Image-guided hypo-fractionated stereotactic radiosurgery to spinal lesions.

OBJECTIVE: This article demonstrates the technical feasibility of noninvasive treatment of unresectable spinal vascular malformations and primary and metastatic spinal tumors by use of image-guided frameless stereotactic radiosurgery. METHODS: Stereotactic radiosurgery delivers a high dose of radiation to a tumor volume or vascular malformation in a limited number of fractions and minimizes the dose to adjacent normal structures. Frameless image-guided radiosurgery was developed by coupling an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator that guides the therapy beam to treatment sites within the spine or spinal cord, in an outpatient setting, and without the use of frame-based fixation. The system relies on skeletal landmarks or implanted fiducial markers to locate treatment targets. Sixteen patients with spinal lesions (hemangioblastomas, vascular malformations, metastatic carcinomas, schwannomas, a meningioma, and a chordoma) were treated with total treatment doses of 1100 to 2500 cGy in one to five fractions by use of image-guided frameless radiosurgery with the CyberKnife system (Accuray, Inc., Sunnyvale, CA). Thirteen radiosurgery plans were analyzed for compliance with conventional radiation therapy. RESULTS: Tests demonstrated alignment of the treatment dose with the target volume within +/-1 mm by use of spine fiducials and the CyberKnife treatment planning system. Tumor patients with at least 6 months of follow-up have demonstrated no progression of disease. Radiographic follow-up is pending for the remaining patients. To date, no patients have experienced complications as a result of the procedure. CONCLUSION: This experience demonstrates the feasibility of image-guided robotic radiosurgery for previously untreatable spinal lesions.

Current status and optimal use of radiosurgery.

The field of stereotactic radiosurgery is rapidly advancing as a result of both improvements in radiosurgical equipment and better physician understanding of the clinical applications of stereotactic radiosurgery. This article will review recent developments in the field of radiosurgery, including advances in our understanding of the treatment of brain metastases and arteriovenous malformations, as well as the use of stereotactic radiosurgery as a boost following conventional radiation for nasopharyngeal carcinoma to minimize the rate of local recurrence. In addition, improved understanding of the radiobiology of normal neurologic structures adjacent to tumors undergoing radiosurgery has led to the use of fractionated stereotactic radiosurgery for the treatment of acoustic neuromas and tumors bordering the anterior visual pathways. Finally, a breakthrough in radiosurgery involving the development and use of frameless, image-guided stereotactic radiosurgery has allowed for both dose homogeneity and treatment of intracranial lesions based on nonisocentric treatment algorithms that result in improved target conformality. This same frameless radiosurgical system has also expanded the scope of radiosurgery to include the treatment of extracranial lesions throughout the body.

Stereotactic radiosurgery and hypofractionated stereotactic radiotherapy for residual or recurrent cranial base and cervical chordomas.

OBJECT: In patients with chordomas the lesions often recur. Furthermore, the location of some chordomas within the base of the skull and the cervical spine can prevent complete resection from being achieved. Previous series have shown that stereotactic radiosurgery can be used as a treatment for residual chordomas with good overall results. The authors review their experience in using linear accelerator (LINAC) stereotactic radiosurgery to treat patients with recurrent and/or residual cranial base and cervical chordomas. METHODS: Ten patients with chordomas (eight with cranial base and two with cervical lesions [below C-2]) underwent LINAC stereotactic radiosurgery. The mean patient age was 49 years (range 30-73 years). There were seven men and three women. Three patients had undergone one prior surgery, five had undergone two previous surgeries, and two had undergone three prior operations. The mean radiation dose was 19.4 Gy (range 18-24 Gy), and the maximum intratumoral dose averaged 27 Gy (range 24.1-33.1 Gy). The mean secondary collimator size was 14.4 mm (range 7.5-20 mm). The volume of the tumor treated ranged from 1.1 to 21.5 ml. In five patients a standard frame-based LINAC radiosurgery system was used, whereas in the other five the CyberKnife, a frameless image-guided LINAC radiosurgical system, was used. All patients were available for follow-up review, which averaged 4 years (range 1-9 years). Over the course of follow up, one chordoma (10%) was smaller in size, seven were stable, and two chordomas progressed (one in a patient who underwent reoperation and a second course of stereotactic radiosurgery, and the second in a patient who underwent reoperation alone). There were no new neurological deficits noted following radiosurgery in the eight of 10 patients in whom there was no tumor progression, and no patient developed radiation-induced necrosis. CONCLUSIONS: Stereotactic radiosurgery can be used to treat patients with recurrent or residual chordomas with excellent tumor control rates. Longer follow-up review in larger series is warranted to confirm these findings.

Robotics and radiosurgery--the cyberknife.

The Cyberknife is a dedicated image-guided robotic radiosurgical device. While clinical results with intracranial lesions are comparable to frame-based radiosurgical techniques, recent experience demonstrates the potential to broadly expand the scope of radiosurgery to many extracranial sites.

Robotic motion compensation for respiratory movement during radiosurgery.

Tumors in the chest and abdomen move during respiration. The ability of conventional radiation therapy systems to compensate for respiratory motion by moving the radiation source is inherently limited. Since safety margins currently used in radiation therapy increase the radiation dose by a very large amount, an accurate tracking method for following the motion of the tumor is of the utmost clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery. Thus, the therapeutic beam is moved by a robotic arm, and follows the moving target tumor. To determine the precise position of the moving target, we combine infrared tracking with synchronized X-ray imaging. Infrared emitters are used to record the motion of the patient's skin surface. A stereo X-ray imaging system provides information about the location of internal markers. During an initialization phase (prior to treatment), the correlation between the motions observed by the two sensors (X-ray imaging and infrared tracking) is computed. This model is also continuously updated during treatment to compensate for other, non-respiratory motion. Experiments and clinical trials suggest that robot-based methods can substantially reduce the safety margins currently needed in radiation therapy.

Image-guided radiosurgery for the spine and pancreas.

A robotic image-guided radiosurgical system has been modified to treat extra-cranial sites using implanted fiducials and skeletal landmarks to locate the treatment targets. The system has been used to treat an artero-venous malformation in the cervical spine, a recurrent schwannoma of the thoracic spine, a metastatic adenocarcinoma of the lumbar spine, and three pancreatic cancers. During each treatment, the image guidance system monitored the position of the target site and relayed the target coordinates to the beam-pointing system at discrete intervals. The pointing system then dynamically aligned the therapy beam with the lesion, automatically compensating for shifts in target position. Breathing-related motion of the pancreas lesions was managed by coordinating beam gating with breath-holding by the patient. The system maintained alignment with the spine lesions to within +/- 0.2 mm on average, and to within +/- 1 mm for the pancreatic tumors. This experience has demonstrated the feasibility of using image-guided robotic radiosurgery outside the cranium.

Acquired cerebral arteriovenous malformation induced by an anaplastic astrocytoma: an interesting case.

High grade gliomas foster an environment rich in angiogenic factors that promote neovascularity. We report a case of a cerebral arteriovenous malformation, which developed in the setting of a high grade astrocytoma. The patient presented with complaints of confusion and left hemiparesis. An initial cerebral angiogram was normal. Repeat angiography six weeks later demonstrated an extremely vascular lesion with arteriovenous shunting involving the right thalamus and occipital lobe. Histopathologic evaluation of open biopsy and autopsy specimens demonstrated a high grade astrocytoma in association with an arteriovenous malformation. Immunohistochemical staining with VEGF was diffusely positive. A possible role for the hyperangiogenic environment of a high grade astrocytoma resulting in the development of an arteriovenous malformation is discussed.

Stereotactic radiosurgery in patients with multiple brain metastases.

OBJECT: Patients with multiple brain metastases are often treated primarily with fractionated whole-brain radiation therapy (WBRT). In previous reports the authors have shown that patients with four or fewer brain metastases can benefit from stereotactic radiosurgery in addition to fractionated WBRT. In this paper the authors review their experience using linear accelerator stereotactic radiosurgery to treat patients with multiple brain metastases. METHODS: Fifty-three patients with 149 brain metastases underwent stereotactic radiosurgery. The mean age of patients was 53.1 years (range 20-78 years). There were 23 men and 30 women. The primary tumor location was lung (27 patients), melanoma (10), breast (six), ovary (six), and other (four). All patients harbored at least two metastatic tumors treated with radiosurgery; 27 patients (51%) harbored two lesions, 17 (32%) three lesions, eight (15%) four lesions, and one patient (2%) harbored five lesions. The mean radiation dose administered was 19.6 Gy (range 14-30 Gy), and the mean secondary collimator size was 15.7 mm (range 7.5-40 mm). One hundred thirty-two (89%) of the 149 treated tumors were available for review on magnetic resonance (MR) imaging at 3 months posttreatment. Fifty-two percent were smaller in size, 31% were stable, 9% had increased in size, and 8% had disappeared. New metastatic tumors appeared in 12 (23%) of the 53 patients on MR imaging within 6 months posttreatment. Radiation-induced necrosis occurred at the site of eight (5.4%) of the 149 tumors at 6 months. Seven tumors (4.7%) subsequently required surgical resection for either tumor progression (four cases) or worsening edema from radiation-induced necrosis (three cases). Median actuarial survival was 9.6 months. CONCLUSIONS: Stereotactic radiosurgery can be used to treat patients with up to four brain metastases with a 91% rate of either decrease or stabilization in tumor size and a low rate of radiation-induced necrosis. In the authors' study only a small number of patients subsequently required surgical resection of a treated lesion.

Current treatment of patients with multiple brain metastases.

The management of patients with multiple brain metastases remains a difficult challenge for neurosurgeons. This patient population has a poor prognosis when compared with those harboring a solitary brain metastasis, and historically treatment has generally consisted of administering whole-brain radiotherapy once the diagnosis of multiple brain metastases is made. Resection can be useful in a subset of patients with multiple metastases in whom one or two of the lesions are symptomatic, as this may provide rapid reduction of mass effect and edema. Furthermore, the authors of recent studies have shown that stereotactic radiosurgery can be used in certain patients with multiple brain metastases as part of the treatment regimen. In this review the authors outline the treatment options and indications as well as a management strategy for the treatment of patients with multiple brain metastases.

Fractionated stereotactic radiosurgery and preservation of hearing in patients with vestibular schwannoma: a preliminary report.

OBJECTIVE: Microsurgery and stereotactic radiosurgery (SRS) for vestibular schwannomas are associated with a relatively high incidence of sensorineural hearing loss. A prospective trial of fractionated SRS was undertaken in an attempt to preserve hearing and minimize incidental cranial nerve injury. METHODS: Thirty-three patients with vestibular schwannomas were treated with 2100 cGy in three fractions during a 24-hour period using conventional frame-based linear accelerator radiosurgery. The median tumor diameter was 20 mm (range, 7-42 mm). Baseline and follow-up evaluations included audiometry and contrast-enhanced magnetic resonance imaging. End points were tumor progression, preservation of serviceable hearing, and treatment-related complications. RESULTS: Thirty-one patients (32 tumors) were assessable for tumor progression and treatment-related complications and 21 patients for preservation of serviceable hearing, with a median follow-up interval of 2 years (range, 0.5-4.0 yr). Tumor regression or stabilization was documented in 30 patients (97%) and tumor progression in 1 (3%). The patient with tumor progression remains asymptomatic and has not required surgical intervention. Five patients (16%) developed trigeminal nerve injury at a median of 6 months (range, 4-12 mo) after SRS; two of these patients had preexisting trigeminal neuropathy. One patient (3%) developed facial nerve injury (House-Brackmann Class 3) 7 months after SRS. Preservation of useful hearing (Gardner-Robertson Class 1-2) was 77% at 2 years. All patients with pretreatment Gardner-Robertson Class 1 to 2 hearing maintained serviceable (Class 1-3) hearing as of their last follow-up examination. CONCLUSION: Three-fraction SRS with a conventional stereotactic frame is feasible and well tolerated in the treatment of acoustic neuroma. This study demonstrates a high rate of hearing preservation and few treatment-related complications among a relatively high-risk patient cohort (tumors >15 mm or neurofibromatosis Type 2). Longer follow-up will be required to assess the durability of tumor control.

Remote-rendered 3D CT angiography (3DCTA) as an intraoperative aid in cerebrovascular neurosurgery.

OBJECTIVE: To assess the viability and utility of network-based rendering in the treatment of patients with cerebral aneurysms, we implemented an intraoperative rendering system and protocol using both three-dimensional CT angiography (3DCTA) and perspective volume rendering (PVR). MATERIALS AND METHODS: A Silicon Graphics InfiniteReality engine was connected via a Fast Ethernet network to a workstation in the neurosurgical operating room. A protocol was developed to isolate bone and vessels using an appropriate transfer function. Three-dimensional CT angiogram images were volume rendered and transmitted to the workstation using a bandwidth-conserving remote rendering system, and were rotated, cut using clipping planes, and viewed using normal and perspective views. Twelve patients with intracranial aneurysms were examined at surgery using this system. RESULTS: Rendering performance at optimal operating bandwidths (50-60 Mb/s) was excellent, with regeneration of a high-resolution image in less than 1 s. Network performance varied in two cases, slowing image regeneration. Surgeons found the images to be useful as an adjunct to conventional imaging in understanding the morphology of complex aneurysms and their relationship to the skull base. CONCLUSIONS: Intraoperative volume rendering using 3DCTA is achievable over a network, can reduce hardware costs by amortizing hardware among multiple users, and provides useful imaging information during the surgical treatment of cerebral aneurysms. Future operating suites may incorporate network-transmitted three-dimensional images as additional sources of imaging information.

Stereotactic radiosurgical boost following radiotherapy in primary nasopharyngeal carcinoma: impact on local control.

PURPOSE: Treatment of patients with nasopharyngeal carcinoma using external beam radiation therapy (EBRT) alone results in significant local recurrence. Although intracavitary brachytherapy can be used as a component of management, it may be inadequate if there is extension of disease to the skull base. To improve local control, stereotactic radiosurgery was used to boost the primary tumor site following fractionated radiotherapy in patients with nasopharyngeal carcinoma. METHODS AND MATERIALS: Twenty-three consecutive patients were treated with radiosurgery following radiotherapy for nasopharyngeal carcinoma from 10/92 to 5/98. All patients had biopsy confirmation of disease prior to radiation therapy; Stage III disease (1 patient), Stage IV disease (22 patients). Fifteen patients received cisplatinum-based chemotherapy in addition to radiotherapy. Radiosurgery was delivered using a frame-based LINAC as a boost (range 7 to 15 Gy, median 12 Gy) following fractionated radiation therapy (range 64.8 to 70 Gy, median 66 Gy). RESULTS: All 23 patients (100%) receiving radiosurgery as a boost following fractionated radiation therapy are locally controlled at a mean follow-up of 21 months (range 2 to 64 months). There have been no complications of treatment caused by radiosurgery. However, eight patients (35%) have subsequently developed regional or distant metastases. CONCLUSIONS: Stereotactic radiosurgical boost following fractionated EBRT provides excellent local control in advanced stage nasopharynx cancer and should be considered for all patients with this disease. The treatment is safe and effective and may be combined with cisplatinum-based chemotherapy.

Symptomatic vasospasm after resection of a suprasellar pilocytic astrocytoma: case report and possible pathogenesis.

BACKGROUND: Cerebral vasospasm from pathology other than subarachnoid hemorrhage is uncommon. A case of severe vasospasm after resection of a suprasellar pilocytic astrocytoma is reported. METHODS: A 45-year-old male presented with headache, left facial numbness, bilateral visual loss, and ataxia. Evaluation revealed a large suprasellar tumor, which was resected. Pathologic examination showed pilocytic astrocytoma. The patient developed hemiparesis and aphasia on the fifth postoperative day. Vascular spasm was documented on angiography and by transcranial Doppler. RESULTS: Intraarterial papaverine resulted in moderate angiographic improvement. Attempts to open middle cerebral artery branches with angioplasty were unsuccessful. The patient subsequently developed a left middle cerebral artery infarct. CONCLUSIONS: To our knowledge, this is the first description of vasospasm after resection of an astrocytoma. Possible mechanisms contributing to this unusual complication after resection of tumors are discussed.

Percutaneous transfemoral embolization of an indirect carotid-cavernous fistula with cortical venous access to the cavernous sinus. Case report.

The authors present the case of a 61-year-old man with an indirect carotid-cavernous fistula (CCF). Many now advocate a primary transvenous approach to deal with such lesions, with packing and thrombosis of the cavernous sinus leading to fistula obliteration. Transvenous access to the cavernous sinus via the inferior petrosal sinus is the usual route of access; both surgical and transfemoral superior ophthalmic vein approaches are also well described. In the case presented, the anatomy of the CCF was unfavorable for these approaches and its dominant venous egress was via a single enlarged arterialized cortical vein. The cavernous sinus was accessed with a transfemoral retrograde approach to the cortical draining vein. Successful CCF embolization was documented radiographically and clinically. To the authors' knowledge, this procedure has not been previously described in the English literature.

Treatment of nasopharyngeal carcinoma: stereotactic radiosurgical boost following fractionated radiotherapy.

Treatment of patients with nasopharyngeal carcinoma (NPC) using external beam radiation therapy (XRT) alone results in significant local recurrence. To improve local control, stereotactic radiosurgery (SRS) was used to boost radiation to the primary tumor site following XRT in 23 patients with NPC. SRS was delivered utilizing a frame-based linear accelerator as a boost (range 7-15 Gy, median 12 Gy) following XRT (range 64.8- 70 Gy, median 66 Gy). In all 23 patients (100%) receiving SRS following XRT local control was achieved at a mean follow-up of 21 months (range 2-64 months). There have been no complications of treatment caused by SRS. However, 8 patients (35%) have subsequently developed regional or distant metastases. SRS boost following XRT provides excellent local control in NPC and should be considered for patients with skull base involvement.

Intracranial nasal dermoid sinus cyst associated with colloid cyst of the third ventricle. Case report and new concepts.

A case of a 16-year-old male with both a nasal dermoid sinus cyst (NDSC) and a third ventricle colloid cyst is presented. The NDSC was excised via a single-stage combined intracranial-extracranial approach and the third ventricle colloid cyst was resected endoscopically. The pathogenetic theories of NDSC and third ventricle colloid cyst are discussed, and an embryological explanation for the simultaneous development of the two lesions in this patient is explored. This case is best classified among congenital developmental malformations in a category we propose to call 'anterior neuropore corridor defects.'

CARABEAMER: a treatment planner for a robotic radiosurgical system with general kinematics.

Stereotactic radiosurgery is a minimally invasive procedure that uses a focused beam of radiation as an ablative instrument to destroy brain tumors. To deposit a high dose of radiation in a tumor, while reducing the dose to healthy tissue, a large number of beams are crossfired at the tumor from multiple directions. The treatment planning problem (also called the inverse dosimetry problem) is to compute a set of beams that produces the desired dose distribution. So far its investigation has focused on the generation of isocenter-based treatments in which the beam axes intersect at a common point, the isocenter. However this restriction limits the applicability of the treatments to tumors which have simple shapes. This paper describes CARABEAMER, a new treatment planner for a radiosurgical system in which the radiation source can be arbitrarily positioned and oriented by a six-degree-of-freedom manipulator. This planner uses randomized techniques to guess a promising initial set of beams. It then applies space partitioning and linear programming techniques to compute the energy to be delivered along each beam. Finally, it exploits the results of the linear program to iteratively adapt and improve the beam set. Experimental results obtained with CARABEAMER on both patient and synthetic cases are presented and discussed. These results demonstrate that a radiosurgical system with general kinematics can deliver treatments in which the region receiving a high dose closely matches the shape of the tumor, even in complicated cases. They also suggest new research directions which are discussed at the end of the paper.

Treatment of cavernous sinus tumors with linear accelerator radiosurgery.

Since 1989, 79 patients with benign or malignant cavernous sinus tumors, have been treated at Stanford University with linear accelerator (linac) radiosurgery. Radiosurgery has been used as (1) a planned second-stage procedure for residual tumor following surgery, (2) primary treatment for patients whose medical conditions preclude surgery, (3) palliation of malignant lesions, and (4) definitive treatment for small, well-localized, poorly accessible tumors. Mean patient age was 52 years (range, 18 to 88); there were 28 males and 51 females. Sixty-one patients had benign tumors; 18 had malignant tumors. Mean tumor volume was 6.8 cm(3) (range 0.5 to 22.5 cm(3)) covered with an average of 2.3 isocenter (range, 1 to 5). Radiation dose averaged 17.1 Gy. Mean follow-up was 46 months. Tumor control or shrinkage, or both, varied with pathology. Radiographic tumor improvement was most pronounced in malignant lesions, with greater than 85% showing reduction in tumor size; benign tumors (meningiomas and schwannomas) had a 63% control rate and 37% shrinkage rate, with none enlarging. We concluded that stereotactic radiosurgery is a valuable tool in managing cavernous sinus tumors. There was excellent control and stabilization of benign tumors and palliation of malignant lesions.