Treatment outcome after linac-based radiosurgery in cerebral arteriovenous malformations: Retrospective analysis of factors affecting obliteration

Risk for Hemorrhage the First 2 Years After Gamma Knife Surgery for Arteriovenous Malformations: An Update

BACKGROUND

Knowledge about the natural course of brain arteriovenous malformations (AVMs) have increased during the past 20 years, as has the number of AVMs treated, especially larger ones. It is thus timely to again analyze the risk for hemorrhage after Gamma Knife Surgery (GKS).

OBJECTIVE

To confirm or contradict conclusions drawn 20 years ago regarding factors that affect the risk for post-GKS hemorrhage.

METHODS

The outcome after GKS was studied in 5037 AVM patients followed for up to 2 years. The relation between post-treatment hemorrhage rate and a number of patient, AVM, and treatment parameters was analyzed. The results were also compared with the results from our earlier study.

RESULTS

The annual post-treatment hemorrhage rate was 2.4% the first 2 years after GKS. Large size, low treatment dose, and old age were independent risk factors for AVM hemorrhage. After having compensated for the factors above, peripheral AVM location and female sex, at least during their child bearing ages, were factors associated with a lower post-GKS hemorrhage rate.

CONCLUSION

Large AVMs (>5 cm 3 ) treated with low doses (≤16 Gy) had higher and small AVMs treated with high doses a lower risk for hemorrhage as compared with untreated AVMs. This was detectable within the first 6 months after GKS. No difference in hemorrhage rate could be detected for the other AVMs. Based on our findings, it is advisable to prescribe >16 Gy to larger AVMs, assuming that the risk for radiation-induced complications can be kept at an acceptable level.

Linac-based stereotactic radiosurgery for brain arteriovenous malformations

PURPOSE

Linac stereotactic radiosurgery (SRS) is gaining popularity as a form of radiation treatment for cerebral arteriovenous malformations (AVMs) since the theory of combined radiosurgical and endovascular treatment poses much uncertainty and due to significant technical progress for SRS. This study focuses on how to evaluate obliteration and re-bleeding rates, and to determine factors and adverse effects influencing obliteration after linac-based SRS for cerebral AVMs.

MATERIAL AND METHODS

From a statistical record of 71 patients, 31 had partial embolisation, five surgery and 29 had no prior treatment. Using Kaplan-Meier survival and life table analyses, actuarial obliteration and annual bleeding hazard rates were calculated after SRS.

RESULTS

After a follow up of 1, 2 and 3 years the actual obliteration rates were 22, 59 and 66%, respectively whereby it was noted that prior embolization had no effect on the obliteration rate. Annual bleeding hazard rates were further analyzed after stereotactic radiosurgery to be 2.1% and 1.4% for the first and second year respectively. Asymptomatic abnormalities were detected after imaging in 33.9% of patients. A dose of less than 18 Gy significantly reduced the obliteration probability.

CONCLUSION

SRS is a therapeutic option for intracerebral AVM. In general, there is a low rate of morbidity and a high probability of nidus obliteration.

Long-term outcomes of 170 brain arteriovenous malformations treated by frameless image-guided robotic stereotactic radiosurgery: Ramathibodi hospital experience

This study was conducted to report long-term outcomes of the frameless robotic stereotactic radiosurgery (SRS) for brain arteriovenous malformation (AVM) at Ramathibodi Hospital.Retrospective data of patients with brain AVM (bAVM), who underwent CyberKnife SRS (CKSRS) at Ramathibodi Hospital from 2009 to 2014, were examined. Exclusion criteria were insufficient follow-up time (<36 months) or incomplete information. Patients' demographics, clinical presentation, treatment parameters, and results were analyzed. Excellent outcome was defined as AVM obliteration without a new neurological deficit. Risk factors for achieving excellent outcome were assessed.From a total of 277 CKSRS treatments for bAVM during the 6 years, 170 AVMs in 166 patients met the inclusion criteria. One hundred and thirty-nine cases (81.76%) presented with hemorrhages from ruptured bAVMs. Almost two-thirds underwent embolization before radiosurgery. With the median AVM volume of 4.17 mL, three-quarters of the cohort had single-fraction CKSRS, utilizing the median prescribed dose of 15 Gray (Gy). In the multisession group (25.29%), the median prescribed dose and the AVM volume were 27.5 Gy and 22.3 mL, respectively. An overall excellent outcome, at a median follow-up period of 72.45 months, was observed in 99 cases (58.24%). Seven AVMs (4.12%) ruptured after CKSRS but 1 patient suffered a new neurological deficit. Two patients (1.18%) were classified into the poor outcome category but there were no deaths. Negative factors for excellent outcome, by multivariate regression analysis, were the male sex and multisession SRS delivery, but not age, history of AVM rupture, previous embolization, or AVM volume.Despite relatively larger bAVM and utilizing a lower prescribed radiation dose, the excellent outcome was within the reported range from previous literature. This study offers one of the longest follow-ups and the largest cohorts from the frameless image-guided robotic SRS community.

Pediatric Intracranial Arteriovenous Malformation: Long-Term Outcomes with Linear Accelerator (LINAC)-Based Radiosurgery

Purpose

To analyze and report the long-term outcomes of intracranial arteriovenous malformations (AVM) treated with linear accelerator (LINAC)-based radiosurgery (LBRS) in the pediatric population.

Methods and Materials

A series of 34 pediatric patients (≤18 years old) who were treated between 2002 and 2016 were analyzed. All patients were treated with LBRS in a single fraction, with a median dose of 16.8 Gy to the 80% isodose line. Median age at treatment was 14.4 years (range 5.5-18.9). Median AVM volume was 2.91 mL (range 0.228-27.313). Median modified radiosurgery-based AVM score was 0.83 (range 0.18-2.96). The most common presenting symptom was intracranial hemorrhage (ICH) (n = 22, 64.7%). Nine patients underwent intervention before LBRS, which included prior embolization or resection. Seven lesions were in eloquent locations, defined as basal ganglia, thalamus, or brainstem. Cerebral angiography was done to confirm obliteration.

Results

Median follow-up time was 98 months (range 36-200 months). Twenty-two of the 34 lesions were obliterated (64.7%) with median time to obliteration of 37 months (range 14-79). No deaths occurred during the follow up period; however, two patients experienced ICH after treatment. Three other patients were treated for symptomatic radiation necrosis.

Conclusions

Treatment of intracranial AVM with LBRS in the pediatric population is demonstrated to be safe and effective with long-term follow up.

Evaluation of a new software prototype for frameless radiosurgery of arteriovenous malformations

Background

In order to locate an arteriovenous malformation, typically, a digital subtraction angiography (DSA) is carried out. To use the DSA for target definition an accurate image registration between CT and DSA is required. Carrying out a non-invasive, frameless procedure, registration of the 2D-DSA images with the CT is critical. A new software prototype is enabling this frameless procedure. The aim of this work was to evaluate the prototype in terms of targeting accuracy and reliability based on phantom measurements as well as with the aid of patient data. In addition, the user’s ability to recognize registration mismatches and quality was assessed.

Methods

Targeting accuracy was measured with a simple cubic, as well as with an anthropomorphic head phantom. Clearly defined academic targets within the phantoms were contoured on the CT. These reference structures were compared with the structures generated within the prototype. A similar approach was used with patient data, where the clinically contoured target served as the reference structure.

An important error source decreasing the target accuracy comes from registration errors between CT and 2D-DSA. For that reason, the tools in BC provided to the user to check these registrations are very important. In order to check if the user is able to recognize registration errors, a set of different registration errors was introduced to the correctly registered CT and 2D-DSA image data sets of three different patients. Each of six different users rated the whole set of registrations within the prototype.

Results

The target accuracy of the prototype was found to be below 0.04 cm for the cubic phantom and below 0.05 cm for the anthropomorphic head phantom. The mean target accuracy for the 15 patient cases was found to be below 0.3 cm.

In the registration verification part, almost all introduced registration errors above 1° or 0.1 cm were detected by the six users. Nevertheless, in order to quantify and categorize the possibility to detect mismatches in the registration process more data needs to be evaluated.

Conclusion

Our study shows, that the prototype is a useful tool that has the potential to fill the gap towards a frameless procedure when treating AVMs with the aid of 2D-DSA images in radiosurgery. The target accuracy of the prototype is similar to other systems already established in clinical routine.

Modern robot-assisted radiosurgery of cerebral angiomas-own experiences, system comparisons, and comprehensive literature overview

Cerebral arteriovenous malformations (AVMs) are rare vascular lesions potentially responsible for substantial neurological morbidity and mortality. Over the past four decades, radiosurgery has become a valid therapeutic option for many patients with small intracranial AVMs, but reports describing the use of robotic stereotactic radiosurgery (SRS) are rare. The purposes of this study are to describe the efficacy and toxicity of robotic SRS for AVMs and to review the literature. The reports of 48 consecutive patients treated with SRS were reviewed. A total dose of 18 Gy in a single fraction was prescribed to the 70% isodose line. Efficacy (i.e., total obliteration of the AVM) and toxicity were analyzed. Literature search was performed on Embase and PubMed for the terms "Radiosurgery and AVMs", "Cyberknife and AVMs" and "Radiation therapy and AVMs." The median follow-up was 41 months. The median AVM volume was 2.62 cm³. The incidence of obliteration was 59% at 3 years. Regarding toxicity, 92% of patients remained symptom-free, 66% developed radiogenic edema on MRI, and none developed radionecrosis. Forty-one patients (85%) had embolization prior to SRS. Our study was incorporated in an exhaustive review of 25 trials categorized by SRS technique. In this review, the median follow-up was 60 months. The median nidus volume was 2 cm³. The median overall obliteration rate for SRS was 68% (range 36 to 92). The median embolization rate prior to SRS was 31% (range 8.23 to 90). Compared to other studies, tolerability was excellent and the obliteration rate was acceptable but probably affected by the high embolization rate prior to radiosurgery. Our study suggests that a higher dose is feasible. A larger cohort with a longer follow-up period will be needed to confirm the safety and effectiveness, and subsequently validate different prognosis and predictive scores with this treatment modality to maximize the benefits of this technology for selected patients in the long term.

Multistage stereotactic radiosurgery for large cerebral arteriovenous malformations using the Gamma Knife platform

PURPOSE

Radiosurgery is an established technique to treat cerebral arteriovenous malformations (AVMs). Obliteration of larger AVMs (> 10-15 cm³ or diameter > 3 cm) in a single session is challenging with current radiosurgery platforms due to toxicity. We present a novel technique of multistage stereotactic radiosurgery (SRS) for large intracranial arteriovenous malformations (AVM) using the Gamma Knife system.

MATERIALS/METHODS

Eighteen patients with large (> 10-15 cm³ or diameter > 3 cm) AVMs, which were previously treated using a staged SRS technique on the Cyberknife platform, were retrospectively selected for this study. The AVMs were contoured and divided into 3-8 subtargets to be treated sequentially in a staged approach at half to 4 week intervals. The prescription dose ranged from 15 Gy to 20 Gy, depending on the subtarget number, volume, and location. Gamma Knife plans using multiple collimator settings were generated and optimized. The coordinates of each shot from the initial plan covering the total AVM target were extracted based on their relative positions within the frame system. The shots were regrouped based on their location with respect to the subtarget contours to generate subplans for each stage. The delivery time of each shot for a subtarget was decay corrected with ⁶⁰ Co for staging the treatment course to generate the same dose distribution as that planned for the total AVM target. Conformality indices and dose-volume analysis were performed to evaluate treatment plans.

RESULTS

With the shot redistribution technique, the composite dose for the multistaged treatment of multiple subtargets is equivalent to the initial plan for total AVM target. Gamma Knife plans resulted in an average PTV coverage of 96.3 ± 0.9% and a PITV of 1.23 ± 0.1. The resulting Conformality indices, V_12Gy and R₅₀ dose spillage values were 0.76 ± 0.05, 3.4 ± 1.8, and 3.1 ± 0.5 respectively.

CONCLUSION

The Gamma Knife system can deliver a multistaged conformal dose to treat large AVMs when correcting for translational setup errors of each shot at each staged treatment.

The Role of Preradiosurgical Embolization in the Management of Grades III, IV, and V Arteriovenous Malformations

Objective

To evaluate the role of preradiosurgical embolization on obliteration rate, reduction of size, irradiation dose, and neurological outcome, in 90 patients presenting large arteriovenous malformations (AVMs).

Methods

Between October 1993 and October 2006, 90 radiosurgical procedures were performed to treat brain AVMs Spetzler–Martin (SM) grades III, IV, and V at the Department of Radiosurgery and Radiology of the Real e Benemérita Associação Portuguesa de Beneficência de São Paulo, São Paulo, Brazil. Fifty-nine patients had embolization before radiosurgery and complete clinical and radiologic follow-up for at least 3 years. Inclusion criteria were as follow: SM grades III, IV, and V AVMs, no previous treatment, and clinical and radiological (angiogram and MRI) follow-up for at least 3 years. Obliteration rate, reduction of size, irradiation dose, and neurological outcome were compared in these two cohorts of patients. Mann–Whitney test, “Student’s t-test,” and χ² tests were used for statistical analysis, as appropriate. The level of significance was determined at p < 0.05.

Results

The mean size of the AVMs that underwent embolization was significantly greater when compared with non-embolized group (p < 0.05). Embolization significantly reduced the AVM diameter. Irradiation dose was significantly smaller in the embolized group (p < 0.05). No significant differences in final clinical outcomes, postprocedural radiological findings, rate of occlusion, and need for additional procedures were observed between the two groups (p < 0.05).

Conclusion

Preradiosurgical embolization of large AVMs does not result in impaired obliteration rate compared with cases treated with radiosurgery alone. It did not add further morbidity and presented benefits of reducing size of the AVMs. Preradiosurgical embolization may facilitate the coverage of the AVM with the effective irradiation dose. Combined management may be effective for selected large lesions considered unsuitable for radiosurgery and otherwise untreatable.

3D-Printing of Arteriovenous Malformations for Radiosurgical Treatment: Pushing Anatomy Understanding to Real Boundaries

Radiosurgery of arteriovenous malformations (AVMs) is a challenging procedure. Accuracy of target volume contouring is one major issue to achieve AVM obliteration while avoiding disastrous complications due to suboptimal treatment. We describe a technique to improve the understanding of the complex AVM angioarchitecture by 3D prototyping of individual lesions. Arteriovenous malformations of ten patients were prototyped by 3D printing using 3D rotational angiography (3DRA) as a template. A target volume was obtained using the 3DRA; a second volume was obtained, without awareness of the first volume, using 3DRA and the 3D-printed model. The two volumes were superimposed and the conjoint and disjoint volumes were measured. We also calculated the time needed to perform contouring and assessed the confidence of the surgeons in the definition of the target volumes using a six-point scale. The time required for the contouring of the target lesion was shorter when the surgeons used the 3D-printed model of the AVM (p=0.001). The average volume contoured without the 3D model was 5.6 ± 3 mL whereas it was 5.2 ± 2.9 mL with the 3D-printed model (p=0.003). The 3D prototypes proved to be spatially reliable. Surgeons were absolutely confident or very confident in all cases that the volume contoured using the 3D-printed model was plausible and corresponded to the real boundaries of the lesion. The total cost for each case was 50 euros whereas the cost of the 3D printer was 1600 euros. 3D prototyping of AVMs is a simple, affordable, and spatially reliable procedure that can be beneficial for radiosurgery treatment planning. According to our preliminary data, individual prototyping of the brain circulation provides an intuitive comprehension of the 3D anatomy of the lesion that can be rapidly and reliably translated into the target volume.

Outcome of cerebral arteriovenous malformations after linear accelerator reirradiation

Background:

The aim of this study was to evaluate the clinical outcome of patients undergoing single-dose reirradiation using the Linear Accelerator (LINAC) for brain arteriovenous malformations (AVM).

Methods:

A retrospective study of 37 patients with brain AVM undergoing LINAC reirradiation between April 2003 and November 2011 was carried out. Patient characteristics, for example, gender, age, use of medications, and comorbidities; disease characteristics, for example, Spetzler–Martin grading system, location, volume, modified Pollock–Flickinger score; and treatment characteristics, for example, embolization, prescription dose, radiation dose–volume curves, and conformity index were analyzed. During the follow-up period, imaging studies were performed to evaluate changes after treatment and AVM cure. Complications, such as edema, rupture of the blood–brain barrier, and radionecrosis were classified as symptomatic and asymptomatic.

Results:

Twenty-seven patients underwent angiogram after reirradiation and the percentage of angiographic occlusion was 55.5%. In three patients without obliteration, AVM shrinkage made it possible to perform surgical resection with a 2/3 cure rate. A reduction in AVM nidus volume greater than 50% after the first procedure was shown to be the most important predictor of obliteration. Another factor associated with AVM cure was a prescription dose higher than 15.5 Gy in the first radiosurgery. Two patients had permanent neurologic deficits. Factors correlated with complications were the prescription dose and maximum dose in the first procedure.

Conclusion:

This study suggests that single-dose reirradiation is safe and feasible in partially occluded AVM. Reirradiation may not benefit candidates whose prescribed dose was lower than 15.5 Gy in the first procedure and initial AVM nidus volume did not decrease by more than 50% before reirradiation.

Stereotactic radiosurgery with and without embolization for intracranial arteriovenous malformations: a systematic review and meta-analysis

OBJECT

The effectiveness and risk of stereotactic radiosurgery (SRS) in the management of partially embolized intracranial arteriovenous malformations (AVMs) remain controversial. The aim of this analysis was to assess current evidence regarding the efficiency and safety of SRS for AVM patients with and without prior embolization.

METHODS

To compare SRS in patients with and without embolization, the authors conducted a meta-analysis of studies by searching the literature via PubMed and EMBASE for the period between January 2000 and December 2013, complemented by a hand search. Primary outcome was the rate of AVM obliteration on a 3-year follow-up angiogram. Secondary outcome was the rate of hemorrhage at 3 years after SRS. Tertiary outcome was permanent neurological deficits related to radiation-induced changes.

RESULTS

Ten studies eligible for analysis included 1988 patients: 593 had undergone embolization followed by SRS and 1395 had undergone SRS alone. The AVM obliteration rate was significantly lower in patients who had undergone embolization followed by SRS than in those who had undergone SRS alone (41.0% vs 59%, OR 0.46, 95% CI 0.37-0.56, p < 0.00001). However, the rates of hemorrhage (7.3% vs 5.6%, OR 1.17, 95% CI 0.74-1.83, p = 0.50) and permanent neurological deficits related to radiation-induced changes (3.3% vs 3.4%, OR 1.41, 95% CI 0.64-3.11, p = 0.39) were not significantly different between the two groups.

CONCLUSIONS

Embolization before SRS significantly decreases the AVM obliteration rate. However, there is no significant difference in the risk of hemorrhage and permanent neurological deficits after SRS alone and following embolization. Further validation by well-designed prospective or randomized cohort studies is still needed.

Analysis of the targeting uncertainty of a stereotactic frameless radiosurgery technique for arteriovenous malformation

In order to target arteriovenous malformations (AVM) in a frameless approach, registration of two-dimensional (2D) digital-subtracted-angiographs (DSA) with three-dimensional (3D) computed tomography (CT) is required. Targeting accuracy and delineation of a frameless 2D-DSA and 3D-CT image registration tool based on bony anatomy of the skull was evaluated. This frameless approach assures accurate target localization and can be used in a clinical setting.

Factors Predictive of Obliteration After Arteriovenous Malformation Radiosurgery

Objective:

To investigate predictive factors of complete obliteration following treatment with linac-based stereotactic radiosurgery for intracerebral arteriovenous malformations.

Methods:

Archived plans for 48 patients treated at the British Columbia Cancer Agency and who underwent post-treatment digital subtraction angiography to assess obliteration were studied. Actuarial estimates of obliteration were calculated using the Kaplan-Meier method. Univariate and multivariate Cox proportional hazards models were used for analysis of incidence of obliteration. Log-rank test was used to search for parameters associated with obliteration.

Results:

Complete nidus obliteration was achieved in 38/48 patients (79.2%). Actuarial rate of obliteration was 75.9% at 4 years (95% confidence interval 63.1%-88.6%). On univariate analysis, prescribed dose to the margin (p=0.002) and dose to isocentre (p=0.022) showed statistical significance. No parameters were significant in a multivariate model. According to the log-rank test, prescribed dose to the margin of >20 Gy (p=0.004) and dose to the isocentre of >25 Gy (p=0.004) were associated with obliteration.

Conclusion:

Reported series in the literature suggest a number of different factors are predictive of complete obliteration of arteriovenous malformations following radiosurgery. However, differing definitions of volume and complete obliteration makes direct comparison between series difficult. This study demonstrates that complete obliteration of the nidus following linear accelerator-based stereotactic radiosurgery for arteriovenous malformations appears to be most closely related to the prescribed marginal dose. In particular, a marginal dose of >20Gy is strongly associated with obtaining complete obliteration of the nidus.

Staged-volume radiosurgery for large arteriovenous malformations: a review

Stereotactic radiosurgery is an effective management strategy for properly selected patients with arteriovenous malformations (AVMs). However, the risk of postradiosurgical radiation-related injury is higher in patients with large AVMs. Multistaged volumetric management of large AVMs was undertaken to limit the radiation exposure to the surrounding normal brain. This strategy offers a promising method for obtaining high AVM obliteration rates with minimal normal tissue damage. The use of embolization as an adjunctive method in the treatment of large AVMs remains controversial. Unfortunately, staged-volume radiosurgery (SVR) has a number of potential pitfalls that affect the outcome. The aim of this article is to highlight the role of SVR in the treatment of large AVMs, to discuss the outcome comparing it to other treatment modalities, and to discuss the potential improvement that could be introduced to this method of treatment.

Linear accelerator stereotactic radiosurgery in the management of intracranial arteriovenous malformations: long-term outcome

BACKGROUND

Arteriovenous malformation (AVM) is one of the cerebrovascular diseases that bear a high risk of hemorrhage. The treatment modalities include microsurgical resection, endovascular embolization, stereotactic radiosurgery, or combinations that vary widely. Several large series have been reported, while data from Asian populations were few. The aim of this study was to examine the efficacy of linear accelerator stereotactic radiosurgery (LINAC SRS) for the treatment of intracranial AVMs, to evaluate the hemorrhage rate and to analyze associated factors.

METHODS

One hundred and sixteen patients with AVM were treated with LINAC SRS in a single institute between September 1994 and May 2005 and were retrospectively evaluated. The demographics of patients, clinical characteristics of AVM, the treatment modalities, and the parameters of the LINAC SRS were analyzed. Delayed toxicity and hemorrhage rate after treatment were also evaluated. The AVM obliteration and bleed rates were calculated using the Kaplan-Meier method and Cox regression analyses.

RESULTS

The efficacy rate with total obliteration after treatment was 81.9% (95 of 116 patients). The median interval to achieve total obliteration was 49 months. Microsurgical resection combined with SRS for residual AVMs achieved better obliteration rates compared to SRS alone (statistically significant, p = 0.001), while no significant difference was found between the embolization group and the group with no prior treatment (p = 0.895). The Spetzler-Martin grade of AVM is a relative factor of obliteration, higher grades resulting in a worse outcome (p = 0.009). Obliteration was significantly influenced by AVM volume in univariate analysis (p = 0.034), and volume <5 cm(3) contributed to improved obliteration (p = 0.01). There was no statistically significant difference in the hemorrhagic rate and the complication rate between ruptured and unruptured AVMs, while the unruptured group had a higher obliteration rate (p = 0.024). The annual hemorrhage rate after LINAC SRS treatment was 1.9%. The bleeding rate was 3.3% in the first year after radiosurgery, 2.1% in the second year, 1.9% between the second and fifth year, and 1.5% between the fifth and tenth year. Patients with hemorrhagic events before radiosurgery appeared to have a higher rebleeding risk during the latency period. Twenty-three patients (19.8%) had late adverse effects with regard to posttreatment radiological follow-up, but only 1 (0.8%) had newly developed neurological deficits.

CONCLUSION

LINAC SRS achieved a high obliteration rate and reduced the risk of hemorrhage effectively in ruptured and unruptured intracranial AVMs. Prior microsurgical resection provided better outcome, while embolization showed no benefit. Adverse effects after treatment are acceptable and require long-term follow-up.

Intensity-modulated stereotactic radiosurgery for arteriovenous malformations: guidance for treatment planning

Background

Stereotactic Radiosurgery (SRS) is a common tool used to treat Arteriovenous Malformations (AVMs) in anatomical locations associated with a risk of surgical complications. Despite high rates of clinical effectiveness, SRS carries a risk of toxicity as a result of radiation injury to brain tissue. The use of intensity-modulated radiotherapy (IMRT) has increased because it may lead to improved PTV conformity and better Normal Tissue (NT) sparing compared to 3D Conformal Radiotherapy (3DCRT). The aim of this study was twofold: 1) to develop simple patient stratification rules for the recommendation of IMRT planning strategies over 3DCRT in the treatment of AVMs with SRS; and 2) to estimate the impact of IMRT in terms of toxicity reduction using retrospectively reported data for symptomatic radiation injury following SRS.

Methods

Thirty-one AVM patients previously treated with 3DCRT were replanned in a commercial treatment planning system using 3DCRT and static gantry IMRT with identical beam arrangements. The radiotherapy planning metrics analyzed included AVM volume, diameter, and volume to surface area ratio. The dosimetric endpoints analyzed included conformity index improvements and NT sparing measured by the maximum NT dose, and the volume of surrounding tissue that received 7Gy and 12Gy.

Results

Our analysis revealed stratified subsets of patients for IMRT that were associated with improved conformity, and those that were associated with decreased doses to normal tissue. The stratified patients experienced an improvement in conformity index by −6-68%, a reduction in the maximum NT dose by −0.5-12.3%, a reduction in the volume of NT receiving 7Gy by 1-8 cc, and a reduction in the volume of NT receiving 12Gy by 0–3.7 cc. The reduction in NT receiving 12Gy translated to a theoretical decrease in the probability of symptomatic injury by 0–9.3%.

Conclusions

This work indicates the potential for significant patient improvements when treating AVMs and provides rules to predict which patients are likely to benefit from IMRT.

Advances in Radiosurgery for Arteriovenous Malformations of the Brain

Arteriovenous malformations of the brain are a considerable source of morbidity and mortality for patients who harbor them. Although our understanding of this disease has improved, it remains in evolution. Advances in our ability to treat these malformations and the modes by which we address them have also improved substantially. However, the variety of patient clinical and disease scenarios often leads us into challenging and complex management algorithms as we balance the risks of treatment against the natural history of the disease. The goal of this article is to provide a focused review of the natural history of cerebral arteriovenous malformations, to examine the role of stereotactic radiosurgery, to discuss the role of endovascular therapy as it relates to stereotactic radiosurgery, and to look toward future advances.

Multi-staged robotic stereotactic radiosurgery for large cerebral arteriovenous malformations

PURPOSE

To investigate a multi-staged robotic stereotactic radiosurgery (SRS) delivery technique for the treatment of large cerebral arteriovenous malformations (AVMs). The treatment planning process and strategies to optimize both individual and composite dosimetry are discussed.

METHODS

Eleven patients with large (30.7 ± 19.2 cm(3)) AVMs were selected for this study. A fiducial system was designed for fusion of targets between planar angiograms and simulation CT scans. AVMs were contoured based on single contrast CT, MRI and orthogonal angiogram images. AVMs were divided into 3-8 sub-target volumes (3-7 cm(3)) for sequential treatment at 1-4 week intervals to a prescription dose of 16-20 Gy. Forward and inversely developed treatment plans were optimized for 95% coverage of the total AVM volume by dose summation from each sub-volume, while minimizing dose to surrounding tissues. Dose-volume analysis was used to evaluate the PTV coverage, dose conformality (CI), and R50 and V12 Gy parameters.

RESULTS

The treatment workflow was commissioned and able to localize within 1mm. Inverse optimization outperformed forward planning for most patients for each index considered. Dose conformality was shown comparable to staged Gamma Knife treatments.

CONCLUSION

The CyberKnife system is shown to be a practical delivery platform for multi-staged treatments of large AVMs using forward or inverse planning techniques.

Intracranial arteriovenous malformations treated with LINAC-based conformal radiosurgery: validation of the radiosurgery-based arteriovenous malformation score as a predictor of outcome

OBJECTIVE

To validate the radiosurgery-based arteriovenous malformation score (RBAS) as a predictor of outcome in patients with arteriovenous malformations (AVMs) treated with LINAC-based conformal radiosurgery.

METHODS

We analysed 40 patients with a mean follow-up of 22 months. One patient (2.5%) pertained to Spetzler-Martin Grade I, 11 (27.5%) to Grade II, 19 (47.5%) to Grade III, eight (20%) to Grade IV and one (2.5%) to grade V. The mean RBAS was 2.0 (range: 0.76-5.56). The mean obliteration prediction index (OPI) and the Karlsson index (KI) were 0.74 (range: 0.2-2.86) and 109.48 (range: 3.0-350.7) respectively. Outcomes were analysed according to the OPI, KI and RBAS.

RESULTS

We analysed different cutoff points in the RBAS and found a significant difference to predict the outcome in four scores: 1.2, 1.6, 1.7 and 1.8. In the group with RBAS < or = 1.8, 13 (68%) had an excellent outcome and six (33%) did not, while with RBAS>1.8, seven (32%) had an excellent outcome and 14 (67%) did not (p = 0.02). We did not find any correlation between Spetzler-Martin grading scale or OPI and outcome (p = 0.7 and p = 0.3 respectively). The KI predicted the excellent outcome in 8/9 patients (89%) with KI < or = 27 and in 12/31 patients (39%) with KI>27 (p = 0.08).

CONCLUSION

The RBAS seems to be a good predictor of outcome in patients with AVMs treated with LINAC-based conformal radiosurgery as in patients treated with Gamma Knife. It remains only to find the best cutoff point based on a larger series and longer follow-up.

Tomotherapy radiosurgery for arteriovenous malformations--current possibilities and future options with helical tomotherapy dynamic jaws?

This planning study was performed to compare stereotactic linac based radiosurgery of Arteriovenous Malformations (AVM) with current Helical Tomotherapy (HT) and future HT techniques. For 10 patients with AVM, dose distributions and treatment times of “regular” HT delivery (Reg 2.5/1/0.6 cm field width), Running-Start-Stop Treatment (RSS 5/2.5 cm), Axial Mode (Axial 5 cm) and Dynamic Jaw/Dynamic Couch delivery with a maximum field width of 5 cm (DJDC 5) were analysed and compared to linac-based stereotactic radiosurgery. Axial produced the fastest treatment (Axial 4:47 min vs. Linac 32:42 min) at the cost of large brain exposure (V_10% 289 ml). Except for Reg 0.6, all other HT techniques achieved significantly shorter treatment times than linac-based treatment (e.g. Reg 1, 19:42 min, DJDC 6:30 min). However, high-dose brain exposure (V_60%) was higher in all HT plans (e.g. Reg 0.6, 10 ml, Linac 9 ml), and only Reg 0.6 showed better low-dose exposure (V_10% of 167 ml vs. 199 ml, not significant). Neither current nor future HT modes in their current version outperformed linac-based stereotactic radiosurgery. However, AVM with special geometry might still benefit from HT.

Treatment for brain arteriovenous malformation in the 1998-2011 period and review of the literature

PURPOSE

The results of the treatment of pial AVM provided at our neurosurgical centre are presented. Based on these results and on an overview of literary data on the efficacy and complications of each therapeutic modality, the algorithm of indications, as used at our institution, is presented. COHORT OF PATIENTS: The series comprises 195 patients, aged 9 to 87 years and treated in the years 1998-2011. The surgical group consists of 76 patients; of these, 49 patients solely received endovascular treatment, 25 were consulted and referred directly to the radiosurgical unit, and the remaining 45 were recommended to abide by the strategy of "watch and wait".

RESULTS

In the surgical group, serious complications were 3.9 %, at a 96.1 % therapeutic efficacy. As for AVM treated with purely endovascular methods, serious procedural complications were seen in 4.1 % of patients, with efficacy totalling 32.7 %. One observed patient suffered bleeding, resulting in death. For comparison with literary data for each modality, a survival analysis without haemorrhage following monotherapy for AVM with each particular modality was carried out.

CONCLUSIONS

Based on our analysis, we have devised the following algorithm of treatment: 1. We regard surgical treatment as the treatment of choice for AVM of Spetzler-Martin (S-M) grades I and II, and only for those grade III cases that are surgically accessible. 2. Endovascular intervention should mainly be used for preoperative embolisation, as a curative procedure for lower-grade AVM in patients with comorbidities, and as palliation only for higher-grade cases. 3. Stereotactic irradiation with Leksell Gamma Knife (LGK) is advisable, mainly for poorly accessible, deep-seated grade-III AV malformations. In the case of lower grades, the final decision is left to the properly informed patient. 4. Observation should be used as the method of choice in AVM of grades IV and V, where active therapy carries greater risk than the natural course of the disease.

Factors predictive of symptomatic radiation injury after linear accelerator-based stereotactic radiosurgery for intracerebral arteriovenous malformations

PURPOSE

To investigate predictive factors in the development of symptomatic radiation injury after treatment with linear accelerator-based stereotactic radiosurgery for intracerebral arteriovenous malformations and relate the findings to the conclusions drawn by Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC).

METHODS AND MATERIALS

Archived plans for 73 patients who were treated at the British Columbia Cancer Agency were studied. Actuarial estimates of freedom from radiation injury were calculated using the Kaplan-Meier method. Univariate and multivariate Cox proportional hazards models were used for analysis of incidence of radiation injury. Log-rank test was used to search for dosimetric parameters associated with freedom from radiation injury.

RESULTS

Symptomatic radiation injury was exhibited by 14 of 73 patients (19.2%). Actuarial rate of symptomatic radiation injury was 23.0% at 4 years. Most patients (78.5%) had mild to moderate deficits according to Common Terminology Criteria for Adverse Events, version 4.0. On univariate analysis, lesion volume and diameter, dose to isocenter, and a V(x) for doses ≥8 Gy showed statistical significance. Only lesion diameter showed statistical significance (p < 0.05) in a multivariate model. According to the log-rank test, AVM volumes >5 cm(3) and diameters >30 mm were significantly associated with the risk of radiation injury (p < 0.01). The V(12) also showed strong association with the incidence of radiation injury. Actuarial incidence of radiation injury was 16.8% if V(12) was <28 cm(3) and 53.2% if >28 cm(3) (log-rank test, p = 0.001).

CONCLUSIONS

This study confirms that the risk of developing symptomatic radiation injury after radiosurgery is related to lesion diameter and volume and irradiated volume. Results suggest a higher tolerance than proposed by QUANTEC. The widely differing findings reported in the literature, however, raise considerable uncertainties.

Proposal for a new prognostic score for linac-based radiosurgery in cerebral arteriovenous malformations

PURPOSE

We evaluate patient-, angioma-, and treatment-specific factors for successful obliteration of cerebral arteriovenous malformations (AVM) to develop a new appropriate score to predict patient outcome after linac-based radiosurgery (RS).

METHODS AND MATERIALS

This analysis in based on 293 patients with cerebral AVM. Mean age at treatment was 38.8 years (4-73 years). AVM classification according Spetzler-Martin was 55 patients Grade I (20.5%), 114 Grade II (42.5%), 79 Grade III (29.5%), 19 Grade IV (7.1%), and 1 Grade V (0.4%). Median maximum AVM diameter was 3.0 cm (range, 0.3-10 cm). Median dose prescribed to the 80% isodose was 18 Gy (range, 12-22 Gy). Eighty-five patients (29.1%) had prior partial embolization; 141 patients (51.9%) experienced intracranial hemorrhage before RS. Median follow-up was 4.2 years.

RESULTS

Age at treatment, maximum diameter, nidus volume, and applied dose were significant factors for successful obliteration. Under presumption of proportional hazard in the dose range between 12 and 22 Gy/80% isodose, an increase of obliteration rate of approximately 25% per Gy was seen. On the basis of multivariate analysis, a prediction score was calculated including AVM maximum diameter and age at treatment. The prediction error up to the time point 8 years was 0.173 for the Heidelberg score compared with the Kaplan-Meier value of 0.192. An increase of the score of 1 point results in a decrease of obliteration chance by a factor of 0.447.

CONCLUSION

The proposed score is linac-based radiosurgery-specific and easy to handle to predict patient outcome. Further validation on an independent patient cohort is necessary.

Linac stereotactic radiosurgery for the treatment of small arteriovenous malformations: lower doses can be equally effective

OBJECTIVE

The purpose of this study was to examine the efficacy and toxicity of treating small arteriovenous malformations (AVMs) (≤3 cm in diameter) with a median marginal applied dose of 14 Gy.

METHODS

Two hundred and thirteen patients diagnosed with AVMs were treated between January 1991 and December 2005. Seventy-three percent of the patients had hemorrhaged prior to treatment, 13% had had previous surgery and 19.2% had had previous embolization. The median follow-up duration was 48.1 months.

RESULTS

The Kaplan-Meier analysis estimated that the 36-month obliteration rate was 65.5% for patients undergoing their first stereotactic radiosurgery (SRS) and 68.3% for those undergoing repeated SRS. The Kaplan-Meier analysis estimated the 60-month AVMs obliteration rate for the entire cohort to be 82.4%. The median time to AVM obliteration was 40 ± 2.8 months. We found a statistically significant relationship between the time of obliteration and the following factors: site of the AVMs (sites other than brainstem), a higher prescribed dose and a positive history of previous hemorrhage. Thirteen patients (7.6%) experienced toxicities.

CONCLUSIONS

SRS was an effective and safe treatment for AVMs ≤3 cm in diameter, with acceptable toxicity.

Role of external beam radiotherapy for arteriovenous malformation of the pancreas

Pancreatic arteriovenous malformation (PAVM) is rare and is mainly reported from Asian countries. We incidentally encountered an asymptomatic, early-stage PAVM in a patient who presented with portal venous distention, Child B liver cirrhosis, and hepatoma. The PAVM had multiple feeding arteries and drainage into the portal vein and varices. Because surgery was not indicated, after considering the risks and bene-fits the patient chose treatment with 40 Gy of conformal radiotherapy for 4 weeks. Computed tomography performed 6 months later revealed reduction in the size of the PAVM. Treatment had lasting effects for 18 months without significant toxicity. As observed in many reports of radiotherapy for various AVMs, the radiotherapy may stall self-augmenting growth of the AVM. Conventional fractionated radiotherapy of 40 Gy may be a useful choice for early-stage PAVM.

Repeat Radiosurgery for Intracranial Arteriovenous Malformations

BACKGROUND

Despite a high success rate in the stereotactic radiosurgical treatment of intracranial arteriovenous malformations (AVMs) that cannot be safely resected with microsurgery, some patients must be managed after treatment failure.

OBJECTIVE

To provide an update on the use of repeat linear accelerator radiosurgery as a treatment for failed AVM radiosurgery at the University of Florida.

METHODS

We reviewed 103 patients who underwent repeat radiosurgical treatment for residual AVM at the University of Florida between December 1991 and December 2007. Each of these patients had at least 2 radiosurgical treatments for the same AVM. Patient information, including AVM nidus volume, prescription dose, age, and sex, was collected at the time of initial treatment and again at the time of retreatment. Patients were followed up after treatment with magnetic resonance, computed tomography, and angiographic imaging at standard intervals to determine the status of their AVM. The median follow-up after retreatment was 31 months.

RESULTS

Between the first and second treatments, the median AVM nidus volume was decreased by 69% (from a median volume of 12.7 to 4.0 cm3), allowing the median prescribed dose to be increased from 1500 cGy on initial treatment to 1750 cGy on retreatment. The final obliteration rate on retreatment was 65.3%. After salvage retreatment, 5 patients (4.9%) experienced radiation-induced complications, and 6 patients (5.8%) experienced posttreatment hemorrhage.

CONCLUSION

Repeat radiosurgery is a safe and effective salvage treatment for AVMs.

Integration of three-dimensional rotational angiography in radiosurgical treatment planning of cerebral arteriovenous malformations

PURPOSE

Accuracy in delineating the target volume is a major issue for successful stereotactic radiosurgery for arteriovenous malformations. The aim of the present study was to describe a method to integrate three-dimensional (3D) rotational angiography (3DRA) into CyberKnife treatment planning and to investigate its potential advantages compared with computed tomography angiography (CTA) and magnetic resonance angiography.

METHODS AND MATERIALS

A total of 20 patients with a diagnosis of cerebral arteriovenous malformation were included in the present study. All patients underwent multislice computed tomography and 3D-volumetric CTA, 3DRA, and 3D magnetic resonance angiography. The contouring of the target and critical volumes was done separately using CTA and thereafter directly using 3DRA. The composite, conjoint, and disjoint volumes were measured.

RESULTS

The use of CTA or 3DRA resulted in significant differences in the target and critical volumes. The target volume averaged 3.49 ± 3.01 mL measured using CTA and 3.26 ± 2.93 mL measured using 3DRA, for a difference of 8% (p < .05). The conjoint and disjoint volume analysis showed an 88% volume overlap. The qualitative evaluation showed that the excess volume obtained using CTA was mostly tissue surrounding the nidus and venous structures. The mean contoured venous volume was 0.67 mL measured using CTA and 0.88 mL (range, 0.1-2.7) measured using 3DRA (p < .05).

CONCLUSIONS

3DRA is a volumetric angiographic study that can be integrated into computer-based treatment planning. Although whether 3DRA provides superior accuracy has not yet been proved, its high spatial resolution is attractive and offers a superior 3D view. This allows a better 3D understanding of the target volume and distribution of the radiation doses within the volume. Additional technical efforts to improve the temporal resolution and the development of software tools aimed at improving the performance of 3D contouring are warranted.

Repeated linac-based radiosurgery in high-grade cerebral arteriovenous-malformations (AVM) Spetzler-Martin grade III to IV previously treated with radiosurgery

BACKGROUND

Aim was to access outcome and toxicity of repeated linac-based radiosurgery in incompletely obliterated cerebral AVM.

PATIENTS AND METHODS

Between 1998 and 2008, 11 patients were treated with repeated radiosurgery. The median dose to the 80%-isodose was 15 Gy (range, 12-18 Gy). During initial radiosurgery the median dose was 18 Gy (range, 9-22 Gy).

RESULTS

The median time interval between initial radiosurgery and re-treatment was 9 years (range, 4-16 years). The median follow-up was 26 months (range, 2-115 months). Treatment response was seen in 8 patients (89%). Complete (partial) obliteration was achieved in 5 (3) patients (56%, 33%, respectively).The median time to complete obliteration was 26 months (range, 5-45 months). Pre-existing neurological symptoms improved in 2 patients (18%), were stable in 7 patients (64%) and worsened in 2 patients (18%). Prevalence of intracranial hemorrhage was 9% (1/11). Post-re-treatment intracranial hemorrhage rate was 2.7% (1/38 years at risk). During follow-up, no secondary malignancies or toxicity>grade III were observed.

CONCLUSION

Repeated linac-based radiosurgery in incompletely obliterated cerebral AVM is an effective treatment option with a high rate of treatment response and an acceptable risk for side effects. Marginal doses above 15 Gy might further improve the rate of complete obliterations.

The radiosurgical treatment of arteriovenous malformations: obliteration, morbidities, and performance status

OBJECTIVE

This study examined the single-center treatment outcomes of arteriovenous malformations (AVMs) of the brain using stereotactic radiosurgery, with regard to obliteration, predictive factors, morbidities, and patient performance status.

PATIENTS AND METHODS

127 patients were treated between 1990 and 2008 by use of linear accelerator or Gamma Knife. Their median age was 37 years, the median AVM volume was 7.3 cc (range, 0.014-113.13 cc), and the median follow-up duration was 42 months (range, 6-209 months). Forty-two percent of patients presented with intracranial hemorrhage, 31% received embolization, and 8% underwent prior resection. Thirty-one percent of patients received more than one round of radiosurgery.

RESULTS

64% of patients had complete obliteration confirmed by magnetic resonance imaging or angiography. Positive predictors of obliteration included pretreatment hemorrhage (p = 0.042), smaller AVM volume (odds ratio = 1.25; 95% CI, 1.03-1.52), and larger marginal dose (odds ratio = 0.292; 95% CI, 0.100-0.820), whereas embolization (p < 0.001) was a negative predictor . The annual risk of hemorrhage after radiosurgery was 2.2%, and the risk of death as a result of hemorrhage was 0.6-1.3%. Eleven percent of patients reported new or worsened neurologic symptoms. Radiosurgery was effective in treating AVM-related headaches (p < 0.001) but did not improve the performance status of patients.

CONCLUSIONS

Stereotactic radiosurgery is an effective tool in the treatment of AVMs and amelioration of AVM-related headaches, but it did not affect the patients' performance status. Factors affecting obliteration include prior hemorrhage, marginal dose, prior embolization, and AVM volume. Risk of hemorrhage persists in the latency period after radiosurgery, and it remains finite even after complete obliteration.

Clinical outcome after repeated radiosurgery for brain arteriovenous malformations

INTRODUCTION

We assessed the clinical and radiological outcome after repeated radiosurgery for brain arteriovenous malformations (bAVMs) after failure of initial radiosurgery.

MATERIALS AND METHODS

Fifteen patients underwent repeated radiosurgery. The mean bAVM volume at first radiosurgery (S1) was 4.6 +/- 4.3 ml and that at second radiosurgery (S2) was 2.1 +/- 2.5 ml. The median marginal dose was 18 Gy at S1, and 21 Gy at S2. Modified Rankin Scale (MRS) score was determined in all patients at last follow-up (FU).

RESULTS

Complete obliteration was reached in nine patients (60%). Median time to obliteration was 50 months after S2. An excellent outcome (no new neurologic deficiencies, complete obliteration) was reached in seven patients (47%). Eleven patients (73%) showed a MRS1. Radiation-induced complications occurred in 20%, of which 13% occurred after S2. Radiological complications included cyst formation (n = 1), radiation-related edema (n = 4), and radiation necrosis (n = 1), resulting in an increasing mean MRS of 0.5 at S1, 0.6 at S2, to 0.8 at FU. No (re-)bleedings were encountered during 137-patient years at risk.

DISCUSSION

Repeated radiosurgery is a viable option for the treatment of small remnant bAVMs. We report 20% permanent radiation-induced complications. Such complications were mainly seen in relatively large, and therefore difficult to treat, bAVMs.

Gene expression signatures in the peripheral blood after radiosurgery of human cerebral arteriovenous malformations

PURPOSE

To unravel biological mechanisms potentially resulting in the obliteration process after radiosurgery (RS) of human cerebral arteriovenous malformations (AVMs) by investigating molecular signatures on the transcriptomic level in peripheral blood of patients.

PATIENTS AND METHODS

Venous blood samples were obtained at definite points of time before and after RS. The samples were tested for radiation-induced changes regarding biological markers (mRNA) using cDNA and oligo-microarray technology. The corresponding expression profiles were correlated with clinical data and obliteration signs in radiologic imaging.

RESULTS

The proof of principle that RS outcome can be successfully correlated with transcriptomics of cellular blood components as disease parameter was demonstrated. The authors identified 76 differentially regulated genes (p < 0.001) after RS. Interestingly, in particular genes with known roles in anti-angiogenic and pro-coagulative pathways were identified as potentially relevant. In particularly, the authors found a significant downregulation of neuropilin-2, protein C inhibitor and cyclin-dependent kinase 6. They also found that low pretreatment blood mRNA levels of TLR4 (toll-like receptor 4) and STAT3 (signal transducer and activator of transcription 3) correlated with fast obliteration of AVMs.

CONCLUSION

The authors report on a novel technique for molecular biological analysis of blood from patients with cerebral AVM treated with RS. Differential regulation of genes in peripheral blood was successfully correlated with RS and time to obliteration of AVMs. The identified genes indicate a potential new methodology to monitor RS, which may result in an individualized therapy and optimized follow-up.

Validation of the radiosurgery-based arteriovenous malformation score in a large linear accelerator radiosurgery experience

Object

The radiosurgery-based arteriovenous malformation (AVM) score (RBAS) is a grading system designed to predict patient outcomes after Gamma Knife surgery for AVMs. This study seeks to validate independently the predictive nature of the RBAS, not only after single treatment but for retreatment, and to assess the overall outcome regardless of number of radiosurgeries.

Methods

The authors analyzed 403 patients treated with linear accelerator (LINAC) radiosurgery for AVMs between May 1988 and June 2008. The AVM scores were determined by the following equation: AVM score = (0.1 × volume in cm3) + (0.02 × age in years) + (0.3 × location). The location values are as follows: frontal/temporal = 0, parietal/occipital/corpus callosum/cerebellar = 1, and basal ganglia/thalamus/brainstem = 2.

Results

Testing demonstrated that the RBAS correlated with excellent outcomes after single or repeat radiosurgery (p < 0.001 for both variables). One hundred sixty-two (49%) of 330 patients had excellent outcomes (obliteration without deficit) after a single treatment. Excellent outcomes were achieved in 74, 64, 50, and 11% of patients with AVM scores of < 1.0 (Group 1), between 1.0 and < 1.8 (Group 2), between 1.8 and < 2.5 (Group 3), and ≥ 2.5 (Group 4), respectively. Fifty-one patients (70%) obtained radiosurgical cure and 46 (63%) achieved excellent outcomes after repeat radiosurgery. Of these, 100% achieved excellent outcomes in Group 1, 70% did so in Group 2, 47% in Group 3, and 14% in Group 4. The RBAS correlated with excellent outcomes after overall treatment (p < 0.001). Two hundred seventy-seven patients (69%) obtained AVM obliteration, and 62% achieved excellent outcomes. In Group 1, 87% achieved excellent outcomes, 75% did so in Group 2, 61% in Group 3, and 24% in Group 4.

Conclusions

The RBAS is a good predictor of patient outcomes after LINAC radiosurgery.

Stereotactic radiosurgery with an upper partial denture

A 54-year-old male with partial denture underwent stereotactic radiosurgery with an infrared camera-guided system for a metastatic brain tumor arising from lung cancer. Although this method utilizes a biteplate mounted on the upper jaw to detect head movement, the patient only had four teeth in his upper jaw. In order to stabilize the biteplate, the maxillary denture was fixed to the biteplate with an autopolymerizing resin. In addition, the rest-occlusal position of the lower jaw was impressed on the inferior surface of the biteplate with an autopolymerizing resin. To assess reproducibility and stability, the distance between the left and right incus and left and right markers was measured during pre-planning, as well as before and after stereotactic irradiation. Wearing the biteplate ensures the accuracy of radiotherapy planning for the implementation of radiosurgery in patients who have many maxillary teeth missing. However, a large degree of error was observed when the biteplate was removed.

Thrombosis and hemorrhage in the acute period following Gamma Knife surgery for arteriovenous malformation

Bleeding of an arteriovenous malformation (AVM) following stereotactic radiosurgery (SRS) is a known risk during the latency interval, but hemorrhage in the 30-day period following radiosurgery rarely has been reported in the literature. The authors present the case of a 57-year-old man who underwent Gamma Knife surgery for a large AVM, and they provide radiographic documentation of a thrombus in the primary draining vein immediately preceding an AVM hemorrhage within 9 days after radiosurgery. They postulate that the pathophysiology of an AVM hemorrhage in the acute period following SRS is related to an association among tissue irradiation, acute inflammatory response, and vessel thrombosis.

The authors also review the literature on risk factors for hemorrhage due to untreated and radiosurgically treated AVMs. Recent evidence on the role of inflammation in the pathogenesis of AVMs and the pathophysiology of AVM rupture is presented. Inflammatory markers have been demonstrated in brain AVM tissue, and the association between inflammation and AVM hemorrhage has been established. There is an acute inflammatory response following tissue irradiation, resulting in structural and functional vascular changes that can lead to vessel thrombosis. Early hemorrhage following radiosurgical treatment of AVMs may be related to the acute inflammatory response and associated vascular changes that occur in irradiated tissue. In the first stage of a planned 2-stage Gamma Knife treatment for a large AVM in the featured case, the superior posteromedial portion of the primary draining vein was included in the treatment field. The authors present the planning images and subsequent CT scans demonstrating a new venous thrombus in the primary draining vein. An acute inflammatory response following radiosurgery with resultant acute venous thrombus formation and venous obstruction is proposed as one mechanism of an AVM hemorrhage in this patient. Radiographic evidence of the time course of thrombosis and hemorrhage supports the hypothesis that acute venous obstruction is a cause of intracranial hemorrhage.

Special aspects of diagnostic imaging for radiosurgery of arteriovenous malformations

OBJECTIVE

Radiosurgery can be considered a well-established option for the treatment of arteriovenous malformations (AVMs). The exact application of the therapeutic dose is based on the availability of imaging data sets with superior image quality that can be superimposed using an image fusion algorithm. For follow-up studies, the quantitative comparison of the respective image data sets also plays an important role. Until now, digital subtraction angiography (DSA) has been a mandatory tool for treatment planning and follow-up procedures. The aim of this study was to investigate whether a suitable computed tomographic (CT) and/or magnetic resonance (MR) angiography procedure can replace DSA and, if so, in which cases.

METHODS

For 34 AVM patients, various MR data sets were used together with the stereotactically localized CT and DSA data sets for treatment planning. To define the AVM nidus precisely, all available MR data sets were fused onto the CT data set by the use of an automatic image fusion algorithm. The nidus was outlined in both localized DSA projections, resulting in the DSA target volume. Subsequently, the DSA target volume was adapted by inclusion of the available CT/MR data sets (localized and/or fused, slice by slice), resulting in the final target volume. Finally, both volumes were compared and analyzed. For precise comparison purposes, all available digital follow-up studies were fused.

RESULTS

In all cases, the thin-slice MR data sets (1-mm slice width) that included T1-weighted series and time of flight angiographies have been precisely fused onto the stereotactically localized treatment planning CT. The final target volume was compared with the DSA target volume as follows. In 19 cases, the final target volume was larger than the DSA target volume; in six cases, it was smaller; and in five cases, it was approximately equal. The difference was significant (Wilcoxon test, difference <0.0001; t test, t = 3.01; P > 0.005). In four cases, outlining the AVM was not possible without DSA. In five patients, a two- or three-vessel DSA was needed because there were different AVM compartments. In cases in which a previous partial embolization had been undergone by the patient, the use of superimposed CT sets with and without contrast medium was important to define the completely embolized partial volumes that were not subject to treatment. The inclusion of the DSA images enabled a better identification of those arterialized veins that did not belong to the nidus. In six cases, the follow-up MR studies showed contrast enhancements overlapping the AVM nidus as a result of brain-blood barrier disturbances (T1-weighted series with contrast). In seven cases, perifocal reactions were primarily observed (T2-weighted series) 12 months after treatment with rather low clinical relevance.

CONCLUSION

By integrating all available imaging modalities, the exact three-dimensional definition of the AVM nidus was safely realized for all patients. Stereotactic DSA data acquisition remains a crucial tool for safe nidus definition in radiosurgery treatment planning and cannot, therefore, be discarded at present. It is recommended that a quantitative comparison of all MR follow-up studies be established.

Treatment of arteriovenous malformations using Gamma Knife surgery: the experience at the University of Washington from 2000 to 2005

Object

The purpose of this study was to examine the efficacy and toxicity of treating arteriovenous malformations (AVMs) with the model 3C Gamma Knife at the University of Washington Medical Center.

Methods

Ninety-five evaluable patients with 99 treatable AVMs were treated at the University of Washington Medical Center from April 2000 through June 2005. The median patient age at the time of treatment was 40 years (range 6–68 years). The male to female patient ratio was 0.98:1. The median AVM volume treated was 3.8 cm3 (range 0.12–32 cm3). Forty-four percent of the patients had hemorrhaged prior to treatment. The median peripheral Gamma Knife surgery dose was 20 Gy with a median of 12 isocenters treated. The median follow-up duration was 38 months (range 3–91 months). Eighty-one percent of the patients had no previous stereotactic radiosurgery (SRS), whereas the remaining 19% had previously been treated with linear accelerator–based SRS.

Results

The Kaplan–Meier estimated 6-year AVM obliteration rate for the entire cohort was 71.4%. The Kaplan–Meier estimated 6-year obliteration rate was 72% for patients having no prior SRS and 54.5% for those undergoing repeat SRS. The median time to AVM obliteration was 47 months, with 90% of the obliterations occurring between 24 and 58 months. Eight patients (7.4%) experienced late toxicities. There were 2 fatal bleeds and 13 (13.8%) nonfatal bleeds after Gamma Knife surgery.

Conclusions

Gamma Knife surgery is an effective treatment for AVMs, resulting in an excellent obliteration rate with acceptable toxicity.

[Advances in radio-oncology. From precision radiotherapy with photons to ion therapy with protons and carbon ions]

Modern techniques in radiation oncology, such as fractionated stereotactic radiotherapy (FSRT), stereotactic radiosurgery (SRS) or intensity modulated radiotherapy (IMRT) allow the application of high local doses to defined treatment volumes, while normal structures in close vicinity can be spared; high local control rates can be achieved, while treatment-related toxicity can be minimized. Innovative Hi-Art tomotherapy systems offer an alternative, combining a 6 MV photon accelerator with a CT scanner. Ion beams, such as protons and carbon ions, have been shown to be beneficial for distinct tumor entities. Both offer a characteristic physical dose distribution with an inverse dose profile contributing to beneficial dose conformality. Carbon ions also offer the advantage of increased relative biological effectiveness. For certain tumor types, a significant increase in local control and survival rates could be obtained with carbon ions.

[Treatment options for arteriovenous malformations]

Cerebral arteriovenous malformations are errors in the development of vasculature with shunts between cerebral arteries and veins, which manifest predominantly as intracerebral hemorrhage. To prevent hemorrhage, a complete obliteration of the arteriovenous malformation is necessary. For this purpose, techniques of microsurgery, radiotherapy, and embolization alone or in combination are available. This review article presents the treatment options and also summarizes available data from the literature on which therapy should be chosen in which situation and when watchful waiting should be preferred.

Risk of Hemorrhage and Obliteration Rates of LINAC-Based Radiosurgery for Cerebral Arteriovenous Malformations Treated After Prior Partial Embolization

PURPOSE

We investigate patient outcome, risk of hemorrhage, and factors affecting obliteration after LINAC-based radiosurgery (RS) for cerebral arteriovenous malformations (AVM) treated after partial embolization.

METHODS AND MATERIALS

This analysis is based on 50 patients treated after prior embolization. According to the Spetzler-Martin criteria the AVM classification was as follows: 9 patients, Grade I (18%); 19, Grade II (38%); 18, Grade III (36%); and 4, Grade IV (8%). Median RS-based AVM score was 1.41. Median single dose was 18 Gy/ 80% isodose (range, 15-22 Gy) and median AVM volume was 4.0 cc (range, 0.2-22.6 cc). In all, 34 patients (68%) experienced hemorrhage before RS. Median follow-up was 3.1 year (range, 8.5 months to 15 years).

RESULTS

Actuarial complete obliteration rate was 67% after 3 years and 78% after 4 years. The complete obliteration rate was significantly higher in AVM <3 cm (92% vs. 60%, p < 0.01) and in AVM Spetzler-Martin Grade I/II (90% vs. 59%, p < 0,01). Intracranial hemorrhage after RS was seen in 6 patients (12%) after 8.5 months median. Annual bleeding risk was 7.9% after 1 year and 2.2% after 2 years. It was found that AVM diameter > or =3 cm (p < 0.006), AVM volume > or =4 cc (p < 0.01), AVM score > or =1.5 (p < 0.03), and single dose <18 Gy (p < 0.03) were associated with a significant higher bleeding risk.

CONCLUSIONS

The rate of obliteration after RS in AVM treated after prior partial embolization depends on size as well as Spetzler-Martin grade. The risk of intracranial hemorrhage is not increased after RS and depends on AVM score, size, and volume, as well as on applied single dose.

Therapy of brain arteriovenous malformations: multimodality treatment from a balanced standpoint

The three therapeutic modalities for arteriovenous malformation (AVM) treatment (surgery, embolization, and radiotherapy) developed in the past years with specific tools, each tool with its own qualities. Soon after the implementation of embolization for treatment of AVMs, this technique was used in combination with microsurgery; since the development of radiosurgery, treatment algorithms combining embolization with surgery and eventual subsequent radiosurgery, embolization with radiosurgery, or surgery with subsequent radiosurgery have been reported. These different combinations have been in use under the term multimodality treatment for many years, but the algorithms regarding the combination of tools, which tool has priority, and how the risk levels of each tool are assessed shows great variability among institutions. Centers with a surgical background see embolization as a technique to increase surgical feasibility and radiosurgery as a tool to complete subtotal AVM excision. Institutions with an endovascular background embolize AVMs with the aim of maximal occlusion rates and view surgery or radiosurgery as a technique to be used if the goal of total endovascular occlusion cannot be achieved. Radiosurgeons receive patients after incomplete embolization or surgical extirpation or a combination of both.

Particle radiation therapy using proton and heavier ion beams

Particle beams like protons and heavier ions offer improved dose distributions compared with photon (also called x-ray) beams and thus enable dose escalation within the tumor while sparing normal tissues. Although protons have a biologic effectiveness comparable to photons, ions, because they are heavier than protons, provide a higher biologic effectiveness. Recent technologic developments in the fields of accelerator engineering, treatment planning, beam delivery, and tumor visualization have stimulated the process of transferring particle radiation therapy (RT) from physics laboratories to the clinic. This review describes the physical, biologic, and technologic aspects of particle beam therapy. Clinical trials investigating proton and carbon ion RT will be summarized and discussed in the context of their relevance to recent concepts of treatment with RT.