Radiation necrosis following gamma knife surgery: a case-controlled comparison of treatment parameters and long-term clinical follow up

Clinical, dosimetric, and radiographic correlation of radiation injury involving the brainstem and the medial temporal lobes following stereotactic radiotherapy for neoplasms of central skull base

Stereotactic Radiotherapy (SRT) is more commonly used for skull base tumors in conjunction with the technical development of radiation intensity modulation. Purpose of this study is to correlate clinical and radiographic characteristics of delayed radiation injury (RI) occurring around central skull base following SRT with SRT dosimetric data. Total of six patients were identified to have developed RI in the vicinity of SRT target volume out of 141 patients who received SRT in he center or near-center of the skull base. The images and medical records were retrospectively reviewed. The analysis was performed for RI location, time of development, imaging and clinical characteristics and evolution of RI and correlated with SRT dosimetric analysis using image fusion with follow-up MRI scans. Mean follow-up time was 24 +/- 9 months. During the follow-up period, twelve sites of RI were found in 6 patients. They were clinically symptomatic in 4/6 patients (66.6%) at median 12.5 months after SRT. Mean time interval between SRT and detection of RI was 9 +/- 3, 18.5 +/- 5, and 13.5 months for brainstem, temporal lobe, and cerebellum/labyrinth lesions, respectively. All RI lesions were included in the region of high SRT doses. After steroid and symptomatic treatment, 50% of RI lesions showed complete response, and 40% showed partial response. RI can occur around the skull base because of irregular shape of target tumor, its close proximity to normal brain parenchyma, and inhomogeneity of dose distribution. Brainstem lesions occurred earlier than temporal lobe RI. The majority of the RI lesions, not mixed with the tumor in this study, showed radiographic and clinical improvement with steroid and symptomatic treatments.

Radiation dose-volume effects in the brain

We have reviewed the published data regarding radiotherapy (RT)-induced brain injury. Radiation necrosis appears a median of 1-2 years after RT; however, cognitive decline develops over many years. The incidence and severity is dose and volume dependent and can also be increased by chemotherapy, age, diabetes, and spatial factors. For fractionated RT with a fraction size of <2.5 Gy, an incidence of radiation necrosis of 5% and 10% is predicted to occur at a biologically effective dose of 120 Gy (range, 100-140) and 150 Gy (range, 140-170), respectively. For twice-daily fractionation, a steep increase in toxicity appears to occur when the biologically effective dose is >80 Gy. For large fraction sizes (>or=2.5 Gy), the incidence and severity of toxicity is unpredictable. For single fraction radiosurgery, a clear correlation has been demonstrated between the target size and the risk of adverse events. Substantial variation among different centers' reported outcomes have prevented us from making toxicity-risk predictions. Cognitive dysfunction in children is largely seen for whole brain doses of >or=18 Gy. No substantial evidence has shown that RT induces irreversible cognitive decline in adults within 4 years of RT.

Equivalence in dose fall-off for isocentric and nonisocentric intracranial treatment modalities and its impact on dose fractionation schemes

PURPOSE

To investigate whether dose fall-off characteristics would be significantly different among intracranial radiosurgery modalities and the influence of these characteristics on fractionation schemes in terms of normal tissue sparing.

METHODS AND MATERIALS

An analytic model was developed to measure dose fall-off characteristics near the target independent of treatment modalities. Variations in the peripheral dose fall-off characteristics were then examined and compared for intracranial tumors treated with Gamma Knife, Cyberknife, or Novalis LINAC-based system. Equivalent uniform biologic effective dose (EUBED) for the normal brain tissue was calculated. Functional dependence of the normal brain EUBED on varying numbers of fractions (1 to 30) was studied for the three modalities.

RESULTS

The derived model fitted remarkably well for all the cases (R(2) > 0.99). No statistically significant differences in the dose fall-off relationships were found between the three modalities. Based on the extent of variations in the dose fall-off curves, normal brain EUBED was found to decrease with increasing number of fractions for the targets, with alpha/beta ranging from 10 to 20. This decrease was most pronounced for hypofractionated treatments with fewer than 10 fractions. Additionally, EUBED was found to increase slightly with increasing number of fractions for targets with alpha/beta ranging from 2 to 5.

CONCLUSION

Nearly identical dose fall-off characteristics were found for the Gamma Knife, Cyberknife, and Novalis systems. Based on EUBED calculations, normal brain sparing was found to favor hypofractionated treatments for fast-growing tumors with alpha/beta ranging from 10 to 20 and single fraction treatment for abnormal tissues with low alpha/beta values such as alpha/beta = 2.

A quantitative comparison of radiosurgical treatment parameters in vestibular schwannomas: the Leksell Gamma Knife Perfexion versus Model 4C

PURPOSE

The world's first Gamma Knife Perfexion (PFX)was installed in Marseille in July 2006. The aim of this study was to investigate the impact of the PFX technology on the quality of dose planning for vestibular schwannomas (VS).

METHODS

When the PFX was first introduced, a comparative randomized prospective study of 200 patients was conducted.Seventy-eight of the 200 patients in that study had VS, of whom 38 were randomized to treatment with the Gamma Knife Model 4C (group 4C) and 40 were randomized to treatment with PFX (group P1). The authors also incorporated a matched group of 40 patients with VS consecutively treated with PFX after the initial learning curve period (group P2). Dose planning was compared and evaluated by measuring the conformity index (CI), selectivity index (SI), gradient index(GI), energy index (EI), unit isocenters (UI) and cochlear dose. Patients were also stratified into subgroups according to target volume (> or = 0.5 ml).

RESULTS

In the whole population, CI, EI and cochlear dose were significantly better in group P2 (CI=0.917, EI=1.35,cochlear dose=3.55) than in group 4C (CI=0.864, EI=1.27,cochlear dose=5.10). In the subgroup of lesions > or = 0.5 ml, CI,GI, EI, UI and cochlear dose in group P2 (CI=0.929, GI=2.67, EI=1.37, UI=10.6, cochlear dose=3.55) were significantly better than in group 4C (CI=0.874, GI=2.85, EI=1.30, UI=14.5, cochlear dose=5.10).

CONCLUSIONS

The investigation of the dose planning capabilities of the PFX on a cohort of VS demonstrates a better conformity and energy distribution, with better cochlear sparing and without any particular drawback. In addition,there is an improvement in peripheral dose gradient in larger lesions. Further clinical studies will be required before drawing any conclusions about the clinical benefit achieved by these dose planning improvements.

Relationship between volume, dose and local control in stereotactic radiosurgery of brain metastasis

The aim of this study is to analyse the efficacy of linear accelerator stereotactic radiosurgery (SRS) on prognostic factors, local control rate and survival in patients with brain metastasis. Patients with either a single metastasis or up to 4 multiple brain metastases with a maximum tumour diameter of 40 mm for each tumour and a Karnofsky Performance Status (KPS) > or = 70 were eligible for SRS. SRS was applied to 150 lesions in 86 consecutive patients with a median age of 60 years (median 1 and mean 1.7 lesions per patient, mean KPS 86). Median overall survival was 6.2 months after SRS and 9.7 months from diagnosis of brain metastasis. Multivariate analysis revealed that a KPS of 90 or more (p = 0.009) and female sex (p = 0.003) were associated with a longer survival. Radiation dose < or = 15 Gy (p = 0.017) and KPS < 90 (p = 0.013) were independent predictors of a shorter time to local failure. Five patients showed evidence of radionecrosis with a median survival of 14.8 months. Addition of WBRT neither led to improvement of survival nor to improvement of local control. Improved local control following SRS for brain metastases was associated with KPS > or =90, a radiation dose > 15 Gy and a PTV < 13 cc. The potential of hypofractionated stereotactic radiotherapy (SRT) for brain metastases of larger volume warrants further study.

Utility of apparent diffusion coefficient in predicting the outcome of Gamma Knife-treated brain metastases prior to changes in tumor volume: a preliminary study

OBJECT

Gamma Knife surgery (GKS) is often the sole treatment for brain metastases. The authors hypothesized that early post-GKS measures of the relative apparent diffusion coefficient (rADC) could predict therapeutic response, recurrence, and radionecrosis prior to changes in tumor volume.

METHODS

Magnetic resonance (MR) images of 25 metastatic tumors in 15 patients were reviewed. Inclusion criteria included a history of surgery or GKS, a minimum tumor diameter of 5 mm at treatment, and a minimum of two follow-up MR images. Tumor volumes were normalized to baseline, and tumor ADC values were normalized to normal-appearing white matter (rADC). A successful therapeutic response (STR) was defined by a monotonically decreasing tumor volume throughout the follow-up period. Magnetic resonance spectroscopy was used to classify non-STRs as radionecrosis or tumor recurrence. All tumors exhibited a decreased normalized volume (mean 37%) at the first follow-up examination (range 33-124 days after GKS, mean 54 days), and three distinct rADC patterns subsequently evolved: Group 1 (STR [10 cases]), monotonically decreasing volume with gradually increasing rADC; Group 2 (radionecrosis [three cases]), initial volume reduction followed by gradual increase, with initial rapidly increasing rADC followed by more gradual increase or plateau; and Group 3 (recurrent tumor [12 cases]), initial volume decrease followed by increase, with a preceding gradual decrease in the rADC.

CONCLUSIONS

The rADC patterns outperform initial post-GKS tumor volume in predicting the long-term response to treatment. Decreasing tumor volume with an increasing rADC predicts an STR. For lesions with increasing volume, antecedent rADC reduction predicts recurrence, whereas a rapidly increasing rADC predicts radionecrosis. Evaluation of the rADC at the initial post-GKS follow-up examination appears to be a useful prognostic measure of metastatic tumor response.

Extensive white matter changes after stereotactic radiosurgery for brain arteriovenous malformations: a prognostic sign for obliteration?

OBJECTIVE

Perinidal high-signal-intensity changes on T2-weighted magnetic resonance imaging can be seen surrounding radiosurgically treated brain arteriovenous malformations (AVM). Occasionally, these signal intensity changes develop far beyond the irradiated volume. A retrospective analysis of both the pre- and postradiosurgery magnetic resonance imaging and angiographic studies was performed to analyze the cause of these extensive perinidal white matter changes.

METHODS

The pre- and postradiosurgical magnetic resonance imaging and angiographic studies of 30 patients with T2 high-signal-intensity changes surrounding a brain AVM were analyzed retrospectively. Patients were divided into 2 groups on the basis of the extension of the signal intensity changes within or beyond the 10-Gy isodose area. The angiographic analysis was focused on the venous drainage pattern (deep versus superficial), venous stenosis, and the number of draining veins before and after radiosurgery. In addition, the obliteration rate was determined for the 2 subgroups.

RESULTS

Fourteen patients (47%) showed high-signal-intensity changes far beyond the 10-Gy isodose area. A single draining vein was more often present in these patients with extensive T2 hyperintensity signal changes than in the other group. Obliteration was achieved in 12 (88%) of 14 patients with extensive signal intensity changes, as opposed to 8 (50%) of 16 patients in the other group.

CONCLUSION

High-signal-intensity changes after radiosurgery for brain AVMs, far beyond the 10-Gy isodose area on T2-weighted images, are especially seen in brain AVMs draining through a single vein. The higher occlusion rate of brain AVMs under these circumstances is well appreciated.

Effect of composite sector collimation on average dose fall-off for Gamma Knife Perfexion

OBJECT

The new capability of composite sector collimation in Gamma Knife Perfexion produces complex, nonspherical, and nonelliptical dose distributions. In this study, the authors investigated the effect of composite sector collimation on average dose fall-off compared with the previous Gamma Knife model.

METHODS

A general formalism was derived to describe the peripheral dose distribution of all Gamma Knife models in the form of (V/V(0)) = (D/D(0))(gamma), where V is the volume of the peripheral isodose line with the value of D, V(0) is the reference prescription isodose volume, D(0) is the prescription dose, and gamma is the fitting parameter that determines how fast the dose falls off near the target. Based on this formula, the authors compared 40 cases involving patients treated with Gamma Knife Perfexion with 40 similar cases involving patients treated with Gamma Knife model 4C. The cases were grouped based on the use of the sector collimators in the treatment planning process. For each group as well as all cases combined, the mean gamma values were compared by means of the Student t-test for varying ranges of the peripheral dose distribution-from 100% of the prescription dose to 75, 50, and 25% of the prescription dose.

RESULTS

The fit of general formula to the data was excellent for both Gamma Knife Perfexion and Gamma Knife 4C with R(2)> 0.99 for all the cases. The overall gamma values (mean +/- 2 standard deviations) were as follows: gamma = -1.74 +/- 0.47 (Model 4C) versus -1.77 +/- 0.40 (Perfexion) within 100-75% of the prescription dose; gamma = -1.57 +/- 0.26 (Model 4C) versus -1.58 +/- 0.25 (Perfexion) within 100-50% of the prescription dose; gamma = -1.47 +/- 0.18 (Model 4C) versus -1.50 +/- 0.16 (Perfexion) within 100-25% of the prescription dose. No statistical significance between the mean differences for Gamma Knife Perfexion and Model 4C was found within these ranges. The probability values were 0.65, 0.84, and 0.22, respectively.

CONCLUSIONS

The use of composite sector collimators in Gamma Knife Perfexion demonstrated no statistically significant effects on the volume-averaged dose fall-off near a target periphery for typical treatment cases.

Gamma Knife surgery of large meningiomas: early response to treatment

PURPOSE

Gamma Knife treatment is traditionally limited to tumours with a diameter not exceeding 3-3.5 cm. The current paper presents 97 patients with meningiomas with a minimum volume of 10 cm(3), treated with a prescription dose of 12 Gy (or sometimes less to protect neighbouring structures). The post-treatment assessment of these patients, the early response to treatment and the complications of treatment are presented.

METHODS

There were 97 patients, 70 females and 27 males. The mean age was 48.1 years (range 20.4-87.2 years). The mean follow-up was 54 months (range 25-86 months). All tumours had a volume of 10 cm(3) or more. The mean volume was 15.9 cm(3) (range 10.0-43.2 cm(3)). Post-treatment follow-up used quantitative and qualitative assessments, which are described.

RESULTS

No tumour continued to grow. Twenty-seven were smaller and 72 unchanged in volume. Three patients suffered adverse radiation effects (defined as a new post-treatment oedema detected on the magnetic resonance image with or without contrast leakage). In one case this was silent. In two cases the clinical and radiological effects were temporary and resolved completely.

CONCLUSIONS

It is suggested on the basis of this material that the dosimetry used here permits the safe Gamma Knife treatment of larger meningiomas within the range reported. The early radiological response is encouraging, but further follow-up is needed to check long term tumour control. A qualitative method of tumour volume assessment is presented. It seems to be a simpler and more reliable way of assessing tumour volume changes than other methods currently in routine use.

Adverse radiation effects after Gamma Knife Surgery in relation to dose and volume

INTRODUCTION

The relationship between target volume and adverse radiation effects (AREs) at low prescription doses requires elucidation. The development of AREs in three series of patients treated in the Gamma Knife is analysed in relation to prescription dose and target volume.

MATERIALS AND METHODS

There were three groups. In group 1, there were of 275 patients with meningiomas; in group 2, 132 patients with vestibular schwannomas; and in group 3, 107 patients with arteriovenous malformations (AVMs). The minimum follow-up for each group was more than 24 months. All patients were followed up at six monthly intervals. The patients with tumours received a prescription dose of 12 Gy, which was varied to protect normal structures but not in relation to tumour volume per se. The desired AVM prescription dose was 25 Gy, but this was also reduced to protect normal structures and to keep the total dose within certain pre-defined limits. All AREs refer to intra-parenchymal increased perilesional T2 signal on MR irrespective of clinical correlation.

RESULTS

There was no relationship between tumour volume and the development of ARE in the tumour groups. There was a highly significant relationship between target volume and the development of ARE for the AVMs with their much higher dose. Radiation-induced clinical trigeminal and facial nerve deficits with both vestibular schwannomas and meningiomas were always associated with an increased T2 signal in the neighbouring brainstem parenchyma.

CONCLUSIONS

The relationship between target volume and the risk of adverse radiation effects may not apply with lower prescription doses. Individual radiosensitivity may explain why a minority suffer AREs unrelated to target volume. It is possible that radiation-induced brainstem parenchymal damage with concomitant cranial nerve deficits may be commoner after radiosurgery than is usually thought. If tumour control with lower doses is adequate, radiosurgery could be safely considered for larger targets associated with a high risk from microsurgery.

DVHs evaluation in brain metastases stereotactic radiotherapy treatment plans

PURPOSE

The aim of this work is to report a retrospective study of radiobiological indicators based on Dose-Volume Histograms analysis obtained by stereotactic radiotherapy treatments.

METHODS AND MATERIALS

Fifty-five patients for a total of sixty-seven brain metastases with a mean target volume of 8.49 cc were treated by Dynamic Conformal Arc Therapy (DCAT) and Intensity-Modulated Stereotactic Radiotherapy (IMRST). The Delivered prescription dose was chosen on the basis of tumor size and location so as to ensure a 100% isodose coverage to the target volume.

RESULTS

The treatment plans reported a mean value of 10% and 2.19% for the inhomogeneity and conformal index, respectively. The F factor showed we overdosed sixty-three patients delivering an additional 7% dose more than calculated values. The radiobiological parameters: TCP and NTCP showed a complete tumor control limiting the organs at risk damage.

CONCLUSION

One goal of stereotactic radiotherapy is to design a treatment plan in which the steep dose gradient achievable minimizes the amount of radiation delivered outside the tumor region. This technique allows to deliver a much larger dose to the target without exceeding the radiation-related tolerance of normal tissues and improving patients' quality of life.

Radiation necrosis of the brain after radiosurgery for vestibular schwannoma

OBJECTIVE

The objective of this study was to obtain a better understanding of radiation-induced brain necrosis after stereotactic radiation therapy for vestibular schwannomas.

STUDY DESIGN

We conducted a retrospective case analysis.

SETTING

The study took place at a tertiary referral center.

PATIENTS

We report on the case of a patient treated with stereotactic radiation who developed radiation-induced necrosis of the ipsilateral temporal lobe.

INTERVENTION

The various interventions in patients with radiation-induced necrosis include steroid treatment, decompression, and hyperbaric oxygen therapy; these are discussed briefly in this article. Owing to the limited symptoms in our patient, she was observed.

MAIN OUTCOME MEASURE

The outcome measure that we evaluated was radiation-induced necrosis of the brain after stereotactic radiation therapy for a vestibular schwannoma.

RESULTS

Patients who undergo stereotactic radiation therapy for vestibular schwannomas are at risk for radiation-induced brain necrosis.

CONCLUSION

We support the development of a national database that would track the long-term complications of stereotactic radiation therapy to help patients make a more informed decision for the treatment of their vestibular schwannomas.

Boosting Central Target Dose by Optimizing Embedded Dose Hot Spots for Gamma Knife Radiosurgery

AIMS

To develop a boost technique for Gamma Knife radiosurgery by embedding and optimizing dose hot spots inside a conventional Gamma Knife plan.

METHODS

An optimization algorithm was developed to automatically arrange the pattern and adjust the intensities of the embedded dose hot spots. We compared the treatment plans of the optimized boost technique with the conventional Gamma Knife treatment plans, where dose hot spots were scattered randomly within the target volume.

RESULTS

We found the embedded boost plans significantly increased the maximum dose of the target (on average 31% or 5-6 Gy). The mean dose to the target was increased by an averaged 7.1% (1.5-2 Gy). In contrast, the dose to the adjacent normal brain was strictly maintained with the dose volume histograms differing less than 0.5% between the boost treatment plans and the conventional treatment plans. The planning effort and treatment time was comparable between the two techniques.

CONCLUSION

We have demonstrated a simple and an effective technique for increasing the central target dose without affecting the normal brain sparing for Gamma Knife radiosurgery.

Histopathology of radiation necrosis with severe peritumoral edema after gamma knife radiosurgery for parasagittal meningioma. A report of two cases

BACKGROUND

Gamma knife radiosurgery (GKS) has been an effective treatment for meningiomas. Nevertheless, it still has certain risks. We present 2 cases of parasagittal meningioma after GKS complicated with radiation necrosis and peritumoral edema. The results of histologic examination are discussed.

CASE DESCRIPTION

Two cases of parasagittal meningioma received GKS. Symptomatic peritumoral edema developed 3-4 months after GKS. Both of them underwent surgical resection of their tumor afterwards. Histologic examination showed necrotic change inside the tumor and infiltration of inflammatory cells in both cases. Hyalinization of blood vessels was seen in the 2nd case. The patients had improvement of neurologic function after surgical resection. Imaging performed 3 months after surgical resection showed alleviation of brain edema.

CONCLUSION

After radiosurgery peritumoral edema tends to occur in meningiomas with a parasagittal position. Radiation necrosis, infiltration of inflammatory cells, and radiation injury to the vasculature causing hyalinization of blood vessels are suggested as the underlying histopathology.

Image fusion analysis of volumetric changes after interstitial low-dose-rate iodine-125 irradiation of supratentorial low-grade gliomas

The aim of this study was to compare the volumes of tumor necrosis, reactive zone and edema with the three-dimensional dose distributions after brachytherapy treatments of gliomas. The investigation was performed an average of 14.2 months after low-dose-rate (125)I interstitial irradiation of 25 inoperable low-grade gliomas. The prescribed dose was 50-60 Gy to the tumor surface. Dose planning and image fusion were performed with the BrainLab-Target 1.19 software. In the CT/ MRI images, the "triple ring" (tumor necrosis, reactive ring and edema) developing after the interstitial irradiation of the brain tumors was examined. The images with the triple ring were fused with the planning images, and the isodose curves were superimposed on them. The volumes of the three regions were measured. The average dose at the necrosis border was determined from the isodose distribution. For quantitative assessment of the dose distributions, the dose nonuniformity ratio (DNR), homogeneity index (HI), coverage index (CI) and conformal index (COIN) were calculated. The relative volumes of the different parts of the triple ring after the interstitial irradiation compared to the reference dose volume were the following: necrosis, 40.9%, reactive zone, 47.1%, and edema, 367%. The tumor necrosis developed at 79.1 Gy on average. The average DNR, HI, CI and COIN were 0.45, 0.24, 0.94 and 0.57, respectively. The image fusion analysis of the volume of tumor necrosis, reactive ring and edema caused by interstitial irradiation and their correlation with the dose distribution provide valuable information for patient follow-up, treatment options, and effects and side effects of radio therapy.

Normal Tissue Tolerance Dose Metrics for Radiation Therapy of Major Organs

Late organ toxicity from therapeutic radiation is a function of many confounding variables. The total dose delivered to the organ and the volumes of organ exposed to a given dose of radiation are 2 important variables that can be used to predict the risk of late toxicity. Three-dimensional radiation planning enables accurate calculation of the volume of tissue exposed to a given dose of radiation, graphically depicted as a dose-volume histogram. Dose metrics obtained from this 3-dimensional dataset can be used as a quantitative measure to predict late toxicity. This review summarizes the published clinical data on the risk of late toxicity as a function of quantitative dose metrics and attempts to offer suggested dose constraints for radiation treatment planning.

Radiobiology of brain metastasis: applications in stereotactic radiosurgery

Stereotactic radiosurgery is a neurosurgical modality in which a target lesion can be irradiated while sparing normal brain tissue. In some respects, brain metastasis is well suited for radiosurgery, as metastatic lesions tend to be small and well circumscribed and displace (but do not infiltrate) normal brain tissue, facilitating the delivery of radiation. Advances in stereotactic radiosurgical planning, such as blocking patterns and beam shaping, have allowed further targeting of discrete lesions while minimizing the effect of radiation toxicity on the central nervous system. In this paper the authors review the radiobiology of brain metastases and stereotactic radiosurgical approaches that can be used to treat these tumors safely.

Intratumoral hemorrhage after remote subtotal microsurgical resection and gamma knife radiosurgery for vestibular schwannoma

Our report describes the occurrence of intratumoral hemorrhage in a vestibular schwannoma, which was treated with microsurgical resection thirteen years and gamma knife surgery (GKS) more than two years prior to the event. Although rare, it is apparent that bleeding into a vestibular schwannoma remains a possibility, even after the tumor has responded favorably to GKS. Long-term followup of patients with vestibular schwannoma who have been treated with GKS is advisable to assess treatment response and to detect adverse events (e.g. hemorrhage) suspected on clinical grounds.

Killing two birds with one stone: a dosimetric study of dual target radiosurgery using a single isocenter

The treatment of hematogenous brain metastases is a frequent indication for stereotactic radiosurgery (SRS). It is common for more than one metastasis to be treated during the same SRS session. We retrospectively identified four cases where our m3 micro multileaf collimator (mMLC) was used to create two distinct apertures and treat adjacent lesions using a single isocenter. For these four cases, single isocenter plans with static conformal beams were dosimetrically compared to plans utilizing two isocenters with static conformal beams or conformal arcs. The effects on dose homogeneity, dose conformity, and the minimum isodose separating the two targets are minor and variable. On the other hand, the use of a single isocenter technique consistently halves delivery time and decreases the integral dose to normal tissue. For small adjacent metastases, which can simultaneously be encompassed within the high-resolution portion of the m3/Novalis mMLC collimator, the use of a single rather than a dual isocenter technique is feasible and generally advantageous.

Recurrent late cerebral necrosis with aggressive characteristics after radiosurgical treatment of an arteriovenous malformation

✓Late cerebral radiation necrosis usually occurs within 3 years of stereotactic radiosurgery. The authors report on a case of recurrent radiation necrosis with rapid clinical deterioration and imaging findings resembling those of a malignant glioma. This 68-year-old man, who had a history of a left posterior temporal and thalamic arteriovenous malformation (AVM) treated with linear accelerator radiosurgery 13 years before presentation and complicated by radiation necrosis 11 years before presentation, exhibited new-onset mixed aphasia, right hemiparesis, and right hemineglect. Imaging studies demonstrated hemorrhage and an enlarging, heterogeneously enhancing mass in the region of the previously treated AVM. The patient was treated medically with corticosteroid agents, and stabilized temporarily. Unfortunately, his condition worsened precipitously soon thereafter, requiring the placement of a shunt for relief of obstructive hydrocephalus. Further surgical intervention was offered, but the patient’s family opted for hospice care instead. The patient died 10 weeks after initially presenting to the authors’ institution, and the results of an autopsy demonstrated radiation necrosis.

Symptomatic radiation necrosis can occur more than a decade after stereotactic radiosurgery, necessitating patient follow up during a longer period of time than currently practiced. Furthermore, there is a need for more careful reporting on the natural history of such cases to clarify the pathogenesis of very late and recurrent radiation necrosis after radiosurgery and to define patient groups with a higher risk for these entities.

Gamma knife radiosurgery for cerebral arteriovenous malformations in children/adolescents and adults. Part I: Differences in epidemiologic, morphologic, and clinical characteristics, permanent complications, and bleeding in the latency period

PURPOSE

To compare the epidemiologic, morphologic, and clinical characteristics of 92 children/adolescents (Group A) and 362 adults (Group B) with cerebral arteriovenous malformations (cAVMs) considered suitable for radiosurgery; to correlate radiosurgery-related permanent complication and post-radiosurgery bleeding rates in the 75 children/adolescents and 297 adults available for follow-up.

METHODS AND MATERIALS

Radiosurgery was performed with a model C 201-source Co60 Leksell Gamma Unit (Elekta Instruments, Stockholm, Sweden). Fisher exact two-tailed, Wilcoxon rank-sum, and two-sample binomial exact tests were used for statistical analysis.

RESULTS

There were significant differences between the two populations in sex (p = 0.015), clinical presentation (p = 0.001), and location (p = 0.008). The permanent complication rate was lower in younger (1.3%) than in older patients (5.4%), although the difference was not significant (p = 0.213). The postradiosurgery bleeding rate was lower in Group A (1.3%) than in Group B (2.7%) (p = 0.694), with global actuarial bleeding rates of 0.56% per year and 1.15% per year, respectively.

CONCLUSIONS

The different characteristics of child/adolescent and adult cAVMs suggest that they should be considered two distinct vascular disorders. The similar rates of radiosurgery-related complications and latency period bleeding in the two populations show that gamma knife radiosurgery does not expose young patients to a higher risk of sequelae than that for older patients.

Long-Term Survival After Gamma Knife Radiosurgery for Primary and Metastatic Brain Tumors

In this paper, we studied factors related to long-term survival after gamma knife radiosurgery (GKS) for primary and metastatic brain tumors. We examined all cases of brain metastases and malignant glioma treated with GKS between September 1994 and December 1998. All patients with survival exceeding 2 years were studied retrospectively using prospectively acquired data. A total of 22 patients, with an average age of 56, were identified, which accounts for 11% of the total patients treated during this time interval. Seventeen of 22 are still alive with a mean follow-up of 48 months. Sixteen patients had metastatic tumors, whereas 6 had a malignant glioma. Thirteen of 15 patients with metastases had a controlled primary site, and the other 2 patients did not have a primary site identified. These 2 patients were among the 3 that died during the follow-up period. Fourteen patients developed symptomatic radiation necrosis by MRI criteria with 4 confirmed by biopsy. Quality-of-life factors were assessed in 20 of 22 patients using a modified Spitzer scale, which showed a high level of functioning in all of the long-term survivors (mean score 8.65 of 10), and only 1 patient had a Karnofsky Performance Score of less than 70. We conclude that radiosurgery provides a noninvasive and effective way of controlling brain tumors, while preserving quality of life.

Survival in relation to radiotherapeutic modality for brain metastasis: whole brain irradiation vs. gamma knife radiosurgery

The purpose of this report is to evaluate and compare the survival of patients with brain metastasis (BRM) treated by whole brain irradiation (WBI) using linear energy accelerator (LINAC) and by stereotactic radiosurgery using gamma knife. This study consists of a series of 67 patients with BRM treated with WBI between 1998 and 1999 and 53 patients with BRM treated with gamma knife radiosurgery (GKRS) between 2000 and 2001. A retrospective study of the data was performed and the overall survival between these 2 groups was analyzed. The comparability of these 2 groups was tested by chi2 and t test values. Log-rank test was used in the survival comparison. The 1-year survival rate was 26.3% and 22.6%, and corresponding mean survival was 7.8 months and 6.7 months for WBI and GKRS groups, respectively. There was no statistically significant difference between these 2 groups' survival. It was evident from imaging defined lesions that with GKRS the lesions were reduced, stabilized, or disappeared in 89% of cases. Survival of patients with BRM treated with WBI or GKRS was similar in these series. The present study suggests that good tumor response by GKRS does not translate in longer patient survival.

Radionecrosis of the Inferior Occipital Lobes With Altitudinal Visual Field Loss After Gamma Knife Radiosurgery

A patient had bilateral superior altitudinal visual field defects because of radionecrosis of the inferior occipital lobes after gamma knife radiosurgery for a recurrent atypical cerebellar meningioma. Although radionecrosis of the anterior visual pathway has been well-documented, this is the first report of visual field loss associated with occipital lobe radionecrosis. The treatment dose this patient received is within the range of predicted tolerable radiosurgical dosing, although this patient was at increased risk for radionecrosis secondary to previous external beam radiotherapy. By offering an effective, noninvasive treatment, radiosurgery has changed the management of intracranial lesions. Radiosurgery targets a discrete volume of tissue and relatively spares the surrounding normal tissue. Radiation injury, or radionecrosis, is the only significant complication of radiosurgery (). We present a case of bilateral occipital lobe radionecrosis after gamma knife surgery that resulted in bilateral superior altitudinal defects.

Dose-volume prediction of radiation-related complications after proton beam radiosurgery for cerebral arteriovenous malformations

OBJECT

The use of radiosurgery for the treatment of cerebral arteriovenous malformations (AVMs) and other lesions demands an accurate understanding of the risk of radiation-related complications. Some commonly used formulas for predicting risk are based on extrapolation from small numbers of animal experiments, pilot human treatment series, and theoretical radiobiological considerations. The authors studied the incidence of complications after AVM radiosurgery in relation to dose, volume, and other factors in a large patient series.

METHODS

A retrospective review was conducted in 1329 patients with AVM treated by Dr. Raymond Kjellberg at the Harvard Cyclotron Laboratory (HCL) between 1965 and 1993. Dose and volume were obtained from HCL records, and information about patient follow up was derived from concurrent clinical records, questionnaires, and contact with referring physicians. Multivariate logistic regression with bootstrapped confidence intervals was used. Follow up was available in 1250 patients (94%); the median follow-up duration was 6.5 years. The median radiation dose was 10.5 Gy and the median treatment volume was 33.7 cm(3). Twenty-three percent of treated lesions were smaller than 10 cm(3). Fifty-one permanent radiation-related deficits occurred (4.1%). Of 1043 patients treated with a dose predicted by the Kjellberg isoeffective centile curve to have a less than 1% complication risk, 1.8% suffered radiation-related complications. Actual complication rates were 4.7% for 128 patients treated at Kjellberg risk centile doses of 1 to 1.8%, and 34% for 61 patients treated at risk centile doses of 2 to 2.5%. The fitted logistic model showed that complication risk was related to treatment dose and volume, thalamic or brainstem location, and patient age.

CONCLUSIONS

The Kjellberg isoeffective risk centile curve significantly underpredicted actual risks of permanent complications after proton beam radiosurgery for AVMs. Actual risks were best predicted using a model that accounted for treatment dose and volume, lesion location, and patient age.

Delayed radiation necrosis with extensive brain edema after gamma knife radiosurgery for multiple cerebral cavernous malformations--case report

A 39-year-old man presented with multiple intracranial cavernous malformations manifesting as intractable seizures persisting for more than 20 years. He underwent gamma knife radiosurgery (GKRS) for right frontal and left temporal cavernous malformations. He began to suffer from progressive left hemiparesis and inattention 2 years 5 months after the GKRS. Magnetic resonance imaging showed abnormal ring enhancement and extensive brain edema around the right frontal lesion. Conservative therapies such as external decompression, low-dose barbiturates, and mild hypothermia had no effect on his clinical status. Stereotactic biopsy of the ring-enhanced area demonstrated gliosis. Signs of cerebral herniation appeared, so we performed partial resection of the right frontal lobe. His symptoms recovered immediately. Subsequent hyperbaric oxygen (HBO) therapy significantly improved the extensive brain edema. Delayed radiation necrosis associated with potentially fatal brain edema may occur after GKRS for cavernous malformations. Internal decompression and subsequent HBO therapy were very effective for the treatment of these lesions.

Spontaneous haemorrhage into metastatic brain tumours after stereotactic radiosurgery using a linear accelerator

OBJECTIVE

To determine the incidence and clinical characteristics of spontaneous haemorrhage into metastatic brain tumours after radiosurgery.

METHODS

Intratumour haemorrhage rate, clinical features, and treatment were evaluated in 54 patients with 131 brain metastases of varying origin who were treated using linear accelerator radiosurgery. The marginal dose was maintained constant at 20 or 25 Gy, irrespective of tumour size.

RESULTS

Haemorrhage was identified in 7.4% of the metastases (five tumours in four patients) before radiosurgery and in 18.5% (10 tumours in 10 patients) after radiosurgery. In three cases, haemorrhage into the tumour after radiosurgery was symptomatic. Half the haemorrhages occurred within one month of radiosurgery. The changes in tumour size observed at the time of haemorrhage were an increase in one tumour, no change in five, and a decrease in four. Haemorrhage into a tumour after radiosurgery was more likely to occur in female patients, in tumours with a larger volume on pretreatment neuroimaging, and in tumours treated with a larger number of isocentres or a higher maximum dose. Haemorrhagic features in the patients or their tumours on presurgical assessment were not disposing factors to haemorrhage after radiosurgery.

CONCLUSIONS

When larger brain metastases are aggressively treated by radiosurgery, better local control may be attained but there may also be a higher risk of haemorrhage soon after the treatment.

Stereotactic radiosurgery for meningiomas

Meningiomas are benign tumors attached to the dura that typically have a slow growth rate. After gliomas, they are the most common primary tumor of the brain. They are ideal radiobiological targets because single-fraction radiation has a high biologically effective dose. Furthermore, a highly conformal radiation plan can provide effective treatment to the tumor while sparing the surrounding brain. Meningioma control rates range from 90 to 95%, and the risk of morbidity is low. Radiosurgery is an excellent treatment for asymptomatic, small- to moderate-sized meningiomas. It is also ideal for patients with incompletely resected meningiomas, recurrent meningiomas, and risk factors precluding conventional surgery.

Late bilateral temporal lobe necrosis after conventional radiotherapy

A 63-year-old woman presented with radionecrosis in the bilateral temporal lobes manifesting as dementia about 30 years after undergoing conventional radiotherapy for pituitary adenoma. Computed tomography and magnetic resonance (MR) imaging showed edema and cystic lesions in both temporal lobes. The mass in the left temporal lobe was excised. MR imaging 12 days after surgery showed reduced edema. Her dementia had improved. Radionecrosis usually occurs between several months and a few years after radiotherapy. The incidence of radionecrosis is estimated as 5%, but may be higher with longer follow-up periods. Clinical reports have suggested that larger total doses of radiation are associated with earlier onset of delayed necrosis and the fractional dose is the most significant factor causing cerebral radionecrosis. Radionecrosis can occur long after conventional radiotherapy or stereotactic radiosurgery using a linac-based system or a gamma knife unit.

Thalamic lesions produced by gamma thalamotomy for movement disorders

Object. The treatment of Parkinson disease and other kinds of involuntary movement by gamma knife radiosurgery (GKS) is presented. This is an extension of previous work. The clinical course and thalamic lesions were the main factors examined.

Methods. Seventeen new cases were added to the previously reported 36 cases. The course and results for the whole series of 53 patients were examined. Treatment was undertaken using a single 4-mm collimator shot to deliver 130 Gy to the target. The target was determined in the previously treated patients by using classic methods involved in conventional stereotactic thalamotomy with microrecording. More recently, target localization has been performed by relating the target point to the total length of the thalamus. Points may then be defined as percentages of that length measured from the anterior pole. Targets can then be determined in relationship to the appropriate percentage.

Thirty-five patients have been followed for more than 2 years and the longest follow up was 8 years. Two kinds of thalamic lesion were seen after GKS. Volumetric analysis on MR imaging revealed that the larger lesion was 400 to 500 mm3 at the beginning and gradually decreased in size. The smaller lesion occupied approximately 200 mm3 and also shrank over several months. Eighty percent of the treated cases showed good results and no significant complications, with the tremor subsiding at 1 year (Type 1). Several cases deviated from this standard course in four different ways (Types 2–5). If tremor persisted, conventional stereotactic thalamotomy with microrecording was performed. During such operations, normal neuronal activity was recorded from the region adjacent to the GKS thalamotomy target. This was the region showing a high signal on MR imaging. The activity patterns included the rhythmical grouped discharge of tremor rhythm.

Conclusions. Gamma thalamotomy for functional disorders is still under development, but because the results with careful target planning are satisfactory, there are grounds for increasing optimism.

Analysis of repeat stereotactic radiosurgery for progressive primary and metastatic CNS tumors

PURPOSE

To identify and evaluate the pretreatment and patient factors that would predict for complications after repeat radiosurgery.

METHODS AND MATERIALS

The data from 26 patients who underwent re-irradiation with Gamma Knife surgery after a previous procedure in the same or subjacent location were available for evaluation. The range of follow-up was 1-45 months (mean 10). The mean minimal and maximal initial dose and volume for all 26 patients was 16.2 Gy (range 12-22), 31.0 Gy (range 22.2-40.0), and 12.4 cm(3) (range 1.20-70.84), respectively. The mean marginal and maximal repeated radiosurgery dose and volume for all 26 patients was 14.9 Gy (range 12-22.5), 29.7 Gy (range 18.0-45.0) and 12.8 cm(3) (range 1.10-39.20), respectively.

RESULTS

Tumor control was significantly better statistically (p = 0.0129) for benign tumors (6 of 6, 100% actuarial rate at 4 years) compared with malignant tumors (7 of 20, 35% actuarial rate at 3 years, 3 of 4 metastatic tumors and 2 of 10 primary malignant gliomas). The retreatment volume for radiosurgery correlated significantly with the probability of neurologic decline (any cause) (p = 0.0181).

CONCLUSION

Repeat radiosurgery can be performed for recurrent tumors with minimal central nervous system toxicity, especially for benign tumors, with reasonable tumor control.