Stereotactic radiosurgery for intracranial arteriovenous malformations using a standard linear accelerator

We have previously described the development of a technique which utilizes a standard linear accelerator to provide stereotactic, limited field radiation. The radiation is delivered using a modified and carefully calibrated 6 MV linear accelerator. Precise target localization and patient immobilization is achieved using a Brown-Roberts-Wells (BRW) stereotactic head frame which is in place during angiography, CT scanning, and treatment. Seventeen arteriovenous malformations (AVMs) have been treated in 16 patients from February 1986 to July 1988. Single doses of 1500-2500 cGy were delivered using multiple non-coplanar arcs with small, sharp edged x-ray beams to lesions less than 2.7 cm in greatest diameter. The dose distribution from this technique has a very rapid dropoff of dose beyond the target volume. Doses were prescribed at the periphery of the AVMs, typically to the 80-90% isodose line. Eleven of 16 patients have been followed by repeat angiography at least 1 year following treatment. Five of 11 have had complete obliteration of their AVM in 1 year and an additional three patients have achieved complete obliteration by 24 months. There have been no incidences of rebleeding or serious complications in any patient. We conclude that stereotactic radiosurgery using a standard linear accelerator is an effective and safe technique in the treatment of intracranial AVMs and the results compare favorably to the more expensive and elaborate systems that are currently available for stereotactic treatments.     

Quality assurance in stereotactic radiosurgery using a standard linear accelerator

Methods have recently been developed for using standard linear accelerators to perform stereotactic radiosurgery. The accuracy necessary to perform this procedure requires an intensive quality assurance program to encompass all aspects of dose calibration and mechanical integrity of the treatment unit, the treatment planning process, and treatment delivery. The programs developed at the Joint Center for Radiation Therapy (JCRT) include testing of the linear accelerator and the stereotactic system, cross checking of the treatment planning process, and a quality assurance check list of the treatment delivery procedure. This report outlines in detail the quality assurance program currently in use at the JCRT.     

Stereotactic irradiation using a linear accelerator for brain metastasis from renal cell carcinoma

Background The role of stereotactic irradiation using a linear accelerator for brain metastasis from renal cell carcinoma was investigated. Methods Fifteen brain metastases in 11 patients with a history of renal cell carcinoma were treated using convergent narrow x-ray beams from a linear accelerator and rigid fixation of the head with a stereotactic frame. Twelve metastatic tumors in8 patients were irradiated with 25 Gy at the center in a single fraction, and single tumors in 3 patients received the following doses: 25 Gy in 5 fractions, 28 Gy in 3 fractions, or 35 Gy in 4 fractions Results The actuarial local control rate at 12 months was 90.6%. Twelve (92%) of 13 lesions that produced neurologic symptoms before stereotactic irradiation showed an improvement of symptoms. No complication related to the irradiation was observed. The median survival time was 6 months. Conclusion Stereotactic irradiation is more effective in achieving local control than is conventional radiotherapy, and achieves improvement in symptoms and survival rates similar to those of surgical resection of the brain metastasis from renal cell carcinoma. Urologists and oncologists should be aware of the usefulness of stereotactic radiation in the management of patients with renal cell carcinoma.     

Radiosurgery for arteriovenous malformations of the brain using a standard linear accelerator: rationale and technique

We have recently initiated a program for irradiating small, unresectable arteriovenous malformations (AVM's) in the brain. The treatments are delivered using a modified and carefully calibrated 6 MV linac. We are using high, single doses (15 to 25 Gy) with a goal of sclerosing the vessels and preventing hemorrhages. This technique, radiosurgery, is somewhat controversial in the radiotherapy community. Since the treatment is given in a single sitting, rather than in the more conventional pattern of multiple small daily fractions, there is some concern about late radiation damage to the normal brain tissue. However an extensive review of the literature leads us to the conclusion that if a technique is used that keeps the volume irradiated to high dose small, radiosurgery is a safe and efficacious treatment for small (less than 2.5 cm) AVM's. To decrease the risk of necrosis of normal brain tissue, it is important to confine the high dose region as tightly as possible to the target volume. Precise target localization and patient immobilization is achieved using a stereotactic head frame which is used during angiography, CT scanning, and during the radiation treatment. This minimizes the margin of safety that must be added to the target volume for errors in localization and set-up. The treatment is delivered using multiple noncoplanar arcs, with small, sharp edged X ray beams, and with the center of the AVM at isocenter. This produces a rapid dropoff of dose beyond the target volume. Early results in our first few patients are encouraging.     

Stereotactic percutaneous single dose irradiation of brain metastases with a linear accelerator

The effectivity of stereotactic percutaneous single dose irradiations in the treatment of solitary brain metastases has been assessed in a series of 12 consecutive patients. Only radioresistant deeply localized metastases have been treated. Photon-irradiation was carried out with the convergent beam technique using stereotactic localization methods, in a linear accelerator facility. In 11 of the 12 patients no side effects occurred. The first 7 patients, who could be observed 3 months or longer, have been studied in detail. In each of these cases single dose irradiation with 20-30 Gy yielded arrest of tumor growth. In one case a marked decrease in contrast enhancement and in four cases shrinkage of the metastasis as well as a marked decrease of the edema occurred. In every patient a marked, sometimes dramatic improvement of the clinical condition was achieved, beginning a few days after irradiation. Stereotactic radiosurgery is a valuable tool in the treatment of inoperable, radioresistant brain metastases, the major advantage being high efficacy and smoothness of the procedure, as well as extremely short hospitalization times (2-3 days).     

Risk analysis of linear accelerator radiosurgery

To evaluate the toxicity of steriotactic single-dose irradiation and to compare the own results with already existing risk prediction models.

Computed tomography (CT) or magnetic-resonance (MR) images, and clinical data of 133 consecutive patients treated with linear accelerator radiosurgery were analyzed retrospectively. Using the Cox proportional hazards model the relevance of treatment parameters and dose-volem relationships on the occurrence of radiation-induced tissue changes (edema, localized blood-brain barrier breakdown) were assessed.

Sixty-two intraparenchymal lesions (arteriovenous malformation (AVM): 56 patients, meningioma: 6 patients) and 73 skull base tumors were selected for analysis. The median follow-up was 28.1 months (range: 9.0–58.9 months). Radiation-induced tissue changes (32 out of 135, 23.7%) were documented on CT or MR images 3.6–58.7 months after radiosurgery (median time: 17.8 months). The actuarial risk at 2 years for the development of neuroradiological changes was 25.8% for all evaluated patients, 38.4% for intraparenchymal lesions, and 14.6% for skull base tumors. The coefficient: total volume receiving a minimum dose of 10 Gy (VTREAT10) reached statistical significance in a Cox proportional hazards model calculated for all patients, intraparenchymal reached statistical significance in a Cox proportional hazards model calculated for all patients, intraparenchymal lesions, and AVMs. Is skull base tumors, the volume of normal brain tissue covered by the 10 Gy isodose line (VBRAIN10) was the only significant variable.

These results demonstrate the particular vulnerability of normal brain tissue to single dose irradiation. Optimal conformation of the therapeutic isodose line to the 3D configuration of the target volume may help to reduce side effects.     

Stereotactic radiosurgery, X: clinical isodosimetry of gamma knife versus linear accelerator X-knife for pituitary and acoustic tumours

Several review articles have compared gamma unit versus linear accelerator (linac)-based radiosurgery systems, concluding that the dose gradient 'fall-off' at the margin of the target (expressed as the distance between isodoses) is very similar for both techniques as far as single isocentre treatment volumes up to 1.5 cm diameter are concerned, and that the two radiosurgical systems are, in general, comparable. 'Fine tuning' of the gamma unit can be carried out by using multiple isocentre plans, the differential use of small collimator sizes (down to 4 mm) and field weightings, and adroit use of the gamma angle, and selective beam blocking. Multiple isocentre plans, beam modification, restriction of gantry angles and arc lengths, and microcollimation can similarly improve the isodose gradients from linac units. In both instances, the dosimetric advantages occur along selected aspects of the target perimeter border. However, the more frequent use of multiple isocentred 'shots' on the gamma unit achieves greater conformity indices for more complex target volumes, but at the expense of steeper internal dose gradients. We studied two patients with tumours close to or arising from radiosensitive special sensory nerves (optic and cochlear) to compare and contrast fine tuning of the two technologies. In a previously irradiated patient with a pituitary adenoma, the dose gradient achieved at the rostral margin, adjacent to the optic chiasma, was steeper on the gamma unit (due to the concentration of small collimator shots rostrally and beam blocking), which was therefore the dosimetrically preferred technique. In contrast, the vastly smaller internal dose gradient (11% for linac/X-knife versus 100% for Gamma Knife) and the ability to fractionate on the X-knife system, gave a large dosimetric advantage to the X-knife plan in the treatment of an acoustic neuroma, where the intracanalicular component of the cochlear nerve traversed the target volume. This advantage also pertains to the cochlear ramus of the internal auditory (labyrinthine) artery and the facial nerve. Our published work on X-knife radiosurgery of acoustic neuroma has documented improvement of hearing after therapy and may be relevant in this regard. That there are advantages in physical dose distribution and fractionation, producing a reduction in the biological dose in normal tissue, argues for the use of linac technology in acoustic neuromas. Craniopharyngiomas enveloping the optic nerve/chiasma will similarly be better treated by the linac X-knife system. It is apparent that different radiosurgery systems may be indicated in particular neuro-oncological situations.     

A system for stereotactic radiosurgery with a linear accelerator

A small field irradiation technique to deliver high doses of single fraction photon radiation to small, precisely located volumes (0.5 to 8 cm3) within the brain has been developed. Our method uses a modified Brown-Roberts-Wells (BRS), CT-guided, stereotactic system and a 6 MV linear accelerator equipped with a special collimator (diameters of 12.5 mm to 30.0 mm projected to isocenter) located 23 cm from isocenter. Target localization via planar angiography has been added. Treatment consists of a series of arcing beams using both gantry and couch rotations. During treatment, the patient's head is immobilized independently of the radiotherapy couch and is precisely positioned without reference to room lasers or light field. A precise verification of alignment precedes each treatment. Extensive performance tests have shown that a target, localized by CT, can be irradiated with a positional accuracy of 2.4 mm in any direction with 95% confidence. If angiography is used for localization, the results are better. The dose 1.0 cm outside the target volume is less than 20% of the prescribed dose for a medium sized collimator.     

Stereotactic radiosurgery of petroclival meningiomas: a multicenter study

Petroclival meningiomas are difficult to treat due to their intimate location with critical structures, and complete microsurgical resection is often associated with significant morbidity. In this study, we evaluate the outcomes of petroclival meningiomas treated with Gamma Knife radiosurgery (GKRS) as an adjunct to microsurgery or a primary treatment modality. A multicenter study of 254 patients with a benign petroclival meningioma was conducted through the North American Gamma Knife Consortium. One hundred and forty patients were treated with upfront radiosurgery, and 114 following surgery. Multivariate analysis was used to determine predictors of favorable defined as no tumor progression following radiosurgery and the absence of any new or worsening neurological function. At mean follow up of 71 months (range 6–252), tumor volumes increased in 9 % of tumors, remained stable in 52 %, and decreased in 39 %. Kaplan–Meier actuarial progression free survival rates at 3, 5, 8, 10, and 12 years were 97, 93, 87, 84, and 80 % respectively. At last clinical follow-up, 93.6 % of patients demonstrated no change or improvement in their neurological condition whereas 6.4 % of patients experienced progression of symptoms. Favorable outcome was achieved in 87 % of patients and multivariate predictors of favorable outcome included smaller tumor volume (OR = 0.92; 95 % CI 0.87–0.97, p = 0.003), female gender (OR 0.37; 95 % CI 0.15–0.89, p = 0.027), no prior radiotherapy (OR 0.03; 95 % CI 0.01–0.36, p = 0.006), and decreasing maximal dose (OR 0.92; 95 % CI 0.96–0.98, p = 0.010). GKRS of petroclival meningiomas achieves neurological preservation in most patients and with a high rate of tumor control.     

Stereotactic radiosurgery for the treatment of brain metastases

Background: The objective of this systematic review was to summarise the current evidence concerning radiosurgical treatment (SRS) of newly diagnosed brain metastasis and to compare SRS as a single or additional treatment to treatment alternatives with regard to medical effectiveness and safety.Methods: A structured search of electronic databases was performed to identify relevant publications from 2002 through 2007. Studies targeting patients with brain metastases were included. Standardised quality assessment and data extraction were performed.Results: Of 1496 publications, 16 studies were included. The mean survival in most studies was less than 12 months. There was evidence that SRS plus WBRT was associated with improved local tumour control and neurological functioning compared to either treatment alone. Only in patients with single metastasis, this resulted in improved survival. There was inconclusive evidence when comparing SRS to WBRT, Neurosurgery (NS) or Hypofractionated Radiotherapy (HCSRT). The Quality of life (Qol) was not investigated.Conclusion: SRS plus WBRT was associated with improved local tumour control and neurological functioning compared to either treatment alone. Only in certain patients, this resulted in improved survival. Methodologically rigorous studies are therefore warranted to investigate further treatment options, and in view of the poor prognosis, to investigate Qol and neurological functioning.     

Stereotactic radiosurgery for brain metastases: results and prognostic factors

This study was conducted to determine prognostic factors for tumor response and patient survival after stereotactic radiosurgery (SRS) for brain metastasis. Eighty-four patients with brain metastasis underwent SRS at a single institution. After fixation of the head with a stereotactic frame, computed tomography treatment planning was performed. The metastatic lesion was treated with multiple arcs to a median dose of 19 Gy. Forty-seven patients (56%) had a solitary brain lesion. Fifty-nine patients (70%) had evidence of extracranial disease at the time of SRS. The median survival duration from SRS was 7 months. Sixty-three percent of the patients had an objective radiographic response to SRS, which in turn was associated with superior central nervous system control. Age, collimator size, number of arcs, tumor location, and histology did not influence objective response rates. Patients who had a solitary lesion or who received treatment within 2 weeks after diagnosis were more likely to have an objective response than were those who did not (P < 0.05). Progressive brain disease accounted for 37% of the deaths. Nineteen patients (23%) had an in-field relapse. Four severe complications were attributed to SRS. This study confirms the role of SRS as an acceptable treatment option for patients with solitary or limited brain metastases. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 157-162 (2000).     

Stereotactic radiosurgery in the treatment of brain metastases: The current evidence

Chemotherapy has made substantial progress in the therapy of systemic cancer, but the phar-macological efficacy is insufficient in the treatment of brain metastases. Fractionated whole brain radiotherapy (WBRT) has been a standard treatment of brain metastases, but provides limited local tumor control and often unsatisfactory clinical results. Stereotactic radiosurgery using Gamma Knife, Linac or Cyberknife has overcome several of these limitations, which has influenced recent treatment recommendations. This present review summarizes the current literature of single session radiosurgery concerning survival and quality of life, specific responses, tumor volumes and numbers, about potential treatment combinations and radioresistant metastases.     

X射线立体定向放射治疗配合全脑照射治疗脑转移瘤疗效分析

目的　分析X射线立体定向放射治疗(SRS)配合全脑照射治疗脑转移瘤的作用。方法　对55例脑转移瘤患者进行SRS配合全脑照射,17例行单纯SRS治疗。全脑照射采用8?MVX射线,1.5～2.0 Gy/次,DT30～42 Gy,4～5周;SRS处方剂量为18～30 Gy,SRS前行全脑放射治疗39例,SRS后行全脑放射治疗16例。结果　SRS加全脑照射组病变完全消失(CR)占60.0%,部分消失(PR)占32.7%,无变化(NC)占7.3%,总缓解率(CR+PR)为92.7%;与单纯SRS组的35.0%、41.2%、23.5%、76.2%相比差异无显著性意义（χ2=3.47,P＞0.05）。SRS加全脑照射组复发率为14.5%,中位复发时间为10个月,中位生存时间为13个月;与单纯SRS组的41.2%、4个月、7.5个月相比差异有显著性意义(χ     

Stereotactic radiosurgery of the postoperative resection cavity for brain metastases

PURPOSE: The purpose of this study was to analyze results of adjuvant stereotactic radiosurgery (SRS) targeted at resection cavities of brain metastases without whole-brain irradiation (WBI). METHODS AND MATERIALS: Patients who underwent SRS to the tumor bed, deferring WBI after resection of a brain metastasis, were retrospectively identified. RESULTS: Seventy-two patients with 76 cavities treated from 1998 to 2006 met inclusion criteria. The SRS was delivered to a median marginal dose of 18.6 Gy (range, 15-30 Gy) targeting an average tumor volume of 9.8 cm(3) (range, 0.1-66.8 cm(3)). With a median follow-up of 8.1 months (range, 0.1-80.5 months), 65 patients had follow-up imaging assessable for control analyses. Actuarial local control rates at 6 and 12 months were 88% and 79%, respectively. On univariate analysis, increasing values of conformality indices were the only treatment variables that correlated significantly with improved local control; local control was 100% for the least conformal quartile compared with 63% for the remaining quartiles. Target volume, dose, and number of sessions were not statistically significant. CONCLUSIONS: In this retrospective series, SRS administered to the resection cavity of brain metastases resulted in a 79% local control rate at 12 months. This value compares favorably with historic results with observation alone (54%) and postoperative WBI (80-90%). Given the improved local control seen with less conformal plans, we recommend inclusion of a 2-mm margin around the resection cavity when using this technique.     

Stereotactic radiosurgery for brain metastases from primary head and neck carcinomas: a retrospective analysis

Journal of Neuro-Oncology - Patients with head and neck malignancies commonly develop metastatic disease, yet rarely do these carcinomas metastasize to the brain. Stereotactic radiosurgery (SRS) is...     

Estimation of complications for linear accelerator radiosurgery with the integrated logistic formula

Radiosurgery techniques permit high doses of single fraction irradiation to be administered to small volumes of tumor with relative sparing of surrounding brain tissue. The tolerance of surrounding normal brain tissue to dose distributions from linear accelerator radiosurgery with different collimator sizes is an important factor that must be estimated by anyone using these treatment techniques. The exponential and linear quadratic versions of the integrated logistic formula were used to estimate the probability of brain necrosis at different doses for radiosurgical dose distributions administered by a 6 MV linear accelerator with a 5 arc technique for collimator sizes from 12.5 to 30 mm in diameter. Dose-volume isoeffect curves for a 3% risk of brain necrosis from linear accelerator radiosurgery were then calculated. These curves approximate those calculated for gamma knife radiosurgery and a published 1% dose-volume isoeffect line predicted for proton beam irradiation. Similar dose-volume isoeffect curves were calculated for single fraction radiosurgery boosts administered after 30 Gy of whole brain irradiation in 12 fractions. The integrated logistic formula appears to be a useful tool for estimating tolerance and providing guidelines for prescribing radiation doses for linear accelerator radiosurgery.