Evaluation of CyberKnife Frameless Real-Time Image-Guided Stereotactic Radiosurgery for Spinal Lesions

[Artificial intelligence and its applications in medicine I: introductory background to AI and robotics]

La tecnología y la medicina siguen un camino paralelo durante las últimas décadas. Los avances tecnológicos van modificando el concepto de salud y las necesidades sanitarias están influyendo en el desarrollo de la tecnología.

La inteligencia artificial (IA) está formada por una serie de algoritmos lógicos suficientemente entrenados a partir de los cuales las máquinas son capaces de tomar decisiones para casos concretos a partir de normas generales.

Esta tecnología tiene aplicaciones en el diagnóstico y seguimiento de pacientes con una evaluación pronóstica individualizada de los mismos.

Además,si combinamos esta tecnología con la robótica, podemos crear máquinas inteligentes que hagan propuestas diagnósticas o que sean mucho más eficientes en su trabajo.

Por lo tanto la IA va a ser una tecnología presente en nuestro trabajo cotidiano a través de máquinas o programas informáticos, que de manera más o menos transparente para el usuario, van a ir siendo una realidad cotidiana en los procesos sanitarios. Los profesionales sanitarios tenemos que conocer esta tecnología, sus ventajas y sus inconvenientes, porque va a ser una parte integral de nuestro trabajo.

En estos dos artículos pretendemos dar una visión básica de esta tecnología adaptada a los médicos con un repaso de su historia y evolución, de sus aplicaciones reales en el momento actual y una visión de un futuro en el que la IA y el Big Data van a conformar la medicina personalizada que caracterizará al siglo XXI.

CyberKnife Frameless Radiosurgery for the Treatment of Extracranial Benign Tumors

Limited data exists for the use of radiosurgery for benign extracranial tumors. The purpose of this study was to evaluate the feasibility, toxicity, and local control of patients with benign extracranial lesions treated with the CyberKnife Frameless Radiosurgery System. From September 2001 thru January 2004, 59 benign tumors in 44 patients were treated using the CyberKnife a frameless image-guided radiosurgery system. Of these tumors, there were 21 neurofibromas, ten schwannomas, eight meningiomas, eight hemangioblastomas, seven paragangliomas, two hemangiopericytomas, one pseudotumor, one ependymoma, and one arteriovenous malformation (AVM). The anatomic locations of these tumors were spinal (25 cervical, four thoracic, 14 lumbar, and two sacral), neck (eight), orbital (three), brainstem (one), and foramen magnum (one). All patients were treated in a single fraction except three lesions were treated in a fractionated manner. The median treatment delivery time per fraction was 59 minutes (range 11–194). Twenty three lesions initially underwent surgical resection. Ten lesions received prior external beam radiation with a median dose 48 Gy (range 40–54 Gy), and one lesion received two prior CyberKnife treatments for a total dose of 32 Gy to the 80% isodose line. The median follow-up was eight months (range 1–25 months). Acute and late toxicity was graded using the National Cancer Institute Common Toxicity Criteria (CTC) scale. Symptomatic response was documented as “improved,” “stable,” or “progression”. The median tumor dose delivered was 16.0 Gy to the 80% isodose line (range 10–31 Gy). The median tumor volume was 4.3 cc (range 0.14–98.6 cc). The median spinal cord volume receiving more than 8 Gy was 0.035 cc (range 0–2.5 cc) and the median maximum spinal cord dose 11.5 Gy (range 0–19.8 Gy). There were no patients that suffered a significant (Grade 3, 4, or 5) acute toxicity. There was no observed late toxicity. 78% of patients experienced an improvement of their pre-treatment symptoms while only one patient experienced symptom progression. Of the 26 patients who underwent follow-up imaging, the local control rate was 96%. This study suggests that CyberKnife Radiosurgery is a safe and efficacious treatment modality for benign tumors, even for those patients with recurrent previously irradiated lesions.

Development of system using beam's eye view images to measure respiratory motion tracking errors in image-guided robotic radiosurgery system

The accuracy of the CyberKnife Synchrony Respiratory Tracking System (SRTS) is considered to be patient-dependent because the SRTS relies on an individual correlation between the internal tumor position (ITP) and the external marker position (EMP), as well as a prediction method to compensate for the delay incurred to adjust the position of the linear accelerator (linac). We aimed to develop a system for obtaining pretreatment statistical measurements of the SRTS tracking error by using beam's eye view (BEV) images, to enable the prediction of the patient-specific accuracy. The respiratory motion data for the ITP and the EMP were derived from cine MR images obtained from 23 patients. The dynamic motion phantom was used to reproduce both the ITP and EMP motions. The CyberKnife was subsequently operated with the SRTS, with a CCD camera mounted on the head of the linac. BEV images from the CCD camera were recorded during the tracking of a ball target by the linac. The tracking error was measured at 15 Hz using in-house software. To assess the precision of the position detection using an MR image, the positions of test tubes (determined from MR images) were compared with their actual positions. To assess the precision of the position detection of the ball, ball positions measured from BEV images were compared with values measured using a Vernier caliper. The SRTS accuracy was evaluated by determining the tracking error that could be identified with a probability of more than 95% (Ep95). The detection precision of the tumor position (determined from cine MR images) was < 0.2 mm. The detection precision of the tracking error when using the BEV images was < 0.2mm. These two detection precisions were derived from our measurement system and were not obtained from the SRTS. The median of Ep95 was found to be 1.5 (range, 1.0-3.5) mm. The difference between the minimum and maximum Ep95 was 2.5mm, indicating that this provides a better means of evaluating patient-specific SRTS accuracy. A suitable margin, based on the predicted patient-specific SRTS accuracy, can be added to the clinical target volume.

New therapeutics in spine metastases

The number of patients who will develop metastatic spinal tumors is estimated to be between 5 and 10% of all cancer patients. As the therapy for systemic cancer improves, the number of patients developing symptomatic spinal tumors that require local therapy will increase. Over the last 10 years there has been a dramatic evolution in our ability to treat spinal tumors. These advances have not only been created by improvements in surgical techniques and instrumentation, but also developments in radiographic imaging, radiation therapy and chemotherapy. It is important for spine surgeons, radiologists, and radiation and medical oncologists to continue developing techniques for spinal salvage that will improve pain relief, achieve mechanical stability, improve or maintain neurologic function and sustain local tumor control. The evolution of these technologies will help to provide palliation and improve quality of life for patients with metastatic disease.

Stereotactic radiosurgery and radiation therapy for spinal tumors

Spinal tumors constitute 15% of all CNS neoplasms. Radiation therapy can be administered for palliation of pain and spinal cord compression. However, the amount of radiation that can be administered is often limited by the tolerance of the spinal cord, especially in cases where prior radiation therapy has been given. Stereotactic radiosurgery and radiotherapy allow the delivery of a higher dose of radiation to spinal lesions, while limiting the spinal cord dose to below the tolerance level. These are technically demanding procedures and should be performed only when proper equipment and expertise are available. Data on spinal stereotactic radiosurgery and radiotherapy have emerged in recent years. This review summarizes the clinical applications of stereotactic radiosurgery and radiotherapy for spinal tumors.

Medical Robotics

Medical robotics is an interdisciplinary field that focuses on developing electromechanical devices for clinical applications. The goal of this field is to enable new medical techniques by providing new capabilities to the physician or by providing assistance during surgical procedures. Medical robotics is a relatively young field, as the first recorded medical application occurred in 1985 for a brain biopsy. It has tremendous potential for improving the precision and capabilities of physicians when performing surgical procedures, and it is believed that the field will continue to grow as improved systems become available. This chapter offers a comprehensive overview about medical robotics field and its applications. It begins with an introduction to robotics, followed by a historical review of their use in medicine. Clinical applications in several different medical specialties are discusssed. The chapter concludes with a discussion of technology challenges and areas for future research.

Medical Robotics

Medical robotics is an interdisciplinary field that focuses on developing electromechanical devices for clinical applications. The goal of this field is to enable new medical techniques by providing new capabilities to the physician or by providing assistance during surgical procedures. Medical robotics is a relatively young field, as the first recorded medical application occurred in 1985 for a brain biopsy. It has tremendous potential for improving the precision and capabilities of physicians when performing surgical procedures, and it is believed that the field will continue to grow as improved systems become available. This chapter offers a comprehensive overview about medical robotics field and its applications. It begins with an introduction to robotics, followed by a historical review of their use in medicine. Clinical applications in several different medical specialties are discusssed. The chapter concludes with a discussion of technology challenges and areas for future research.

Reduction of prostate intrafractional motion from shortening the treatment time

This study aims to quantify the reduction of the intrafractional motion when the prostate intensity modulated radiation therapy (IMRT) treatment time is shortened. Prostate intrafractional motion data recorded by the Calypso system for 105 patients was analyzed. Statistical distributions of the prostate displacements for the regular IMRT treatment and the first 1, 2, 3 and 5 min of the treatment were calculated and used for treatment margin estimation for all the selected patients. The treatment margins estimated for the first 1, 2, 3 and 5 min were compared with those for the regular IMRT treatment to quantify the reduction of the motion. If the treatment can be completed within 5 (3) min, the standard deviation of the prostate displacement could be reduced by up to 45% and the required treatment margins could be reduced to 1.2 (1.1), 0.9 (0.8), 2.2 (1.9), 1.9 (1.5), 1.9 (1.7) and 2.8 (2.4) mm from 1.5, 1.1, 2.8, 3.0, 2.4 and 3.9 mm in the left, right, superior, inferior, anterior and posterior directions, respectively. The same work was also performed for 19 of the 105 patients who exhibited the largest motion with 30% of their treatment time having 3D motion more than 3 mm. For this group of patients, the required margins change to 1.4 (1.2), 0.8 (0.8), 1.8 (1.6), 2.3 (1.8), 1.7 (1.5) and 3.4 (2.8) mm from 1.9, 1.2, 1.7, 3.7, 1.6 and 4.9 mm in the six directions when the treatment time is reduced to 5 (3) min. The intrafractional motion effects on prostate treatment are significantly smaller and the required margins can be therefore reduced when the treatment is shortened.

Radiosurgery of spinal meningiomas and schwannomas

Purpose of this study is to analyze local control, clinical symptoms and toxicity after image-guided radiosurgery of spinal meningiomas and schwannomas. Standard treatment of benign spinal lesions is microsurgical resection. While a few publications have reported about radiosurgery for benign spinal lesions, this is the first study analyzing the outcome of robotic radiosurgery for benign spinal tumors, treated exclusively with a non-invasive, fiducial free, single-fraction setup. Thirty-six patients with spinal meningiomas or schwannomas were treated, utilizing a robotic radiosurgery system (CyberKnife®, Accuray Inc. Sunnyvale CA), and were followed prospectively. Medical history, histology, clinical symptoms and radiographic outcome were recorded. Thirty-nine spinal lesions were treated because of tumor recurrence, remnants after microsurgery, multiple lesions, or rejection of open surgery. Median age was 45 years (range 18–80 years). Median target volume was 3.4 cm³ (range 0.2–43.4 cm³). Histology revealed 28 schwannomas and 11 meningiomas (WHO grade I). All spinal levels were affected. Median prescription dose was 14 Gray (95% C.I. 13.4–14 Gy) to the 70% isodose. After a median follow-up of 18 months (range 6–50 months) no local tumor progression was detected. 20 lesions (51%) remained stable, 19 tumors (49%) decreased in size. One patient with schwannomatosis was treated repeatedly for three new tumor locations. Pain was the initial symptom in 16 of 25 schwannoma patients, and in 3 of 11 patients with meningiomas. Pain levels decreased in 8/19 patients. All but one patient with motor deficits remained clinically stable. No myelopathic signs where found. Single-session radiosurgery for benign spinal tumors in selected patients has proven to inhibit tumor progression within the observed period without signs of early toxicity. Radiosurgery offers an additional treatment option, if microsurgery is not feasible in cases of tumor recurrence, post-resection remnants, multiple lesions, or medical comorbidity.

Fiducial-free CyberKnife radiosurgery for residual metastatic spinal tumor after decompression and instrumentation

Stereotactic spinal radiotherapy is a promising technology for use in the multidisciplinary management of benign and malignant spinal tumors. We present two patients with residual metastatic spinal tumors and their treatment with CyberKnife (Accuray, Sunnyvale, CA, USA) after decompression and instrumentation, one of which was successful and the other not. A 73-year-old male patient was admitted with bilateral extremity weakness (Grade IV) and voiding difficulty that had developed 2 days previously. CyberKnife treatment for the residual tumor after surgery with decompression and instrumentation was attempted, but could not be performed due to imaging interference caused by the instrumentation. A second patient, a 49-year-old male, was admitted with right extremity weakness and voiding difficulty that had developed 5 months previously. In this patient, we were able to perform CyberKnife treatment on the residual tumor after decompression and instrumentation. Based on these two patients, we believe that fiducial-free CyberKnife treatment is not suitable for treatment of residual metastatic spinal tumors at the upper thoracic levels, after decompression with instrumentation. This is due to the difficulties in matching digitally reconstructed radiographs with live radiographic images, as a result of the larger inclination and smaller vertebral body surface at the upper thoracic level.

Simultaneous anti-angiogenic therapy and single-fraction radiosurgery in clinically relevant metastases from renal cell carcinoma

OBJECTIVE

• To analyse the safety and efficacy of simultaneous standard anti-angiogenic therapy and stereotactic radiosurgery (SRS) in patients with spinal and cerebral metastases from renal cell carcinoma.

PATIENTS AND METHODS

• In all, 106 patients with spinal (n= 55) or cerebral (n= 51) metastatic lesions and an Eastern Cooperative Oncology Group status of 0 or 1 were treated with sorafenib or sunitinib and simultaneous SRS. • The primary endpoint was local control. • Secondary endpoints were toxicity and overall survival.

RESULTS

• Median follow up was 14.7 months (range 1-42 months). Forty-five patients were treated with sunitinb and 61 patients with sorafenib. Two patients had asymptomatic tumour haemorrhage after SRS. • No skin toxicity, neurotoxicity or myelopathy occurred after SRS, and SRS did not alter the adverse effects of anti-angiogenic therapy. • Local tumour control 15 months after SRS was 98% (95% confidence interval 89-99%). The median pain score before SRS was 5 (range 1-8) and was lowered to 0 (range 0-2, P < 0.01) after SRS. There were no treatment-related deaths or late complications after SRS. • Overall survival was 17.4 months in patients with spinal lesions and 11.1 month in patients with cerebral lesions (P= 0.038).

CONCLUSIONS

• Simultaneous systemic anti-angiogenic therapy and SRS for selected patients with renal cell carcinoma who have spinal and cerebral metastases is safe and effective. • Single-fraction delivery allows for efficacious integration of focal radiation treatment into oncological treatment concepts without additional toxicity. • Further studies are needed to determine the limits of SRS for renal cell carcinoma metastases outside the brain and spine.

Imaging in radiation oncology: a perspective

This paper reviews the integration of imaging and radiation oncology, and discusses challenges and opportunities for improving the practice of radiation oncology with imaging.

An inherent goal of radiation therapy is to deliver enough dose to the tumor to eradicate all cancer cells or to palliate symptoms, while avoiding normal tissue injury. Imaging for cancer diagnosis, staging, treatment planning, and radiation targeting has been integrated in various ways to improve the chance of this occurring. A large spectrum of imaging strategies and technologies has evolved in parallel to advances in radiation delivery. The types of imaging can be categorized into offline imaging (outside the treatment room) and online imaging (inside the treatment room, conventionally termed image-guided radiation therapy). The direct integration of images in the radiotherapy planning process (physically or computationally) often entails trade-offs in imaging performance. Although such compromises may be acceptable given specific clinical objectives, general requirements for imaging performance are expected to increase as paradigms for radiation delivery evolve to address underlying biology and adapt to radiation responses. This paper reviews the integration of imaging and radiation oncology, and discusses challenges and opportunities for improving the practice of radiation oncology with imaging.

Clinical results of cyberknife(r) radiosurgery for spinal metastases

OBJECTIVE

Primary treatment of spinal metastasis has been external beam radiotherapy. Recent advance of technology enables radiosurgery to be extended to extracranial lesions. The purpose of this study was to determine the clinical effectiveness and safety of stereotactic radiosurgery using Cyberknife in spinal metastasis.

METHODS

From June, 2002 to December, 2007, 129 patients with 167 spinal metastases were treated with Cyberknife. Most of the patients (94%) presented with pain and nine patients suffered from motor deficits. Twelve patients were asymptomatic. Fifty-three patients (32%) had previous radiation therapy. Using Cyberknife, 16-39 Gy in 1-5 fractions were delivered to spinal metastatic lesions. Radiation dose was not different regarding the tumor pathology or tumor volume.

RESULTS

After six months follow-up, patient evaluation was possible in 108 lesions. Among them, significant pain relief was seen in 98 lesions (91%). Radiological data were obtained in 83 lesions. The mass size was decreased or stable in 75 lesions and increased in eight lesions. Radiological control failure cases were hepatocellular carcinoma (5 cases), lung cancer (1 case), breast cancer (1 case) and renal cell carcinoma (1 case). Treatment-related radiation injury was not detected.

CONCLUSION

Cyberknife radiosurgery is clinically effective and safe for spinal metastases. It is true even in previously irradiated patients. Compared to conventional radiation therapy, Cyberknife shows higher pain control rate and its treatment process is more convenient for patients. Thus, it can be regarded as a primary treatment modality for spinal metastases.

Cord dose specification and validation for stereotactic body radiosurgery of spine

Effective dose to a portion of the spinal cord in treatment segment, rather than the maximum point dose in the cord surface, was set as the dose limit in stereotactic-body radiosurgery (SBRS) of spine. Such a cord dose specification is sensitive to the volume size and position errors. Thus, we used stereotactic image guidance to minimize phantom positioning errors and compared the results of a 0.6-cm(3) Farmer ionization chamber and a 0.01-cm(3) compact ionization chamber to determine the detector size effect on 9 SBRS cases. The experimental errors ranging from 2% to 7% were estimated by the deviation of the mean dose in plans to the chamber with spatial displacements of 0.5 mm. The mean and measured doses for the large chamber to individual cases were significantly (approximately 17%) higher than the doses with the compact chamber placed at the same point. Our experimental results shown that the mean doses to the volume of interest could represent the measured cord doses. For the 9 patients, the mean doses to 10% of the cord were about 10 Gy, while the maximum cord doses varied from 11.6 to 17.6 Gy. The mean dose, possibly correlated with the cord complication, provided us an alternative and reliable cord dose specification in SBRS of spine.

Cost-utility analysis of the cyberknife system for metastatic spinal tumors

OBJECTIVE

Using decision analysis, a cost-utility study evaluated the cost-effectiveness of CyberKnife (Accuray, Inc., Sunnyvale, CA) stereotactic radiosurgery (SRS) in comparison to external beam radiation therapy in the treatment of metastatic spinal malignancies.

METHODS

The published literature provided evidence on the effectiveness of the comparator interventions in the absence of primary outcomes data. Costs of care were derived from Centers for Medicare and Medicaid Services fee schedules. A Markov model was constructed from the payer perspective to simulate the outcomes of patients undergoing nonchemotherapeutic interventions for metastatic spinal tumors. Because cancer therapies bear significant health and economic consequences, the impact of treatment-related toxicities was integrated into the model. Given the terminal nature of these conditions and the limited life expectancy of the patient population, the time horizon for the analysis was limited to 12 months.

RESULTS

Patients treated with CyberKnife SRS gained an additional net health benefit of 0.08 quality-adjusted life year; the calculated cost of CyberKnife SRS was $1933 less than external beam radiation therapy for comparable effectiveness. The incremental cost per benefit for this strategy ($41 500 per quality-adjusted life year) met payers' willingness-to-pay criteria.

CONCLUSION

Cost-utility analysis demonstrated that CyberKnife SRS was a superior, cost-effective primary intervention for patients with metastatic spinal tumors compared with conventional external beam radiation therapy.

Extracranial radiosurgery--applications in the management of benign intradural spinal neoplasms

Stereotactic radiosurgery has enabled the delivery of higher doses of radiation and decreased fractionation due to improved accuracy. Spinal radiosurgery has been increasingly utilized for the management of metastatic extradural spinal disease. However, surgical resection remains the primary treatment strategy for intradural spinal tumors. Preliminary evidence suggests that radiosurgical ablation with stereotactic radiation for intradural spinal lesions may be efficacious in certain clinical scenarios. Local tumor control, pain relief, and improvement in neurologic function with minimal morbidity have been reported in short-term follow-up. However, long-term efficacy of radiosurgery in the management of intradural spinal neoplasms necessitates further validation. As extracranial radiosurgery is a newly evolving modality, a continuative review of the current literature is appropriate. Until a standardized therapeutic window of safety and efficacy can be determined, the recommendation of radiosurgical applications for benign spinal tumors should be reserved for carefully selected cases.

Technological approaches to in-room CBCT imaging

The use of Cone-Beam Computed Tomography (CBCT) in Image-Guided Radiation Therapy (IGRT) has become increasingly feasible and popular in recent years. Advances and developments in Flat-Panel Imager (FPI) technology and image reconstruction software allow for linac-mounted 3D CBCT imaging. Taking CBCT images on a daily/weekly basis, offers the possibility to guide the treatment beam according to tumour motion and to apply changes to the treatment plan if necessary. This however raises the issue of additional imaging dose and thus increases in secondary cancer risk. The performance characteristics of kV-CBCT and MV-CBCT solutions currently offered by Elekta, Siemens and Varian are compared in this paper in terms of additional imaging dose and image quality. The review also outlines applications of CBCT for IGRT and Adaptive Radiotherapy (ART). As CBCT is not the only in-room IGRT platform, helical MV-CT (Tomotherapy) and in-room CT designs are also presented.

Stereotactic Body Radiation Therapy: Evaluation of Setup Accuracy and Targeting Methods for a New Couch Integrated Immobilization System

A new stereotactic frame system was designed at Indiana University to utilize the precision motion control of newer accelerator couches and treat obese patients previously untreatable in other frame systems during stereotactic body radiation therapy (SBRT). The repositioning accuracy and target reproducibility of this frame was evaluated in the treatment of both lung and liver tumors. The external coordinate system on the new frame was validated using a phantom system. Translational motions were carried out using couch motors. Five patients were treated with SBRT and twenty-three verification CT scans were acquired. The displacement of the gross tumor volume (GTV) and adjacent vertebral body between the original CT scan and the verification CT scans was determined. The mean setup accuracy for the patient study was less than 5 mm. Mean displacement of the GTV was 3.0 mm (0.0–6.0 mm) in the lateral (x) direction, 4.1 mm (0.0–8.9 mm) in the superior-inferior (y) direction, and 2.6 mm (0.0–10.0 mm) in the cranio-caudal (z) direction. Comparison of vertebral body position showed mean displacement of 2.4 mm (0.0 to 8.0 mm), 1.9 mm (0.0 mm to 2.0 mm), and 0.9 mm (0.0 to 5.0 mm) for the same shift directions. Repositioning could be accurately carried out from an initial reference position using the treatment couch controllers. Adequate set-up accuracy using a frame system capable of accommodating wide girth patients was achieved and was comparable to other published studies for narrower frames. With these results, a 5 mm expansion for PTV margins remains the standard for our institution.

PATIENT POSITIONING USING IMPLANTED GOLD MARKERS WITH THE NOVALIS BODY SYSTEM IN THE THORACIC SPINE

OBJECTIVE

To evaluate the effectiveness of implanted gold marker registration compared with bony fusion alignment for patient positioning using the Novalis Body system.

METHODS

Eighteen treatment fractions of stereotactic spinal radiotherapy were analyzed for three patients who each had three implanted gold seeds placed near their spinal lesions before radiotherapy. At each treatment session, the registration was first performed using bony fusion and then verified by another bony fusion, followed by registration with implanted markers. The software reported the calculated shifts for both methods. In addition, the actual three-dimensional coordinate positions of the markers were read using PTDReader software. Implanted marker positions were analyzed for variations in individual maker coordinate displacement, interseed distances, and area transcribed by them. Measured positional differences between the two fusion methods were applied to actual treatment plans to assess the resulting dosimetric differences in the treatment plans.

RESULTS

Both fusion algorithms were shown to localize the patient well, within 1.5 mm, but the implanted marker fusion consistently related less deviation from the planned isocenter, by approximately 0.5 mm, than did the bony fusion. Exceptions to this localization occurred when the average interseed distances were less than 3.0 cm and resulted in the two registration methods being equivalent. Implanted spine markers were also shown to have less than 0.7 mm deviation from the planned marker coordinates, indicating no migration of the seeds. Dose distributions were found to be highly dependant on differences in fusion method, with spinal cord doses up to 350% greater with bony fusion than with implanted markers.

CONCLUSION

Implanted markers used with the Novalis Body system have been shown to be more effective in patient positioning than the bony fusion method in the thoracic spine.

Robotic catheter ventriculostomy: feasibility, efficacy, and implications

OBJECT

Robotic applications hold great promise for improving clinical outcomes and reducing complications of surgery. To date, however, there have been few widespread applications of robotic technology in neurosurgery. The authors hypothesized that image-guided robotic placement of a ventriculostomy catheter is safe, highly accurate, and highly reproducible.

METHODS

Sixteen patients requiring catheter ventriculostomy for ventriculoperitoneal (VP) shunt or reservoir placement were included in this retrospective study. All patients underwent image-guided robotic placement of a ventricular catheter, using a preoperatively defined trajectory.

RESULTS

All catheters were placed successfully in a single pass. There were no catheter-related hemorrhages and no injuries to adjacent neural structures. The mean distance of the catheter tip from the target was 1.5 mm. The mean operative times were 112 minutes for VP shunt placement and 42.3 minutes for reservoir placement. The mean operative times decreased over the course of the study by 49% for VP shunts and by 19% for reservoir placement.

CONCLUSIONS

The robotic placement of a ventriculostomy catheter using a preplanned trajectory is safe, highly accurate, and highly reliable. This makes single-pass ventriculostomy possible in all patients, even in those with very small ventricles, and may permit catheter-based therapies in patients who would otherwise be deemed poor surgical candidates because of ventricle size. Robotic placement also permits careful preoperative study and optimization of the catheter trajectory, which may help minimize the risks to bridging veins and sulcal vessels.

CHAINED LIGHTNING, PART II

THE FUNDAMENTAL PRINCIPLE in the radiosurgical treatment of neurological conditions is the delivery of energy to a lesion with minimal injury to surrounding structures. The development of radiosurgical techniques from Leksell's original design has focused on the refinement of various methodologies to achieve energy containment within a target. This article is the second in a series reviewing the evolution of radiosurgical instruments with respect to issues of energy beam generation and delivery for improved conformal therapy.

Continuing with concepts introduced in an earlier article, this article examines specific aspects of beam delivery and the emergence of stereotactic radiosurgery as a measure for focusing energy beams within a target volume. The application of stereotactic principles and devices to gamma ray and linear accelerator-based energy sources provides the methodology by which energy beams are generated and targeted precisely in a focal lesion. Advanced technological systems are reviewed, including fixed beams, dynamic radiosurgery, multileaf collimation, beam shaping, and robotics as various approaches for manipulating beam delivery. Radiosurgical instruments are also compared with regard to mechanics, geometry, and dosimetry. Finally, new radiosurgical designs currently on the horizon are introduced. In exploring the complex history of radiosurgery, it is evident that the discovery and rediscovery of ideas invariably leads to the development of innovative technology for the next generation.

Precision required for dose-escalated treatment of spinal metastases and implications for image-guided radiation therapy (IGRT)

INTRODUCTION

To evaluate the precision required in dose-escalated IMRT treatment of spinal metastases and paraspinal tumors.

METHODS

In IMRT treatment plans of nine patients with spinal metastases (n=7) and paraspinal tumors (n=2) translational patient positioning errors (0-10mm) and rotational errors (0-7.5 degrees ) were simulated. The dose to the spinal cord (D5(spine)) resulting from these simulations was evaluated and NTCP for spinal cord necrosis was calculated. All patient set-up errors observed during treatment were simulated and the influence on D5(spine) was investigated.

RESULTS

To keep the dose distribution to the spinal cord within +/-5% (+/-10%) of the prescribed dose, maximum tolerable errors of 1mm (2mm) in the transversal plane, 4mm (7mm) in superior-inferior direction and maximum rotations of 3.5 degrees (5 degrees ) were calculated on average. The translational and rotational component of clinically observed set-up errors increased D5(spine) by 23+/-14% and 3+/-2% on average, respectively.

CONCLUSION

Steep dose gradients of IMRT planning require very high precision. In selected patients correction of both translational and rotational errors may be beneficial.

Advances in image-guided radiation therapy

Imaging is central to radiation oncology practice, with advances in radiation oncology occurring in parallel to advances in imaging. Targets to be irradiated and normal tissues to be spared are delineated on computed tomography (CT) scans in the planning process. Computer-assisted design of the radiation dose distribution ensures that the objectives for target coverage and avoidance of healthy tissue are achieved. The radiation treatment units are now recognized as state-of-the-art robotics capable of three-dimensional soft tissue imaging immediately before, during, or after radiation delivery, improving the localization of the target at the time of radiation delivery, to ensure that radiation therapy is delivered as planned. Frequent imaging in the treatment room during a course of radiation therapy, with decisions made on the basis of imaging, is referred to as image-guided radiation therapy (IGRT). IGRT allows changes in tumor position, size, and shape to be measured during the course of therapy, with adjustments made to maximize the geometric accuracy and precision of radiation delivery, reducing the volume of healthy tissue irradiated and permitting dose escalation to the tumor. These geometric advantages increase the chance of tumor control, reduce the risk of toxicity after radiotherapy, and facilitate the development of shorter radiotherapy schedules. By reducing the variability in delivered doses across a population of patients, IGRT should also improve interpretation of future clinical trials.

Image-guided radiosurgical ablation of intra- and extra-cranial lesions

For decades since its introduction, stereotactic radiosurgery (SRS) was used only to treat intracranial lesions because intracranial targets could be immobilized and located relative to a rigid metal frame affixed to the patient's head. Lesions outside the head were generally not treated with SRS because it is difficult to immobilize extracranial lesions and to attach stereotactic frames elsewhere on the body. Advances in computerized image guidance and robotics allowed the development of systems, such as the CyberKnife SRS System (Accuray, Inc, Sunnyvale, CA), that could target intracranial lesions without the stereotactic frame. Enhancements have resulted in a radiation delivery system that can accurately deliver high-dose, focal radiation to lesions in the spine, chest, and abdomen, even if they move during respiration. In this review we will describe the technical features of frameless SRS systems and briefly review their application to treating intracranial and extracranial lesions, focusing in particular on spinal lesions.

Technical description, phantom accuracy, and clinical feasibility for fiducial-free frameless real-time image-guided spinal radiosurgery

Object

The authors describe the technical application of the Xsight Spine Tracking System, data pertaining to accuracy obtained during phantom testing, and the initial clinical feasibility of using this fiducial-free alignment system with the CyberKnife in spinal radiosurgery.

Methods

The Xsight integrates with the CyberKnife radiosurgery system to eliminate the need for implantation of radiographic markers or fiducials prior to spinal radiosurgery. It locates and tracks spinal lesions relative to spinal osseous landmarks. The authors performed 10 end-to-end tests of accuracy using an anthropomorphic head and cervical spine phantom. Xsight was also used in the treatment of 50 spinal lesions in 42 patients. Dose planning was based on 1.5-mm-thick computed tomography slices in which an inverse treatment planning technique was used.

All lesions could be treated using the fiducial-free tracking procedure. Phantom tests produced an overall mean targeting error of 0.52 ± 0.22 mm. The setup time for patient alignment averaged 6 minutes (range 2–45 minutes). The treatment doses varied from 12 to 25 Gy to the median prescription isodose of 65% (40 to 70%). The tumor volume ranged between 1.3 and 152.8 cm3The mean spinal cord volume receiving greater than 8 Gy was 0.69 ± 0.35 cm3No short-term adverse events were noted during the 1- to 7-month follow-up period. Axial and radicular pain was relieved in 14 of 15 patients treated for pain.

Conclusions

Fiducial-free tracking is a feasible, accurate, and reliable tool for radiosurgery of the entire spine. By eliminating the need for fiducial implantation, the Xsight system offers patients noninvasive radiosurgical intervention for intra- and paraspinal tumors.

Image-guided intensity-modulated radiation therapy of spine tumors

Recent advancements in imaging technology have made it possible to deliver very precise radiotherapy. By imaging the patient at the time of actual treatment, immediate corrections in patient positioning and set-up errors have become possible. Reduction in these types of treatment errors has had a significant impact upon the radiotherapeutic management of spine tumors because doses of radiation that exceed spinal cord tolerance can now be given within very close proximity to the cord. Also, the normal tissue margin around the target volume can be reduced, resulting in less of the dose being delivered to nearby critical organs. These factors have combined to improve patient outcomes, both in terms of tumor control and lower toxicity. The recent medical literature has reflected a growing interest in the application of image-guided technology to the treatment of paraspinal tumors. This review summarizes the significant contributions to the medical literature over the past calendar year.

Accurate setup of paraspinal patients using a noninvasive patient immobilization cradle and portal imaging

Because of the proximity of the spinal cord, effective radiotherapy of paraspinal tumors to high doses requires highly conformal dose distributions, accurate patient setup, setup verification, and patient immobilization. An immobilization cradle has been designed to facilitate the rapid setup and radiation treatment of patients with paraspinal disease. For all treatments, patients were set up to within 2.5 mm of the design using an amorphous silicon portal imager. Setup reproducibility of the target using the cradle and associated clinical procedures was assessed by measuring the setup error prior to any correction. From 350 anterior/posterior images, and 303 lateral images, the standard deviations, as determined by the imaging procedure, were 1.3 m, 1.6 m, and 2.1 in the ant/post, right/left, and superior/inferior directions. Immobilization was assessed by measuring patient shifts between localization images taken before and after treatment. From 67 ant/post image pairs and 49 lateral image pairs, the standard deviations were found to be less than 1 mm in all directions. Careful patient positioning and immobilization has enabled us to develop a successful clinical program of high dose, conformal radiotherapy of paraspinal disease using a conventional Linac equipped with dynamic multileaf collimation and an amorphous silicon portal imager.

Modelling 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning

The goal of this work is to build a multiple source model to represent the 6 MV photon beams from a Cyberknife stereotactic radiosurgery system for Monte Carlo treatment planning dose calculations. To achieve this goal, the 6 MV photon beams have been characterized and modelled using the EGS4/BEAM Monte Carlo system. A dual source model has been used to reconstruct the particle phase space at a plane immediately above the secondary collimator. The proposed model consists of two circular planar sources for the primary photons and the scattered photons, respectively. The dose contribution of the contaminant electrons was found to be in the order of 10(-3) of the total maximum dose and therefore has been omitted in the source model. Various comparisons have been made to verify the dual source model against the full phase space simulated using the EGS4/BEAM system. The agreement in percent depth dose (PDD) curves and dose profiles between the phase space and the source model was generally within 2%/1 mm for various collimators (5 to 60 mm in diameter) at 80 to 100 cm source-to-surface distances (SSD). Excellent agreement (within 1%/1 mm) was also found between the dose distributions in heterogeneous lung and bone geometry calculated using the original phase space and those calculated using the source model. These results demonstrated the accuracy of the dual source model for Monte Carlo treatment planning dose calculations for the Cyberknife system.

Paraspinal nerve sheath tumors

Spinal tumors compose a vast heterogeneous group of neoplasms that are classified by origin into vertebral column, spinal canal, or paraspinal region tumors. Tumors with both intraspinal (intracanalicular) and paraspinal (extracanalicular) components that communicate via an intravertebral foramen are defined as "dumbbell tumors." This article focuses on the characteristics of a few types of paraspinal tumors, with special emphasis on the management of nerve sheath dumbbell tumors.