Stereotactic heavy-ion Bragg peak radiosurgery for intra-cranial vascular disorders: method for treatment of deep arteriovenous malformations

A Practical Primer on Particle Therapy

PURPOSE

Particle therapy is a promising treatment technique that is becoming more commonly used. Although proton beam therapy remains the most commonly used particle therapy, multiple other heavier ions have been used in the preclinical and clinical settings, each with its own unique properties. This practical review aims to summarize the differences between the studied particles, discussing their radiobiological and physical properties with additional review of the available clinical data.

METHODS AND MATERIALS

A search was carried out on the PubMed databases with search terms related to each particle. Relevant radiobiology, physics, and clinical studies were included. The articles were summarized to provide a practical resource for practicing clinicians.

RESULTS

A total of 113 articles and texts were included in our narrative review. Currently, proton beam therapy has the most data and is the most widely used, followed by carbon, helium, and neutrons. Although oxygen, neon, silicon, and argon have been used clinically, their future use will likely remain limited as monotherapy.

CONCLUSIONS

This review summarizes the properties of each of the clinically relevant particles. Protons, helium, and carbon will likely remain the most commonly used, although multi-ion therapy is an emerging technique.

Historical Progress of Stereotactic Radiation Surgery

Radiosurgery and stereotactic radiotherapy have established themselves as precise and accurate areas of radiation oncology for the treatment of brain and extracranial lesions. Along with the evolution of other methods of radiotherapy, this type of treatment has been associated with significant advances in terms of a variety of modalities and techniques to improve the accuracy and efficacy of treatment. This paper provides a comprehensive overview of the progress in stereotactic radiosurgery (SRS) over several decades, and includes a review of various articles and research papers, commencing with the emergence of stereotactic techniques in radiotherapy. Key clinical aspects of SRS, such as fixation methods, radiobiology considerations, quality assurance practices, and treatment planning strategies, are presented. In addition, the review highlights the technological advancements in treatment modalities, encompassing the transition from cobalt-based systems to linear accelerator-based modalities. By addressing these topics, this study aims to offer insights into the advancements that have shaped the field of SRS, that have ultimately enhanced the accuracy and effectiveness of treatment.

Effect of high-dose delivery on the attachment of meningiomas in Gamma Knife surgery: a retrospective study

BACKGROUND

Meningiomas have vascular supply from the tumor attachment on the dura mater. Gamma Knife radiosurgery (GKS) is known to have a vascular obliterating effect. This study aims to determine the benefits of high-dose irradiation to the tumor attachment compared to conventional dose planning in the long-term control of tumor growth with GKS.

METHODS

Two different dose plannings were retrospectively compared in 75 patients with meningioma treated with GKS as a primary treatment. Forty-three patients were irradiated over 20 Gy to the tumor attachment. The remaining 32 patients were treated with conventional-dose planning. Tumor growth control, reduction of enhancement on the gadolinium-enhanced magnetic resonance imaging (MRI), and neurological status were retrospectively assessed.

RESULTS

The maximum dose on the tumor attachment was significantly higher in the high-dose group (23 Gy) than in the conventional group (16 Gy). The tumor margin was irradiated with the median of the 50% isodose line in both groups. The prescription doses resulted in 14 Gy and 12 Gy, respectively. The tumor control rate achieved 91% in both groups during the median follow-up period of 54 months. A decrease of enhancement on follow-up MRI was noted in one patient in each group. Kaplan-Meier analysis revealed no statistical difference in the progression-free survival between the two groups. The number of patients with improved neurological status showed no statistical difference.

CONCLUSIONS

No obvious benefit of high-dose irradiation to the tumor attachment and margin was found in tumor control and neurological status in the long term.

Radiochirurgia con acceleratore lineare: 5 anni di esperienza clinica

Gli autori utilizzano una tecnica di radiochirurgia con acceleratore lineare dal 1982. La tecnica è basata su irradiazioni multiple ad archi intersecantisi focalizzate stereotassicamente su un bersaglio.

Dopo che una valutazione meccanica e dosimetrica ha dimostrato la validità della procedura, la tecnica è stata impiegata su un gruppo selezionato di pazienti. Dal novembre 1982 al marzo 1988 sono stati trattati 155 casi. Tra loro 72 erano affetti da malformazioni arterovenose cerebrali, 16 da gliomi a bassa malignità, 8 da neurinoma dell'acustico, 8 da meningiomi e 11 da tumori maligni radiosensibili: in questi gruppi di pazienti la tecnica si è dimostrata sicura ed efficace. I risultati vengono paragonati a quelli ottenuti con la Gamma Unit di Leksell e col Ciclotrone di Kjellberg.

Multimodal treatment strategies for complex pediatric cerebral arteriovenous fistulas: contemporary case series at Barrow Neurological Institute

OBJECT Pediatric cerebral arteriovenous fistulas (AVFs) are rare but potentially lethal vascular lesions. Management strategies for these lesions have undergone considerable evolution in the last decade with the advent of new endovascular, surgical, and radiosurgical technologies. This study sought to review current treatment strategies and long-term clinical outcomes at a high-volume cerebrovascular institute. METHODS A retrospective chart review was performed on patients with a diagnosis of cerebral AVF from 1999 to 2012. Patients with carotid-cavernous fistulas, vein of Galen malformations, and age > 18 years were excluded from final analysis. Medical history, surgical and nonsurgical treatment, and clinical outcomes were documented. Pre- and postoperative angiograms were analyzed to assess for obliteration of the fistula. RESULTS Seventeen patients with pial AVFs (29.4%), dural AVFs (64.7%), or mixed pial/dural AVFs (5.9%) were identified. The majority of lesions were paramedian (70.6%) and supratentorial (76.5%). The study population had a mean age of 6.4 years, with a slight male predominance (52.9%), and the most common presenting symptoms were seizures (23.5%), headaches (17.6%), congestive heart failure (11.7%), and enlarging head circumference (11.7%). Among patients who underwent intervention (n = 16), 56.3% were treated with endovascular therapy alone, 6.3% were treated with open surgery alone, and 37.5% required a multimodal approach. Overall, 93.8% of the treated patients received endovascular treatment, 43.8% received open surgery, and 12.5% received radiosurgery. Endovascular embolysates included Onyx (n = 5), N-butyl cyanoacrylate (NBCA; n = 4), or coil embolization (n = 7) with or without balloon assistance (n = 2). Complete angiographic obliteration was achieved in 87.5% at the last follow-up evaluation (mean follow-up 3.1 years). One infant with incomplete AVF obliteration died of congestive heart failure, and 1 patient with complete obliteration died of acute sinus thrombosis, with an overall complication rate of 18.8%. CONCLUSIONS Pediatric cerebral AVFs are challenging neurosurgical lesions. Although advancements in endovascular therapy in the last decade have greatly changed the natural course of this disease, a multidisciplinary approach remains necessary for a large subset of patients. Surgeon experience with a thorough analysis of preoperative imaging is paramount to achieving acceptable clinical outcomes.

Radiation therapy in neurologic disease

Radiotherapy is a primary mode of treatment of many of the disease entities seen by the neurologist. Therefore knowledge of how ionizing radiation works and when it is indicated is a crucial part of the field of Neurology. The neurologist may also be confronted with some of the side effects and complications or radiotherapy treatment. This chapter attempts to serve as a review of the current day process of radiotherapy, a brief review of biology and physics of radiation, and how it is used in the treatment diseases which are common to the Neurologist. In addition we review the more commonly seen side effects and complications of treatment which may be seen by the neurologist.

A practical grading scale for predicting outcome after radiosurgery for arteriovenous malformations: analysis of 1012 treated patients

Object

The authors performed a study to review outcomes following Gamma Knife radiosurgery for cerebral arteriovenous malformations (AVMs) and to create a practical scale to predict long-term outcome.

Methods

Outcomes were reviewed in 1012 patients who were followed up for more than 2 years. Favorable outcome was defined as AVM obliteration and no posttreatment hemorrhage or permanent, symptomatic, radiation-induced complication. Preradiosurgery patient and AVM characteristics predictive of outcome in multivariate analysis were weighted according to their odds ratios to create the Virginia Radiosurgery AVM Scale.

Results

The mean follow-up time was 8 years (range 2–20 years). Arteriovenous malformation obliteration occurred in 69% of patients. Postradiosurgery hemorrhage occurred in 88 patients, for a yearly incidence of 1.14%. Radiation-induced changes occurred in 387 patients (38.2%), symptoms in 100 (9.9%), and permanent deficits in 21 (2.1%). Favorable outcome was achieved in 649 patients (64.1%). The Virginia Radiosurgery AVM Scale was created such that patients were assigned 1 point each for having an AVM volume of 2–4 cm3, eloquent AVM location, or a history of hemorrhage, and 2 points for having an AVM volume greater than 4 cm3. Eighty percent of patients who had a score of 0–1 points had a favorable outcome, as did 70% who had a score of 2 points and 45% who had a score of 3–4 points. The Virginia Radiosurgery AVM Scale was still predictive of outcome after controlling for predictive Gamma Knife radiosurgery treatment parameters, including peripheral dose and number of isocenters, in a multivariate analysis. The Spetzler-Martin grading scale and the Radiosurgery-Based Grading Scale predicted favorable outcome, but the Virginia Radiosurgery AVM Scale provided the best assessment.

Conclusions

Gamma Knife radiosurgery can be used to achieve long-term AVM obliteration and neurological preservation in a predictable fashion based on patient and AVM characteristics.

[Ballistic quality assurance]

This review describes the ballistic quality assurance for stereotactic intracranial irradiation treatments delivered with Gamma Knife® either dedicated or adapted medical linear accelerators. Specific and periodic controls should be performed in order to check the mechanical stability for both irradiation and collimation systems. If this step remains under the responsibility of the medical physicist, it should be done in agreement with the manufacturer's technical support. At this time, there are no recent published guidelines. With technological developments, both frequency and accuracy should be assessed in each institution according to the treatment mode: single versus hypofractionnated dose, circular collimator versus micro-multileaf collimators. In addition, "end-to-end" techniques are mandatory to find the origin of potential discrepancies and to estimate the global ballistic accuracy of the delivered treatment. Indeed, they include frames, non-invasive immobilization devices, localizers, multimodal imaging for delineation and in-room positioning imaging systems. The final precision that could be reasonably achieved is more or less 1mm.

Gamma knife radiosurgery for dural arteriovenous fistulas

BACKGROUND

The current management of intracranial dural arteriovenous fistulas (dAVFs) incorporates a multimodal approach involving microneurosurgery, endovascular embolization, and radiosurgery.

OBJECTIVE

To explore the role of Gamma Knife radiosurgery for dAVFs.

METHODS

The series includes patients with dAVFs who had Gamma Knife radiosurgery at the University of Virginia Medical Center between 1989 and 2005 with clinical follow-up through 2008. Medical records were reviewed to obtain clinical history, demographic data, and dosimetry. Radiographic records provided the location and anatomy of the dAVFs. Follow-up angiography was performed 2 to 3 years after treatment, with cure defined as complete obliteration of fistulous flow. Follow-up for clinical symptomology and quality of life was obtained from direct patient and primary physician questionnaires.

RESULTS

Fifty-five patients underwent Gamma Knife radiosurgery for dAVFs during the study period. Twenty patients (36%) presented with intracranial hemorrhage before radiosurgery. Gamma Knife radiosurgery was preceded by craniotomy for microneurosurgical ablation in 11 patients (20%) or endovascular embolization in 36 patients (65%). Follow-up angiography was performed on 46 patients (83%) with documented obliteration in 30 patients (65%). Patients lost to follow-up were classified as treatment failures, adjusting the range of efficacy from 65% to 54%. Three patients (5%) suffered a posttreatment hemorrhage during the follow-up period, but no new permanent neurological deficits resulted from these events.

CONCLUSION

Gamma Knife radiosurgery is an effective adjunct therapy for dAVFs with persistence of flow after open neurosurgical resection or endovascular treatment while still maintaining a role in nonaggressive dAVFs not amenable to either surgery or embolization.

Surgery and radiotherapy: complementary tools in the management of benign intracranial tumors

Historically, radiation therapy has been used extensively in the treatment of malignant and aggressive intracranial tumors, and the importance of its role has been repeatedly verified by prolonged patient survival rates and increased tumor control. As more modern capabilities are employed in surgery and radiotherapy, attention is being directed to the utility of radiation as either primary or secondary treatment of benign tumors. Specifically, primary treatment encompasses irradiation of small benign tumors without biopsy confirmation of tumor type; secondary treatment involves postoperative radiation therapy, with the possibility that less-aggressive tumor resection may be performed in areas that have a higher probability of resultant neurological deficit. Current literature suggests that this is not only a possible treatment strategy, but that it may be superior to more radical resection in some cases, for example, in vestibular schwannomas and meningiomas. This article provides an overview of factors to consider in the use of radiation therapy and reviews the relationships between radiation and surgery, notably the unique complementary role each plays in the treatment of benign intracranial tumors.

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.

Hypofractionated stereotactic radiotherapy for low grade glioma at McGill University: long-term follow-up

Small, well-defined, unresectable low-grade gliomas are attractive targets for stereotactic irradiation. Fractionated stereotactic irradiation of these targets has the theoretical benefit of increased normal tissue sparing beyond that provided by the physical characteristics of stereotactic radiosurgery. From July 1987 to November 1992, 21 patients were treated for low-grade glioma at our institution using a hypofractionated regimen of stereotactic radiotherapy. All patients had well-circumscribed, < 40 mm tumors. No patient had had prior radiotherapy. All lesions were histologically proven WHO grade I or II glial tumors. Lesions involved sensitive brain structures and were deemed unresectable. A typical dose of 42 Gy was delivered in 6 fractions over a two-week period using rigid immobilization and a linac-based dynamic stereotactic radiosurgical technique. Patients had a median age of 23 years (9-74) and were predominantly female (60%). Median tumor diameter was 20 mm. With a median follow-up for living patients of 13.3 years, the actuarial 5, 10, and 15-year overall survival rates are 76%, 71%, and 63%, respectively. Treatment was acutely well tolerated although three patients experienced late post-therapy complications. Our results and those of 241 patients treated in nine other institutional series are reviewed. Despite some examples of favorable short-term outcomes, all reported series are highly selected and thus likely biased. The data regarding the use of SRS is limited and, in our opinion, insufficient to claim a clear therapeutic advantage to SRS in the initial management of low-grade glioma. Our own results with hypofractionated stereotactic radiotherapy are similar to those expected with standard therapy.

Intracranial arteriovenous malformations treated utilizing a linear accelerator-based patient rotator or commercially available radiosurgery system

PURPOSE

To report a single-institution experience with intracranial arteriovenous malformations (AVMs) treated utilizing a linear accelerator-based patient rotator (PR) or BrainLAB (BL) radiosurgery system (BrainLAB AG, Heimstetten, Germany).

METHODS AND MATERIALS

Since 1989, 84 evaluable patients were treated. PR patients (n = 45) were planned/localized on the basis of biplane angiography and treated between 1989 and 2000. BL patients (n = 39) were planned/localized on the basis of CT/MRI and treated since 2000. Kaplan-Meier analyses of survival, nidus obliteration (NO), and any radiographic improvement were undertaken with Cox regression of dose and volume effects.

RESULTS

No significant complication, survival, previous embolization incidence, AVM location or size differences existed between BL/PR patients. The groups differed significantly in prescribed dose (PR: 16.2 Gy, BL: 17.3 Gy, p = 0.004) and isodose (PR: 62%, BL: 79%, p < 0.0001). Estimated 2-year NO rate was 87% for BL patients, 12% for PR patients (p < 0.0001). Ultimate PR NO rate was 67% at 6 years. Dose (p = 0.037) and isodose (p = 0.014) significantly affected PR NO outcome; volume was of borderline significance (p = 0.069). No factors significantly affected BL outcome. Analyses of small (< or = 4.0 cm3), high-dose (> or = 17.0 Gy) PR patients (PR1 group) vs. BL patients still demonstrated greater NO (p = 0.04) and radiographic improvement (p = 0.0004) rates for the BL group. PR1 patients had a 76% 3-year NO rate.

CONCLUSIONS

BL-based radiosurgery achieved a high NO rate, the PR method did not. Differences in outcomes between PR/BL groups may be due to localization methods or an inherent advantage with the BL system.

Natural history, evaluation, and management of intracranial vascular malformations

Intracranial vascular malformations are seen increasingly in clinical practice, primarily because of advances in cross-sectional brain and spinal cord imaging. Commonly encountered lesion types include arteriovenous malformations, cavernous malformations, venous malformations, dural arteriovenous fistulas, and capillary telangiectasias. Patients can experience various symptoms and signs at presentation. The natural history of vascular malformations depends on lesion type, location, size, and overall hemodynamics. The natural history for each lesion subtype is reviewed, with special consideration of the risk of hemorrhage or other adverse outcomes after the lesion is detected and any known predictors of hemorrhage or other outcomes. In practice, these data are compared with the risk of available treatment options as the optimal management is clarified. A multidisciplinary approach including neurosurgery, radiosurgery, interventional neuroradiology, and vascular neurology is most useful in determining the best management strategy.

Do the morphological characteristics of arteriovenous malformations affect the results of radiosurgery?

OBJECT

The authors sought to determine which morphological features of arteriovenous malformations (AVMs) are statistically predictive of preradiosurgical hemorrhage, postradiosurgical hemorrhage, and neuroimaging-defined failure of radiosurgical treatment. In addition, correlation between computerized tomography (CT) scanning and angiography for the identification of AVM structures was investigated.

METHODS

Archived CT dosimetry and available angiographic and clinical data for 268 patients in whom AVMs were treated with linear accelerator radiosurgery were retrospectively reviewed. Many of the morphological features of AVMs, including location, volume, compact or diffuse nidus, neovascularity, ease of nidus identification, number of feeding arteries, location (deep or superficial) of feeding arteries, number of draining veins, deep or superficial venous drainage, venous stenoses, venous ectasias, and the presence of intranidal aneurysms, were analyzed. In addition, a number of patient and treatment factors, including patient age, presenting symptoms, radiation dose, repeated treatment, and radiological outcome, were subjected to multivariate analyses. Two hundred twenty-seven patients were treated with radiosurgery for the first time and 41 patients underwent repeated radiosurgery. Eighty-one patients presented with a history of AVM hemorrhage and 91 patients had AVMs in a periventricular location. Twenty-six patients (10%) experienced a hemorrhage following radiosurgery. Of the 268 patients, 81 (30%) experienced angiographically defined cures, and 37 (14%) experienced MR imaging-defined cures. Eighty-six patients (32%) experienced neuroimaging-defined treatment failure, and 64 underwent insufficiently long follow up. A larger AVM volume (odds ratio [OR] 0.349; p = 0.004) was associated with a decreased rate of pretreatment hemorrhage, whereas periventricular location (OR 6.358; p = 0.000) was associated with an increased rate of pretreatment hemorrhage. None of the analyzed factors was predictive of hemorrhage following radiosurgery. A higher radiosurgical dose was strongly correlated with neuroimaging-defined success (OR 3.743; p = 0.006), whereas a diffuse nidus structure (OR 0.246; p = 0.008) and associated neovascularity (OR 0.428; p = 0.048) were each associated with a lower neuroimaging-defined cure rate. A strong correlation between CT scanning and angiography was noted for both nidus structure (p = 0.000; Fisher exact test) and neovascularity (p = 0.002; Fisher exact test).

CONCLUSIONS

Patients presenting with AVMs that are small or periventricular were at higher risk for experiencing hemorrhage. A higher radiosurgical dose correlated strongly with neuroimaging-defined success. Patients in whom the AVM had a diffuse structure or associated neovascularity were at higher risk for neuroimaging-defined failure of radiosurgery. A strong correlation between CT scanning and angiography in the assessment of AVM structure was demonstrated.

Analysis of factors predictive of success or complications in arteriovenous malformation radiosurgery

OBJECTIVE

This study was undertaken to determine which factors were statistically predictive of radiological and clinical outcomes in the radiosurgical treatment of arteriovenous malformations (AVMs).

METHODS

The computerized dosimetric and clinical data for 269 patients were reviewed. The AVM nidus was hand-contoured on successive enhanced computed tomographic slices through the nidus, to allow detailed determinations of nidus volume, target miss, normal brain tissue treated, dose conformality, and dose gradient. In addition, a number of patient and treatment factors, including Spetzler-Martin grade, presenting symptoms, dose, number of isocenters, radiological outcome, and clinical outcome, were subjected to multivariate analysis.

RESULTS

Two hundred twenty-five patients were treated with radiosurgery for the first time, and 44 patients underwent radiosurgical retreatment. One hundred forty-three patients had AVMs located in or near "eloquent" brain areas and 126 patients did not. Seventy patients demonstrated preoperative neurological findings related to the AVM and 199 did not. Twenty-six patients had previously undergone endovascular treatment and 10 patients had previously undergone surgical treatment of their AVMs. Of the 269 patients studied, 228 experienced no complication, 10 (3.7%) experienced a transient radiation-induced complication, 3 (1%) experienced a permanent radiation-induced complication, and 28 (10%) experienced posttreatment hemorrhage.

CONCLUSION

None of the analyzed factors was predictive of hemorrhage after radiosurgery in this study. The 12-Gy volume was predictive of permanent radiation-induced complications. Eloquent AVM location and 12-Gy volume were correlated with the occurrence of transient radiation-induced complications. Better conformality was correlated with a reduced incidence of transient complications. Lower Spetzler-Martin grades, higher doses, and steeper dose gradients were correlated with radiological success.

Intracranial dural arteriovenous malformations: results of stereotactic radiosurgery in 17 patients

AIM

To assess the efficacy of stereotactic radiosurgery (STRS) for the treatment of dural arteriovenous fistulae (DAVF).

MATERIALS AND METHODS

Between November 1987 and December 1998, 17 patients with a total of 18 DAVF were treated with STRS at the National Centre for Stereotactic Radiosurgery, Sheffield. Clinical and radiological data was collected retrospectively from the case notes and radiological records. Two neuroradiologists classified the pre-STRS appearance of the DAVF using the Borden criteria, and reviewed the follow-up imaging. Up to date follow-up was requested from the GPs and referring consultants.

RESULTS

In retrospect one DAVF had been misdiagnosed and was excluded from the study. The remaining 17 DAVF were located at the tentorium (6), cavernous sinus (3), right parasellar region (1), floor of left middle cranial fossa (1), midline posterior fossa (1), petrous apex (1) and transverse sinus (4). Ten were Borden type I, four were type II, three were type III. Follow-up angiography was available for 13 patients; 10 DAVF were completely obliterated, two showed considerable reduction in size, one showed deterioration. Clinical follow-up was available for 14 of the 16 patients.

CONCLUSION

Stereotactic radiosurgery can successfully obliterate DAVF with few side effects.

A formalism for independent checking of Gamma Knife dose calculations

For stereotactic radiosurgery using the Leksell Gamma Knife system, it is important to perform a pre-treatment verification of the maximum dose calculated with the Leksell GammaPlan (DLGP) stereotactic radiosurgery system. This verification can be incorporated as part of a routine quality assurance (QA) procedure to minimize the chance of a hazardous overdose. To implement this procedure, a formalism has been developed to calculate the dose DCAL(X,Y,Z,dav,t) using the following parameters: average target depth (dav), coordinates (X,Y,Z) of the maximum dose location or any other dose point(s) to be verified, 3-dimensional (3-dim) beam profiles or off-centerratios (OCR) of the four helmets, helmet size i, output factor Oi, plug factor Pi, each shot j coordinates (x,y,z)i,j, and shot treatment time (ti,j). The average depth of the target dav was obtained either from MRI/CT images or ruler measurements of the Gamma Knife Bubble Head Frame. DCAL and DLGP were then compared to evaluate the accuracy of this independent calculation. The proposed calculation for an independent check of DLGP has been demonstrated to be accurate and reliable, and thus serves as a QA tool for Gamma Knife stereotactic radiosurgery.

[Stereotactic one-time irradiation (radiosurgery). The methods, indications and results]

BACKGROUND

Stereotaxy is a method to determine a point in the patient's body by an external coordinate system which is attached to the patient. Radiosurgery uses this method for precise delivery of a high single radiation dose to the patient. The aim is to destroy the tissue in the target and to spare surrounding unaffected normal tissue by a steep dose gradient.

METHODS

Three techniques of percutaneous radiosurgery are available: radiosurgery with ion beams with a cyclotron, spherical arrangement of cobalt-60 sources, the so-called gamma knife, and an adapted linear accelerator. The availability and the good clinical experience lead to a wide spread use of linear accelerator for radiosurgery in recent years. A subsequent development is fractionated stereotactic radiotherapy which combines the precision of radiosurgery with the radiobiological advantage of fractionation.

RESULTS

Only a few indications for radiosurgery are proven by statistically valid studies. One of these is the treatment of small arteriovenous malformation, where obliteration rates of 80% to 100% are reported with only minor toxicity. However, the obliteration rate is reduced significantly in large arteriovenous malformations. A local control rate of 90% is obtained after radiosurgery of brain metastases which is comparable to the results of microsurgical resection followed by adjuvant whole brain radiotherapy. An ongoing EORTC study evaluates the role of adjuvant whole brain radiotherapy after radiosurgery. The survival of the patients with brain metastases is limited by the existence of progressive extracerebral disease. The role of radiosurgery in the treatment of benign tumors is currently evaluated in clinical studies which include: vestibular schwannomas, meningiomas, chordomas and chondrosarcomas and pituitary adenomas. Most of the published studies include only small tumors because radiosurgery is limited by the risk of radionecrosis of adjacent normal tissue, which shows a steep dose volume response relationship. Recent developments of stereotactic radiotherapy include the use of mini-multileaf-collimators and clinical studies on stereotactic radiotherapy of extracranial targets.

CONCLUSIONS

Stereotactic irradiation is a well established treatment technique for intracranial tumors and arteriovenous malformations. Methods are available that allow optimization of dose distributions to irregularly shaped tumors for single dose as well as fractionated stereotactic irradiations by linear accelerator. Therefore the therapeutic potential of this technique has increased and enables also the extracerebral application in controlled clinical studies.

Early surgical treatment of intracerebral hemorrhages caused by AVM: our experience in 10 cases

Between February, 1980, and April, 1993. 10 patients with intraparenchymal hemorrhage due to the bleeding of an arteriovenous malformation (AVM) underwent emergency surgical procedures within an average time of 3 hours (min. 2-max. 7) from casualty to admission. Rapid neurological worsening and mass effect of the extensive intracerebral hemorrhage prompted early surgical treatment. Post-operative angiography was performed to confirm that the malformation had been excluded from the circulation. The aim of this study is to evaluate the role of early surgery in patients requiring emergency surgical procedures for severe neurological injury induced by extensive intracerebral hematoma produced by AVM bleeding.

Pathological changes in surgically resected angiographically occult vascular malformations after radiation

OBJECTIVE

The goal of this study was to evaluate the pathological changes associated with radiation treatment (stereotactic radiosurgery or conventional irradiation) of angiographically occult vascular malformations (AOVMs).

METHODS

Eleven patients underwent surgical resection of an AOVM in the mesial temporal lobe, brain stem, thalamus, or basal ganglia after previous radiation treatment. The indications for surgery were recurrent symptomatic bleeding from the lesion in 10 patients and recurrent intractable seizures in 1 patient. Radiation was used as the initial therapy because the risk of surgical resection was deemed too high. Three patients received conventional radiation therapy of 3000 to 5400 rads at an outside institution. One patient received radiosurgery with the gamma knife at another institution using a dose of 15 Gy to the margin. The remaining 7 patients received stereotactic radiosurgery with a helium-ion particle beam. The dose range was from 18 to 26 Gy equivalents. The interval from radiation to surgical resection ranged from 1 to 10 years, with a mean of 3.5 years. These lesions were compared with 10 nonirradiated cavernous malformations.

RESULTS

One irradiated lesion was identified pathologically as a true arteriovenous malformation despite being angiographically occult. This lesion did not demonstrate significant changes in the vasculature but did have radiation necrosis of the surrounding brain 5 years after 25 Gy equivalents of helium-ion radiosurgery. Two other specimens were too small to identify the type of vascular malformation adequately. Of the remaining eight malformations identified as cavernous malformations, six showed a combination of marked fibrosis of the vascular channels, fibrinoid necrosis, and ferrugination. However, the fibrinoid necrosis was the only finding unique to the irradiated lesions compared with nonirradiated controls. All the irradiated lesions still had patent vascular channels; none were completely thrombosed.

CONCLUSION

Radiosurgery or conventional radiation therapy did not cause histologic vascular obliteration in intracranial AOVMs evaluated 1 to 10 years (mean 3.5 yr) after radiation delivery. It should be recognized that these patients are irradiation failures who may not be representative of all irradiated patients. However, recurrent bleeding from AOVMs may relate to poor radiation response in some patients.

Radiation-related adverse effects observed on neuro-imaging several years after radiosurgery for cerebral arteriovenous malformations

BACKGROUND

To our knowledge, there are no reported arteriovenous malformation (AVM) series in which detailed long-term follow-up results after radiosurgery were described based on the whole patient group.

METHOD

We performed a detailed long-term follow-up study of 53 patients with cerebral AVMs treated with gamma knife (GK) radiosurgery, with emphasis on radiation-related adverse effects detected on neuro-imaging after a long post-irradiation latency period (3-10 years). The post-GK follow-up period was 40-232 months excluding two mortalities, the mean being 112 and the median being 111 months.

RESULTS

Three patients (5.6%) have, as yet, refused all neuro-imaging follow-up studies. Complete nidus obliteration was confirmed angiographically in 32 patients (60.4%) between 1 and 5 post-GK years. In the other 18 patients (34%), despite significant nidus shrinkage being angiographically demonstrated, complete obliteration was not achieved during a 2-7 year follow-up period. There were two mortalities, one AVM-related (massive re-bleeding during the latency period) and the other angiography-related. There were five radiation-related morbidities (9.4%), three of which-hemi-Parkinson syndrome, hemiparesis, and visual field disturbances attributable to delayed cyst formation-manifested at 5.5, 7 and 7 post-GK years, respectively. We also experienced five patients (9.4%) in whom, despite remaining asymptomatic to date, radiation-related adverse effects were seen on neuro-imaging: middle cerebral artery stenosis at 3 post-GK years in one patient; dural arteriovenous fistula at 7 post GK-years in one; delayed cyst formation in two, at 5 and 10 post-GK years; and a small cavitation at 9 post-GK years.

CONCLUSION

Long-term follow-up, particularly with neuro-imaging modalities, is essential even after the "treatment goal" has been attained.

A diffuse white matter ischemic lesion appearing 7 years after stereotactic radiosurgery for cerebral arteriovenous malformations: case report

OBJECTIVE AND IMPORTANCE

Little information is available about radiation-induced complications occurring more than 5 years after radiosurgical treatment for arteriovenous malformations.

CLINICAL PRESENTATION

We present a patient with arteriovenous malformations who experienced hemimotor weakness caused by a diffuse white matter necrotic lesion developing 7 years after gamma knife radiosurgery. The original nidus had been too large (24.1 cm3) to be totally covered and irradiated with a peripheral dose of 20 to 25 Gy. Therefore, the lower half of the nidus, which was adjacent to the major feeding artery, had been partially covered with a 30% isodose volume using two target points with an 18-mm collimator. A central dose of 70 Gy was used to obtain 21 Gy at the periphery. Complete nidus obliteration was angiographically confirmed 38 months after radiosurgery. After a 6-year uncomplicated period, this patient experienced a convulsive seizure and then mild right hemiparesis.

INTERVENTION

Computed tomography demonstrated a diffuse hypodense area in the left white matter, which had not been revealed by the previous examination. With steroid treatment, this patient achieved clinical improvement, although there was no significant improvement in the computed tomography-demonstrated white matter lesion.

CONCLUSION

Although the evaluation of this patient may not be sufficient and further examinations may be necessary, we tentatively conclude that the computed tomography-demonstrated hypodense lesion in this patient is a radiation-related necrotic lesion. Long-term follow-up is crucial, even after the "treatment goal" has been achieved.

Middle cerebral artery stenosis caused by relatively low-dose irradiation with stereotactic radiosurgery for cerebral arteriovenous malformations: case report

OBJECTIVE AND IMPORTANCE

There have been occasional reports of stenosis or occlusion of major cerebral arteries occurring several years after stereotactic radiosurgery for cerebral arteriovenous malformations. Nevertheless, little information is available regarding the actual irradiation dose to which the affected artery had been exposed.

CLINICAL PRESENTATION

We present a patient with arteriovenous malformations who, although asymptomatic, developed remarkable stenosis of the middle cerebral artery trunk (M1) 3 years after gamma knife radiosurgery. The nidus was covered with a 50% isodose volume. A central dose of 36 Gy was used. A gradual decrease in nidus volume had been suggested by 1- and 2-year postradiosurgical neuroimaging examinations. Three-year postradiosurgical angiography revealed severe segmental stenosis of the M1, as well as remarkable nidus shrinkage.

INTERVENTION

The actual irradiation dose delivered to the affected portion of the artery, as retrospectively determined using a highly accurate three-dimensional analysis technique, was estimated to be 5.1 to 9.8 Gy.

CONCLUSION

This case suggests that a normal major artery, if located close to the target volume, may be affected by low-dose irradiation (10 Gy or even slightly less) delivered with radiosurgery, although a decrease in blood flow through the M1 because of nidus shrinkage or associated stenosis of the distal middle cerebral artery, as well as other unknown factors, may also contribute to proximal M1 stenosis.

Microsurgical results for small arteriovenous malformations accessible for radiosurgical or embolization treatment

OBJECTIVE

A consecutive series of microsurgically treated small arteriovenous malformations (AVMs), up to 3 cm in diameter, which are theoretically ideal candidates for radiosurgery or embolization, is described. We intended to elucidate the safety and efficacy of the microsurgical removal of AVMs, as compared with the results for radiosurgery and embolization reported in the literature.

METHODS

Sixty-two patients (32 female and 30 male patients) ranging in age from 7 to 72 years (mean age, 33.3 yr) were included in the series. Of these, 46.8% presented with intracerebral hemorrhage and 24.2% presented with seizures. The 62 patients underwent microsurgical removal of their small (<3 cm) cerebral AVMs by the same surgeon. Twenty-six AVMs (41.9%) were assigned Spetzler-Martin Grade I, 24 (38.7%) were assigned Grade II, and 12 (19.4%) were assigned Grade III. Thirty-three AVMs (53.2%) were located in eloquent brain regions. All patients underwent postoperative control angiography and clinical follow-up after 3 and 6 months.

RESULTS

The AVMs were extirpated, as confirmed by angiography, in all except one patient, thereby accounting for a 98.4% success rate per angiographic findings. The rate of immediate new postoperative neurological deficits or worsening of preexisting neurological deficits was 27.4%, and the rate of permanent significant neurological deficits was 3.2% at late follow-up. The rate of permanent significant deficits occurring after the microsurgical removal of small AVMs in eloquent regions was 6.1%. The mortality rate in the reported series was 0%. The surgical morbidity rate was 9.7%.

CONCLUSION

Microsurgery for small AVMs is superior to radiosurgery or interventional neuroradiology because of its high rate of efficacy and low rate of permanent morbidity and because immediate cure of the AVMs can be achieved in the vast majority of patients. The place for radiosurgery in the treatment of small AVMs needs to be more sharply defined after careful assessment of relevant cases by an experienced vascular neurosurgeon.

Photon beams for radiosurgery produced by laser Compton backscattering from relativistic electrons

The frontal collisions of a laser beam with relativistic electrons result in Compton-backscattered photons. The energy of these photons is dependent on the laser and electron energy in the range from kilo-electron-volts to tens of mega-electron-volts. In a sufficiently narrow backscattering angle the photons are nearly monochromatic. Over the past 30 years there have been several attempts to produce photon beams by laser backscattering from relativistic electrons stored in magnetic ring structures. One aim is to produce photons in the high mega-electron-volt energy range with fluxes useful for nuclear physics research; another is to produce photons in the high kilo-electron-volt energy range, which would be useful for medical applications, such as coronary angiography or treatment of tumour. Our present interest is to investigate the possibility of using 34 keV to 10 MeV photon beams for applications in stereotactic functional radiosurgery. We foresee the possibility of neurosurgical operations through the intact skull with precise and effective destruction of deeply lying millimetre-sized targets with minimal effects on intervening structures, high reproducibility and good prediction of the results. Our paper presents: a Monte Carlo study of radiosurgery based on cross firing with 34 keV to 100 MeV photon beams and 200 and 580 MeV proton beams, a theoretical description of the kinematics of Compton backscattering and estimates of the backscattered photon flux from several combinations of laser cavities at Nd:YAG (1.17 eV) and CO2 (0.117 eV) laser energies and electron storage rings energies in the range 0.1-1.3 GeV. As examples, existing magnetic structures, such as the DA phi NE Accumulator in the lower energy range and the Trieste Synchrotron Light Source ELETTRA in the higher energy range have been utilized in the calculations. The Monte Carlo study has shown that radiosurgery with photon beams of energies in mega-electron-volt energy range enables precise destruction of deeply lying millimetre-sized targets with minimal effects on intervening structures. Its precision is comparable to that of radiosurgery with 200-580 MeV proton beam, but our hope is that radiosurgery with lower energy photon beams could be more precise and less expensive. An average dose of 200 Gy can be delivered to a target of diameter 2 mm at the centre of an 18 cm diameter phantom in 1 h using photon beams of fluences 7.3 x 10(10), 1.8 x 10(10), 6.5 x 10(8), 2.2 x 10(8), 8.6 x 10(7) and 7.8 x 10(6) photons per second at 34 keV, 100 keV, 1 MeV, 3 MeV, 10 MeV and 100 MeV per cross section of beam of 2 mm diameter, respectively. 34-100 keV photon beams were studied in the hope of finding a strong enhancement of their efficiency if a stable high-Z element were to be introduced into the target's DNA. It is shown that, with a low-energy ring running at about 0.4 GeV and a Nd:YAG laser, it would be possible to obtain the required 3 MeV photon beam flux to deliver the average dose within 1 h, assuming an average distance between the source and the target of about 5 m. With a similar machine used at about 1.3 GeV and a CO2 laser, a 3 MeV photon beam is obtained and the exposure time can be reduced to less than 1 min, assuming a roughly 10 m distance between source and target (here a beam angle of 0.1 mrad only had to be considered due to the larger angular energy and yield spread). With a lower electron energy of 138 MeV and a CO2 laser, a 34 keV photon beam can be produced. More than 45 h would be needed to deliver the same dose. We hope that this time could be shortened considerably if stable iodine were introduced into the target with the help of a DNA-seeking molecular carrier. In this case the geometrical precision would be further improved.

Stereotactic radiosurgery for arteriovenous malformations of the brain using a standard linear accelerator: the Lyon experience

Radiosurgery (RS) was initiated in Lyon in October 1989. The technique was adapted from that described by Lutz and Saunders in Boston (BRW stereotactic frame). Irradiation is delivered with 18-MV photons produced by a LINAC. From December 1989 to December 1992, 41 patients with arteriovenous malformations were treated by RS; the median age was 33 years. The largest lesion diameter was 11.2-38.5 mm. Fifteen to 20 Gy were delivered on the 70% isodose line. Angiography was performed at 2 years post-treatment in 32 patients demonstrating an overall complete thrombosis rate of 81.3%. This incidence was significantly correlated with the Spetzler and Martin grade before RS (P = 0.0055). Two patients (4.9%) experienced haemorrhage after radiosurgical treatment and one died from an intracerebral-intraventricular haemorrhage. Four patients (9.7%) experienced permanent radiation-induced neurological complications.

Computed tomography slice-by-slice target-volume delineation for stereotactic proton irradiation of large intracranial arteriovenous malformations: an iterative approach using angiography, computed tomography, and magnetic resonance imaging

PURPOSE

Target-volume delineation for stereotactic irradiation is problematic for large and irregularly shaped arteriovenous malformations (AVMs). The purpose of this report is to quantify modifications in the target volume that result from iterative treatment planning that incorporates multimodality imaging data.

METHODS AND MATERIALS

Stereotactic neuroimaging procedures were performed for 20 consecutive patients with AVM volumes > 10 cm3. Angiographically defined extrema were transformed into computed tomography (CT) space. The resulting target contours were then modified by a multidisciplinary treatment planning team after iterative review of angiographic, CT, and magnetic resonance imaging (MRI) data. Volumes of interest and dose-volume histograms for proton irradiation were calculated before and after iterative target delineation.

RESULTS

Initial (angiographically defined) target volumes ranged from 15.3 to 96.1 cm3 (mean, 43.6 cm3). Final (iteratively defined) target volumes ranged from 10.7 to 114.0 cm3 (mean, 38.4 cm3). The volume of presumed normal tissue excluded by iterative planning ranged from 2.6 to 47.0 cm3 (mean, 15.5 cm3). Initially untargeted AVM, most commonly obscured by embolization material, was identified in all cases (range, 0.3 to 57.8 cm3; mean, 10.3 cm3). Corresponding dose-volume histograms demonstrated marked differences regarding lesion coverage and sparing of normal tissue structures.

CONCLUSIONS

Iterative target-volume delineation resulted in significant modifications from initial, angiographically defined target volumes. Substantial amounts of apparently normal tissue were excluded from the final target, and additional abnormal vascular structures were identified for incorporation. We conclude that an iterative multimodality approach to target-volume delineation may improve the overall results for stereotactic irradiation of large and complex AVMs.

The role of radiosurgery and particulate embolization in the treatment of dural arteriovenous fistulas

Over the past 5 years 29 patients with dural arteriovenous fistulas (AVFs) were treated by the authors using the Leksell radiosurgical gamma knife unit. Within 2 days after radiosurgery, 17 patients with AVFs that exhibited retrograde pial or cortical venous drainage (12 patients) and/or produced intractable bruit (eight patients) underwent particulate embolization of external carotid feeding vessels. The rationale for this treatment strategy was that radiosurgery was expected to cause obliteration of most fistulas after 12 to 36 months. In patients with bruit, ocular symptoms, or in those at risk for hemorrhage, treatment with embolization after radiosurgery kept the fistulas angiographically visible for radiosurgical targeting yet offered palliation of symptoms and temporary, partial protection from hemorrhage during the latency period. In 12 patients, preobliteration embolization immediately reduced (10 patients) or eliminated (two patients) retrograde pial venous drainage. To date, no lesion has hemorrhaged after treatment. Angiography 1 to 3 years posttreatment in 18 patients showed total obliteration of 13 fistulas (72%) and partial obliteration of five (28%). Radiosurgery, followed by embolization when retrograde pial venous drainage, intractable bruit, and/or major external carotid artery supply is present, appears to be a promising treatment for selected patients with symptomatic dural AVFs.

Gamma knife radiosurgery for arteriovenous malformations: long-term follow-up results focusing on complications occurring more than 5 years after irradiation

The detailed long-term follow-up results of 40 patients treated for cerebral arteriovenous malformations with gamma knife radiosurgery are presented, with special reference to postradiosurgical complications that can develop many years after irradiation. The follow-up period after radiosurgery was 54 to 205 months, excluding one mortality, with a mean and a median of 106 and 97 months, respectively. One patient (2.5%) has, to date, refused all neuroimaging follow-up examinations. Complete nidus obliteration was angiographically confirmed in 26 patients (65%) between 1 and 5 years after radiosurgery. In the remaining 13 patients (32.5%), although significant shrinkage of each nidus was angiographically demonstrated, complete obliteration was not attained during a 3- to 7-year period of follow-up after radiosurgery. Among these 13 patients, 1 underwent surgical extirpation of the nidus and 5 underwent second courses of gamma knife radiosurgery between 3 and 6 years after initial treatment; in 3 of the 5 patients, complete nidus obliteration was angiographically confirmed between 1 and 3 years after the second course of radiosurgery. There were no radiation- or arteriovenous malformation-related mortalities. However, we did experience one angiography-related mortality. We also experienced one morbidity (probably caused by hemorrhagic stroke), which developed 5 years after 2-year postradiosurgical angiography had demonstrated complete obliteration, and three radiation-related morbidities, two of which (hemiparkinsonian syndrome and visual field disturbances caused by delayed cyst formation) occurred 5.5 and 7 years, respectively, after irradiation. Furthermore, we observed another two patients who, although asymptomatic to date, showed delayed cyst formation on magnetic resonance imaging 5 and 10 years after irradiation, respectively. In total, 3 (23%) of 13 patients who underwent computed tomography and/or magnetic resonance imaging more than 5 years after radiosurgery showed delayed cyst formation. In conclusion, long-term follow-up, particularly with the use of neuroimaging techniques, is necessary even after the treatment goal has been achieved.

Neuroimaging studies of postobliteration nidus changes in cerebral arteriovenous malformations treated by gamma knife radiosurgery

BACKGROUND

Following radiosurgical treatment, the majority of patients with arteriovenous malformations (AVMs) are periodically examined by means of computed tomography (CT) and magnetic resonance imaging (MRI) to assess the attainment of nidus obliterations, as well as adverse radiation effects in the surrounding brain. However, few neuroimaging studies of the long-term results following complete obliterations, confirmed by angiography, have been published to date.

METHODS

CT, MRI, magnetic resonance (MR) angiographic and angiographic images, obtained after angiographic confirmation of complete nidus obliteration, were reviewed in 11 AVM patients treated with gamma knife radiosurgery. The period between angiographic confirmation of nidus obliteration and these most recent examinations was 12-84 months (mean, 29 months).

RESULTS

In ten patients who were assessed by CT, the obliterated nidus was shown to be isodense (eight cases). A significant time-related decrease in contrast enhancement was observed within 1 to 2 postobliteration years (five/seven cases). Eight patients were evaluated by MRI. On T1-weighted imaging, the nidus was shown to be hypointense (six cases) or a mixture of hypointense and isointense areas (two cases). On T2-weighted imaging, nidus intensity varied more than than observed on T1-weighted imaging, and time-related intensity increases were observed (two/seven cases). No flow-signal void was demonstrated in any of these cases. In four of the seven cases, in which serial postobliteration follow-up MRI studies were conducted, significant gadolinium enhancement persisted 3 years or more after obliteration (maximum of 7 years). No vascular abnormalities were demonstrated in seven patients who were assessed by conventional angiography and/or MR angiography.

CONCLUSIONS

Radiosurgery-induced changes in a nidus may continue for several years after angiography has shown complete AVM obliteration.

Gamma knife radiosurgery for cerebral arteriovenous malformations: an autopsy report focusing on irradiation-induced changes observed in nidus-unrelated arteries

BACKGROUND

In radiosurgical treatment for an arteriovenous malformation (AVM), the effects of irradiation on the intranidal and perinidal angioarchitectures have seldom been analyzed histologically. An autopsy case is reported, studying an AVM treated by gamma knife radiosurgery. Postmortem studies following AVM-unrelated death were performed after a 2-year angiography had demonstrated complete nidus obliteration. Irradiation-induced changes were also observed in surrounding nidus-unrelated arteries and the choroid plexus, both of which were within the irradiation target.

METHODS

Microscopic studies were performed using a coronal section of the brain including the center of the AVM, on which the percent isodose volume gradient, corrected with a magnification rate, was superimposed.

RESULTS

This study disclosed that intimal hypertrophy can occur in a normal, AVM-unrelated pial artery due to irradiation of 10 Gy or more and that more remarkable intimal hypertrophy with fragmentation of the elastic laminae, or even complete occlusion, can occur in these arteries with 25 Gy. Similarly, irradiation-induced degeneration was present in the choroid plexus, which had been exposed to doses varying from 10 Gy to 25 Gy.

CONCLUSIONS

A normal surrounding blood vessel may also be affected by high-dose, single-fraction irradiation though the abnormal vessels have been reported to be more susceptible.

Treatment planning optimization by conjugate gradients and simulated annealing methods in stereotactic radiosurgery

PURPOSE

This paper presents a new optimization method of treatment planning in linac stereotactic radiosurgery.

METHODS AND MATERIALS

On a workstation integrating x-rays, computed tomography (CT), magnetic resonance imaging (MRI), and digital subtracted angiography (DSA) images, we first determine the outlines of the target volume and surrounding healthy tissues to spare. To achieve complete optimization of the treatment plans, this method decomposes the optimization process in two steps. The position of the isocenters and the diameter of the collimators are first deduced by a conjugate gradients method, from the position and size of ellipsoids or spheres modeling the target volume. The other irradiation parameters, such as the isocenter dose, the aperture, and the weight of each irradiation plane and of their irradiation sectors are finally deduced by a simulated annealing optimization algorithm.

RESULTS

The system can perform multitarget/multisector treatment plans that are automatically obtained in a satisfactory time (as a rule, 20 min for a two-target irradiation), much faster than the time needed for a manual treatment planning. We present the results in two cases: the simulation of a single-target treatment and a two-target real treatment with constraints. In these two cases, we can control the dose received by target and sensitive volumes.

CONCLUSION

This method achieves an excellent conformation of the estimated isodose curves with the outlines of the target volume, which allows us to avoid the surrounding healthy tissues, thanks to the different weighting factors given on each volume concerned according to the importance we grant to each of them.

[Linear accelerator radiosurgery]

Radiosurgery is the precise radiation of a known intracranial target with a high dose of energy, sparing the adjacent nervous tissue. Technological advances in the construction of linear accelerators, stereotactic instruments and in computer sciences made this technique easier to perform and affordable. The main indications for radiosurgery are inoperable cerebral vascular malformations, vestibular and other cranial schwannomas, skull base meningiomas, deep seated gliomas and cerebral metastases. More recently, the development of fraccionated stereotactic radiotherapy increased the spectrum of indications to bigger lesions and to those adjacent to critical nervous structures. We present our initial experience in the treatment of 31 patients. An adequate control of the neoplastic lesions was obtained and the adequate time of observation is still needed to evaluate the results in arteriovenous malformations.

Stereotactic radiosurgical treatment of cerebral arteriovenous malformations. Gamma Unit Radiosurgery Study Group

OBJECTIVE

To assess the role of clinical factors, size of lesion, site of involvement, and radiation dose in patients with cerebral arteriovenous malformations (AVMs) who underwent stereotactic radiosurgical treatment.

DESIGN

We reviewed the results in 121 patients with cerebral AVMs treated with the Leksell "Gamma Knife" between January 1990 and December 1993 at the Mayo Clinic in Rochester, Minnesota.

MATERIAL AND METHODS

The following strict dose-volume protocol was used: AVMs 2.0 cm or smaller in diameter (volume, 4.2 cm3 or less) received 20 Gy to the margin of the nidus, those between 2.1 and 3.0 cm in diameter (4.3 to 14.1 cm3) received 18 Gy to the margin, and those that exceeded 3.0 cm in diameter (more than 14.1 cm3) received 16 Gy to the margin. Lesions that involved the brain stem received a radiosurgical dose of 18 Gy or less to the margin. Patients participated in regular follow-up clinical and imaging studies for up to 55 months.

RESULTS

Follow-up cerebral angiography in 43 patients demonstrated total obliteration of the AVM nidus in 31 (72.1%), including 5 of 7 (71.4%) who had AVMs with a volume larger than 10 cm3. Clinical follow-up revealed that 111 patients (91.7%) had a stable or improved outcome, 3 had a nonfatal AVM hemorrhage, 2 suffered a fatal hemorrhage, and 2 died of causes not directly attributed to the AVM or radiosurgical treatment. Two patients had new or increased, nondisabling neurologic deficits as a result of treatment, and one patient had a temporary partial eyelid ptosis.

CONCLUSION

Our findings suggest that previous theories about the relationship between AVM size and rate of obliteration after radiosurgical treatment may need revision. Our experience confirms that radiosurgical treatment for cerebral AVMs is safe and effective, even in cases for which the latency period before obliteration is longer than 2 years.

The role of high-dose, single-fraction irradiation in small and large intracranial arteriovenous malformations

PURPOSE

Radiosurgery with external beam irradiation is an accepted treatment for small intracranial vascular malformations. It has been proven effective and safe for lesions with volumes of less than 4 cc. However, there is only some limited clinical data for malformations of grade 4 and grade 5, according to Spetzler and Martin.

METHODS AND MATERIALS

At the Heidelberg radiosurgery facility equipped with a linear accelerator, 212 patients with cerebral arteriovenous malformations have been treated since 1984. Thirty-eight percent of the arteriovenous malformations treated were classified inoperable, 14% grade 5, 19% grade 4, and 29% grades 1-3. Radiation doses between 10 and 29 Gy were applied to the 80% isodose contour.

RESULTS

Above a threshold dose of 18 Gy, the overall obliteration rate was 72%. After 3 years, the obliteration rates were 83% with volumes of less than 4.2 cc, 75% with volumes of up to 33.5 cc, and 50% with volumes of up to 113 cc. Of the patients presenting with seizures and paresis, 83% and 56%, respectively, showed improvement, which correlated with the degree of obliteration. After a follow-up period of up to 9 years, the rate of radiation-induced severe late complications was 4.3%. In grade 5 lesions, the risk of side effects was 10%. No serious complications occurred if a maximum dose of less than 25 Gy was applied to treatment volumes of less than 33.5 cc.

CONCLUSION

The success of stereotactic high-dose irradiation of arteriovenous malformations depends on the dose applied. The incidence of radiation-induced side effects increased with the applied dose and treatment volumes. From our experience, doses of less than 25 Gy and treatment volumes of up to 33.5 cc are safe and effective. In the future, new techniques of radiosurgery with linear accelerators and dynamically reshaped beams will allow us to apply homogenous dose distributions. Additional use of magnetic resonance angiography for 3D treatment planning will help to identify the nidus more easily.

Assurance of high quality linac-based stereotactic radiosurgery

PURPOSE

Stereotactic radiosurgery is generally a single, high-dose radiation treatment for the brain requiring targeting accuracy on the order of a millimeter. From the initial implementation of radiosurgery, therefore, quality assurance is an ongoing process of paramount importance. In this paper, we outline the basic elements of a quality assurance program for our linear accelerator that has been in use at Washington University Medical Center over the past 2 years.

METHODS AND MATERIALS

Various devices and procedures have been developed to verify the accuracy and safety of the stereotactic radiosurgery regimen. Specifically, we present methods for assessing the attainment of spatially correct patient images, the reliability of the computerized treatment planning system, achieving physical safety for the patient, as well as the proper operation of the radiation treatment device.

RESULTS

Our procedures have allowed us to assure quality patient treatments and, additionally, has permitted monitoring our performance for continual improvement. For example, a plot of targeting accuracy with the number of patients shows an asymptotic approach to a value within 0.6 mm of that ideally expected.

CONCLUSION

To maintain high-quality patient care, one must review critical aspects of the treatment regimen on a periodic basis. Providing for the appropriate level of staff training, periodic reviews of procedures and maintenance of forms are also very important.

Halo ring supporting the Brown-Roberts-Wells stereotactic frame for fractionated radiotherapy

The authors describe a new instrumentation for repositioning of the Brown-Roberts-Wells (BRW) stereotaxic system, useful for precise fractionated radiotherapy. A lucite ring is fixed to the patient's skull with four screws. Another ring, partially open, is then firmly connected co-axially to the lower part of the first one with four spacer-bars. The fixture permits an exact repositioning of the B.R.W. stereotaxic system, placing the target point in the linear accelerator isocenter. The preliminary technical results obtained in five children are reported and the fixture performance, advantages, and perspectives are discussed.

Radiosurgery of carotid-cavernous fistulae

25 cases of carotid-cavernous fistulae (CCF) who underwent radiosurgery with a conventional gamma source from 1977 to 1992 are reported. 22 were low-flow, spontaneous CCFs and 3 were high flow fistulae which had undergone a previous trapping. The total dose delivered was 30 to 40 Gy. 91% to patients with low-flow CCF cured after radiosurgery in a mean time of 7.5 months, presenting improvement in a mean time of 2.3 months. Only one of the high-flow fistulae was cured. Follow-up period ranged between 14 years and 15 months (mean: 50 months). No recurrence was recorded in any case. While intravascular embolotherapy is the treatment of choice for high-flow fistulae, stereotactic radiosurgery may be the elective treatment for low-flow CCF.