Stereotactic radiosurgery of the brain using a standard linear accelerator: a study of early and late effects

An overview of anti-epileptic therapy management of patients with malignant tumors of the brain undergoing radiation therapy

As our surgical, radiation, chemotherapeutic and supportive therapies for brain malignancies improve, and overall survival is prolonged, appropriate symptom management in this patient population becomes increasingly important. This review summarizes the published literature and current practice patterns regarding prophylactic and perioperative anti-epileptic drug use. As a wide range of anti-epileptic drugs is now available to providers, evidence guiding appropriate anticonvulsant choice is reviewed. A particular focus of this article is radiation therapy for brain malignancies. Toxicities and seizure risk associated with cranial irradiation will be discussed. Epilepsy management in patients undergoing radiation for gliomas, glioblastoma multiforme, and brain metastases will be addressed. An emerging but inconsistent body of evidence, reviewed here, indicates that anti-epileptic medications may increase radiosensitivity, and therefore improve clinical outcomes, specifically in glioblastoma multiforme patients.

A prospective patient-focused evaluation of the tolerance and acceptability of a stereotactic radiosurgery procedure

Stereotactic radiosurgery (SRS) is a frequently used non-surgical procedure to treat benign and malignant brain lesions. Few studies have focused on patient perceptions of SRS. The aims of this patient-focused study were to assess patient experiences of SRS, and changes in patient-reported symptoms over 12weeks post-SRS. Using the 6-point Likert Scoring Scale in a diary-format for a less discriminatory evaluation, patients self-reported presence or absence, and severity of physical and psychological symptoms within 24h, 1-week, and 12-weeks post-SRS. Non-parametric repeated measures ANOVA was used to evaluate changes in symptoms. Of the 748 recruited patients, 690 returned the first diary (92%), while 564 patients returned all three diaries for matched responses analysis (82%). Three-quarters of 690 patients reported receiving clear verbal explanations and printed material prior to their procedure, and 99% reported the clinical team were 'very supportive' or gave 'wonderful care'. Fatigue (82%) and headaches (65%) were the most frequently reported symptoms within 24-h post-SRS. Over 12weeks, patients reported significant reductions in headache, nausea, fatigue, anxiety and tension (p<0.001); loss of balance and concentration significantly increased by 12-weeks post-SRS (p<0.001). Some patients attributed symptoms such as fatigue or headaches to the demands of the procedure day. Findings of this study reflect the need to further research patients' physical and psychological symptoms post-SRS, which may differ from the clinicians' perception of the effects of treatment.

Photon Radiosurgery: A Clinical Review

The term radiosurgery has been used to describe a variety of radiotherapy techniques which deliver high doses of radiation to small, stereotactically defined intracranial targets in such a way that the dose fall-off outside the targeted volume is very sharp. Proton, charged particle, gamma unit, and linear accelerator-based techniques appear to be equivalent from the standpoint of accuracy, dose distributions, and clinical results. However, capital and operating costs associated with the use of linear accelerators in general clinical use are much lower. Radiosurgery has an established role in the treatment of arteriovenous malformations and acoustic neurinomas. Interest in these techniques is increasing in neurosurgical and radiation oncological communities, as radiosurgery is rapidly assuming a place in the management of several other conditions, including craniopharyngiomas, meningiomas, and selected malignant lesions.

Early and Late Complications Following Dynamic Stereotactic Radiosurgery and Fractionated Stereotactic Radiotherapy

Between December 1986 and June 1990, 112 patients (116 lesions), underwent treatment with dynamic stereotactic radiosurgery at McGill University. Of the treated lesions, 59 were arteriovenous malformations and 53 were a variety of other neoplastic or non-neoplastic conditions. In 86 lesions, the treatment was delivered in a single fraction and the treatment of the remaining 30 lesions was fractionated. Complications attributed to treatment developed in seven of the 112 patients (6.3%). No relationship was found between complications and prescribed dose, fractionation, collimator diameter, type and anatomical region of the lesion that was treated, or previous irradiation. Although extensive clinical experience will be necessary to determine optimal total doses, the potential role of fractionated treatment, and the tolerance of critical structures to radiosurgery, the relatively low incidence of complications in our series allows us to conclude that radiosurgery is well tolerated by the vast majority of patients.

Stereotactic radiosurgery of intracranial arteriovenous malformations

Stereotactic radiosurgery for intracranial arteriovenous malformations (AVMs) has been performed since the 1970s. When an AVM is treated with radiosurgery, radiation injury to the vascular endothelium induces the proliferation of smooth muscle cells and the elaboration of extracellular collagen, which leads to progressive stenosis and obliteration of the AVM nidus. Obliteration after AVM radiosurgery ranges from 60% to 80%, and relates to the size of the AVM and the prescribed radiation dose. The major drawback of radiosurgical AVM treatment is the risk of bleeding during the latent period (typically 2 years) between treatment and AVM thrombosis.

Cyberknife stereotactic radiosurgery for treatment of atypical (WHO grade II) cranial meningiomas

BACKGROUND

The optimal management of subtotally resected atypical meningiomas is unknown.

OBJECTIVE

To perform a retrospective review of patients with residual or recurrent atypical meningiomas treated with stereotactic radiosurgery (SRS).

METHODS

Twenty-five patients were treated, either immediately after surgery (n = 15) or at the time of radiographic progression or treatment failure (n = 10). SRS was delivered to with a median marginal dose of 22 Gy (range, 16-30) in 1 to 4 fractions (median, 1), targeting a median tumor volume of 5.3 cm³ (range, 0.3-26.0).

RESULTS

With a median follow-up time of 28 months (range, 3-67), the 12-, 24-, and 36-month actuarial local and regional control rates for all patients were 94%, 94%, 74%, and 90%, 90%, 62%, respectively. There were 2 cases of radiation toxicity. On univariate analysis, the number of recurrences before SRS (P = .046), late SRS (ie, waiting until tumor progression to initiate treatment) (P = .03), and age at treatment ≥ 60 years (P = .01) were significant predictors of recurrence. Of the 20 radiation-naïve patients, 2 patients failed with the targeted lesion and 3 elsewhere in the resection bed, resulting in 12-, 24- and 36-month actuarial local and regional control rates of 100%, 100%, 73% and 93%, 93%, 75%, respectively. The overall locoregional control rates at 12, 24, and 36 months were 93%, 93%, and 54%, respectively.

CONCLUSION

Irradiation of the entire postoperative tumor bed may not be necessary for the majority of patients with subtotally resected atypical meningiomas. Patients in this series achieved outcomes comparable to that of historical control rates for larger volume, conventionally fractionated radiotherapy.

Dose tolerance limits and dose volume histogram evaluation for stereotactic body radiotherapy

Almost 20 years ago, Emami et al. presented a comprehensive set of dose tolerance limits for normal tissue organs to therapeutic radiation, which has proven essential to the field of radiation oncology. The paradigm of stereotactic body radiotherapy (SBRT) has dramatically different dosing schemes but, to date, there has still been no comprehensive set of SBRT normal organ dose tolerance limits. As an initial step toward that goal, we performed an extensive review of the literature to compare dose limits utilized and reported in existing publications. The impact on dose tolerance limits of some key aspects of the methods and materials of the various authors is discussed. We have organized a table of 500 dose tolerance limits of normal structures for SBRT. We still observed several dose limits that are unknown or not validated. Data for SBRT dose tolerance limits are still preliminary and further clinical trials and validation are required. This manuscript presents an extensive collection of normal organ dose tolerance limits to facilitate both clinical application and further research.

Permanent Alopecia following Cranial Irradiation in a Child

Background:

Cranial irradiation is commonly used in childhood leukemia, with many potential cutaneous adverse effects. Radiation-induced permanent alopecia owing to scalp fibrosis is a rare but disturbing side effect.

Objective and Conclusion:

Here we report a Saudi boy with acute T-cell lymphoblastic leukemia who developed radiation-induced cicatricial alopecia. Topical treatment using minoxidil solution was tried but was ineffective.

Brain irradiation: effects on normal brain parenchyma and radiation injury

Radiation therapy is a major treatment modality for malignant and benign brain tumors. Concerns of radiation effects on the brain tissue and neurocognitive function and quality of life increase as survival of patients treated for brain tumors improves. In this article, the clinical and neurobehavioral symptoms and signs of radiation-induced brain injury, possible histopathology, and the potential of functional, metabolic, and molecular imaging as a biomarker for assessment and prediction of neurotoxicity after brain irradiation and imaging findings in radiation necrosis are discussed.

Arcuate fasciculus tractography integrated into Gamma Knife surgery

Object

To prevent speech disturbances after Gamma Knife surgery (GKS), the authors integrated arcuate fasciculus (AF) tractography based on diffusion tensor (DT) MR imaging into treatment planning for GKS.

Methods

Arcuate fasciculus tractography was retrospectively integrated into planning that had been previously performed by neurosurgeons and radiation oncologists. This technique was retrospectively applied to 12 patients with arteriovenous malformations adjacent to the AF. Diffusion tensor images were acquired before the frame was affixed to the patient's head and DT tractography images of the AF were created using the authors' original software. The data from DT tractography and stereotactic 3D imaging studies obtained after frame fixation were transported to a treatment planning workstation for GKS and coregistered so that the delivered doses and incidence of posttreatment aphasia could be assessed.

Results

The AF could not be depicted in 2 patients who initially presented with motor aphasia caused by hemorrhaging from arteriovenous malformations. During the median follow-up period of 29 months after GKS, aphasia developed in 2 patients: 30 Gy delivered to the frontal portion of the AF caused conduction aphasia in 1 patient, and 9.6 Gy to the temporal portion led to motor aphasia in the other. Speech dysfunction was not observed after a maximum radiation dose of 10.0–16.8 Gy was delivered to the frontal fibers in 4 patients, and 3.6–5.2 Gy to the temporal fibers in 3.

Conclusions

The authors found that administration of a 10-Gy radiation dose during GKS was tolerated in the frontal but not the temporal fibers of the AF. The authors recommend confirmation of the dose by integration of AF tractography with GKS, especially in lesions located near the temporal language fibers.

Repeat stereotactic radiosurgery for high-grade and large intracranial arteriovenous malformations

BACKGROUND

The treatment of large and high-grade (Spetzler-Martin III-V) AVMs remains a challenge. There is a paucity of literature addressing the efficacy of radiosurgery in this group. We retrospectively analyze our experience with repeat radiosurgery with such AVMs.

METHODS

Between 1989 and 2004, 14 patients with large and high-grade AVMs deemed to be nonoperative candidates were treated with repeat radiosurgery. Patients were treated either on a LINAC or gamma knife-based system at 2- to 3-year intervals with targeting of the entire nidus with each treatment. Patients who did not receive their full treatment course or follow-up at the institution were excluded.

RESULTS

Mean follow-up was 18 months. The complete obliteration rate was 35.7%, with a mean volume reduction of 53% in the remaining lesions. Twenty percent of grade III and 50% of grade IV lesions experienced cure. Complications included persistent headaches (2 patients). Statistical analysis revealed no difference between obliterated and partially obliterated groups with regard to mean pretreatment volume (24.87 cm(3)), median Spetzler-Martin grade (IV), mean follow-up (30.5 months), total delivered dose (3550 cGy), mean dose per stage (13 Gy), median number of stages (2), or mean interval between treatment stages (40 months).

CONCLUSION

The present study demonstrates the potential role of repeat radiosurgery in the treatment of this cohort in the context of our short follow-up. The benefits of repeat therapy could be derived from using lower doses per session and repeat targeting of the lesion in an effort to increase response and decrease complication rates.

Assessment of absorbed dose to thyroid, parotid and ovaries in patients undergoing Gamma Knife radiosurgery

Stereotactic radiosurgery was originally introduced by Lars Leksell in 1951. This treatment refers to the noninvasive destruction of an intracranial target localized stereotactically. The purpose of this study was to identify the dose delivered to the parotid, ovaries, testis and thyroid glands during the Gamma Knife radiosurgery procedure. A three-dimensional, anthropomorphic phantom was developed using natural human bone, paraffin and sodium chloride as the equivalent tissue. The phantom consisted of a thorax, head and neck and hip. In the natural places of the thyroid, parotid (bilateral sides) and ovaries (midline), some cavities were made to place TLDs. Three TLDs were inserted in a batch with 1 cm space between the TLDs and each batch was inserted into a single cavity. The final depth of TLDs was 3 cm from the surface for parotid and thyroid and was 15 cm for the ovaries. Similar batches were placed superficially on the phantom. The phantom was gamma irradiated using a Leksell model C Gamma Knife unit. Subsequently, the same batches were placed superficially over the thyroid, parotid, testis and ovaries in 30 patients (15 men and 15 women) who were undergoing radiosurgery treatment for brain tumours. The mean dosage for treating these patients was 14.48 +/- 3.06 Gy (10.5-24 Gy) to a mean tumour volume of 12.30 +/- 9.66 cc (0.27-42.4 cc) in the 50% isodose curve. There was no significant difference between the superficial and deep batches in the phantom studies (P-value < 0.05). The mean delivered doses to the parotid, thyroid, ovaries and testis in human subjects were 21.6 +/- 15.1 cGy, 9.15 +/- 3.89 cGy, 0.47 +/- 0.3 cGy and 0.53 +/- 0.31 cGy, respectively. The data can be used in making decisions for special clinical situations such as treating pregnant patients or young patients with benign lesions who need radiosurgery for eradication of brain tumours.

Current role of radiation therapy in the management of malignant brain tumors

The objective of this article is to explain how the current management of malignant brain tumors has evolved, using the foundation of evidence-based literature. Radiotherapy plays a central role in the multidisciplinary management of primary brain tumors and brain metastases. The techniques of radiotherapy continue to be refined to optimize local control while minimizing potential treatment-related neurocognitive toxicities.

Repeatability of functional MRI for conformal avoidance radiotherapy planning

PURPOSE

To establish the repeatability of functional magnetic resonance imaging (fMRI) examinations in order to develop an appropriate margin for functional organs at risk (fOAR) in the radiotherapy planning process.

MATERIALS AND METHODS

This work investigates the variability of motor cortex activation in the left and right hemispheres of 15 normal subjects. The uncertainty of the absolute position and volume of the activation was determined for each volunteer by repeating the fMRI examination three times in a single scan session.

RESULTS

Our study proposes the use of 2.9 mm and 2.2 mm margins for the left and right motor cortices, respectively.

CONCLUSION

From the sample of 15 volunteers we established an appropriate planning margin that is considered to represent the uncertainty in spatially measuring the fOAR for a single fMRI examination. The work will be of interest to anyone investigating the clinical robustness of fMRI.

Advanced-technology radiation therapy in the management of bone and soft tissue sarcomas

BACKGROUND

For patients with sarcomas, radiotherapy can be used as neoadjuvant, adjuvant, or primary local therapy, depending on the site and type of sarcoma, the surgical approach, and the efficacy of chemotherapy.

METHODS

The authors review the current status of advanced technology radiation therapy in the management of bone and soft tissue sarcoma.

RESULTS

Advances in radiotherapy have resulted in improved treatment for bone and soft tissue sarcomas. Intensity-modulated radiation therapy (IMRT) uses modifications in the intensity of the photon-beam from a linear accelerator across the irradiated fields to enhance dose conformation in three dimensions. For proton-beam radiation therapy, the nuclei of hydrogen atoms are accelerated in cyclotrons or synchrotrons, extracted, and transported to treatment rooms where the proton beam undergoes a series of modifications that conform the dose in a particular patient to the tumor target. Brachytherapy and intraoperative radiation therapy have generally been used to treat microscopic residual disease in patients with sarcomas. These technologies deliver dose to tumor cells with irradiation of limited volumes of normal tissue. Patients who may benefit from technically advanced radiotherapy include those with skull base and spine/paraspinal sarcomas, Ewing's sarcoma, and retroperitoneal/extremity sarcomas.

CONCLUSIONS

Advances in radiation therapy technology, particularly IMRT, proton-beam or other charged-particle radiation therapy, brachytherapy, and intraoperative radiation therapy, have led to improved treatment for patients with bone and soft tissue sarcomas.

Permanent alopecia after cranial irradiation: Dose–response relationship

PURPOSE

To develop a dose-response relationship for the occurrence of permanent alopecia after cranial irradiation and to analyze potential confounding variables that may contribute to this unwanted and often unavoidable complication of treatment.

METHODS AND MATERIALS

Twenty-six patients were enrolled in this study. Three reviewers independently assessed 61 scalp regions and assigned a score for the degree of alopecia in each region using a 4-point scale. Patient and treatment data were collected using a patient questionnaire and outpatient medical chart review. The hair follicle dose was calculated for each scalp region and correlated with the alopecia score for that region. A dose-response relationship was established using the data from these correlations.

RESULTS

Permanent alopecia correlated significantly with the follicle dose only (p < 0.001). A personal history of alopecia and the use of chemotherapy correlated with permanent alopecia with borderline statistical significance (p = 0.059 and p = 0.068, respectively). Patient age, family history of baldness, gender, tobacco use, diabetes, and beam energy did not correlate with alopecia.

CONCLUSION

We report the first human dose-response relationship describing the effect of the follicle dose on the subsequent development of permanent scalp alopecia after cranial irradiation. This information will assist the radiation oncologist, physicist, and dosimetrist in designing a treatment plan that might minimize the risk of this untoward side effect of cranial irradiation.

Univariate analysis of factors correlated with tumor control probability of three-dimensional conformal hypofractionated high-dose radiotherapy for small pulmonary or hepatic tumors

PURPOSE

To show the factors correlated with tumor control probability (TCP) after three-dimensional conformal hypofractionated high-dose radiotherapy (3D-CHHRT) for small pulmonary or hepatic tumors.

METHODS AND MATERIALS

We enrolled 34 patients with 42 lesions (13 lung carcinomas, 6 hepatocellular carcinomas, and 23 lung or liver metastases) treated with 3D-CHHRT alone, with simple immobilization devices, between July 1997 and January 2002. We prescribed 45 Gy in three fractions at the 90-100% isodose line of the planning target volume. The median follow-up period was 18 months (range, 4-46 months). We calculated the TCP using the Kaplan-Meier method and univariate analysis for the following factors: age, gender, primary site, histologic type, tumor size, and previous treatment.

RESULTS

Overall, the 2-year TCP of 3D-CHHRT was 83.6%. Local recurrence was observed in 6 lesions within 1 year after treatment. We showed that tumor size was the only significant factor to correlate with the TCP in univariate analysis. The 2-year TCP for tumors <3 cm or > or =3 cm in diameter was 95.0% and 58.3%, respectively (p = 0.0022). No severe adverse effects were observed.

CONCLUSION

The TCP for tumors <3 cm in diameter was excellent for 3D-CHHRT.

Hypofractionated stereotactic radiotherapy alone without whole-brain irradiation for patients with solitary and oligo brain metastasis using noninvasive fixation of the skull

PURPOSE

To evaluate the efficacy and toxicity of hypofractionated stereotactic radiotherapy (HSRT) using noninvasive fixation of the skull on solitary or oligo brain metastatic patients as an alternative to stereotactic radiosurgery (SRS) using invasive fixation.

PATIENTS AND METHODS

The subjects were 87 patients who had 4 or fewer brain metastases (50 solitary, 37 oligometastases). Treatment was conducted on 159 metastases by using a linac-based stereotactic system. The median isocentric dose was 35 Gy in 4 fractions. Whole-brain irradiation was not applied as an initial treatment. For the salvage treatment of metachronous brain metastases, repeat HSRT or whole-brain irradiation was applied.

RESULTS

The actuarial 1-year local tumor control rate was 81%. Treatment-related complications were observed in 4 patients in the early period (<3 months) and in 2 patients in the late period. The median survival period was 8.7 months. Metachronous brain metastases occurred in 30 patients, and none of the 18 patients who were eligible for salvage HSRT refused to receive it again.

CONCLUSIONS

Hypofractionated stereotactic radiotherapy achieved tumor control and survival equivalent to those of SRS reported in the literature. The results suggested that HSRT could be an alternative for solitary or oligo brain metastatic patients with less toxicity and less invasiveness compared to SRS.

A review of stereotactic radiosurgery in the management of brain metastases

This review addresses the epidemiology, historical reports, current issues, data and controversies involved in the management of brain metastases. The literature regarding surgery, whole brain radiation therapy, stereotactic radiosurgery or some combination of those treatments is discussed as well as issues of cost-effectiveness. Ongoing prospective randomized trials will further elucidate the optimal management for patients with brain metastases. Until those data are available, clinicians are encouraged to apply the existing data reviewed here in conjunction with best clinical judgment. A brief clinical guide is as follows. Patients with a solitary metastasis in an operable location and symptomatic mass effect should undergo surgery. Patients with poor performance status (KPS < 70) or more than three brain metastases should receive WBRT alone. Patients with 1-3 brain metastases and KPS >or= 70, should receive WBRT + SRS. If the patient refuses WBRT or needs salvage after WBRT, then SRS alone is appropriate. Clinicians should not be too dogmatic and should always apply the best clinical judgment.

Functional magnetic resonance imaging aided radiation treatment planning

Functional MRI (magnetic resonance imaging) allows one to noninvasively identify various eloquent cortices in the brain. The integration of cortical activation information into radiosurgical treatment planning may provide an alternative to prevent or minimize radiation damage to eloquent cortex. A novel approach of directly integrating the fMRI (functional magnetic resonance imaging) brain map into treatment planning is proposed. Three brain tumor patients have been studied using this method with motor and/or visual paradigms. Brain activation was demonstrated in eloquent cortex at the precentral gyrus (motor area) and medial occipital lobe (visual area). The activation maps were transferred to a treatment planning workstation, (XKnife), and 3D (three-dimensional) activation maps were generated and co-registered to a 3D CT (computed tomography) anatomical data set, which provided the calibration localizer, for treatment planning. Radiosurgery was designed based on both functional and structural information by the medical team consisting of a radiation oncologist, a neurosurgeon and a physicist. The average maximum dose for the tumor was 2113 cGy. The average maximum dose for tissue surrounding the tumor was 1600 cGy. The average dose with fMRI information to the eloquent cortex was 163.4 cGy over three patients, while without fMRI information it was 240.5 cGy. The average percentage dose reduction over three patients is 32%. The results suggest that using this method can reduce the dose to the eloquent cortex. This approach provides the physician with additional information for treatment planning and may spare the patient unnecessary radiation exposure to adjacent eloquent cortices.

Results of hypofractionated stereotactic re-irradiation on 13 locally recurrent nasopharyngeal carcinomas

Thirteen patients with locally recurrent, previously-irradiated nasopharyngeal carcinoma were treated with linac-based hypofractionated stereotactic radiotherapy (24 Gy in two or four fractions). One- and 3-year overall survival were 54 and 31%. Three patients were free of disease at 30, 34 and 65 months. No severe acute or late complications were seen.

Five year results of LINAC radiosurgery for arteriovenous malformations: outcome for large AVMS

PURPOSE

For radiosurgery of large arteriovenous malformations (AVMs), the optimal relationship of dose and volume to obliteration, complications, and hemorrhage is not well defined. Multivariate analysis was performed to assess the relationship of multiple AVM and treatment factors to the outcome of AVMs significantly larger than previously reported in the literature.

METHODS AND MATERIALS

73 patients with intracranial AVMs underwent LINAC radiosurgery. Over 50% of the AVMs were larger than 3 cm in diameter and the median and mean treatment volumes were 8.4 cc and 15.3 cc, respectively (range 0.4-143.4 cc). Minimum AVM treatment doses varied between 1000-2200 cGy (median: 1600 cGy).

RESULTS

The obliteration rates for treatment volumes < 4 cc, 4-13.9 cc, and > or = 14 cc were 67%, 58%, and 23%, respectively. AVM obliteration was significantly associated with higher minimum treatment dose and negatively associated with a history of prior embolization with particulate materials. No AVM receiving < 1400 cGy was obliterated. The incidence of post-radiosurgical imaging abnormalities and clinical complications rose with increasing treatment volume. For treatment volumes > 14 cc receiving > or = 1600 cGy, the incidence of post-radiosurgical MRI T2 abnormalities was 72% and the incidence of radiation necrosis requiring resection was 22%. The rate of post-radiosurgical hemorrhage was 2.7% per person-year for AVMs with treatment volumes < 14 cc and 7.5% per person-year for AVMs > or = 14 cc.

CONCLUSION

As AVM size increases, the dose-volume range for the optimal balance between successful obliteration and the risk of complications and post-radiosurgical hemorrhage narrows.

Immediate side effects of stereotactic radiotherapy and radiosurgery

PURPOSE

Despite increased utilization of fractionated stereotactic radiation therapy (SRT) or stereotactic radiosurgery (SRS), the incidence and nature of immediate side effects (ISE) associated with these treatment techniques are not well defined. We report immediate side effects from a series of 78 patients.

MATERIALS AND METHODS

Intracranial lesions in 78 adult patients were treated with SRT or SRS, using a dedicated linear accelerator. Those lesions included 13 gliomas, 2 ependymomas, 19 metastatic tumors, 15 meningiomas, 12 acoustic neuromas, 4 pituitary adenomas, 1 optic neuroma, 1 chondrosarcoma, and 11 arteriovenous malformations (AVM). SRT was used in 51 and SRS in 27 patients. Mean target volume was 9.0 cc. Eleven patients received prior external-beam radiation therapy within 2 months before SRT/SRS. Any side effects occurring during and up to 2 weeks after the course of radiation were defined as ISE and were graded as mild, moderate, or severe. The incidence of ISE and the significance of their association with several treatment and pretreatment variables were analyzed.

RESULTS

Overall, 28 (35%) of 78 patients experienced one or more ISE. Most of the ISE (87%) were mild, and consisted of nausea (in 5), dizziness/vertigo (in 5), seizures (in 6), and new persistent headaches (in 17). Two episodes of worsening neurological deficit and 2 of orbital pain were graded as moderate. Two patients experienced severe ISE, requiring hospitalization (1 seizure and 1 worsening neurological deficit). ISE in 6 cases prompted computerized tomography of the brain, which revealed increased perilesional edema in 3 cases. The incidence of ISE by diagnosis was as follows: 46% (6 of 13) for gliomas, 50% (6 of 12) for acoustic neuromas, 36% (4 of 11) for AVM, 33% (5 of 15) for meningiomas, and 21% (4 of 19) for metastases. A higher incidence of dizziness/vertigo (4 of 12 = 33%) was seen among acoustic neuroma patients than among other patients (p< 0.01). There was no significant association of dizziness/vertigo with either a higher average and maximum brainstem dose (p = 0.74 and 0.09, respectively) or with 2-Gy equivalents of the average and maximum brainstem doses (p = 0.28 and 0.09, respectively). Higher RT dose to the margin and higher maximum RT dose were associated with a higher incidence of ISE (p = 0.05 and 0.01, respectively). However, when RT dose to the margin was converted to a 2-Gy dose-equivalent, it lost its significance as predictor of ISE (p = 0.51). Recent conventional external-beam radiation therapy, target volume, number of isocenters, collimator size, dose inhomogeneity, prescription isodose, pretreatment edema, dose of prior radiation, fraction size (2.0-7.0 Gy with SRT and 13.0-21.0 Gy with SRS), fractionation schedule, and dose to brainstem were not significantly associated with ISE. ISE occurred in 26% (8) of 31 patients taking corticosteroids prior to SRT/SRS and in 20 (42%) of 47 patients not taking them (p = 0.15).

CONCLUSION

ISE occur in one third of patients treated with SRT and SRS and are usually mild or moderate and self-limited. Dizziness/vertigo are common and unique for patients with acoustic neuromas and are not associated with higher brainstem doses. We are unable to detect a relationship between ISE and higher margin or maximum RT doses. No specific conclusion can be drawn with regard to the effect of corticosteroids, used prior to SRS/SRT, on the occurrence of ISE.

Fractionated stereotactic radiotherapy of small intracranial malignancies

PURPOSE

To retrospectively evaluate the effectiveness of fractionated stereotactic radiotherapy (FSRT) in patients with small intracranial malignancies.

METHODS AND MATERIALS

From July 1991 to March 1997, 80 patients with a total of 121 brain or skull-base tumors were treated with FSRT alone, and were followed for periods ranging from 3 to 62 months (median 9.8). The majority of patients received 42 Gy in 7 fractions over 2.3 weeks, but in July 1993, protocols using smaller fraction doses were introduced for patients whose radiation-field diameters were larger than 3 cm or whose tumors were close to critical normal tissues.

RESULTS

For 64 patients with metastatic brain tumors the overall median survival was 8.3 months and 1-year actuarial survival rate was 33%. Significant prognostic factors were: the presence of extracranial tumors, pre-treatment performance status, and the lung as a primary site. Patients without extracranial tumors prior to FSRT had a median survival of 21.2 months. For seven patients with high-grade glioma, 1-year actuarial local control rate was 75%, with a median survival of 10.3 months. For patients with skull-base tumors the local control was achieved in 6 of 6 patients (100%), with a median survival of 30.7 months. No one suffered from acute complications, but three patients, two of whom had undergone FSRT as the third course of radiotherapy, developed late radiation injuries.

CONCLUSION

Overall high local control and low morbidity rates suggest that FSRT is an effective and safe modality, even for those with a history of prior irradiation. However, patients with risk factors should be treated with smaller fraction doses.

Prognostic factors in lung cancer with brain metastasis

BACKGROUND AND PURPOSE

Metastasis to the brain develops in 25% of all patients with lung cancer. Although the outcome is usually poor, there seems to be a subset of patients with favorable prognostic factors who may live longer. Prognostic factors were analyzed retrospectively in 103 patients with brain metastases from lung carcinoma to identify patients who would benefit from more intensive treatment strategies.

MATERIALS AND METHODS

Between October 1991 and December 1994, 103 patients with brain metastasis from lung cancer were irradiated with palliative intent. Palliation was defined as 50% or more regression of neurological signs and symptoms 2 weeks after the completion of cranial radiotherapy. Local (related to the lung tumor) symptom status at the time of brain metastasis, the presence of metastases other than brain, multiplicity of brain metastases on CT scan and time of occurrence of brain metastasis were the factors which were evaluated with multivariate analysis.

RESULTS

Palliation was accomplished in 85% of cases. Palliation duration ranged from 0.5 to 54 months (median 3 months). The overall median survival was 5 months. Only one patient is under follow-up without any symptoms related to the brain metastasis. According to the multivariate analysis survival was significantly decreased in the presence of symptoms related to the primary tumor (P = 0.001).

CONCLUSION

The presence of symptoms related to the primary tumor at the time of brain metastasis is one of the factors that can be used to distinguish patients with a favorable outcome. In patients with favorable prognostic factors and thus longer survival probability, the role of boost dose after whole brain radiotherapy or surgical resection in suitable cases needs to be investigated.

Anaesthetic considerations for children undergoing stereotactic radiosurgery

An anaesthetic case report of children undergoing stereotactic radiosurgery is presented, with a review of the inherent unique anaesthetic challenges. Twelve stereotactic radiosurgery procedures performed at The Prince of Wales Hospital, Sydney, were retrospectively reviewed. Despite differences in approach by individual anaesthetists to managing these children, an overall safe sequence may be evolved. The use of stereotactic radiosurgery for paediatric neuropathology is reviewed. The potential anaesthetic problems related to the paediatric patient and the peculiarities of the procedure are discussed and related to our series.

Beam shaping for conformal fractionated stereotactic radiotherapy: a modeling study

PURPOSE

The patient population treated with fractionated stereotactic radiotherapy (SRT) is significantly different than that treated with stereotactic radiosurgery (SRS). Generally, lesions treated with SRT are larger, less spherical, and located within critical regions of the central nervous system; hence, they offer new challenges to the treatment planner. Here a simple, cost effective, beam shaping system has been evaluated relative to both circular collimators and an ideal dynamically conforming system for effectiveness in providing conformal therapy for these lesions.

METHODS AND MATERIALS

We have modeled a simple system for conformal arc therapy using four independent jaws. The jaw positions and collimator angle are changed between arcs but held fixed for the duration of each arc. Eleven previously treated SRT cases have been replanned using this system. The rectangular jaw plans were then compared to the original treatment plans which used circular collimators. The plans were evaluated with respect to tissue sparing at 100%, 80%, 50%, and 20% of the prescription dose. A plan was also done for each tumor in which the beam aperture was continuously conformed to the beams eye view projection of the tumor. This was used as an ideal standard for conformal therapy in the absence of fluence modulation.

RESULTS

For tumors with a maximum extent of over 3.5 cm the rectangular jaw plans reduced the mean volume of healthy tissue involved at the prescription dose by 57% relative to the circular collimator plans. The ideal conformal plans offered no significant further improvement at the prescription dose. The relative advantage of the rectangular jaw plans decreased at lower isodoses so that at 20% of the prescription dose tissue involvement for the rectangular jaw plans was equivalent to that for the circular collimator plans. At these isodoses the ideal conformal plans gave substantially better tissue sparing.

CONCLUSION

A simple and economical field shaping device has been shown to provide all of the beam shaping advantage of a hypothetical ideal dynamically conforming system at the prescription level. This system may be immediately implemented in the clinic. It offers a substantial advantage over the currently used circular collimators in the high dose region with equivalent performance in the low dose region.

Efficacy and feasibility of stereotactic radiosurgery in the primary management of unfavorable pediatric ependymoma

Stereotactic radiosurgery was given as a boost in the initial radiation management of five children with localized intracranial ependymoma. Preliminary results in young children with high-risk tumors indicate good local control without excessive neurotoxicity.

Current perspectives in gliomas

The annual incidence of primary central nervous system tumors, including gliomas, is increasing, however, the prognosis of these tumors remains poor with a median survival of only 5 years. The imaging of tumors by computerised tomography, magnetic resonance imaging and newer methods such as positron emission tomography and proton magnetic resonance spectroscopy (1H-MRS) is increasing our knowledge of tumor biology and extent of the disease. Advances within the field of neurosurgery have improved operative procedures reducing mortality and morbidity. Furthermore, radiotherapy planning, tumor targeting and repositioning for treatment have all improved initial tumor management. The role of adjuvant chemotherapy remains controversial. Chemotherapy for advanced and recurrent disease has been extensively investigated, and although improvements in quality of life have been recorded, no prolongation of survival has been documented. With new discoveries and increasing knowledge of the physiology and molecular biology of these tumors the potential for targeting therapy at a genetic level is becoming increasingly promising. This review provides an overview of these current perspectives in glioma management.

Radiosurgery and accelerated radiotherapy for patients with glioblastoma

OBJECTIVE

To assess the feasibility, toxicity, and local control of stereotactic radiosurgery followed by accelerated external beam radiotherapy (AEBR) for patients with glioblastoma multiforme.

MATERIALS AND METHODS

Six males and eight females, with a median age of 67.5 years (range 45-78 years), entered the study. Karnofsky performance status was 90 for five, 80 for six, and 60 for three patients. Following surgery, the patients were left with a residual mass 4 cm. Radiosurgery was delivered with a single dose of 20 Gy to the 90% isodose surface corresponding to the contrast-enhancing edge of the tumour. A total AEBR dose of 60 Gy in 30 fractions was delivered using a concomitant boost technique over four weeks.

RESULTS

Median survival time was 40 weeks (range 17-80 weeks). Actuarial survivals at 12 and 18 months were 43% and 14%, respectively. The median time to progression was 25 weeks (range 2-77 weeks). One patient developed a seizure on the day of stereotactic radiosurgery. Two patients experienced somnolence at 47 and 67 days post-radiotherapy. Eight patients remained steroid-dependent. Radiological evidence of leukoencephalopathy was observed in one patient, and brain necrosis in two additional patients at 30 and 63 weeks. One of these two patients with brain necrosis developed complete loss of vision in one eye, and decreased vision in the contralateral eye at 63 weeks.

CONCLUSION

Stereotactic radiosurgery followed by AEBR was feasible but was associated with late complications. The use of such radiosurgical boost for patients with glioblastoma multiforme should be reserved for those patients entering controlled clinical trials.

Dosimetric results from a feasibility study of a novel radiosurgical source for irradiation of intracranial metastases

PURPOSE

A feasibility study addressing the role of a new miniature x-ray device, the Photon Radiosurgery System (PRS), for interstitial radiosurgical treatment of intracranial metastatic neoplasms, was conducted at our institution. To gain insight into the role of PRS vis-à-vis other currently available radiosurgical treatment modalities, dosimetric comparisons of Linac Radiosurgery and proton beam therapy were performed in the treatment of a small approximately spherical metastasis.

METHODS AND MATERIALS

The photon radiosurgery system is a miniature, battery operated, high-voltage x-ray generator that produces low-energy x-rays with an effective energy of 10-20 keV emanating from the tip of a probe stereotactically inserted into small tumors (< 3 cm in diameter) in humans. Patients, 18 years or older, with supratentorial mass lesions less than 3 cm in diameter were eligible if they were likely to survive their systemic cancer and be capable of self-care for more than 4 months. Patients were ineligible if presenting with infratentorial lesions, contraindications for biopsy, or receipt of chemotherapy or radiotherapy within 4 weeks were ineligible.

RESULTS

Fourteen patients with metastatic supratentorial lesions were treated from December 1992 to December 1993 for metastatic tumors to the brain. Single doses of 10-20 Gy were delivered to spherical targets of 10 to 35 mm in diameter. Treatment, including biopsy, pathologic review and radiation treatment, generally took less than 3 h. One patient, later found to have an ischemic stroke, developed a small hemorrhage from the biopsy that preceded interstitial irradiation. There were no other complications. Median survival was 10 months. Three locally recurrent lesions failed at 3.5, 4, and 10 months after treatment. All patients had stable or improved Karnofsky status for 2 weeks to 21 months after treatment. The PRS dosimetry appears at least as good as that obtained using 6 MV Linac or 160 MeV protons. Analyses of dose-volume histograms comparing the volumes of normal CNS tissue irradiated employing each of the respective modalities suggest a small sparing of normal tissue with PRS, as opposed to linac or protons, in this patient population with small, approximately spherical tumors.

CONCLUSIONS

The PRS device provides a unique cost and time efficient procedure for providing interstitial radiation therapy immediately following histologic confirmation of malignancy in patients undergoing biopsy of intracranial lesions. The PRS treatment appears safe, and preliminary data suggest no evidence of treatment-related morbidity within the life span of the selected patient population. When treating small, spherical lesions, PRS appears to offer a modest dosimetric advantage over Linac or proton beam therapy in sparing normal tissue. These encouraging results have prompted a Phase II trial that is currently underway. Further efforts are necessary in the design of a clinically relevant trial addressing the role of fractionated external beam radiation therapy with boost vs. PRS treatment with WBRT in the treatment of single metastases.

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

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

Radiosurgery for cerebral arteriovenous malformations: assessment of early phase magnetic resonance imaging and significance of gadolinium-DTPA enhancement

PURPOSE

To evaluate the initial changes within the nidus of arteriovenous malformations (AVMs) and to assess the reaction to the brain tissue surrounding AVMs after radiosurgery by serial magnetic resonance (MR) imaging.

METHODS AND MATERIALS

Twenty-one patients, treated using 60Co gamma knife unit with cerebral AVMs, were retrospectively evaluated. Forty-seven follow-up MR images of the 21 patients were performed including 10 patients with two or more serial gadolinium enhanced studies (Gd-MR). Two or more sequential MR angiographies (MRA) were obtained in 13 patients. Three-dimensional (3D) time-of-flight MRA and two-dimensional (2D) phase contrast MRA were used in 13 patients for evaluating the flow changes of AVMs. The follow-up period after radiosurgery ranged from 3 to 30 months (average 10.8 months) and the interval time of MRI ranged from 34 days to 13 months (average 4.9 months).

RESULTS

Reduction of nidus size was observed in 14 of 21 patients (67%) between 4 to 13 months on spin echo (SE) images. Complete obliteration was observed on SE images in 4 of these 14 patients; three were confirmed by conventional angiography. New hyperintense areas surrounding the nidus on T2s-weighted images (T2WI) developed in 9 of the 14 patients who showed nidus reduction between 5 to 17 months after radiosurgery; in three patients, size of the hyperintense area started to decrease between 6 to 7 months after its appearance. Probable radiation necrosis of pons developed in one patient 26 months after radiosurgery. The irradiated area within the AVM nidus was significantly enhanced in 8 of the 10 patients who underwent Gd-MR. The degrees of enhancement within the nidus increased with time in 7 of the 10 patients. Overall, total enhancement of irradiated areas was observed in four of the 10 patients; in three of the four, the enhancement decreased in size and degree, indicating nidus reduction. In three patients who had a partial volume irradiation within the nidus, the enhancing areas corresponded with the exact portions of irradiated volume. The nidus reduction was observed in 7 of the 13 patients on MRA during 5 to 13 months after radiosurgery. MRA was more useful compared to SE images in four of the seven patients in evaluating the size change of AVM nidus, feeding arteries, and draining veins.

CONCLUSION

Magnetic resonance imaging and MRA were useful in assessing the progress of nidus reduction. T2-weighted imaging was sensitive to radiation-induced reaction in and around the AVM nidus. The enhancement within the AVM nidus on Gd-MR may represent the initial sign of nidus reduction and demonstrates the exact location of irradiation in the nidus. The changes of the enhancement pattern are presumed to represent the processes of nidus reduction and irradiated reaction within the AVM nidus.

Conductive interstitial hyperthermia in the treatment of intracranial metastatic disease

BACKGROUND

Intracranial metastases commonly complicate oncologic care affecting 140,000 patients per year in the United States. Treatment of these tumors is difficult and often unsuccessful. Hyperthermia is a treatment alternative that has shown promise in treating cancer in other areas. Therefore it was employed in an attempt to provide increased tumor control in CNS metastases.

METHODS

This Phase I and Phase II clinical trial of interstitial hyperthermia with recurrent or progressive intracranial metastatic disease was undertaken to evaluate complications, delivery of heat and patient outcome.

RESULTS

Feared complications of clinically significant bleeding, increased mass, or infection from the interstitial implant and treatment did not occur. The seizures which occurred in 4 patients were controlled with additional anticonvulsants. Three venous thromboembolic events were treated medically and with percutaneously placed inferior vena cava filters. The KPS of the majority of patients declined slightly with treatment but rebounded to near baseline within several months. CT scans demonstrated decrease or stabilization of tumor volumes in 7 of the 13 patients. In 4 of these patients, regression or stabilization persisted until death from nonCNS disease.

CONCLUSIONS

Interstitial hyperthermia therapy for intracranial metastases is technically feasible and may provide increased tumor control. In this small series, it did not cause unreasonable complications. This therapy has some positive effect, but requires study of more patients before its role is definitively known. Combining hyperthermia with brachytherapy and/or chemotherapy is being evaluated.

Quantitative magnetic resonance and isotopic imaging: early evaluation of radiation injury to the brain

PURPOSE

Using magnetic resonance (MR) and isotopic imaging to investigate the cerebral alterations after highdose single-fraction irradiation on a pig model. We assessed the nuclear magnetic resonance (NMR) relaxation times as early markers of radiation injury to the healthy brain.

METHODS AND MATERIALS

A total of 17 animals was studied; 15 irradiated and 2 unirradiated controls. Pigs were irradiated with a 12 MeV electron beam at a rate of 2 Gy/min. Ten animals received 40 Gy at the 90% isodose, five animals received 60 Gy, and two animals were unirradiated. The follow-up intervals ranged from 2 days to 6 months. T1-weighted scans, T2-weighted scans, and scintigrams were performed on all animals to study neurological abnormalities, cerebral blood flow, and blood-brain barrier (BBB) integrity. T1 and T2 relaxation times were measured in selected regions of interest (ROIs) within the irradiated and contralateral hemispheres. A ratio T1 after irradiation/T1 before irradiation, and a ratio T2 after irradiation/T2 before irradiation, were calculated, pooled for each dose group, and followed as a function of time after irradiation.

RESULTS

Scintigraphy visualized the brain perfusion defect and BBB disruption in all irradiated brains. The ratio T2 after irradiation/T2 before irradiation was proportional to the effective dose received. The T2 ratio kinetics could be analyzed in three phases:an immediate and transient phase, two long-lasting phases, which preceded compression of the irradiated lateral ventricle, and edema and necrosis at later stages of radiation injury, respectively. The magnetic resonance imaging (MRI) observations correlated well with histological analysis.

CONCLUSION

The results show that quantitative imaging is a sensitive in vivo method for early detection of cerebral radiation injury. The reliability and dose dependence of T2 relaxation time may offer new opportunities to detect and understand brain pathophysiology after high-dose single-fraction irradiation.

Clinical brain radionuclide imaging studies

A recent survey of the knowledge and practice of both positron-emission tomography (PET) and single-photon emission computed tomography (SPECT) of the brain among referring physicians in Europe (neurologists and psychiatrists) showed a disquieting lack of knowledge of the potential of these methodologies in the investigation and management of patients of their own specialities. The need to bring the knowledge of the potential of these techniques to the practicing physicians is paramount. It is imperative that the methodologies and concepts that preside over the application of these techniques in neurology and psychiatry must become more uniform if an impact is to be felt at a clinical level. There is clear improvement in the instrumentation available with the new state-of-the-art tomographic devices and with the development of new technetium-based radiopharmaceuticals for the study of cerebral perfusion. The constant progress made with ligands that permit the study of neurotransmission, tumor metabolism, and turnover do expand our capability to improve the knowledge concerning neurophysiology, neuropathology, and neuropharmacology of a variety of disease states. PET and SPECT will be progressively included in protocols aimed at stratifying patients with dementia, monitoring therapeutic trials, and improving our ability to determine outcome. Clinical usefulness of PET and SPECT begin to emerge in cerebral vascular disease, in the identification of cerebral death, in epilepsy, in cerebral trauma, in the investigation of HIV-positive patients with cerebral involvement, and in the monitoring of tumor recurrence and postirradiation damage. This review article outlines a current perspective of SPECT and PET as practiced in Europe, its potential, and its limitations.

Radiation response of the central nervous system

This report reviews the anatomical, pathophysiological, and clinical aspects of radiation injury to the central nervous system (CNS). Despite the lack of pathognomonic characteristics for CNS radiation lesions, demyelination and malacia are consistently the dominant morphological features of radiation myelopathy. In addition, cerebral atrophy is commonly observed in patients with neurological deficits related to chemotherapy and radiation, and neurocognitive deficits are associated with diffuse white matter changes. Clinical and experimental dose-response information have been evaluated and summarized into specific recommendations for the spinal cord and brain. The common spinal cord dose limit of 45 Gy in 22 to 25 fractions is conservative and can be relaxed if respecting this limit materially reduces the probability of tumor control. It is suggested that the 5% incidence of radiation myelopathy probably lies between 57 and 61 Gy to the spinal cord in the absence of dose modifying chemotherapy. A clinically detectable length effect for the spinal cord has not been observed. The effects of chemotherapy and altered fractionation are also discussed. Brain necrosis in adults is rarely noted below 60 Gy in conventional fractionation, with imaging and clinical changes being observed generally only above 50 Gy. However, neurocognitive effects are observed at lower doses, especially in children. A more pronounced volume effect is believed to exist in the brain than in the spinal cord. Tumor progression may be hard to distinguish from radiation and chemotherapy effects. Diffuse white matter injury can be attributed to radiation and associated with neurological deficits, but leukoencephalopathy is rarely observed in the absence of chemotherapy. Subjective, objective, management, and analytic (SOMA) parameters related to radiation spinal cord and brain injury have been developed and presented on ordinal scales.

Linear accelerator radiosurgery for arteriovenous malformations: the relationship of size to outcome

Between May, 1988 and August, 1993, 158 patients with arteriovenous malformations (AVMs) were treated radiosurgically at the University of Florida. A mean dose of 1560 cGy was directed to the periphery of the lesions, which had a mean volume of 9 cc (0.5 to 45.3 cc). One hundred thirty-nine of these individuals were treated with one isocenter. The mean follow-up interval was 33 months with clinical information available on 153 of these patients. Patients were followed until magnetic resonance (MR) studies suggested complete AVM thrombosis. An arteriogram was then performed, if possible, to verify occlusion status. If arteriography revealed any persistent nidus at 36 months posttreatment, the residual nidus was re-treated. Outcome categories of AVMs analyzed included the following possibilities: 1) angiographic cure; 2) angiographic failure; 3) re-treatment; 4) MR image suggested cure; 5) MR image suggested failure; 6) patient refused follow-up evaluation; 7) patient lost to follow-up study; or 8) patient deceased. The endpoints for success or failure of radiosurgery were as follows: angiographic occlusion (success), re-treatment (failure), and death due to AVM hemorrhage (failure). Fifty-six patients in this series reached one of the endpoints. Successful endpoints were seen in 91% of AVMs between 1 and 4 cc in volume, 100% of AVMs 4 to 10 cc in volume, and 79% of AVMs greater than 10 cc in volume. The more traditional measure of radiosurgical success, percentage of angiograms showing complete obliteration, was obtained in 81% of AVMs between 1 and 4 cc in volume, 89% of AVMs between 4 and 10 cc in volume, and 69% of AVMs greater than 10 cc in volume. A detailed analysis of the relationship of all outcome categories to size is presented.

Single isocenter treatment planning for homogeneous dose delivery to nonspherical targets in multiarc linear accelerator radiosurgery

PURPOSE

Conventional radiosurgery refers to single isocenter focused beam irradiation of small intracranial targets with a single collimator. Conventional radiosurgery is characterized by spherical-shaped isodose surfaces. Nonspherical targets require a different approach to avoid exposing a large volume of nontarget brain tissue to high dose, particularly for lesions larger than 25 mm. Multiple isocenters are frequently used to treat nonspherical large targets, but multiple isocenter treatments are associated with a relative dose inhomogeneity of approximately 100% within the target volume, and may be correlated with an increased rate of complications. The feasibility of conformally treating elongated targets to an approximately homogeneous dose using a single isocenter methodology will be demonstrated.

METHODS AND MATERIALS

A prolate ellipsoid of revolution, 25 mm in diameter, 35 mm in length, positioned at five representative locations in a head phantom, was used as a target model. The alignment of the target was taken to be parallel in turn to each of the three principal axes of the head model (A/P, R/L, and C/C). Dose conformation is achieved by nonuniform arc weighting, selective limitation of the extent of individual arcs, and the use of different collimator apertures for the different arcs in accordance with the aperture size required to encompass the target for that arc. Treatment plans were selected based on considerations of dose-volume histograms and conformation of the 80% dose surface with the surface of the target. The goal was that the minimum target dose would not be less than 80% of the maximum dose.

RESULTS

Practical treatment plans for which the minimum target dose exceeded 80% were obtained for the three orthogonal orientations of the target for the five target locations. Plan parameters were essentially independent of the target position, dependent only on target orientation. The 80% isodose contour surface enclosed on average 2.8 cm3 larger volume (range: 2.1-3.9 cm3) than the prescribed 11.45 cm3 target. The minimum dose to the target ranged from 80.1 to 84.5%, and the average dose to the target was 94.26%. The 80-to-50% dose volume enclosed an average of 14.8 cm3 of nontarget volume (range: 12.7-15.9 cm3). Average deviation in the principal planes of the 80% isodose lines from the surface of the target volume was 0.95 mm for the 25 mm dimension (range 0.0 to +1.9 mm) and 0.86 mm (range 0.0 to + 2.4 mm) for the 35 mm dimension.

CONCLUSION

Standardized single isocenter treatment plans with the isocenter at the center of the target can achieve good conformation of the dose distribution to targets elongated along any of the principal axes, and located anywhere in the brain.

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSION

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

Stereotactic radiotherapy for pediatric and adult brain tumors: preliminary report

PURPOSE

Stereotactic radiotherapy is a new modality that combines the accurate focal dose delivery of stereotactic radiosurgery with the biological advantages of conventional radiotherapy (1.8-2.0 Gy/day using 25-30 fractions). The modality requires sophisticated treatment planning, dedicated high-energy linear accelerator, and relocatable immobilization devices. We report here our early experience using stereotactic radiotherapy for intracranial neoplasms.

METHODS AND MATERIALS

Between June 1992 and September 1993, we treated 82 patients with central nervous system lesions using stereotactic radiotherapy, delivered from a dedicated 6 MV stereotactic linear accelerator. A head fixation frame provided daily relocatable setup using a dental plate for all patients over 8 years of age. A modified head frame, which does not require a mouthpiece, was used for children requiring anesthesia. The patients ranged in age from 9 months to 76 years. Thirty-three patients were children less than 21 years of age. Selection criteria for the protocol included: (a) focal, small (< 5 cm) radiographically distinct lesions known to be radiocurable (pituitary adenoma, craniopharyngioma, meningioma, acoustic neuroma, pilocytic astrocytoma, retinoblastoma), and (b) lesions located in regions not amenable to surgery or radiosurgery such as the brain stem or chiasm. Standard fractionation and conventional doses were delivered. Patients with low-grade astrocytoma, oligodendroglioma, or ependymoma were treated using a dose escalation regime consisting of conventional doses plus a 10% increase.

RESULTS

Although follow-up is 16 months (range 3-16 months), posttreatment radiographic studies in 77 patients have been consistent with changes similar to those found after conventional radiation therapy. To date, reduction of up to 50% of the original volume has been noted in 19 out of 77 patients, and 4 patients had a complete response, 2 with dysgerminoma, and 1 each with astrocytoma and retinoblastoma. In 56 patients disease was either stable or the follow-up was too short for evaluation. While the follow-up is relatively short, there have been no in-field or marginal recurrences. The only unexpected radiographic findings were in three patients with pilocytic astrocytomas, who developed asymptomatic edema in the treatment volume. Accuracy in daily fractionation was excellent. In over 2000 patient setups with 41,000 scalp measurements, reproducibility was found to be within 0.41 mm (median) of baseline readings, allowing for precise immobilization throughout the treatment course. The treatment in all cases was well tolerated with minimal acute effects. Our stereotactic radiotherapy facility can provide fractionated therapy for 10-12 patients a day efficiently and accurately.

CONCLUSIONS

The treatment and relocatable stereotactic head frames were well tolerated with minimal acute effects. No long-term sequelae have been noted, although the observation period is short. To fully define the role of stereotactic radiotherapy, we are conducting prospective studies to evaluate neurocognitive and neuroendocrine effects. We expect that this innovative approach will make a significant impact on the treatment of intracranial neoplasms, particularly in children.

The prevention of radiosurgery-induced nausea and vomiting by ondansetron: evidence of a direct effect on the central nervous system chemoreceptor trigger zone

Nausea and emesis are significant side effects in patients undergoing stereotactic radiosurgery for brain lesions in the region of the chemoreceptor trigger zone (area postrema of the brain). Even with the current antiemetic treatment (prochlorperazine +/- corticosteroids), those side effects remain significant. The purpose of this study is twofold: [1] to evaluate the efficacy of ondansetron in inhibiting nausea and emesis in stereotactic radiosurgery patients and [2] to demonstrate that ondansetron's locus of action is the central nervous system (CNS) chemoreceptor trigger zone in the area postrema. In a pilot study, 10 patients receiving > or = 350 cGy in a single fraction of radiosurgery to the region of the area postrema received 32 mg ondansetron iv 1 hour prior to treatment +/- corticosteroids. In a retrospective analysis these results were compared to those of patients with similar features (and matched for radiation dose to the area postrema and the dose of corticosteroids) who received prochlorperazine +/- corticosteroids. Nine of 10 patients in the ondansetron group had no nausea or emesis within 48 hours after treatment; one patient experienced one episode of emesis. In the prochloreperazine group, eight patients had symptoms, three patients needed hospitalization or a physician's care for emesis within 24 hours, and five had nausea with no specific treatment. These preliminary results suggest that ondansetron is a safe and efficient drug to prevent nausea and emesis in this patient group. The precise mechanism of action of ondansetron in these patients is unknown, but is likely due to the drug's serotonin-blocking effect within the CNS. A randomized, prospective study has been started at our institution to confirm these preliminary results.

Stereotactic radiosurgery of vestibular schwannomas with a linear accelerator

The authors describe their initial experience with stereotactic radiosurgery of 22 cases with vestibular schwannomas using a linear accelerator. 14 of them with a follow-up of at least one year were studied. 6-9 months after treatment 86% had central tumour necrosis, 71% tumour shrinkage and none of them evidence of tumour growth 3 patients developed reversible facial nerve impairment, 2 had permanent facial numbness. Hearing diminished in one case out of three with normal hearing and in two out of three with already diminished hearing. Although there is a general consensus that microsurgery is the treatment of choice for these benign tumours, stereotactic radiosurgery challenges this opinion. Stereotactic radiosurgery not only proves to be a valuable alternative for selected cases not suitable for microsurgery, but it is conceivable that it will become the treatment of choice for small vestibular tumours. Tumour control can be obtained in the majority of treated patients with fewer complications and with a higher rate of cranial nerve sparing. This series indicates that linear accelerators can achieve results similar to the Gamma Unit in the treatment of vestibular schwannomas.

Stereotactic radiosurgery of deeply seated low grade gliomas

The authors report the results of a series of 16 cases of low-grade gliomas in whom radiosurgery was performed. This series started in 1977. All the tumours received a single radiosurgical session (with a mean dose of 21.7 Gy, 5-10 mm. collimator; one patient received two sessions and in another patient two different targets were irradiated in the same session). Prior to radiosurgery, six patients received conventional external fractionated radiotherapy, with two lateral fields of up to 10 x 10 cm. and a mean dose of 55.1 Gy and another six patients with tumours less than 5 cm. in diameter, received stereotactic radiotherapy using four fields of up to 5 x 5 cm. and a mean dose of 53.1 Gy. In both cases, conventional fractionation was used, giving a dose of 1.8 to 2 Gy/day. The tumour disappeared in 8 cases (50%) and shunk or ceased its growth in 5 additional cases (31%). In 3 cases of brainstem gliomas in which the clinical condition was previously very poor there was no evolutional change and the patients eventually died. We conclude that radiosurgery is effective in the treatment of deeply seated low-grade gliomas, where it may become the treatment of choice in the absence of other more definitive choices.