2, 2 to 2.9, and 3 to 3.9 cm, respectively, using a linear accelerator-based image-guided system. The primary endpoint was local recurrence (LR). Secondary endpoints included neurocognition Mini-Mental State Examination, Trail Making Test Parts A and B, quality of life (Functional Assessment of Cancer Therapy-Brain), radionecrosis (RN), need for salvage radiation therapy, distant failure (DF) in the brain, and overall survival (OS). Between February 2010 and November 2012, 49 patients with 80 brain metastases were treated. The median age was 61 years, the median KPS was 90, and the predominant histologies were non-small cell lung cancer (25 patients) and melanoma (8). Fifty-five, 19, and 6 lesions were treated to 24, 18, and 15 Gy, respectively. The PTV/GTV ratio, volume receiving 12 Gy or more, and minimum dose to PTV were significantly higher in the 3-mm group (all P<.01), and GTV was similar (P=.76). At a median follow-up time of 32.2 months, 11 patients were alive, with median OS 10.6 months. LR was observed in only 3 lesions (2 in the 1 mm group, P=.51), with 6.7% LR 12 months after SRS. Biopsy-proven RN alone was observed in 6 lesions (5 in the 3-mm group, P=.10). The 12-month DF rate was 45.7%. Three months after SRS, no significant change in neurocognition or quality of life was observed. SRS was well tolerated, with low rates of LR and RN in both cohorts. However, given the higher potential risk of RN with a 3-mm margin, a 1-mm GTV expansion is more appropriate.

Six-Dimensional Setup Variations and Intrafraction Corrections in Image-Guided Frameless Stereotactic Radiosurgery for Trigeminal Neuralgia

Six-Dimensional Setup Variations and Intrafraction Corrections in Image-Guided Frameless Stereotactic Radiosurgery for Trigeminal Neuralgia

TH-A-9A-09: Optimal Feedback Control with Feed Forward for a Robotic 4D Stage in Frameless Stereotactic Radiosurgery

Purpose: A novel 4D robotic system was developed to correct both translational and rotational head motion deviations during frameless image-guided stereotactic radiosurgery (SRS) procedures. The work presents a systematic approach to optimize correction performance. Methods: The system included a robotic 4D (XYZ+Pitch) stage, a head position sensing unit and a control computer. The measured head position signal was processed and a resulting command was sent to the interface of a 4-axis motor controller, through which 4 stepper motors were driven to perform motion compensation. Due to the displacement between the lesion and the pivot of the 4D stage, the rotation of the 4D stage leads to both intended rotational and undesired translational motion of the lesion. To address the issue, feedback control with feed forward was utilized in control law design, and coupling coefficients were online tuned to improve control performance. The synchronization of all 4 axes motion was found to be crucial in the decoupling control. Results: A dynamic 6D head phantom was placed on the top of the 4D stage and was used both to perform pure 4D displacements together with simulating actual framless SRS patient head motion. The 4D stage was applied to compensate such motion. The translational displacement 7 mm and pitch displacement 0.8 degree were corrected in 5 seconds without overshoot, and the steady errors were less than 0.15 mm and 0.04 degree, respectively. For a 15 minutes test with 0.25 mm and 0.07 degree target position tolerance, a subject within tolerance in 1% of the time without motion correction, while this was increased to 99.5% with motion correction. Conclusion: We report a general control design approach for both translational and rotational head motion correction. The experiments demonstrated that control performance of the 4D robotic stage meets real time sub-millimeter accuracy requirement of frameless SRS. Research was partially funded by NIH Grant T32 EB002103-21 from NIBIB. Contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIBIB or NIH.

Outcomes and Toxicity for Hypofractionated and Single-Fraction Image-Guided Stereotactic Radiosurgery for Sarcomas Metastasizing to the Spine

Conventional radiation treatment (20-40 Gy in 5-20 fractions, 2-5 Gy per fraction) for sarcoma metastatic to the spine provides subtherapeutic doses, resulting in poor durable local control (LC) (50%-77% at 1 year). Hypofractionated (HF) and/or single-fraction (SF) image-guided stereotactic radiosurgery (IG-SRS) may provide a more effective means of managing these lesions. Patients with pathologically proven high-grade sarcoma metastatic to the spine treated with HF and SF IG-SRS were included. LC and overall survival (OS) were analyzed by the use of Kaplan-Meier statistics. Univariate and multivariate analyses were performed by the use of Cox regression with competing-risks analysis; all confidence intervals are 95%. Toxicities were assessed according to Common Terminology Criteria for Adverse Events, version 4.0. From May 2005 to November 11, 2012, 88 patients with 120 discrete metastases received HF (3-6 fractions; median dose, 28.5 Gy; n=52, 43.3%) or SF IG-SRS (median dose, 24 Gy; n=68, 56.7%). The median follow-up time was 12.3 months. At 12 months, LC was 87.9% (confidence interval [CI], 81.3%-94.5%), OS was 60.6% (CI, 49.6%-71.6%), and median survival was 16.9 months. SF IG-SRS demonstrated superior LC to HF IG-SRS (12-month LC of 90.8% [CI, 83%-98.6%] vs 84.1% [CI, 72.9%-95.3%] P=.007) and retained significance on multivariate analysis (P=.030, hazard ratio 0.345; CI, 0.132-0.901]. Treatment was well tolerated, with 1% acute grade 3 toxicity, 4.5% chronic grade 3 toxicity, and no grade >3 toxicities. In the largest series of metastatic sarcoma to the spine to date, IG-SRS provides excellent LC in the setting of an aggressive disease with low radiation sensitivity and poor prognosis. Single-fraction IG-SRS is associated with the highest rates of LC with minimal toxicity.

Intrafraction variations in linac-based image-guided radiosurgery of intracranial lesions

PurposeThis study investigated image-guided patient positioning during frameless, mask-based, single-fraction stereotactic radiosurgery of intracranial lesions and intrafractional translational and rotational variations in patient positions. Patients and methodsA non-invasive head and neck thermoplastic mask was used for immobilization. The Exactrac/Novalis Body system (BrainLAB AG, Germany) was used for kV X-ray imaging guided positioning. Intrafraction displacement data, obtained by imaging after each new table position, were evaluated. ResultsThere were 269 radiosurgery treatments performed on 190 patients and a total of 967 setups within different angles. The first measured error after each table rotation (mean 2.6) was evaluated (698 measurements). Intrafraction translational errors were (1 standard deviation [SD]) on average 0.8, 0.8, and 0.7mm for the left–right, superior–inferior, and anterior–posterior directions, respectively, with a mean 3D-vector of 1.0mm (SD 0.9mm) and a range from –5mm to +5mm. On average, 12%, 3%, and 1% of the translational deviations exceeded 1, 2, and 3mm, respectively, in the three directions. ConclusionThe range of intrafraction patient motion in frameless image-guided stereotactic radiosurgery is often not fully mapped by pre- and post-treatment imaging. In the current study, intrafraction motion was assessed by performing measurements at several time points during the course of stereotactic radiosurgery. It was determined that 12% of the intrafraction values in the three dimensions are above 1mm, the usual safety margin applied in stereotactic radiosurgery.