Radiosurgery-induced brain tumor. Case report

Treatment of Brain Arteriovenous Malformations

Brain arteriovenous malformations (AVMs) are a rare entity of vascular anomalies, characteristic of anatomical shunting where arterial blood directly flows into the venous circulation. The main aim of the active treatment policy of brain AVMs is the prevention of haemorrhage. There are well-established treatment strategies that continually improve in their safety and efficacy, primarily due to the advances in imaging modalities, targeted and novel techniques, the development of alternative treatment approaches, and even better experience with the disease itself. There are interesting imaging novelties that may be prospectively applicable in the decision-making and planning of the most effective treatment approach for individual patients with intracranial AVM. Surgery is often considered the first-line treatment; however, each patient should be evaluated individually, and the risks of the active treatment policy should not overcome the benefits of the spontaneous natural history of the disease. All treatment modalities, i.e., surgery, radiosurgery, endovascular embolization, and observation, are justified but need to be meticulously selected for each individual patient in order to deliver the best treatment outcome. This chapter deals with historical and currently applied dogmas, followed by introductions of advances in each available treatment modality of AVM management.

Effect of embolization before stereotactic radiosurgery for brain arteriovenous malformations: a case-control study with propensity score matching

OBJECTIVE

The aim of this study was to evaluate whether endovascular embolization prior to stereotactic radiosurgery (SRS) has a negative impact on nidus obliteration for patients with arteriovenous malformations (AVMs).

METHODS

A total of 704 eligible patients with AVM who did not undergo prior surgery or radiotherapy were evaluated. Of these patients, 593 were treated with SRS only, and 111 were treated with embolization followed by SRS (E+SRS). Most patients in the E+SRS group (88%) underwent embolization with n-butyl-2-cyanoacrylate. In the comparison of radiosurgical outcomes between patients treated with SRS only and E+SRS, these groups were matched in a 1:1 ratio using propensity score matching to eliminate differences in basic characteristics. The primary outcome was to compare the nidus obliteration rates between the SRS-only and E+SRS groups. The secondary outcomes were the comparison of cumulative hemorrhage rates and the incidence of cyst formation or chronic encapsulated hematoma after SRS between these groups.

RESULTS

In the unmatched cohorts, the actuarial 3-, 5-, and 8-year nidus obliteration rates after a single SRS session were 49.6%, 69.4%, and 74.1% in the SRS-only group, respectively, and 30.7%, 50.9%, and 68.6% in the E+SRS group, respectively (p = 0.001). In the matched cohort of 98 patients in each group, the rates were 47.1%, 62.0%, and 69.6% in the SRS-only group and 32.5%, 55.3%, and 75.0% in the E+SRS group, respectively (p = 0.24). There was no significant difference in either cumulative hemorrhage or the incidence of cyst formation or chronic encapsulated hematoma between the groups.

CONCLUSIONS

Pre-SRS embolization did not affect nidus obliteration rates, cumulative hemorrhage rates, or the incidence of cyst formation or chronic encapsulated hematoma as late adverse radiation effects in patients with AVM treated with SRS.

Long-Term Risks of Hemorrhage and Adverse Radiation Effects of Stereotactic Radiosurgery for Brain Arteriovenous Malformations

BACKGROUND

The information about long-term risks of hemorrhage and late adverse radiation effects (AREs) after stereotactic radiosurgery for brain arteriovenous malformations (AVMs) is lacking.

OBJECTIVE

To evaluate the long-term risks of hemorrhage and late ARE rates in patients with AVM treated with Gamma Knife surgery (GKS).

METHODS

We examined 1249 patients with AVM treated with GKS. The Spetzler-Martin grade was I in 313 patients (25%), II in 394 (32%), III in 458 (37%), and IV/V in 84 (7%). The median treatment volume was 2.5 cm3, and the median marginal dose was 20 Gy.

RESULTS

The median follow-up period was 61 months. The 5- and 10-year nidus obliteration rates were 63% and 82%, respectively. The 5- and 10-year cumulative hemorrhage rates were 7% and 10%, respectively. The annual hemorrhage rate was 1.5% for the first 5 years post-GKS, which decreased to 0.5% thereafter. During the follow-up period, 42 symptomatic cyst formations/chronic encapsulated hematomas ([CFs/CEHs], 3%) and 3 radiation-induced tumors (0.2%) were observed. The 10- and 15-year cumulative CF/CEH rates were 3.7% and 9.4%, respectively.

CONCLUSION

GKS is associated with reduced hemorrhage risk and high nidus obliteration rates in patients with AVM. The incidence of late AREs tended to increase over time. The most common ARE was CF/CEH, which can be safely removed; however, careful attention should be paid to the long-term development of fatal radiation-induced tumors.

Glioblastoma Adjacent to Radiosurgically Treated Arteriovenous Malformation: A Case Report and Review of the Literature

Stereotactic radiosurgery (SRS) is a noninvasive therapy for patients suffering from both benign and malignant intracranial pathologies. While SRS allows for increased precision and efficacy, significant risks have been reported, such as radiation necrosis. Although traditional radiation therapies are associated with a well-understood risk of causing tumors or inducing malignancy, the risks associated with SRS are not well understood. Here, we present the case of a patient who underwent SRS post-Onyx embolization of a Spetzler-Martin grade 4 left parasagittal arteriovenous malformation. Four years later, the patient presented with a high-grade glioma adjacent to where the SRS was targeted. SRS has fundamentally altered the way we treat intracranial pathologies. While the risks for SRS-induced glioma appear to be extremely low, this case illustrates that they ought to be considered. Here, we discuss the details of our case and explore the currently available literature. Knowing these potential risks will further aid physicians and patients balance the associated benefits and risks.

'De Novo' Brain AVMs-Hypotheses for Development and a Systematic Review of Reported Cases

Background and Objectives: Brain arteriovenous malformations AVMs have been consistently regarded as congenital malformations of the cerebral vasculature. However, recent case reports describing "de novo AVMs" have sparked a growing debate on the nature of these lesions. Materials and Methods: We have performed a systematic review of the literature concerning de novo AVMs utilizing the PubMed and Google Academic databases. Termes used in the search were "AVM," "arteriovenous," "de novo," and "acquired," in all possible combinations. Results: 53 articles including a total of 58 patients harboring allegedly acquired AVMs were identified by researching the literature. Of these, 32 were male (55.17%), and 25 were female (43.10%). Mean age at de novo AVM diagnosis was 27.833 years (standard deviation (SD) of 21.215 years and a 95% confidence interval (CI) of 22.3 to 33.3). Most de novo AVMs were managed via microsurgical resection (20 out of 58, 34.48%), followed by radiosurgery and conservative treatment for 11 patients (18.97%) each, endovascular embolization combined with resection for five patients (8.62%), and embolization alone for three (5.17%), the remaining eight cases (13.79%) having an unspecified therapy. Conclusions: Increasing evidence suggests that some of the AVMs discovered develop some time after birth. We are still a long way from finally elucidating their true nature, though there is reason to believe that they can also appear after birth. Thus, we reason that the de novo AVMs are the result of a 'second hit' of a variable type, such as a previous intracranial hemorrhage or vascular pathology. The congenital or acquired characteristic of AVMs may have a tremendous impact on prognosis, risk of hemorrhage, and short and long-term management.

Glioblastoma multiforme as a secondary malignancy following stereotactic radiosurgery of a meningioma: case report

The documentation and exact incidence of stereotactic radiosurgery (SRS)-induced neoplasia is not well understood, with most literature restricted to single case reports and single-center retrospective reviews. The authors present a rare case of radiosurgery-induced glioblastoma multiforme (GBM) following radiosurgical treatment of a meningioma. A 74-year-old patient with a sporadic meningioma underwent radiosurgery following surgical removal of a WHO grade II meningioma. Eighteen months later she presented with seizures, and MRI revealed an intraaxial tumor, which was resected and proven to be a glioblastoma. As far as the authors are aware, this case represents the third case of GBM following SRS for a meningioma. This report serves to increase the awareness of this possible complication following SRS. The possibility of this rare complication should be explained to patients when obtaining their consent for radiosurgery.

Gamma Knife Radiosurgery For Brain Vascular Malformations: Current Evidence And Future Tasks

Gamma Knife radiosurgery (GKRS) has long been used for treating brain vascular malformations, including arteriovenous malformations (AVMs), dural arteriovenous fistulas (DAVFs), and cavernous malformations (CMs). Herein, current evidence and controversies regarding the role of stereotactic radiosurgery for vascular malformations are described. 1) It has already been established that GKRS achieves 70–85% obliteration rates after a 3–5-year latency period for small to medium-sized AVMs. However, late radiation-induced adverse events (RAEs) including cyst formation, encapsulated hematoma, and tumorigenesis have recently been recognized, and the associated risks, clinical courses, and outcomes are under investigation. SRS-based therapeutic strategies for relatively large AVMs, including staged GKRS and a combination of GKRS and embolization, continue to be developed, though their advantages and disadvantages warrant further investigation. The role of GKRS in managing unruptured AVMs remains controversial since a prospective trial showed no benefit of treatment, necessitating further consideration of this issue. 2) Regarding DAVFs, GKRS achieves 41–90% obliteration rates at the second post-GKRS year with a hemorrhage rate below 5%. Debate continues as to whether GKRS might serve as a first-line solo therapeutic modality given its latency period. Although the post-GKRS outcomes are thought to differ among lesion locations, further outcome analyses regarding DAVF locations are required. 3) GKRS is generally accepted as an alternative for small or medium-sized CMs in which surgery is considered to be too risky. The reported hemorrhage rates ranged from 0.5–5% after GKRS. Higher dose treatments (>15 Gy) were performed during the learning curve, while, with the current standard treatment, a dose range of 12–15 Gy is generally selected, and has resulted in acceptable complication rates (< 5%). Nevertheless, further elucidation of long-term outcomes is essential.

Chronic encapsulated expanding hematoma after stereotactic radiosurgery of cerebral arteriovenous malformation

Stereotactic radiosurgery has become excellent alternative treatment for cerebral arteriovenous malformations (AVM). This technique has expanded to treatment of larger AVM which is not amenable to surgical management. However, its variable adverse effects should be also taken into considerations sincerely because of radiobiological characteristics such as delayed onset and progressive neurological deteriorations. Herein, we report a case in which progressively expanding hemorrhagic cyst with repeated bleedings so called chronic encapsulated expanding hematoma was developed on several years after radiosurgery treatment. Neurological and radiological findings were improved by surgical removal.

Comparison of the Long-term Efficacy and Safety of Gamma Knife Radiosurgery for Arteriovenous Malformations in Pediatric and Adult Patients

It is debated whether the efficacy and long-term safety of gamma knife radiosurgery (GKRS) for arteriovenous malformations (AVMs) differs between adult and pediatric patients. We aimed to clarify the long-term outcomes of GKRS in pediatric patients and how they compare to those in adult patients. We collected data for 736 consecutive patients with AVMs treated with GKRS between 1990 and 2014 and divided the patients into pediatric (age < 20 years, n = 144) and adult (age ≥ 20 years, n = 592) cohorts. The mean follow-up period in the pediatric cohort was 130 months. Compared to the adult patients, the pediatric patients were significantly more likely to have a history of hemorrhage (P < 0.001). The actuarial rates of post-GKRS nidus obliteration in the pediatric cohort were 36%, 60%, and 87% at 2, 3, and 6 years, respectively. Nidus obliteration occurred earlier in the pediatric cohort than in the adult cohort (P = 0.015). The actuarial rates of post-GKRS hemorrhage in the pediatric cohort were 0.7%, 2.5%, and 2.5% at 1, 5, and 10 years, respectively. Post-GKRS hemorrhage was marginally less common in the pediatric cohort than in the adult cohort (P = 0.056). Cyst formation/encapsulated hematoma were detected in seven pediatric patients (4.9%) at a median post-GKRS timepoint of 111 months, which was not significantly different from the rate in the adult cohort. Compared to adult patients, pediatric patients experience earlier therapeutic effects from GKRS for AVMs, and this improves long-term outcomes.

Ruptured de novo Aneurysm following Gamma Knife Surgery for Arteriovenous Malformation: Case Report

Stereotactic radiosurgery is a well-known treatment tool for arteriovenous malformations (AVMs). The method has high validity and minimal invasiveness, but late-onset problems involving tumor formation and vasculopathy induced by radiation have been reported. We present a rare case of a radiation-induced ruptured de novo aneurysm following Gamma Knife surgery (GKS) for an AVM. A 17-year-old, right-handed male underwent GKS for AVM at the left parietal lobe. After 3 years, a follow-up angiogram showed a residual AVM at the angular gyrus. Then, a 2nd GKS was performed for the residual lesion. Six years after the 1st GKS, the AVM disappeared on the angiogram. Seven years later, he suffered a sudden onset of headache. A left carotid angiogram revealed a ruptured aneurysm at the M2-M3 junction of the middle cerebral artery parietal branch. Coil embolization was performed, and the aneurysm was occluded. The patient was discharged without any neurologic deficits.

Dosimetric comparison between intensity-modulated radiotherapy and RapidArc with single arc and dual arc for malignant glioma involving the parietal lobe

The aim of the present study was to evaluate the difference in treatment plan quality, monitor units (MUs) per fraction and dosimetric parameters between IMRT (intensity-modulated radiotherapy) and RapidArc with single arc (RA1) and dual arc (RA2) for malignant glioma involving the parietal lobe. Treatment plans for IMRT and RA1 and RA2 were prepared for 10 patients with malignant gliomas involving the parietal lobe. The Wilcoxon matched-pair signed-rank test was used to compare the plan quality, monitor units and dosimetric parameters between IMRT and RA1 and RA2 through dose-volume histograms. Dnear-max (D2%) to the left lens, right lens and left optical nerve in RA1 were less compared with those in IMRT; D2% to the right lens and right optic nerve in RA2 were less compared with those in IMRT. D2% to the optic chiasma in RA2 was small compared with that in RA1. The median dose (D50%) to the right lens and right optic nerve in RA1 and RA2 was less compared with the identical parameters in IMRT, and D50% to the brain stem in RA2 was less compared with that in RA1. The volume receiving at least 45 Gy (V45) or V50 in normal brain tissue (whole brain minus the planning target volume 2; B-P) in RA1 was less compared with that in IMRT. V30, V35, V40, V45, or V50 in B-P in RA2 was less compared with that in IMRT. The MUs per fraction in RA1 and RA2 were significantly less compared with those in IMRT. All differences with a P-value<0.05 were considered to be significantly different. In conclusion, RA1 and RA2 markedly reduced the MUs per fraction, and spared partial organs at risk and B-P compared with IMRT.

Radiosurgery for Medial Temporal Lobe Epilepsy Resulting from Mesial Temporal Sclerosis

Medial temporal lobe epilepsy associated with mesial temporal sclerosis (MTS) is perhaps the most well-defined epilepsy syndrome that is responsive to structural interventions such as surgery. Several minimally invasive techniques have arisen that provide additional options for the treatment of MTS while potentially avoiding many of open surgery's associated risks. By evading these risks, they also open up treatment options to patients who otherwise are poor surgical candidates. Radiosurgery is one of the most intensively studied of these alternatives and has found a growing role in the treatment of medial temporal lobe epilepsy.

Role of Evaluating MGMT Status and 1p36 Deletion in Radiosurgery-Induced Anaplastic Ependymoma That Rapidly and Completely Resolved by Temozolomide Alone: Case Report and Review of the Literature

Stereotactic gamma knife surgery (GKS)-induced brain tumors are extremely rare, and no ependymal tumors induced by GKS have been reported. Therefore, little is known about their clinical, pathologic, and genetic features. In addition, a regimen of adjuvant chemotherapy for anaplastic ependymoma (AE) has not been established. A 77-year-old man presented with a gait disturbance and left-side cerebellar ataxia more than 19 years after GKS performed for a cerebellar arteriovenous malformation. Imaging studies demonstrated an enhancing mass in the irradiated field with signs of intraventricular dissemination. Surgical resection confirmed the diagnosis of AE. Temozolomide (TMZ) was administrated postoperatively because the methylated promoter region of O(6)-methylguanine-DNA methyltransferase (MGMT) and 1p36 deletion were observed. Surprisingly, images 16 days after TMZ initiation demonstrated a complete resolution of the residual tumor that was maintained after three cycles of TMZ. This first case report of GKS-induced AE emphasizes the importance of genetic evaluation of MGMT and chromosomal deletion of 1p36 that are not commonly performed in primary ependymal tumors. In addition, it is speculated that a GKS-induced tumor may have a different genetic background compared with the primary tumor because the pathogenesis of the tumors differed.

Growing Organized Hematomas Following Gamma Knife Radiosurgery for Cerebral Arteriovenous Malformation : Five Cases of Surgical Excision

Organized hematoma is a rare complication that can develop following gamma knife radiosurgery (GKS) for cerebral arteriovenous malformation (AVM). Here, we describe 5 patients with growing organized hematomas that developed from completely obliterated AVMs several years after GKS. The patients were 15, 16, 30, 36, and 38 years old at the time of GKS, respectively, and 3 patients were female. Four AVMs were located in the lobe of the brain, and the remaining AVM were in the thalamus. Between 2-12 years after GKS, patients developed progressive symptoms such intractable headache or hemiparesis and enhancing mass lesions were identified. Follow-up visits revealed the slow expansion of the hematomas and surrounding edema. Steroids were ineffective, and thus surgery was performed. Histology revealed organized hematomas with a capsule, but there was no evidence of residual AVMs or vascular malformation. After surgery, the neurological symptoms of all patients improved and the surrounding edema resolved. However, the hematoma continued to expand and intraventricular hemorrhage developed in 1 patient whose hematoma was only partially removed. GKS for cerebral AVM can be complicated by growing, organized hematomas that develop after complete obliteration. Growing hematomas should be surgically evacuated if they are symptomatic. Radical resection of the hematoma capsule is also strongly recommended.

De Novo Aneurysm Formation Following Gamma Knife Surgery for Arteriovenous Malformation: A Case Report

Background Stereotactic radiosurgery plays a critical role in the treatment of central nervous system neoplasm and cerebrovascular malformations. This procedure is purportedly less invasive, but problems occurring later including tumor formation, necrosis, and vasculopathy-related diseases have been reported. Clinical Presentation We report on a 65-year-old man who had experienced a de novo aneurysm in an irradiated field and an acute onset of right hemiparesis and aphasia. He had undergone gamma knife radiosurgery to treat an arteriovenous malformation 15 and 12 years prior, with 18 and 22 Gy marginal doses. At current admission, radiologic studies showed a de novo aneurysm in the irradiated field without recurrence of malformation. The aneurysm was resected. Histologic findings showed a disruption of the internal elastic lamina accompanied by fibrous degeneration. Conclusion Stereotactic radiosurgery is a promising treatment tool, but long-term risks have not been fully researched. The treatment procedure for benign lesions should be chosen prudently.

Glioblastoma after AVM radiosurgery. Case report and review of the literature

BACKGROUND

Stereotactic radiosurgery (SRS) is considered to be a relatively safe procedure in cerebral arteriovenous malformation management. There are very few reported cases of SRS-associated/induced malignancies.

METHODS

We show the case of a 21-year-old female who presented with a 21-mm(3) ruptured AVM in the right mesial frontocallosal region. Embolization and/or radiosurgery was proposed. She preferred radiosurgery. The AVM was treated with CyberKnife(®) SRS.

RESULTS

She presented behavior changes 6 years after SRS. MRI showed a right subcortical frontal lesion with increased perfusion, more consistent with high-grade glioma. The lesion's center was within the irradiated region of the previous SRS, having received an estimated radiation dose of 4 Gy. Pathological examination noted a hypercellular tumor showing astrocytic tumor cells with moderate pleomorphism in a fibrillary background, endothelial proliferation, and tumor necrosis surrounded by perinecrotic pseudopalisades. Numerous mitotic figures were seen. The appearances were those of glioblastoma, WHO grade IV, with neuronal differentiation. SRS-associated/-induced GBM after treatment of a large AM is exceptional. SRS-associated/-induced malignancies are mostly GBMs and occur on average after a latency of 9.4 years, within very low-dose peripheral regions as well as the full-dose regions; 33.3 % of patients were under 20 years at the time of SRS, and in 66 % the lesion treated was a vascular pathology.

CONCLUSION

Although it is unlikely that the risk of radiation-induced cancer will change the current standard of practice, patients must be warned of this potential possibility before treatment.

The incidence of second brain tumors related to cranial irradiation

Secondary brain tumor (SBT) is a devastating complication of cranial irradiation (CI). We reviewed the literature to determine the incidence of SBT as related to specific radiation therapy (RT) treatment modalities. The relative risk of radiation-associated SBT after conventional and conformal RT is well established and ranges from 5.65 to 10.9; latent time to develop second tumor ranges from 5.8 to 22.4 years, depending on radiation dose and primary disease. Theories and dosimetric models suggest that intensity-modulated radiation therapy may result in an increased risk of SBT, but clinical evidence is limited. The incidence of stereotactic radiosurgery-related SBT is low. Initial data suggest that no increased risk from proton therapy and dosimetric models predict a lower incidence of SBT compared with photons. In conclusion, the incidence of SBT related to CI is low. Longer follow-up is needed to clarify the impact of intensity-modulated radiation therapy, proton therapy and other developing technologies.

Radiation-associated secondary brain tumors after conventional radiotherapy and radiosurgery

Although there is not enough strong molecular evidence for radiation to be a causal factor for the development of secondary brain tumors, a relationship has still been found. There is a slight but significant 2-2.7% increased risk of secondary brain tumors after conventional radiotherapy. However, this risk is small and should not preclude the use of radiotherapy as an effective treatment for uncontrolled pituitary tumors. The risk of radiosurgery-associated secondary brain tumors has not been precisely determined. Taking into account the considerable number of patients who received radiosurgery worldwide and the small number of secondary brain tumors, radiosurgery seems to be a safe treatment modality. This review summarizes the pathogenesis, prevalence and characteristics of secondary brain tumors after conventional radiotherapy and stereotactic radiosurgery for pituitary adenomas.

Complications of gamma knife neurosurgery and their appropriate management

There are four main risks with Gamma Knife neurosurgery. Firstly, there are direct complications that would not have arisen if the patient had not undergone the specific treatment under consideration. For radiosurgery, the direct complications are radiation-induced damage to the tissues, which may be temporary or permanent. They may be expressed clinically or be clinically silent. In addition, there are complications that are specific to certain diseases and their locations, such as pituitary failure following treatment of pituitary adenomas and deafness, facial palsy, or trigeminal deficit following the treatment of vestibular schwannomas. Second, there are indirect or management-related complications arising from delayed control of the disease process, such as a re-bleed after treatment of a vascular lesion before its occlusion. Third, there is the risk of induction of neoplasia from irradiation of normal tissue or tumor. These are separate processes. An example of the first would be induction of a glioma after treatment of a vascular malformation. An example of the second would be induction of malignant change in a benign vestibular schwannoma. Finally, there is treatment failure, where tumors continue to grow after treatment or vascular malformations fail to occlude.

Radiation-induced glioma following CyberKnife® treatment of metastatic renal cell carcinoma: a case report

INTRODUCTION

Post-stereotactic radiation-induced neoplasms, although relatively rare, have raised the question of benefit regarding CyberKnife® treatments versus the risk of a secondary malignancy. The incidence of such neoplasms arising in the nervous system is thought to be low, given the paucity of case reports regarding such secondary lesions.

CASE PRESENTATION

Here we describe a case of a 43-year-old Middle Eastern woman with primary clear cell renal cell carcinoma and a metastatic focus to the left brain parenchyma who presented with focal neurologic deficits. Following post-surgical stereotactic radiation in the region of the brain metastasis, the patient developed a secondary high-grade astrocytoma nearly 5 years after the initial treatment.

CONCLUSION

Although the benefit of CyberKnife® radiotherapy treatments continues to outweigh the relatively low risk of a radiation-induced secondary malignancy, knowledge of such risks and a review of the literature are warranted.

Gamma knife surgery-induced ependymoma after the treatment of meningioma - a case report

Gamma knife surgery is widely used for a number of neurological disorders. However, little is known about its long-term complications such as carcinogenic risks. Here, we present a case of a radiosurgery-induced ependymoma by gamma knife surgery for the treatment of a spinal meningioma in a 7-year-old patient. In light of reviewing the previous reports, we advocate high caution in making young patients receive this treatment.

Radiotherapy for prolactin-secreting pituitary tumors

Review the medical and surgical management of patients with prolactinomas and provide an in-depth appraisal of the role of radiotherapy in the treatment of prolactinomas. A thorough review of the pertinent literature was carried out and relevant topics were identified. Topics covered in this comprehensive review include: indications for the use of radiotherapy, choice between conventional radiotherapy and stereotactic radiosurgery, as well as the benefits and potential complications associated with each modality. Due to the excellent response rates with medical management, and rapid symptom relief afforded by resection or debulking surgery in patients who do not respond or tolerate medical therapy, radiotherapy is reserved for patients who do not respond to dopamine agonists and surgery. Both external beam radiotherapy and stereotactic radiosurgery retain important roles in the treatment of refractory or recurrent prolactinomas. Choosing the optimal approach is crucial in maximizing tumor control outcomes and minimizing the risks associated with treatment. The primary determinants of optimal radiation approach are proximity of the tumor to the optic apparatus and tumor size, with radiosurgery being our recommended treatment of choice unless the tumor is larger than 3-4 cm or within 3 mm of the optic nerves, chiasm or tracts. Optimal multidisciplinary management requires the identification of appropriate candidates for radiotherapy in order to take full advantage of treatment options available for each patient.

Glioblastoma following radiosurgery for meningioma

We report a patient who underwent gamma knife radiosurgery to treat recurrent meningioma after microsurgery and thereafter developed secondary malignancy adjacent to the original tumor. A 47-year-old woman had underwent resection of the olfactory groove meningioma. Then radiosurgery was done three times over 4 year period for the recurrent tumor. After 58 months from the initial radiosurgery, she presented with headache and progressive mental dullness. Huge tumor in bifrontal location was revealed in MRI. Subsequent operation and pathological examination confirmed diagnosis of glioblastoma. This case fits the criteria of radiation-induced tumor and the clinical implication of the issue is discussed.

A case of high-grade undifferentiated sarcoma after surgical resection and stereotactic radiosurgery of a vestibular schwannoma

Stereotactic radiosurgery has become a more frequently used treatment modality for vestibular schwannomas; a few reports of malignant transformation and/or radiation-associated tumors have surfaced. The majority of these reported cases were in patients with underlying neurofibromatosis. The authors report a case of a 74-year-old man with rapid progression of a cerebellar-pontine angle tumor 14 years after surgical resection of a vestibular schwannoma (VS) from the same site, and 6 years after stereotactic radiosurgery. A pathological study of the recent tumor showed a high-grade spindle cell neoplasm that bore no resemblance to the initial schwannoma. The patient had no diagnosis of neurofibromatosis. Secondary malignancy occurred in a non-neurofibromatosis patient 6 years after stereotactic radiosurgery. It is our belief that documentation of such cases will provide important evidence that helps evaluate the long-term effect of radiosurgery for VS. Such observations can influence clinical decisions regarding the choice of treatment modalities.

A contemporary review of stereotactic radiotherapy: inherent dosimetric complexities and the potential for detriment

OBJECTIVE

The advantages of highly localised, conformal treatments achievable with stereotactic radiotherapy (SRT) are increasingly being extended to extracranial sites as stereotactic body radiotherapy with advancements in imaging and beam collimation. One of the challenges in stereotactic treatment lies in the significant complexities associated with small field dosimetry and dose calculation. This review provides a comprehensive overview of the complexities associated with stereotactic radiotherapy and the potential for detriment.

METHODS

This study is based on a comprehensive review of literature accessible via PubMed and other sources, covering stereotactic radiotherapy, small-field dosimetry and dose calculation.

FINDINGS

Several key issues were identified in the literature. They pertain to dose prescription, dose measurement and dose calculation within and beyond the treatment field. Field-edge regions and penumbrae occupy a significant portion of the total field size. Spectral and dosimetric characteristics are difficult to determine and are compounded by effects of tissue inhomogeneity. Measurement of small-fields is made difficult by detector volume averaging and energy response. Available dosimeters are compared, and emphasis is given to gel dosimetry which offers the greatest potential for three-dimensional small-field dosimetry. The limitations of treatment planning system algorithms as applied to small-fields (particularly in the presence of heterogeneities) is explained, and a review of Monte Carlo dose calculation is provided, including simplified treatment planning implementations. Not incorporated into treatment planning, there is evidence that far from the primary field, doses to patients (and corresponding risks of radiocarcinogenesis) from leakage/scatter in SRT are similar to large fields.

CONCLUSIONS

Improved knowledge of dosimetric issues is essential to the accurate measurement and calculation of dose as well as the interpretation and assessment of planned and delivered treatments. This review highlights such issues and the potential benefit that may be gained from Monte Carlo dose calculation and verification via three-dimensional dosimetric methods (such as gel dosimetry) being introduced into routine clinical practice.

Radiation-Induced Sarcoma in a Large Vestibular Schwannoma Following Stereotactic Radiosurgery: Case Report

BACKGROUND AND IMPORTANCE:

Stereotactic radiosurgery (SRS) has been employed with increasing frequency in the treatment of benign intracranial tumors. While the risk for radiation-induced malignancy has been well studied for fractionated external beam radiation, reports of SRS-associated malignancy have only begun to emerge over the past 10 years.

CLINICAL PRESENTATION:

We present a case of a rapidly enlarging, presumed sporadic vestibular schwannoma in a 51-year-old man treated with SRS. Serial imaging over the next 7.5 years demonstrated good radiographic response with consistent involution of the tumor. The patient then developed rapid neurologic deterioration and sustained tumor growth on follow-up imaging. The tumor was resected via a translabyrinthine approach, and pathologic analysis demonstrated undifferentiated high-grade pleomorphic sarcoma (UHGPS).

CONCLUSION:

This is the first report of undifferentiated high-grade pleomorphic sarcoma (formerly called malignant fibrous histiocytoma) following SRS. This case demonstrates the difficulty of establishing malignant degeneration of a neoplasm following SRS without pretreatment tissue diagnosis. Patients with presumed benign tumors should be counseled about the rare risk of malignant transformation prior to undertaking SRS.

Surgical treatment for late complications following gamma knife surgery for arteriovenous malformations

BACKGROUND

To establish the surgical indications and strategy for late complications following gamma knife surgery (GKS) for arteriovenous malformations (AVMs).

METHODS

Ten male and 7 female patients aged 17-52 years (mean 28.0 years) were retrospectively identified among 686 patients who underwent GKS for AVM at our hospital. Ten patients showed cyst formation (group A), 2 patients had expanding hematoma (group B), and 5 patients had both cyst and expanding hematoma (group C).

RESULTS

The mean nidus volume was 10.1 ml (range 0.1-36 ml), and the mean prescription dose at the nidus margin was 19.9 Gy (range 18-28 Gy). Complete obliteration of the nidus was obtained in 12 patients, partial obliteration in 4, and no change in 1. Cyst formation (group A) was asymptomatic in 5 patients, and symptomatic in 5 patients, manifesting as headache, hemianopia, aphasia, and motor weakness. Expanding hematoma (groups B and C) was associated with surrounding brain edema and was symptomatic in all 7 patients. Cyst opening in 1 patient and placement of an Ommaya reservoir in 2 patients were necessary in group A. Both patients in group B underwent craniotomy. Four of the 5 patients in group C required craniotomy. Another patient in group C was lost to follow-up and the final outcome was unknown.

CONCLUSIONS

Cyst formation is one of the late complications of GKS for AVM. Some cysts show spontaneous regression but others gradually increase in size and become symptomatic, although relatively large asymptomatic cysts are also known. Predicting the future course of a cyst is difficult. Surgery such as placement of an Ommaya reservoir should be considered for symptomatic cases. Expanding hematoma always increases in size and becomes symptomatic, so removal by craniotomy is necessary. Surrounding brain edema decreases rapidly after surgery and neurological symptoms quickly resolve.

Surgical management of pediatric cerebral arteriovenous malformations

BACKGROUND

Arteriovenous malformations (AVMs) are the most common cause of intracerebral hemorrhage in children. Different options exist for their successful management consisting of surgery, endovascular embolization, stereotactic radiosurgery, or a combination of these treatments.

DISCUSSION

In this paper, we discuss the different treatment modalities in the treatment of pediatric cerebral AVMs emphasizing the role of surgery and endovascular embolization as a preoperative strategy.

Advances in the radiosurgical treatment of epilepsy

Radiosurgery is the precise application of focused radiation to a targeted volume area within the brain, which has been identified on MRI. With recent advances, radiosurgical treatment is now being evaluated as an alternative treatment to open resective surgery for intractable epilepsy. Recent prospective trials suggest that radiosurgery may be an effective and safe treatment for medically intractable epilepsy associated with mesial temporal sclerosis, cavernous malformations, and hypothalamic hamartomas.

Management of patients with acoustic neuromas: a Markov decision analysis

OBJECTIVES/HYPOTHESIS

The management of patients with small (<1.5 cm) acoustic neuromas is controversial. Immediate treatment via microsurgical resection or radiosurgery is often advocated. A period of observation is sometimes advised followed by microsurgery or radiosurgery for tumors that demonstrate growth during the observation period. The purpose of this study is to calculate quality-adjusted life expectancy for the most commonly applied management strategies in hypothetical cohorts of patients of various ages.

STUDY DESIGN

Markov decision analysis; societal perspective.

METHODS

Assumptions used in creating this model and event probabilities were obtained from a thorough literature review. Key parameters were identified and defined by the best available evidence. The main outcome measure is the benefit derived from each management strategy in quality-adjusted life years (QALYs). Sensitivity analysis was used to define benchmark performance information for these parameters.

RESULTS

The benefit of a period of observation followed by radiosurgery, if needed, for significant tumor growth is greater then all other strategies for all age groups and both sexes. When compared to observation followed by microsurgery, the additional benefit is small. QALY totals for the two immediate treatment groups were significantly lower than that for the observation groups.

CONCLUSIONS

For patients of all ages, a period of observation during which tumor growth and hearing thresholds are closely monitored is the superior strategy. For tumors that grow substantially or when hearing deteriorates, definitive management via radiosurgery is recommended.

Operative intervention for delayed symptomatic radionecrotic masses developing following stereotactic radiosurgery for cerebral arteriovenous malformations--case analysis and literature review

CASE REPORT

We report two cases of operative intervention that was beneficial in the treatment of delayed symptomatic radionecrotic masses that had developed following stereotactic radiosurgery (SRS) using the gamma knife (GK) for the treatment of cerebral arteriovenous malformations (AVM).

DISCUSSION

Case 1 involved a small craniotomy for decompression of a large cerebral multiloculated cyst, which had become symptomatic 84 months following gamma knife treatment for a left frontal lobe AVM. Case 2 involved surgical excision of an occipital radionecrotic mass 72 months following GK treatment for an occipital AVM. This patient had suffered from longstanding symptomatic cerebral oedema, which on occasions had become life threatening. Case 2 is also the first report of a radionecrotic mass occurring post-SRS for an AVM, which conversely appeared to demonstrate increased uptake on single photon emission computed tomography (SPECT) scan. The first literature review of such delayed symptomatic radionecrotic lesions is presented. There appears to be a late onset of symptoms (average 55 months, range 12-111 months) associated with such radionecrosis. Drainage of such cysts or excision of the mass lesion appears to be consistently beneficial to the patients and appears to be uncomplicated.

CONCLUSION

We recommend early surgical intervention for such delayed symptomatic radionecrotic masses that do not resolve following non-operative management. We also recommend caution in interpretation of SPECT scan results when attempting to differentiate radionecrosis from neoplasia.

Radiation-induced rhabdomyosarcoma of the brainstem in a patient with neurofibromatosis Type 2

Neurofibromatosis Type 2 (NF2) is a rare autosomal dominant disorder characterized by the development of benign tumors of the peripheral nervous system and the CNS, including schwannomas, meningiomas, and ependymomas. The gene responsible for the development of NF2 acts as a tumor suppressor gene. Stereotactic radiotherapy (SRT) or single-fraction stereotactic radiosurgery has been increasingly used in the past decades to treat benign tumors in patients with NF2. These radiotherapy methods are less invasive and can be potentially used to treat multiple tumors in a single session. The risk of inducing malignancy is unclear. Few reports exist of malignant peripheral nerve sheath tumors, meningiomas, or ependymomas occurring after SRT or stereotactic radiosurgery in patients with NF2. The authors present the first documented case of rhabdomyosarcoma following SRT for multiple NF2-associated schwannomas. Compared with patients with sporadic tumors, NF2 patients having a germline tumor suppressor gene defect may be more prone to secondary malignancies after treatment involving radiation therapy.

Radiotherapy and radiosurgery for benign skull base meningiomas

Meningiomas located in the region of the base of skull are difficult to access. Complex combined surgical approaches are more likely to achieve complete tumor removal, but frequently at a cost of treatment related high morbidity. Local control following subtotal excision of benign meningiomas can be improved with conventional fractionated external beam radiation therapy with a reported 5-year progression-free survival up to 95%. New radiation techniques, including stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (FSRT), and intensity-modulated radiotherapy (IMRT) have been developed as a more accurate technique of irradiation with more precise tumor localization, and consequently a reduction in the volume of normal brain irradiated to high radiation doses. SRS achieves a high tumour control rate in the range of 85-97% at 5 years, although it should be recommended only for tumors less than 3 cm away more than 3 mm from the optic pathway because of high risk of long-term neurological deficits. Fractionated RT delivered as FSRT, IMRT and protons is useful for larger and irregularly or complex-shaped skull base meningiomas close to critical structures not suitable for single-fraction SRS. The reported results indicate a high tumour control rate in the range of 85-100% at 5 years with a low risk of significant incidence of long-term toxicity. Because of the long natural history of benign meningiomas, larger series and longer follow-up are necessary to compare results and toxicity of different techniques.

A review of dosimetry studies on external-beam radiation treatment with respect to second cancer induction

It has been long known that patients treated with ionizing radiation carry a risk of developing a second cancer in their lifetimes. Factors contributing to the recently renewed concern about the second cancer include improved cancer survival rate, younger patient population as well as emerging treatment modalities such as intensity-modulated radiation treatment (IMRT) and proton therapy that can potentially elevate secondary exposures to healthy tissues distant from the target volume. In the past 30 years, external-beam treatment technologies have evolved significantly, and a large amount of data exist but appear to be difficult to comprehend and compare. This review article aims to provide readers with an understanding of the principles and methods related to scattered doses in radiation therapy by summarizing a large collection of dosimetry and clinical studies. Basic concepts and terminology are introduced at the beginning. That is followed by a comprehensive review of dosimetry studies for external-beam treatment modalities including classical radiation therapy, 3D-conformal x-ray therapy, intensity-modulated x-ray therapy (IMRT and tomotherapy) and proton therapy. Selected clinical data on second cancer induction among radiotherapy patients are also covered. Problems in past studies and controversial issues are discussed. The needs for future studies are presented at the end.

[Radiosurgery for drug-resistant epilepsies: state of the art, results and perspectives]

BACKGROUND

There is growing interest in the use of radiosurgery in epilepsy. We analyzed our experience in this field in an attempt to define the potential of radiosurgery in epileptology.

MATERIAL AND METHODS

[corrected] Our local clinical experience (134 patients), accumulated over the last 15 years, mainly includes treatment of temporal lobe epilepsy without space-occupying lesions (59 patients), including 53 with pure MTLE, 61 cases of hypothalamic hamartoma, two cases of callosotomy, and 12 other types of epilepsy.

RESULTS

The analysis of our material, as well as other clinical and experimental data, suggest that the use of radiosurgery is beneficial only to patients in whom a strict preoperative definition of the extent of the epileptogenic zone (or network) has been achieved and strict rules of dose planning have been applied. As soon as these principles are not observed, the risk of treatment failure and/or side effects increases dramatically. Long-term outcome data are now available and published for MTLE but not yet for other types of epilepsy. Long-term safety and efficacy in MTLE are comparable to surgical resection but radiosurgery has the advantage of sparing verbal memory in patients operated by Gamma Knife (GK) on the dominant side. In small hamartomas, the efficacy is comparable to microsurgery but with a dramatic reduction in risk.

CONCLUSION

The vast amount of clinical materiel and long-term evaluation now support the use of GK surgery in small hypothalamic hamartomas and MTLE when the patient is at risk of verbal memory loss.

Cumulative diagnostic radiation exposure in children with ventriculoperitoneal shunts: a review

INTRODUCTION

Children may be more vulnerable to diagnostic radiation exposure because of the increased dose-volume ratio and the increased lifetime risk per unit dose of radiation from early exposure. Moreover, recent radiological literature suggests that exposure to ionizing radiation from imaging studies may play a role in the later development of malignancies.

MATERIALS AND METHODS

We review the literature and present two illustrative clinical examples of children (each child developed head and neck malignancies during their late teen years) with hydrocephalus requiring multiple cerebrospinal fluid (CSF) shunt revisions and diagnostic computerized tomography (CT) scans throughout their life.

DISCUSSION

The literature reviewed suggests that children are more prone to diagnostic radiation exposure. Although it is not possible to prove that the multiple diagnostic studies result in malignancies, our review of the literature and illustrative cases describing malignancy risk and radiation exposure should give clinicians pause when considering requesting multiple diagnostic CT studies in children during the evaluation of possible CSF shunt dysfunction. Alternative tests such as "shunt MRI" protocols should be considered for patients and used whenever possible to minimize exposure to ionizing radiation.