Immune Checkpoint Inhibition and Single Fraction Stereotactic Radiosurgery in Non-Small Cell Lung Cancer Brain Metastases: An International Multicenter Study of 395 Patients

PURPOSE/OBJECTIVE(S)

Brain metastases most commonly arise from non-small cell lung cancer (NSCLC). In recent years, immune checkpoint inhibitors (ICI) have demonstrated improvements in overall survival (OS) in NSCLC. However, concerns remain about the risk of radiation necrosis (RN) when ICI are administered with stereotactic radiosurgery (SRS).

MATERIALS/METHODS

Logistic regression was used to evaluate prognostic factors associated with the development of any grade RN and symptomatic RN. Cumulative incidence of RN was evaluated using competing risks analysis and the Fine and Gray model, where the null hypothesis was rejected for p < 0.05.

RESULTS

There were 395 patients with 2,513 brain metastases treated across 11 international institutions included in the analysis. The median follow-up was 14.2 months. Median patient age was 67 years (Interquartile Range [IQR]: 61-73), 53.4% were male, the median Karnofsky Performance Status was 80 (IQR: 80-90), and 88.6% has active extracranial disease at the time of SRS. The median margin dose was 19 Gy (IQR: 18-20), 97.5% of patients were treated on the Gamma Knife ®, 3.8% underwent prior whole brain radiation therapy (WBRT). The median V12 Gy was 5.2 cm3 and 36.5% of patients had a V12 Gy ≥ 10 cm3, anti-PD-1 agents were administered in 91.6% of patients. A V12 Gy ³ 10 cm3 was associated with an increased risk of developing any grade RN; odds ratio (OR): 2.12, p = 0.04 and OR: 2.18; p = 0.03 on univariable and multivariable analysis, respectively. Similarly, a V12 Gy ≥ 10 cm3 was associated with an increased risk of developing symptomatic RN; OR: 3.80, p = 0.003 and OR: 3.95; p = 0.003 on univariable and multivariable analysis, respectively. Receipt of concurrent ICI and prior WBRT were not statistically significant. At 1-year, the cumulative incidence of any grade and symptomatic RN was 4.8% and 3.8%, respectively. The cumulative incidence of any grade RN was 3.8% vs. 5.3% for the concurrent and non-concurrent groups at 1-year, respectively (p = 0.35). The cumulative incidence of symptomatic RN was 3.8% vs. 3.6% for the concurrent and non-concurrent groups at 1-year, respectively (p = 0.95).

CONCLUSION

The risk of any grade and symptomatic RN following SRS and ICI administration for NSCLC brain metastases increases as the V12 Gy exceeds 10 cm3. Concurrent ICI and SRS does not appear to increase this risk. Radiosurgical planning techniques should aim to minimize the V12 Gy.

CT versus MR Imaging in Estimating Cochlear Radiation Dose during Gamma Knife Surgery for Vestibular Schwannomas

BACKGROUND AND PURPOSE

Leksell stereotactic radiosurgery is an effective option for patients with vestibular schwannomas. Some centers use a combination of stereotactic CT fused with stereotactic MR imaging to achieve an optimal target definition as well as minimize the radiation dose delivered to adjacent structures that correlate with hearing outcomes. The present prospective study was designed to determine whether there is cochlear dose variability between MR imaging and CT.

MATERIALS AND METHODS

Fifty consecutive patients underwent stereotactic radiosurgery for vestibular schwannomas. Dose-planning was performed using high-definition fused stereotactic MR imaging and stereotactic CT images. The 3D cochlear volume was determined by delineating the cochlea on both CT and T2-weighted MR imaging. The mean radiation dose, maximum dose, and 3- and 4.20-Gy cochlear volumes were identified using standard Leksell Gamma Knife software.

RESULTS

The median mean radiation dose delivered to the cochlea was 3.50 Gy (range, 1.20-6.80 Gy) on CT and 3.40 Gy (range, 1-6.70 Gy) on MR imaging (concordance correlation coefficient = 0.86, r ² = 0.9, P ≤ .001). The median maximum dose delivered to the cochlea was 6.7 Gy on CT and 6.6 Gy on MR imaging (concordance correlation coefficient = 0.89, r ² = 0.90, P ≤ .001). Dose-volume histograms generated from CT and MR imaging demonstrated a strong level of correlation in estimating the 3- and 4.20-Gy volumes (concordance correlation coefficient = 0.81, r ² = 0.82, P ≤ .001 and concordance correlation coefficient = 0.87, r ² = 0.89, P ≤ .001).

CONCLUSIONS

Both MR imaging and CT provide similar cochlear dose parameters. Despite the reported superiority of CT in identifying bony structures, high-definition MR imaging alone is sufficient to identify the radiation doses delivered to the cochlea.

Facial nerve preservation and tumor control after gamma knife radiosurgery of unilateral acoustic tumors

To assess the long-term risk of facial nerve dysfunction after unilateral acoustic tumor stereotactic radiosurgery, we retrospectively analyzed our initial experience in 98 unilateral acoustic tumor patients who were evaluated at least 2 years after treatment. This observation interval permits an analysis of both the risk of onset and the potential for recovery of facial nerve function. The overall risk of developing any degree of delayed transient or permanent postoperative facial neuropathy was 21.4% (21 of 98 patients). Only one patient undergoing radiosurgery alone had poor residual facial nerve dysfunction worse than House-Brackmann grade III. Normal facial nerve function (House-Brackmann grade 1) was preserved in 95% of patients with small tumors (10 mm or less petrous-pons dimension) and in 90% of patients who had useful hearing and normal facial function preoperatively. Normal facial function was preserved in all patients with intracanalicular acoustic tumors. The risk of delayed facial neuropathy was reduced by performing radiosurgery when tumors were small (1000 mm(3) or less), by enclosing the tumor within the 50% isodose volume, by using multiple small radiation isocenters, and by detailed identification of the tumor volume using stereotactic magnetic resonance imaging.

Gamma knife radiosurgery for multiple sclerosis-related trigeminal neuralgia

BACKGROUND

Surgical options for multiple sclerosis (MS) related to trigeminal neuralgia (TN), a severe and disabling pain disorder, include percutaneous rhizotomy, stereotactic radiosurgery, or microsurgical nerve section. Our goal was to evaluate clinical outcomes after gamma knife radiosurgery (GKRS) in patients with MS with TN.

METHODS

We evaluated clinical outcomes in 37 patients with TN managed over a 12-year period. The maximum TN target dose varied between 70 and 90 Gy. Seventy-eight percent of patients had failed prior surgery. In 9, GKRS was the first procedure. Median follow-up was 56.7 months (range, 6-174). Pain relief was assessed in each patient by physicians who did not participate in the surgery.

RESULTS

Eventual complete pain relief (BNI grade I) after GKRS and reasonable pain control (BNI grade I-IIIb) after GKRS were noted in 23 patients (62.1%) and 36 patients (97.3%) at some point in their course. Reasonable pain control (BNI grade I-IIIb) after GKRS was maintained in 82.6%, 73.9%, and 54.0% of patients after 1, 3, and 5 years. Fourteen patients (37.8%) underwent a second or a subsequent procedure for residual or recurrent pain. Eight patients underwent a second GKRS, 5 underwent percutaneous glycerol rhizotomy, and 1 underwent balloon microcompression. The complication rate after GKRS was 5.4% (new onset of nondisabling paresthesias). No patient developed dysesthesias.

CONCLUSIONS

Gamma knife radiosurgery is the most minimally invasive surgical technique for multiple sclerosis-related trigeminal neuralgia and has low morbidity. For this reason, gamma knife radiosurgery proved to be a satisfactory management strategy for multiple sclerosis-related trigeminal neuralgia.

Fractionation of radiation treatment in acoustics. Rationale and evidence in comparison to radiosurgery

Stereotactic fractionated radiotherapy has been proposed as a strategy to improve upon the results of single-fraction radiosurgery. The rationale for the strategy is that fractionation will allow complciations to be reduced while maintaining the same degree of long-term tumor control. This paper reviews the radiobiological arguements for fractionating radiation treatment of acoustic neuromas and examines claims for improvement in outcome.

Acoustic neuroma radiosurgery. Origins, contemporary use and future expectations

Patients who have an acoustic neuroma (vestibular schwannoma) can be managed with observation, open surgical resection, stereotactic radiosurgery, or fractionated radiotherapy. Increasing numbers of patients are choosing radiosurgery over resection for their tumor. In this report we discuss the history of stereotactic radiosurgery, and the evolution in technique that has led to current results with this approach. We discuss the indications for and expectations with the different treatments. The literature on radiosurgery and radiotherapy is reviewed. It is expected that clinical and basic studies will further improve results.

External beam irradiation of craniopharyngiomas: long-term analysis of tumor control and morbidity

PURPOSE

To delineate the long-term control and morbidity with external beam radiotherapy (EBRT) of craniopharyngiomas.

METHODS AND MATERIALS

Between 1971 and 1992, 24 craniopharyngioma patients underwent EBRT at the University of Pittsburgh. Most (19 of 24) were treated within 1-3 months after subtotal resection. The other prior surgical procedures were biopsy (n = 2) and gross total resection (n = 1); 2 patients did not undergo any surgical procedure. The median follow-up was 12.1 years. The median patient age was 29 years (range 5-69). The total radiation doses varied from 36 to 70 Gy (median 59.75). The normalized total dose (NTD, biologically equivalent dose given in 2 Gy/fraction [alpha/beta ratio = 2]) varied from 28 to 83 Gy (median 55.35).

RESULTS

The actuarial survival rate at 10 and 20 years was 100% and 92.3%, respectively. The actuarial local control rate at 10 and 20 years was 89.1% and 54.0%, respectively. No local failures occurred with doses >or=60 Gy (n = 12) or NTDs >or=55 Gy. The complication-free survival rate at 10 and 20 years was 80.1% and 72.1%, respectively. No complications were noted with an NTD of <or=55 Gy. The actuarial survival free from any adverse outcome (recurrence or complication) was 70.1% and 31.8% at 10 and 20 years, respectively. The adverse outcome-free survival appeared optimized (at 73%) with an NTD of 55-63 Gy. Multivariate analysis found that tumor control correlated significantly with the total dose (p = 0.02), treatment complications with NTD (p = 0.008), and adverse outcome with hypopituitarism on presentation (p = 0.03).

CONCLUSION

We recommend treating craniopharyngioma with 1.6-1.7-Gy dose fractions to 60 Gy to optimize outcome from EBRT.

The case for and against AVM radiosurgery

AVM radiosurgery has been in practice for over 30 years and is now a common method to manage properly selected patients with brain AVMs. The techniques have been refined along with our understanding of the expected response. It is this understanding of expected outcomes that should allow a rational discussion of the pertinent issues for management of patients with AVMs. Some patients will require multimodality approaches. All AVM patients should seek to understand whether stereotactic radiosurgery is an appropriate option for their problem.

Tube angulation improves angiographic targeting of arteriovenous malformations during stereotactic radiosurgery

Stereotactic radiosurgery using the 201 Cobalt-60 source Gamma Knife has been an effective method for obliterating selected cerebral arteriovenous malformations (AVMs). For more than 20,000 patients worldwide, angiography under stereotactic conditions has been the main imaging modality for defining and targeting the AVM nidus. The role of angulation of the X-ray tube for angiographic localization of the AVM during stereotactic Gamma Knife radiosurgery was studied with a phantom. Using current dose-planning software, tube angulation facilitated target visualization, improved three-dimensional dose planning, and has been consistent with the increased probability of complete nidus obliteration.

Protective immune responses elicited in mice by immunization with formulations of poly(lactide-co-glycolide) microparticles

Parenteral administration of microparticle encapsulated DNA elicits immune responses to the encoded antigens. Experiments were performed to test whether the addition of certain lipophilic agents to such formulations enhanced the activity of a beta-galactosidase (beta-gal) DNA vaccine. Addition of either taurocholic acid (TA) or monomethoxy polyethylene-glycol-distearoylphosphatidylehanolamine (PEG-DSPE) increased the efficiency of DNA encapsulation. Immunization of mice with encapsulated DNA formulations containing either compound significantly increased the number of antibody positive responders over that achieved with non-lipid containing particles. Moreover, responding animals demonstrated trends towards higher antibody titers and increased T cell responses. Tumor protection against the CT26.CL25 tumor cell line was demonstrated with lipid and non-lipid containing formulations. These results are the first demonstration of protection obtained by parenteral administration of PLG encapsulated DNA vaccines.

An analysis of the effects of smoking and other cardiovascular risk factors on obliteration rates after arteriovenous malformation radiosurgery

PURPOSE

To assess the relationships of smoking and other cardiovascular disease risk factors (hypertension, diabetes, hypercholesterolemia, and gender) to rates of radiosurgery-induced obliteration of arteriovenous malformations (AVM).

METHODS AND MATERIALS

We evaluated follow-up imaging and clinical data in 329 AVM patients who received gamma knife radiosurgery at the University of Pittsburgh between 1987 and 1994. There were 113 smokers, 29 hypertensives, 5 diabetics, 4 hypercholesterolemics, 159 male patients, and 170 female patients. All patients had regular clinical or imaging follow-up for a minimum of 3 years after radiosurgery.

RESULTS

Multivariate analysis showed that smoking had no effect on AVM obliteration (p > 0.43). Hypertension, diabetes, and hypercholesterolemia had no discernible effect on AVM obliteration in this study (p > 0.78). However, females aged 12-49 had a statistically significant lower in-field obliteration rate than males (78% vs. 89%, p = 0.0102).

CONCLUSION

Smoking has no effect on AVM obliteration. Hypertension, diabetes, and hypercholesterolemia had no discernible effect in this study. Further study is needed to establish whether estrogen has a vascular protective effect that could partially limit radiosurgical AVM obliteration, as suggested by this study.

Stereotactic radiosurgery for residual neurocytoma. Report of four cases

The purpose of this report was to review the results of stereotactic radiosurgery in the management of patients with residual neurocytomas after initial resection or biopsy procedures. Four patients underwent stereotactic radiosurgery for histologically proven neurocytoma. Clinical and imaging studies were performed to evaluate the response to treatment. Radiosurgery was performed to deliver doses to the tumor margin of 14, 15, 16, and 20 Gy, depending on tumor volume and proximity to critical adjacent structures. More than 3 years later, imaging studies revealed significant reductions in tumor size. No new neurological deficits were identified at 53, 50, 42, and 38 months of follow up. The authors' initial experience shows that stereotactic radiosurgery appears to be an effective treatment for neurocytoma.

Does increased nerve length within the treatment volume improve trigeminal neuralgia radiosurgery? A prospective double-blind, randomized study

PURPOSE

To test the hypothesis that increasing the nerve length within the treatment volume for trigeminal neuralgia radiosurgery would improve pain relief.

METHODS AND MATERIALS

Eighty-seven patients with typical trigeminal neuralgia were randomized to undergo retrogasserian gamma knife radiosurgery (75 Gy maximal dose with 4-mm diameter collimators) using either one (n = 44) or two (n = 43) isocenters. The median follow-up was 26 months (range 1-36).

RESULTS

Pain relief was complete in 57 patients (45 without medication and 12 with low-dose medication), partial in 15, and minimal in another 15 patients. The actuarial rate of obtaining complete pain relief (with or without medication) was 67.7% +/- 5.1%. The pain relief was identical for one- and two-isocenter radiosurgery. Pain relapsed in 30 of 72 responding patients. Facial numbness and mild and severe paresthesias developed in 8, 5, and 1 two-isocenter patients vs. 3, 4, and 0 one-isocenter patients, respectively (p = 0.23). Improved pain relief correlated with younger age (p = 0.025) and fewer prior procedures (p = 0.039) and complications (numbness or paresthesias) correlated with the nerve length irradiated (p = 0.018).

CONCLUSIONS

Increasing the treatment volume to include a longer nerve length for trigeminal neuralgia radiosurgery does not significantly improve pain relief but may increase complications.

Brain surgery with image guidance: current recommendations based on a 20-year assessment

Image guidance promotes safe and effective surgical management of a wide array of intracranial diseases. To better define the historical importance of image guidance and to assess the relative contribution of each imaging modality to the safety and efficacy of selected procedures, we reviewed our 20-year experience at a single institution. A retrospective review of our departmental surgical records was performed to identify patients who underwent brain surgery with image guidance between January 1979 and January 1999. We identified the use of intraoperative fluoroscopy, endoscopy, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and angiography in 7,388 patients. During this 20-year interval, advances in neuroimaging were translated into the operating room environment. Fluoroscopic guidance received the highest overall rating and was deemed critical for the performance of successful transsphenoidal surgery (n = 436) and effective percutaneous trigeminal neuralgia management (n = 1,121). Ultrasound and angiography both had limited roles; the latter was important to successful outcomes in 64 patients undergoing aneurysm management (n = 64) and arteriovenous malformation Gamma Knife radiosurgery (n = 786). Endoscopy also had a small role but had limited cost. Beginning in 1982, a dedicated operating room CT scanner was used during both morphologic and functional stereotactic surgery (n = 1,749). After 1986, MRI was used increasingly in the management of selected functional and tumor cases (n = 337); despite great versatility for patients undergoing Gamma Knife radiosurgery, the costs were relatively high. Frameless neuronavigation (n = 263) had excellent versatility and was relatively low in cost. During the last 20 years, image guidance techniques have facilitated minimally invasive brain surgery at our institution. The relative merits of all these imaging tools depended mostly on their versatility and relative costs. Major centers currently contemplating the incorporation of image guidance into routine brain surgery need not reproduce our own learning curve.

Stereotactic radiosurgery of residual or recurrent craniopharyngioma, after surgery, with or without radiation therapy

This study evaluated the role of stereotactic radiosurgery in the multimodality management of craniopharyngioma patients whose prior therapies failed. Ten consecutive patients (3 males and 7 females) had radiosurgery for craniopharyngioma during a 10-year interval. Their ages ranged from 9 to 64 years (median, 14.5 years). The median interval between diagnosis and radiosurgery was 46.5 months. In total, 12 stereotactic radiosurgical procedures were performed to control the solid component of the tumor (2 intrasellar and 10 suprasellar tumors). The median tumor volume was 1.35 cm3. One to 9 isocenters with different beam diameters were used; the median marginal dose was 16.4 Gy; and the dose to the optic apparatus was limited to less than 8 Gy. Clinical and imaging follow-up data were obtained at a median of 63 months (range, 13-150 months) from radiosurgery. Overall, 7 of 12 tumors became smaller or vanished within a median of 8.5 months. Prior visual defects objectively improved in 6 patients. One patient with prior visual defect deteriorated further and lost vision 9 months after radiosurgery. Multimodality therapy is often necessary for patients with refractory solid and cystic craniopharyngiomas. Stereotactic radiosurgery is a reasonable option in select patients with small recurrent or residual craniopharyngioma.

Primum non nocere: Multimodality management strategies when multiple mass lesions strike a single patient

BACKGROUND

The management of multiple symptomatic intracranial pathological processes in a single patient presents a rare and challenging problem for the neurosurgeon and the patient. Neurosurgeons must utilize a full spectrum of neurosurgical options to achieve the best patient outcome.

CASE DESCRIPTION

We present a unique case of a 63-year-old woman who presented with a large convexity meningioma causing headaches, an acoustic neuroma causing deafness and imbalance and a suprasellar arachnoid cyst compromising the visual fields. Therapeutic intervention was staged based on the primum non nocere concept. First, the patient underwent stereotactic intracavitary cyst irradiation using colloidal 32P. Secondly, microsurgical resection of the convexity meningioma was performed. Finally, Gamma Knife radiosurgery of the acoustic neuroma was performed. One year after multimodality management, the patient was neurologically improved. There was no evidence of meningioma or cyst recurrence and the growth of the acoustic neuroma was arrested.

CONCLUSION

This case demonstrates the value of multi-modality treatment of neurosurgical pathology, utilizing minimally invasive techniques when possible.

Comprehensive assessment of hemorrhage risks and outcomes after stereotactic brain biopsy

OBJECT

Stereotactic brain biopsy has played an integral role in the diagnosis and management of brain lesions. At most centers, imaging studies following biopsy are rarely performed. The authors prospectively determined the acute hemorrhage rate after stereotactic biopsy by performing immediate postbiopsy intraoperative computerized tomography (CT) scanning. They then analyzed factors that may influence the risk of hemorrhage and the diagnostic accuracy rate.

METHODS

Five hundred consecutive patients undergoing stereotactic brain biopsy underwent immediate postbiopsy intraoperative CT scanning. Before surgery, routine preoperative coagulation studies were performed in all patients. All medical charts, laboratory results, preoperative imaging studies, and postoperative imaging studies were reviewed. In 40 patients (8%) hemorrhage was detected using immediate postbiopsy intraoperative CT scanning. Neurological deficits developed in six patients (1.2%) and one patient (0.2%) died. Symptomatic delayed neurological deficits developed in two patients (0.4%), despite the fact that the initial postbiopsy CT scans in these cases did not show acute hemorrhage. Both patients had large intracerebral hemorrhages that were confirmed at the time of repeated imaging. The results of a multivariate logistic regression analysis of the risk of postbiopsy hemorrhage of any size showed a significant correlation only with the degree to which the platelet count was below 150,000/mm3 (p = 0.006). The results of a multivariate analysis of a hemorrhage measuring greater than 5 mm in diameter also showed a correlation between the risk of hemorrhage and a lesion location in the pineal region (p = 0.0086). The rate at which a nondiagnostic biopsy specimen was obtained increased as the number of biopsy samples increased (p = 0.0073) and in accordance with younger patient age (p = 0.026).

CONCLUSIONS

Stereotactic brain biopsy was associated with a low likelihood of postbiopsy hemorrhage. The risk of hemorrhage increased steadily as the platelet count fell below 150,000/mm3. The authors found a small but definable risk of delayed hemorrhage, despite unremarkable findings on an immediate postbiopsy head CT scan. This risk justifies an overnight hospital observation stay for all patients after having undergone stereotactic brain biopsy.

Stereotactic radiosurgery for hemangioblastomas of the brain

OBJECTIVE

To assess the effectiveness of stereotactic radiosurgery in achieving tumor control and improving survival in patients with hemangioblastoma, we evaluated results from patients who were managed at the University of Pittsburgh and the Mayo Clinic.

PATIENTS AND METHODS

Twenty-seven patients with 29 hemangioblastomas had stereotactic radiosurgery over a 10 year interval. The mean patient age was 32 years (range, 14-75 years). The tumor volumes varied from 0.36 to 27 ml (mean, 3.2 ml), and the mean tumor margin dose was 16 Gy (range, 11.7-20). Clinical and neuroimaging follow-up was obtained for all patients between 0.5 and 9 years (mean, 4 years) after radiosurgery.

RESULTS

At this assessment, 21 patients (79%) were alive and six (21%) had died. The median survival after radiosurgery was 6.5 years (actuarial 5 year survival = 75.1 +/- 11.5%). The median survival from the initial diagnosis was 15 years. Twenty two of 29 evaluable tumors were controlled locally. The two-year actuarial control rate was 84.5 +/- 7.1% and at five years, 75.2 +/- 8.9%. Multivariate testing of factors affecting good outcome indicated that smaller tumor volume and higher radiosurgical dose (> 18 Gy) were significant.

CONCLUSION

For small to moderate size hemangioblastomas, multiple or recurrent tumors, and for patients who are not surgical candidates, radiosurgery is a safe and effective option to control disease and improve survival.

Stereotactic radiosurgery for motor cortex region arteriovenous malformations

OBJECTIVE

The optimal management of arteriovenous malformations (AVMs) in critical brain locations remains controversial. To reduce the risk of an AVM hemorrhage and to enhance the possibility of preserving neurological function, stereotactic radiosurgery was performed in 33 patients with newly diagnosed or residual AVMs located within the motor cortex. The role of embolization also was examined.

METHODS

During a 9-year study period, 33 patients with AVMs located primarily in the motor cortex region were treated with stereotactic radiosurgery. These patients were followed up radiographically for a minimum of 36 months, or less if obliteration was documented before 36 months had elapsed. Of the 33 patients, 9 underwent embolization and 1 underwent microsurgery before radiosurgery. Nine patients required a second radiosurgery. The mean AVM target volume was 4.35 cc, and the average radiation dose to the AVM margin was 20 Gy. The median follow-up was 36 months (range, 10-91 mo), and angiographic follow-up of eligible patients was performed 24 or 36 months after radiosurgery.

RESULTS

Results were stratified by radiosurgical target volumes: less than 3 cc (Group 1), 3 to 10 cc (Group 2), and greater than 10 cc (Group 3). Overall (including second radiosurgery), 13 (87%) of 15 patients in Group 1 had complete obliteration confirmed by angiography. Nine (64%) of 14 patients in Group 2 exhibited nidus obliteration, and one (25%) of four patients in Group 3 demonstrated obliteration on a magnetic resonance imaging scan. Eight patients (24%) underwent second-stage radiosurgery after angiography revealed a persistent AVM nidus; three patients demonstrated complete obliteration on follow-up angiography. The obliteration rate was higher (87%) for AVMs with less than 3 cc target volume and lower (56%) for those with target volumes larger than 3 cc. One patient experienced worsening neurological function after radiosurgery, and one died from delayed AVM hemorrhage during the latency period. No patient bled after angiographically confirmed AVM obliteration.

CONCLUSION

Stereotactic radiosurgery is a successful and safe management option for patients with motor cortex AVMs. The obliteration of AVMs and the attendant low morbidity rates indicate a primary role for radiosurgery in these patients. Staged radiosurgery may be necessary to increase obliteration rates for larger AVMs or for those that are not obliterated after the first procedure.

Controversies in the management of multiple brain metastases: the roles of radiosurgery and radiation therapy

Multiple brain metastases (BrM) are a common challenge to patients with cancer. Tumour resection is used mainly for patients with large tumours that cause acute neurological syndromes. The prognosis, even after treatment with whole brain radiation therapy (WBRT), is poor with average expected survivals less than six months. For this reason, numerous centres have evaluated the role of stereotactic radiosurgery (SRS) in patients with solitary or multiple tumours. We conducted a randomised trial that compared radiosurgery plus WBRT to WBRT alone. The rate of local failure at one year was 100% after WBRT alone but only 8% in patients who had boost radiosurgery. The median time to local failure was six months after WBRT alone in comparison to 36 months after WBRT plus radiosurgery (p=0.0005). The median time to any brain failure was improved in the radiosurgery group (p=0.002). Survival was related to extent of extracranial disease (p=0.02). Combined WBRT and radiosurgery for patients with two to four BrM significantly improves control of brain disease. WBRT alone, for years the standard treatment, does not appear to provide lasting and effective care for most patients. Controversies remain in patient selection, number of BrM suitable for treatment, concomitant management of extracranial disease, and timing of therapy.

Clinical outcomes after stereotactic radiosurgery for idiopathic trigeminal neuralgia

OBJECT

Stereotactic radiosurgery is an increasingly used and the least invasive surgical option for patients with trigeminal neuralgia. In this study, the authors investigate the clinical outcomes in patients treated with this procedure.

METHODS

Independently acquired data from 220 patients with idiopathic trigeminal neuralgia who underwent gamma knife radiosurgery were reviewed. The median age was 70 years (range 26-92 years). Most patients had typical features of trigeminal neuralgia, although 16 (7.3%) described additional atypical features. One hundred thirty-five patients (61.4%) had previously undergone surgery and 80 (36.4%) had some degree of sensory disturbance related to the earlier surgery. Patients were followed for a maximum of 6.5 years (median 2 years). Complete or partial relief was achieved in 85.6% of patients at 1 year. Complete pain relief was achieved in 64.9% of patients at 6 months, 70.3% at 1 year, and 75.4% at 33 months. Patients with an atypical pain component had a lower rate of pain relief (p = 0.025). Because of recurrences, only 55.8% of patients had complete or partial pain relief at 5 years. The absence of preoperative sensory disturbance (p = 0.02) or previous surgery (p = 0.01) correlated with an increased proportion of patients who experienced complete or partial pain relief over time. Thirty patients (13.6%) reported pain recurrence 2 to 58 months after initial relief (median 15.4 months). Only 17 patients (10.2% at 2 years) developed new or increased subjective facial paresthesia or numbness, including one who developed deafferentation pain.

CONCLUSIONS

Radiosurgery for idiopathic trigeminal neuralgia was safe and effective, and it provided benefit to a patient population with a high frequency of prior surgical intervention.

Results of acoustic neuroma radiosurgery: an analysis of 5 years' experience using current methods

OBJECT

The goal of this study was to define tumor control and complications of radiosurgery encountered using current treatment methods for the initial management of patients with unilateral acoustic neuroma.

METHODS

One hundred ninety patients with previously untreated unilateral acoustic neuromas (vestibular schwannomas) underwent gamma knife radiosurgery between 1992 and 1997. The median follow-up period in these patients was 30 months (maximum 85 months). The marginal radiation doses were 11 to 18 Gy (median 13 Gy), the maximum doses were 22 to 36 Gy (median 26 Gy), and the treatment volumes were 0.1 to 33 cm3 (median 2.7 cm3). The actuarial 5-year clinical tumor-control rate (no requirement for surgical intervention) for the entire series was 97.1+/-1.9%. Five-year actuarial rates for any new facial weakness, facial numbness, hearing-level preservation, and preservation of testable speech discrimination were 1.1+/-0.8%, 2.6+/-1.2%, 71+/-4.7%, and 91+/-2.6%, respectively. Facial weakness did not develop in any patient who received a marginal dose of less than 15 Gy (163 patients). Hearing levels improved in 10 (7%) of 141 patients who exhibited decreased hearing (Gardner-Robertson Classes II-V) before undergoing radiosurgery. According to multivariate analysis, increasing marginal dose correlated with increased development of facial weakness (p = 0.0342) and decreased preservation of testable speech discrimination (p = 0.0122).

CONCLUSIONS

Radiosurgery for acoustic neuroma performed using current procedures is associated with a continued high rate of tumor control and lower rates of posttreatment morbidity than those published in earlier reports.

Imaging the trigeminal nerve and pons before and after surgical intervention for trigeminal neuralgia

OBJECTIVE

To study the various imaging changes occurring in the trigeminal nerve and brainstem in patients before or after trigeminal neuralgia surgery.

METHODS

During a 7-year period, 275 patients with trigeminal neuralgia underwent high-resolution, contrast-enhanced magnetic resonance imaging (MRI) of the pons during gamma knife radiosurgery. Ninety-seven patients had no previous surgical intervention for trigeminal neuralgia, and 178 patients had undergone one or more previous procedures. Two independent observers, one of whom was blinded to patients' clinical details, reviewed MRI scans retrospectively. The analysis of the independent observers was then correlated with all previous therapeutic interventions.

RESULTS

One hundred one MRI scans demonstrated no radiological changes related to trigeminal neuralgia, and 174 MRI scans exhibited some radiological abnormality. The average axial plane diameter of the nerve for all patients was 4 mm (range, 2-6 mm). In the group that had not undergone previous surgery, 65 patients (67%) exhibited vascular compression. In the 88 patients who had undergone previous microvascular decompression, 21 (24%) had evidence of a pontine infarction. Twenty-six patients experienced facial sensory loss, 22 (88%) of whom had undergone previous surgery with evidence of a pontine infarction (n = 11) or perineural scarring (n = 6).

CONCLUSION

The majority of patients who had undergone previous trigeminal neuralgia surgery demonstrated readily identifiable abnormalities of the trigeminal nerve or brainstem. The frequency of such changes correlated with the type and number of procedures. Evidence of vascular compression was detected in the majority of patients. Most patients with postoperative facial sensory loss demonstrate changes in the nerve or pons on MR images.

Two methods for quantifying DNA extracted from poly(lactide-co-glycolide) microspheres

DNA can be formulated with synthetic polymers such as poly(lactide-co-glycolide) (PLG) to generate microparticles. Researchers have used either UV spectroscopy or fluorometry with PicoGreen((R)) dye to quantify PLG-encapsulated DNA. While the sensitivity of DNA detection and quantification by PicoGreen is higher ( approximately 12 pg/ml) compared to UV ( approximately 0.5 microg/ml), each method as an analytical tool has limitations. The premise of this work addresses the usefulness and limitations of each method to determine encapsulation efficiencies in PLG microspheres post-process, and to quantify release of DNA from microspheres during in vitro release experiments. In addition, assay conditions for accurate and reproducible extraction of DNA from PLG microspheres using a biphasic (aqueous/organic) solvent system are described. It was also determined that residual poly(vinyl alcohol) and DNA isoforms (linear, nicked, supercoiled) affected PicoGreen/DNA fluorescence values.

Subnecrotic stereotactic radiosurgery controlling epilepsy produced by kainic acid injection in rats

OBJECT

Any analysis of the potential role of stereotactic radiosurgery for epilepsy requires the experimental study of its potential antiepileptogenic, behavioral, and histological effects. The authors hypothesized that radiosurgery performed using subnecrotic tissue doses would reduce or abolish epilepsy without causing demonstrable behavioral side effects. The kainic acid model in rats was chosen to test this hypothesis.

METHODS

Chronic epilepsy was successfully created by stereotactic injection of kainic acid (8 microg) into the rat hippocampus. Epileptic rats were divided into three groups: high-dose radiosurgery (60 Gy, 16 animals), low-dose (30 Gy, 15 animals), and controls. After chronic epilepsy was confirmed by observation of the seizure pattern and by using electroencephalography (EEG), radiosurgery was performed on Day 10 postinjection. Serial seizure and behavior observation was supplemented by weekly EEG sessions performed for the next 11 weeks. To detect behavioral deficits, the Morris water maze test was performed during Week 12 to study spatial learning and memory. Tasks involved a hidden platform, a visible platform, and a probe trial. After radiosurgery, the incidence of observed and EEG-defined seizures was markedly reduced in rats from either radiosurgically treated group. A significant reduction was noted after high-dose (60 Gy) radiosurgery in Weeks 5 to 9 (p < 0.003). After low-dose (30 Gy) radiosurgery, a significant reduction was found after 7 to 9 weeks (p < 0.04). During the task involving the hidden platform, kainic acid-injected rats displayed significantly prolonged latencies compared with those of control animals (p < 0.05). Hippocampal radiosurgery did not worsen this performance. The probe trial showed that kainic acid-injected rats that did not undergo radiosurgery spent significantly less time than control rats in the target quadrant (p = 0.03). Rats that had undergone radiosurgery displayed no difference compared with control rats and demonstrated better performance than rats that received kainic acid alone (p = 0.04). Radiosurgery caused no adverse histological effects.

CONCLUSIONS

In a rat model, radiosurgery performed with subnecrotic tissue doses controlled epilepsy without causing subsequent behavioral impairment.

Radiosurgery for childhood intracranial arteriovenous malformations

OBJECTIVE

The optimal management of intracranial arteriovenous malformations (AVMs) in children remains controversial. Children with intracranial AVMs present a special challenge in therapeutic decision-making because of the early recognition of their future life-long risks of hemorrhage if they are treated conservatively. The goals of radiosurgery are to achieve complete AVM obliteration and to preserve neurological function. We present long-term outcomes for a series of children treated using radiosurgery.

METHODS

The findings for 53 consecutive children who underwent at least 36 months of imaging follow-up monitoring after radiosurgery were reviewed. The median age at the time of treatment was 12 years (range, 2-17 yr). Thirty-one children (58%) presented after their first intracranial hemorrhaging episodes, two (4%) after their second hemorrhaging episodes, and one (2%) after five hemorrhaging episodes. Nineteen children (36%) presented with unruptured AVMs, and a total of 25 children (47%) exhibited neurological deficits. AVMs were graded as Spetzler-Martin Grade I (2%), Grade II (23%), Grade III (36%), Grade IV (9%), or Grade VI (30%). The median AVM volume was 1.7 ml (range, 0.11-10.2 ml). The median marginal dose was 20 Gy (range, 15-25 Gy).

RESULTS

Results were stratified according to AVM volumes (Group 1, < or =3 ml; Group 2, >3 ml to < or =10 ml; Group 3, >10 ml). Twenty-eight patients (80%) in Group 1 and 11 (64.7%) in Group 2 achieved complete obliteration. The only patient in Group 3 did not achieve obliteration. Complications included brainstem edema (n = 1) and transient pulmonary edema (n = 1). Four patients experienced hemorrhaging episodes, 30, 40, 84, and 96 months after radiosurgery. Multivariate logistic regression analysis demonstrated that only volume was significantly correlated with obliteration rates (P = 0.0109).

CONCLUSION

Radiosurgery is safe and efficacious for selected children with AVMs. The obliteration rates and the attendant low morbidity rates suggest a primary role for stereotactic radiosurgery for pediatric AVMs.

Gamma knife radiosurgery for vestibular schwannomas

Radiosurgery is a surgical procedure associated with minimal functional morbidity and allows patients to return rapidly to their previous level of activity. Most tumors regress in volume with extended follow-up, and the rare occurrence of tumor growth after radiosurgery seems to occur early. Similarly, cranial neuropathy or other neurologic symptoms after irradiation occur within the first few years and are usually mild and transient. Current results indicate a low rate of cranial neuropathy (lower than with any other technique). Useful hearing preservation in patients with NF2 seems to be an attainable goal with more sophisticated radiosurgery techniques. We anticipate the increased use of stereotactic radiosurgery for patients with vestibular schwannomas as more and more smaller sized tumors are identified.

The arteriovenous malformation associated with major arterial occlusion and moyamoya vessels: a cerebral blood flow study

SUMMARY

We report 2 patients with arteriovenous malformation (AVM) associated with complete occlusion of the unilateral middle cerebral artery and moyamoya vessels. Xenon CT CBF study demonstrated diffusely decreased CMF in unilateral or bilateral hemispheres with multiple areas of decreased vascular reserve. A significant reduction of AVM size was seen in one patient who received radiosurgery with marked CBF improvement.

Adjuvant stereotactic radiosurgery for anaplastic ependymoma

OBJECT

The purpose of this retrospective study is to evaluate the role of stereotactic radiosurgery using the Gamma Knife as an adjuvant to other modalities used in the treatment of malignant ependymomas of both children and adults and to assess its efficacy in terms of tumor control and overall survival.

METHOD

Between 1987 and 1998, 22 patients in the age range of 1.5-65 years (mean age 22. 3) with progressive anaplastic ependymoma were treated by stereotactic radiosurgery using the 201 source Co-60 Leksell Gamma Knife at the University of Pittsburgh. The irradiated tumor volume varied from 0.84 to 36.8 cm(3) (mean 13.7). The median dose delivered to the tumor margin was 16.1 Gy (range 10-20), and the mean maximal dose was 32.2 Gy (range 20-40). The disease-free survival, the tumor control rate and the overall survival were recorded to evaluate the efficacy of radiosurgery. The median follow-up from radiosurgery was 21 months (range 4-84).

RESULTS

Median survival after radiosurgery was 2.2 years (46.6 +/- 12.1% 5-year actuarial). Median survival from the initial diagnosis was 10. 1 years (50.3 +/- 12.5% at 5 years, 37.7 +/- 14.4% at 10 years). Reduction or stabilization of the treated tumor was seen in 16 out of 22 (68%) patients. Forty-one percent of the patients eventually developed delayed distant cerebral recurrence outside the treated volume. The 5-year actuarial rates for local control and cranial control at any location were 62.3 +/- 13.6% and 32.4 +/- 10.8%, respectively. No complication occurred as a side effect of radiosurgery.

CONCLUSION

For patients with locally recurrent or progressive anaplastic ependymomas, Gamma Knife stereotactic radiosurgery proved to be safe and effective as a salvage adjuvant therapy to achieve local tumor control and improve survival.

Distinguishing recurrent tumor and radiation necrosis with positron emission tomography versus stereotactic biopsy

With the recent approval of reimbursement for positron emission tomography (PET), it has become important to clarify the utility of this diagnostic study. We evaluated the utility of PET to distinguish radiation necrosis from recurrent tumor in a retrospective review of patients with primary glial neoplasms. Fifteen patients had preoperative contrast-enhanced MRI and PET images followed by stereotactic biopsy or craniotomy and histological confirmation. The sensitivity of PET was 43% (6/14) and the specificity was 100% (1/1). We examined the sensitivity of PET as a function of volumetric contrast enhancement on MRI. Eighty percent of true-positive PET studies occurred with volume enhancement greater than 10 cm(3). Seventy-five percent of false negatives occurred with volume enhancement less than 6 cm(3). Given the clinical significance of distinguishing tumor progression from radiation necrosis, we believe that PET is insufficient to resolve radiation necrosis versus tumor progression.

Radiosurgery for hemangiomas of the cavernous sinus and orbit: technical case report

OBJECTIVE AND IMPORTANCE

Hemangiomas of neurosurgical interest are histologically benign vascular tumors that most often occur in the orbit or cavernous sinus. Hemangiomas can be diagnosed by their characteristic radiographic and angiographic appearance and their tendency to bleed excessively during attempted removal. Intracranial or intraorbital hemangiomas require treatment when they become symptomatic.

CLINICAL PRESENTATION

We report four hemangioma patients who presented with ocular symptoms or signs, such as orbital pain, ophthalmoplegia, proptosis, or impaired visual acuity. Before our evaluation, two patients had each had incomplete resections aborted because of excessive blood loss, one patient had undergone a nondiagnostic transsphenoidal biopsy, and one patient had had an unsuccessful embolization.

INTERVENTION

All four patients were treated with gamma knife radiosurgery. Tumors received a minimal tumor dose that ranged from 14 to 19 Gy. Follow-up evaluations were performed 6 to 24 months after radiosurgery and revealed a reduction in tumor volume in three patients and no tumor progression in the fourth. All patients had symptomatic improvement, but one had persistent diplopia.

CONCLUSION

In this early experience, stereotactic radiosurgery proved to be an effective management strategy that avoided the potentially serious complications associated with surgery or embolization of cavernous sinus hemangiomas.

Functional outcomes after gamma knife thalamotomy for essential tremor and MS-related tremor

Twelve patients with a median age of 75 years underwent gamma knife thalamotomy for essential tremor (ET) (n = 9) or MS-related tremor (n = 3). All 11 evaluable patients noted improvement in action tremor. Six of eight ET patients had complete tremor arrest, and the violent action tremor in all three patients with MS was improved. One patient developed transient arm weakness. Stereotactic radiosurgery for ET and MS-related tremor is safe and effective for patients who may be poor candidates for other procedures.

A comparison of surgical approaches for the management of tremor: radiofrequency thalamotomy, gamma knife thalamotomy and thalamic stimulation

OBJECTIVE

Between April 1994 and January 1999, 39 stereotactic procedures for patients with intractable tremor were performed at the University of Pittsburgh Medical Center. A retrospective analysis of results of radiosurgical thalamotomy (n = 15), MR-guided stereotactic radiofrequency thalamotomy (n = 13), and deep brain thalamic stimulation (DBS; n = 11) was performed to study relative advantages and risks of these procedures.

METHODS

All options were discussed with the patients, but radiosurgery usually was performed in elderly patients with concurrent medical problems. Stereotactic thalamotomy and DBS was performed with MR guidance and macrostimulation. For radiosurgery, a median dose of 140 Gy (range 130-150 Gy) was delivered using a single 4-mm collimator.

RESULTS

Of the 13 patients who underwent radiofrequency thalamotomy, 5 had immediate complete arrest of tremor, 6 had a significant reduction and 2 had partial reduction. All 11 patients who underwent DBS had excellent control of tremor immediately after the procedure, and in longer-term follow-up 10/11 maintained excellent tremor control. Of the 12 evaluable radiosurgery patients, 10 noted excellent relief and 2 had partial relief.

CONCLUSION

Stereotactic procedures for tremor control are safe and effective. Each procedure has specific advantages and disadvantages that are important for patient selection.

The role of stereotactic cyst aspiration for glial and metastatic brain tumors

OBJECTIVE

To evaluate the role of stereotactic cyst aspiration in the context of multimodality management of cystic glial and metastatic tumors, we retrospectively reviewed our experience with 38 patients during a 10-year interval.

METHODS

All 38 patients had one or more computed tomography or magnetic resonance imaging guided stereotactic cyst aspirations. Twenty-seven patients had glial neoplasms and 11 had metastatic brain tumors. Twenty-two patients underwent cyst aspiration as the initial treatment modality while 15 patients had cyst aspiration following previous treatments.

RESULTS

In the immediate postoperative period, 19 of the 27 (70%) patients with gliomas and nine of the 11 (82%) patients with metastatic tumors experienced symptomatic improvement. No procedure-related morbidity was encountered. Twelve patients (31.5%) eventually required a catheter-reservoir system. Thirty-seven percent of patients with cystic glial neoplasms and 18% of patients with metastatic tumors had delayed cytoreductive surgery by craniotomy subsequent to stereotactic cyst aspiration. Reduction in tumor volume following aspiration facilitated Gamma knife radiosurgery in seven patients.

CONCLUSION

Single stereotactic aspiration is a low risk procedure that provides immediate relief of symptoms in patients with cystic brain tumors. It appears to be valuable together with the use of other therapeutic strategies.

Effective treatment of experimental glioblastoma by HSV vector-mediated TNF alpha and HSV-tk gene transfer in combination with radiosurgery and ganciclovir administration

Experiments were carried out in a nude mouse model of human glioblastoma to determine whether gamma-knife radiosurgery combined with herpes simplex virus thymidine kinase (tk) suicide gene therapy and tumor necrosis factor alpha (TNFalpha) gene transfer provided an improved multimodality treatment of this disease. Animals were inoculated intracerebrally with 2 x 10(5) U-87MG human glioblastoma cells to establish brain tumors. At 3 days postinoculation, the tumor region was injected with 2 x 10(6) infectious particles of highly defective herpes simplex viral vectors expressing the viral tk gene with the kinetics of a viral immediate early gene either alone (T.1) or together with TNF alpha (TH:TNF). Subgroups of animals were given daily intraperitoneal injections of ganciclovir (GCV) for 10 days and/or subjected to gamma-knife radiosurgery on the fifth day post tumor-cell implantation. Comparisons of animal survival showed that the TH:TNF vector in combination with radiosurgery and GCV administration provided the most effective therapy; eight of nine animals survived for 75 days compared to four of eight using the next best protocol. These findings suggest that gene therapy in combination with more conventional therapeutic methods may provide an improved strategy for extending the life expectancy of patients afflicted with this ultimately fatal disease.

Decision making for patients with multiple brain metastases: radiosurgery, radiotherapy, or resection?

Object

Multiple brain metastases are a common health problem, frequently found in patients with cancer. The prognosis, even after treatment with whole-brain radiation therapy (WBRT), is poor, with an average expected survival time of less than 6 months. Investigators at numerous centers have evaluated the role of stereotactic radiosurgery in retrospective case series of patients harboring solitary or multiple tumors. Tumor resection is used mainly for patients with large tumors that cause acute neurological syndromes. The authors conducted a randomized trial in which they compared radiosurgery combined with WBRT with WBRT alone.

Methods

Twenty-seven patients were randomized (14 to recieve WBRT alone and 13 to receive WBRT combined with radiosurgery). The rate of local failure at 1 year was 100% after WBRT alone but only 8% in patients in whom boost radiosurgery was performed. The median time to local failure was 6 months after WBRT alone (95% confidence interval (CI) 3.5–8.5) in comparison to 36 months (95% CI 15.6–57) after WBRT and radiosurgery (p = 0.0005). The median time to the development of any brain failure was improved in the combined modality group (p = 0.002). Survival was shown to be related to the extent of extracranial disease (p = 0.02).

Conclusions

Combined WBRT and radiosurgery for the treatment of patients with two to four brain metastases significantly improves control of brain disease. Whole-brain radiation therapy alone does not provide lasting and effective care when treating most patients. Surgical resection remains important for patients with large symptomatic tumors and in whom limited extracranial disease has been demonstrated.

Tissue distribution and persistence in mice of plasmid DNA encapsulated in a PLGA-based microsphere delivery vehicle

Information regarding the distribution and persistence of DNA encapsulated in poly-(lactide co-glycolide) microspheres was collected to provide additional information regarding the safety of DNA vaccines and to support the clinical testing of this new delivery system for DNA. Plasmid DNA was encapsulated in poly(lactide co-glycolide) microspheres and the distribution and persistence of plasmid in murine tissues resulting from parenteral administration were examined by a sensitive PCR assay. Encapsulated DNA delivered by intramuscular or subcutaneous injection can be detected for 100 days post-injection and is distributed primarily at the site of injection and the lymphoid organs. Intravenous administration results in more widespread dissemination with long term persistence limited to the lymphoid organs and those of the reticuloendothelial system. Specific cellular uptake of DNA by professional antigen presenting cells (APCs) following injection suggests the utility of microspheres as DNA delivery agents. Distribution and persistence studies support the safety of encapsulated DNA and the specific cellular uptake of DNA by professional APCs following injection suggests the utility of microspheres as DNA delivery agents.

Repeated radiosurgery for incompletely obliterated arteriovenous malformations

OBJECT

The goal of this study was to define treatment results of repeated arteriovenous malformation (AVM) radiosurgery, namely AVM obliteration and complications.

METHODS

The authors analyzed their experience with repeated AVM radiosurgery performed in 41 patients for whom follow-up review lasted at least 2 years. The median duration of follow up was 34 months (range 7-65 months) after repeated radiosurgery in this group. The residual nidus was located within the area of focus (in field) of the initial radiosurgery in 28 patients (68%). Initial doses to the margin varied from 12.5 to 20 Gy (median 18 Gy). During repeated treatment the dose to the margin varied from 12.5 to 20 Gy (median 17 Gy) and the retreated volumes ranged from 0.4 to 7 cm3 (median 2.1 cm3). Follow-up angiography performed at least 2 years postradiosurgery revealed complete AVM obliteration in 21 (70%) of 30 patients. The estimated overall 2-year obliteration rate, based on findings on magnetic resonance imaging (eight of 11 obliterated) and angiography (29 of 41 obliterated) was 71%. Obliteration rates correlated with margin doses (p = 0.0045) with a trend toward higher rates in cases with in-field nidus persistence (p = 0.0637). The dose-response curve for AVM nidus obliteration was not significantly different from that of the initial radiosurgery. In two patients (5%) intracranial AVM hemorrhage developed within 125.9 risk years after repeated radiosurgery (1.6% per patient year). Persistent symptomatic adverse radiation effects developed in two (5%) of 41 patients following repeated radiosurgery. Postradiosurgical imaging changes were identified in 11 (27%) of 41 patients, which correlated with a 12-Gy volume from repeated surgery (p = 0.019).

CONCLUSIONS

When necessary, repeated AVM radiosurgery achieves obliteration with an acceptable risk. Despite the effects of previous irradiation, repeated radiosurgery required similar or slightly higher radiation doses to achieve the same in-field obliteration rates as those needed to obliterate an AVM that had not been treated by radiation previously.