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William A. Friedman, David L. Blatt, Frank J. Bova, John M. Buatti, William M. Mendenhall and Paul S. Kubilis

✓ Two hundred and one patients with arteriovenous malformations (AVMs) treated radiosurgically between May 1988 and February 1995 are analyzed in this study. Twelve patients sustained a posttreatment hemorrhage during this period. Pretreatment factors associated with increased hemorrhage risk were identified in 11 of these patients and included arterial aneurysms, venous aneurysms, venous outflow obstruction, periventricular location, prior embolization, and prior surgical treatment. A detailed statistical analysis, using both Poisson regression and parametric survival regression techniques, was undertaken to determine whether radiosurgery had any effect on the risk of hemorrhage, when compared to the natural history of the disease, in those patients in whom a complete angiographic cure was not achieved. No evidence was found to support a statistically significant departure from the natural hemorrhage rate at any time period after radiosurgical treatment. Significant risk factors for hemorrhage appeared to correlate with increasing AVM volume.

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William M. Mendenhall, William A. Friedman, John M. Buatti and Francis J. Bova

✓ In this paper the authors evaluate the results of linear accelerator (LINAC)—based stereotactic radiosurgery for acoustic schwannomas.

Fifty-six patients underwent LINAC-based stereotactic radiosurgery for acoustic schwannomas at the University of Florida between July 1988 and November 1994. Each patient was followed for a minimum of 1 year or until death; no patient was lost to follow up. One or more follow-up magnetic resonance images or computerized tomography scans were obtained in 52 of the 56 patients. Doses ranged between 10 and 22.5 Gy with 69.6% of patients receiving 12.5 to 15 Gy. Thirty-eight patients (68%) were treated with one isocenter and the dose was specified to the 80% isodose line in 71% of patients.

Fifty-five patients (98%) achieved local control after treatment. The 5-year actuarial local control rate was 95%. At the time of analysis, 48 patients were alive and free of disease, seven had died of intercurrent disease, and one was alive with disease. Complications developed in 13 patients (23%). The likelihood of complications was related to the dose and treatment volume: 10 to 12.5 Gy to all volumes, three (13%) of 23 patients; 15 to 17.5 Gy to 5.5 cm3 or less, two (9%) of 23 patients; 15 to 17.5 Gy to more than 5.5 cm3, five (71%) of seven patients; and 20 to 22.5 Gy to all volumes, three (100%) of three patients.

Linear accelerator—based stereotactic radiosurgery results in a high rate of local control at 5 years. The risk of complications is related to the dose and treatment volume.

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Thomas L. Ellis, William A. Friedman, Frank J. Bova, Paul S. Kubilis and John M. Buatti

Object. The aim of this study was to evaluate the causes of treatment failure in patients with arteriovenous malformations (AVMs) who underwent radiosurgery, which is increasingly used as a treatment method for selected, surgically high-risk AVMs. Unfortunately, radiosurgical treatment fails in a small but significant percentage of patients. In the time period covered in this study, 72 patients attained angiographically confirmed cures after radiosurgery and 36 were retreated after the initial radiosurgical treatment failed.

Methods. Using a computerized image fusion technique, the initial radiosurgical dosimetry plan was superimposed on the remaining AVM nidus at the time of retreatment. Twenty-six percent of the retreated cases were found to have AVM niduses outside the original treatment isodose line, which means that targeting error was a factor. The retreated group was also statistically compared with the cured group.

Conclusions. Multivariate analysis revealed that the following factors were statistically significant predictors of treatment failure: increasing AVM size, decreasing treatment dose, and increasing Spetzler—Martin grade.

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Kelly D. Foote, William A. Friedman, John M. Buatti, Sanford L. Meeks, Frank J. Bova and Paul S. Kubilis

Object. The aim of this study was to identify factors associated with delayed cranial neuropathy following radiosurgery for vestibular schwannoma (VS or acoustic neuroma) and to determine how such factors may be manipulated to minimize the incidence of radiosurgical complications while maintaining high rates of tumor control.

Methods. From July 1988 to June 1998, 149 cases of VS were treated using linear accelerator radiosurgery at the University of Florida. In each of these cases, the patient's tumor and brainstem were contoured in 1-mm slices on the original radiosurgical targeting images. Resulting tumor and brainstem volumes were coupled with the original radiosurgery plans to generate dose—volume histograms. Various tumor dimensions were also measured to estimate the length of cranial nerve that would be irradiated. Patient follow-up data, including evidence of cranial neuropathy and radiographic tumor control, were obtained from a prospectively maintained, computerized database. The authors performed statistical analyses to compare the incidence of posttreatment cranial neuropathies or tumor growth between patient strata defined by risk factors of interest. One hundred thirty-nine of the 149 patients were included in the analysis of complications. The median duration of clinical follow up for this group was 36 months (range 18–94 months). The tumor control analysis included 133 patients. The median duration of radiological follow up in this group was 34 months (range 6–94 months).

The overall 2-year actuarial incidences of facial and trigeminal neuropathies were 11.8% and 9.5%, respectively. In 41 patients treated before 1994, the incidences of facial and trigeminal neuropathies were both 29%, but in the 108 patients treated since January 1994, these rates declined to 5% and 2%, respectively.

An evaluation of multiple risk factor models showed that maximum radiation dose to the brainstem, treatment era (pre-1994 compared with 1994 or later), and prior surgical resection were all simultaneously informative predictors of cranial neuropathy risk. The radiation dose prescribed to the tumor margin could be substituted for the maximum dose to the brainstem with a small loss in predictive strength. The pons—petrous tumor diameter was an additional statistically significant simultaneous predictor of trigeminal neuropathy risk, whereas the distance from the brainstem to the end of the tumor in the petrous bone was an additional marginally significant simultaneous predictor of facial neuropathy risk.

The overall radiological tumor control rate was 93% (59% tumors regressed, 34% remained stable, and 7.5% enlarged), and the 5-year actuarial tumor control rate was 87% (95% confidence interval [CI] 76–98%). Analysis revealed that a radiation dose cutpoint of 10 Gy compared with more than 10 Gy prescribed to the tumor margin yielded the greatest relative difference in tumor growth risk (relative risk 2.4, 95% CI 0.6–9.3), although this difference was not statistically significant (p = 0.207).

Conclusions. Five points must be noted. 1) Radiosurgery is a safe, effective treatment for small VSs. 2) Reduction in the radiation dose has played the most important role in reducing the complications associated with VS radiosurgery. 3) The dose to the brainstem is a more informative predictor of postradiosurgical cranial neuropathy than the length of the nerve that is irradiated. 4) Prior resection increases the risk of late cranial neuropathies after radiosurgery. 5) A prescription dose of 12.5 Gy to the tumor margin resulted in the best combination of maximum tumor control and minimum complications in this series.

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Timothy C. Ryken, Sanford L. Meeks, Vincent Traynelis, John Haller, Lionel G. Bouchet, Francis J. Bova, Edward C. Pennington and John M. Buatti

Object

The relatively stationary anatomy of the intracranial compartment has allowed the development of stereotactic radiosurgery as an effective treatment option for many intracranial lesions. Difficulty in accurately tracking extracranial targets has limited its development in the treatment of these lesions. The ability to track extracranial structures in real time with ultrasound images allows a system to upgrade and interface pretreatment volumetric images for extracranial applications. In this report the authors describe this technique as applied to the treatment of localized metastatic spinal disease.

Methods

The extracranial stereotactic system consists of an optically tracked ultrasonography unit that can be registered to a linear accelerator coordinate system. Stereotactic ultrasound images are acquired following patient positioning, based on a pretreatment computerized tomography (CT) simulation. The soft-tissue shifts between the virtual CT-based treatment plan and the actual treatment are determined. The degree of patient offset is tracked and used to correct the treatment plan.

The ultrasonography-based stereotactic navigation system is accurate to within an approximate means of 1.5 mm based on testing with an absolute coordinate phantom. A radiosurgical treatment was delivered using the system for localization of a metastatic spinal lesion. Compared with the virtual CT simulation, the actual treatment plan isocenter was shifted 12.2 mm based on the stereotactic ultrasound image. The patient was treated using noncoplanar beams to a dose of 15.0 Gy to the 80% isodose shell in a single fraction.

Conclusions

A system for high-precision radiosurgical treatment of metastatic spinal tumors has been developed, tested, and applied clinically. Optical tracking of the ultrasonography probe provides real-time tracking of the patient anatomy and allows computation of the target displacement prior to treatment delivery. The results reported here suggest the feasibility and safety of the technique.

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John M. Buatti and William A. Friedman

Object. The authors used an alternative strategy to avoid shunt placement for hydrocephalus associated with germinoma, and the ensuing complications.

Methods. Between 1998 and 2000, five patients presenting with germinomas of the pineal area and symptomatic obstructive hydrocephalus were treated with a novel strategy. On arrival, they underwent ventriculostomy placement and one of several surgical procedures to obtain tissue for diagnosis. Within several days of the initial diagnosis, stereotactically guided fractionated radiotherapy was started. All patients experienced rapid tumor shrinkage and resolution of hydrocephalus, allowing discontinuation of external ventricular drainage without the need for permanent shunting of cerebrospinal fluid. To date, follow up reveals 100% radiographically and clinically confirmed tumor control.

Conclusions. Prompt resolution of hydrocephalus and absence of complications make this a potentially valuable therapy for control of germinomas and their symptoms.

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Kelly D. Foote, William A. Friedman, Thomas L. Ellis, Frank J. Bova, John M. Buatti and Sanford L. Meeks

Object. The goal of this study was to evaluate the outcomes of patients who underwent repeated radiosurgery to treat a residual intracranial arteriovenous malformation (AVM) after an initial radiosurgical treatment failure.

Methods. The authors reviewed the cases of 52 patients who underwent repeated radiosurgery for residual AVM at the University of Florida between December 1991 and June 1998. In each case, residual arteriovenous shunting persisted longer than 36 months after the initial treatment; the mean interval between the first and second treatment was 41 months. Each AVM nidus was measured at the time of the original treatment and again at the time of retreatment, and the dosimetric parameters of the two treatments were compared. After retreatment, patients were followed up and their outcomes were evaluated according to a standard posttreatment protocol for radiosurgery for AVMs.

The mean original lesion volume was 13.8 cm3 and the mean volume at retreatment was 4.7 cm3, for an average volume reduction of 66% after the initial treatment failure. Only two AVMs (3.8%) failed to demonstrate size reduction after the primary treatment. The median doses on initial and repeated treatment were 12.5 and 15 Gy, respectively. Five patients were lost to follow up and five refused neuroimaging follow up. One patient died of a hemorrhage shortly after retreatment. Of the remaining 41 patients, 24 had evidence of cure, 15 on angiographic studies and nine on magnetic resonance (MR) images. Seventeen had evidence of treatment failure, 10 on angiographic studies and seven on MR images. By angiographic criteria alone, the cure rate after retreatment was 60%, whereas according to angiographic and MR imaging results, the cure rate was 59%.

Conclusions. Although initial radiosurgical treatment failed to obliterate the AVM in these 52 patients, it did produce a substantial therapeutic effect (volume reduction). This size reduction commonly allowed higher doses to be delivered during radiosurgical retreatment. The results show rates of angiographically confirmed cure comparable to primary treatment and a low incidence of complications, indicating that salvage radiosurgical retreatment is a safe and effective therapy in cases of failed AVM radiosurgery.