Facial nerve preservation and tumor control after gamma knife radiosurgery of unilateral acoustic tumors

To assess the long-term risk of facial nerve dysfunction after unilateral acoustic tumor stereotactic radiosurgery, we retrospectively analyzed our initial experience in 98 unilateral acoustic tumor patients who were evaluated at least 2 years after treatment. This observation interval permits an analysis of both the risk of onset and the potential for recovery of facial nerve function. The overall risk of developing any degree of delayed transient or permanent postoperative facial neuropathy was 21.4% (21 of 98 patients). Only one patient undergoing radiosurgery alone had poor residual facial nerve dysfunction worse than House-Brackmann grade III. Normal facial nerve function (House-Brackmann grade 1) was preserved in 95% of patients with small tumors (10 mm or less petrous-pons dimension) and in 90% of patients who had useful hearing and normal facial function preoperatively. Normal facial function was preserved in all patients with intracanalicular acoustic tumors. The risk of delayed facial neuropathy was reduced by performing radiosurgery when tumors were small (1000 mm(3) or less), by enclosing the tumor within the 50% isodose volume, by using multiple small radiation isocenters, and by detailed identification of the tumor volume using stereotactic magnetic resonance imaging.

Dose reduction improves hearing preservation rates after intracanalicular acoustic tumor radiosurgery

OBJECTIVE

To assess the potential for long-term serviceable hearing preservation in intracanalicular acoustic tumor patients who underwent stereotactic radiosurgery.

METHODS

Between August 1987 and December 1997, 29 patients with intracanalicular acoustic tumors underwent stereotactic radiosurgery at our center using the Leksell gamma knife (Elekta Instruments, Inc., Atlanta, GA). Fifteen assessable patients had serviceable preradiosurgery hearing (pure tone average, < or = 50 dB; speech discrimination score, > or = 50%). We retrospectively analyzed our hearing results and compared hearing preservation in patients who received a minimal tumor dose of 14 Gy or less versus those who received more than 14 Gy to the tumor margin.

RESULTS

No perioperative patient morbidity or mortality was observed. Serviceable hearing was preserved in 11 (73%) of 15 assessable patients (actuarial rate, 65%). Long-term follow-up demonstrated serviceable hearing preservation in 10 (100%) of 10 patients who received marginal tumor doses of 14 Gy or less but in only one of five patients who received more than 14 Gy. Preradiosurgery Gardner-Robertson class was preserved in 49%, and testable hearing was present in 68% of patients who had any testable hearing at presentation. Five patients demonstrated improvement in hearing (three had serviceable and two had nonserviceable hearing before radiosurgery). No patient developed a facial or trigeminal neuropathy. Seven of 13 patients with preoperative tinnitus continued to experience tinnitus in follow-up. Episodic vertigo continued in 3 of the 11 patients who presented with vertigo.

CONCLUSION

Gamma knife radiosurgery (using conformal dose planning, small-beam geometry, and < or = 14 Gy to the margin) prevents tumor growth and achieves excellent hearing preservation rates.

Can hearing improve after acoustic tumor radiosurgery?

Advances in noninvasive diagnostic techniques have enabled physicians to diagnose acoustic tumors early, while hearing is still present. Applications of advanced operative techniques have allowed surgeons to decrease progressively the operative mortality to virtually zero, to save facial nerve function in a large number of patients, and even to preserve serviceable hearing in selected patients. Documented improvement in hearing after acoustic tumor surgery is rare. During the last decade, stereotactic radiosurgery has evolved as a noninvasive surgical option for acoustic tumors. Hearing improvement after radiosurgery has not been reported. The authors observed hearing improvement in 21 out of 487 patients who had radiosurgery during a 10-year interval. This article reviews their experience of hearing improvement after radiosurgery and suggests possible reasons that hearing can not only be retained but also improved in selected patients.

Black holes, white dwarfs and supernovas: imaging after radiosurgery

PURPOSE

To evaluate the imaging and pathological correlates of successful or risk-related stereotactic radiosurgery (SR). Methods and Materials. The ten-year Gamma Knife experience in 2,344 patients at the University of Pittsburgh was reviewed. In addition, the results or radiosurgery primate, rat, and mouse models were analyzed. Successful results and untoward complications were evaluated.

RESULTS

Dose, volume, location and histology affected the imaging changes seen after SR. Imaging changes range from central loss of contrast ('black holes'), shrinkage with diffuse contrast uptake ('white dwarfs'), or stabilization or growth arrest. Limited pathological data indicates that the prevention of cell division coupled with vascular obliteration results in tumor control, whereas a progressive endothelial proliferative and obliterative response results in arteriovenous malformation (AVM) obliteration. Perilesional imaging changes, especially in vascular malformations, may reflect flow phenomena, interstitial edema, or profound reactive astrocytosis ('supernovas').

CONCLUSION

Imaging changes correlate with both success and risks of stereotactic radiosurgery; however, pathological correlates are limited. High resolution neurodiagnostic imaging provides the best quality control available to assess the response to stereotactic radiosurgery. In the future, additional molecular probes are necessary to assess the radiobiological effects of radiosurgery.

Factors associated with successful arteriovenous malformation radiosurgery

OBJECTIVE

To analyze the clinical and angiographic variables that affect the results of arteriovenous malformation (AVM) radiosurgery and to propose a new method of reporting patient outcomes after AVM radiosurgery. This method incorporates both the obliteration status of the AVMs and the postoperative neurological condition of the patient.

METHODS

Patient outcomes were defined as excellent (nidus obliteration and no new deficits), good (nidus obliteration with a new minor deficit), fair (nidus obliteration with a new major deficit), unchanged (incomplete nidus obliteration without a new deficit), poor (incomplete nidus obliteration with any new deficit), and dead. Two hundred twenty patients who underwent AVM radiosurgery at our center before 1992 were subjected to a multivariate analysis with patient outcomes as the dependent variable.

RESULTS

Multivariate analysis determined four factors associated with successful AVM radiosurgery: smaller AVM volume (P=0.003), number of draining veins (P=0.001), younger patient age (P=0.0003), and hemispheric AVM location (P=0.002). Preradiosurgical embolization was a negative predictor of successful AVM radiosurgery (P=0.02).

CONCLUSION

AVM obliteration without new neurological deficits can be achieved in at least 80% of patients with small volume, hemispheric AVMs after single-session AVM radiosurgery. Future studies on AVM radiosurgery should report patient outcomes in a fashion that incorporates all the factors involved in successful AVM radiosurgery.

Radioprotective effects of the 21-aminosteroid U-74389G for stereotactic radiosurgery

OBJECTIVE

Future improvements in the results of stereotactic radiosurgery will be related to better patient selection, dose planning, radiosensitization of the target, and, possibly, protection of the brain surrounding the target. 21-Aminosteroids may provide protection against brain radiation injury by inhibition of lipid peroxidation and a selective action on vascular endothelium. We hypothesized that the 21-aminosteroid U-74389G would reduce radiosurgery-related brain injury without attenuating the target volume response.

METHODS

One hundred and forty-five rats were divided into four experimental groups before undergoing radiosurgery: control (n = 47); low-dose U-74389G (5 mg/kg of body weight, n = 30); high-dose U-74389G (15 mg/kg, n = 20); and methylprednisolone (2 mg/kg, n = 48). The drug was administered 1 hour before radiosurgery (4-mm gamma knife collimator) of the normal rat frontal lobe (single-fraction maximum doses of 50, 100, or 150 Gy) was performed. All brains underwent histological examination at 90 or 150 days to evaluate the diameters of necrosis and the findings of radiation-induced vasculopathy, brain edema, and gliosis.

RESULTS

None of the animals that received 50-Gy radiation developed histological changes, whereas all of the animals that received 150-Gy radiation developed radiation necrosis without drug-induced protection from vascular changes or edema. In animals receiving 100-Gy radiation, high-dose aminosteroid reduced radiation-induced vasculopathy at 90 days (P = 0.06) and at 150 days (P = 0.02) and prevented regional edema at 90 days (P = 0.01) and at 150 days (P = 0.03). Low-dose aminosteroid and corticosteroid provided no protection.

CONCLUSION

The 21-aminosteroid U-74389G provided protection after a single intravenously administered dose of 15 mg/kg against radiation-induced vasculopathy and edema. High-dose 21-aminosteroids seem to have optimal properties for radiosurgery, surrounding brain protection without reducing the therapeutic effect desired within the target volume.

Hemangioblastoma of the posterior fossa. The role of multimodality treatment

The authors made a review of a series of patients with hemangioblastomas of the posterior fossa treated between 1973 and 1993. A total of 32 patients were analyzed with 24 patients receiving resection, 8 patients receiving radiosurgery and 2 patients receiving conventional radiotherapy. The mortality in the patients with a resection was considered acceptable with 2 deaths (8%) and with a morbidity of 3 patients (12.5%). A review of the literature suggests that conventional radiotherapy with high doses (45-60 Gy) may have a role in the post-operative control of hemangioblastomas and in some cases could be employed even before the resection in order to facilitate the surgery. The radiosurgical treatment is regarded like adjuvant. Poor results were obtained with radiosurgery in large tumors where low doses (less than 20 Gy) were used. Because of the rarity and complexity of these tumors, mainly when associated with von Hippel-Lindau disease, a multicenter study could be useful with the assessment of the optimal utilization and combination of these treatment modalities.

Radiosurgery and fractionated radiation therapy: comparison of different techniques in an in vivo rat glioma model

To identify histological changes and effects on survival in rats harboring C6 gliomas, the authors compared radiosurgery to different fractionated radiation therapy regimens including doses of calculated biological equivalence. Rats were randomized to control (54 animals) or treatment groups after implantation of C6 glioma cells into the right frontal brain region. At 14 days, treated rats underwent stereotactic radiosurgery (35 Gy to tumor margin; 22 animals), whole-brain radiation therapy (WBRT) (20 Gy in five fractions; 18 animals), radiosurgery plus WBRT (13 animals), hemibrain radiation therapy (85 Gy in 10 fractions; 16 animals) or single-fraction hemibrain irradiation (35 Gy; 10 animals). When compared to the control group (median survival 22 days), prolonged survival was identified after radiosurgery (p < 0.0001), radiosurgery plus WBRT (p < 0.0001), WBRT alone (p = 0.0002), hemibrain radiation therapy to 85 Gy (p < 0.0001), and 35-Gy hemibrain single-fraction irradiation (p = 0.004). Compared to the control group (mean tumor diameter, 6.8 mm), the tumor size was reduced in all treatment groups except WBRT alone. Reduced tumor cell density was exhibited in rats that underwent radiosurgery (p = 0.006) and radiosurgery plus WBRT (p = 0.009) when compared with rats in the control group, a finding not observed after any fractionated regimen. Increased intratumoral edema was identified after radiosurgery (p = 0.03) and combined treatment (p = 0.05), but not after fractionated radiation therapy or 35-Gy single-fraction hemibrain irradiation. In this animal model, the addition of radiosurgery significantly increased tumor cytotoxicity, potentially at the expense of radiation effects to regional brain. We found no difference in survival benefit or tumor diameter in animals that underwent radiosurgery compared to the calculated biologically equivalent regimen of 10-fraction radiation therapy to 85 Gy. The histological responses after radiosurgery were generally greater than those achieved with biologically equivalent doses of fractionated radiation therapy.

Patient outcomes after stereotactic radiosurgery for "operable" arteriovenous malformations

To define the outcomes after stereotactic radiosurgery performed for smaller volume arteriovenous malformations (AVMs) that are potentially suitable for surgical removal, we retrospectively reviewed our 4-year experience in 65 patients who declined microsurgery. All 65 patients had Spetzler-Martin Grade I or II AVMs and a minimum follow-up of 24 months (median, 29 mo). Symptomatic improvement after radiosurgery occurred in 52% of patients with seizures and in 63% of patients with headaches. The annual risk of AVM hemorrhage during the latency interval after radiosurgery was 3.7%. Five patients (7.7%) had a subsequent hemorrhage (all within 8 mo of radiosurgery); two died, and three recovered (one after hematoma evacuation and two with conservative management). Forty-seven patients (72%) returned to their previous employment status or activity level within 1 week of radiosurgery (92% within 1 yr). No patient suffered radiation-related complications. Twenty-seven (84%) of 32 patients evaluated by postradiosurgical angiography had complete AVM obliteration. Radiosurgery is an effective and less invasive management strategy for Grade I or II AVM patients who are either medically unsuitable for or unwilling to undergo surgical removal. The risk of AVM hemorrhage during the latency interval until obliteration occurs appears to be no different than the natural history of untreated AVMs. These results (including hemorrhage prevention and symptom amelioration) indicate that the conservative management of small AVMs can rarely be justified.

Preservation of cranial nerve function after radiosurgery for nonacoustic schwannomas

Microsurgical resection is the primary management approach for patients with intracranial schwannomas. Recent studies have demonstrated that stereotactic radiosurgery is an effective therapeutic modality for patients with acoustic schwannomas. To define the role of radiosurgery in the management of patients with nonacoustic schwannomas, we reviewed the results of gamma unit stereotactic radiosurgery in six patients with trigeminal and five patients with jugular foramen region schwannomas. No patient with a trigeminal schwannoma demonstrated tumor growth during a mean follow-up of 21 months (range, 7-35 mo), whereas one patient with a jugular foramen region schwannoma had an increase in tumor size 7 months after radiosurgery. No new cranial nerve or brain stem deficits were noted in either patient group after radiosurgery. In this early experience, radiosurgery proved an effective primary or adjuvant technique for selected patients with schwannomas of the trigeminal, glossopharyngeal, or vagus nerves. Using our described method, the safety of radiosurgery was demonstrated on the brain stem, regional cranial nerves, and especially those cranial nerves intimately associated with the tumor.

Potential human error in setting stereotactic coordinates for radiosurgery: implications for quality assurance

PURPOSE

The error frequency in setting stereotactic coordinates for gamma knife radiosurgery was investigated to determine what quality assurance safeguards are necessary.

METHODS AND MATERIALS

A prospective study of 200 consecutive isocenter settings for gamma knife radiosurgery was analyzed to identify the frequency of spontaneous errors in setting and checking stereotactic coordinates (corrected prior to treatment). An additional 25 coordinate errors were introduced at random among the next 200 consecutive isocenter settings to provide additional data on identification of errors.

RESULTS

Stereotactic coordinates required resetting in 12% (24/200) of the isocenters treated due to errors of 0.25-0.50 mm (8%) and 1-20 mm (4%). This comprised 2.2% (26/1200) of the individual coordinate settings. The frequency of these errors was significantly related to the specific directional coordinate set (p = 0.0004) and experience (p = 0.016). Errors were identified by 83.5% (91/109) of the observers checking the settings (60.0% of 0.25 mm errors, 94.6% of errors > or = 0.5 mm, p = 0.0000). Verification of stereotactic coordinates by two observers reduces the probability of an undetected error > or = 0.25 mm to 1/1,392 and to 1/154,712 for errors > or = 1 mm.

CONCLUSION

Errors in setting stereotactic coordinates are common (12% prior to checking) but are corrected with a high degree of confidence by a quality assurance policy requiring coordinate verification by a minimum of two observers.

Treatment volume shaping with selective beam blocking using the Leksell gamma unit

The Leksell gamma unit at the University of Pittsburgh uses 201 highly focused 60Co beams arranged in a hemispherical array. Selective beam blocking can be used to modify the treatment volume into ellipsoid shapes oriented in different directions to match better the shape of the target volume. Dose distributions for different blocking patterns were calculated using specially developed computerized 3-D treatment planning software. The changes in dose distribution with different blocking patterns predicted by computer were verified by film densitometry. Techniques for using selective beam blocking to match more closely the treatment volume to the intended target volume have the potential of reducing the likelihood of complications for radiosurgery with the Leksell gamma unit and need to be further developed.

Separation of dose-gradient effect from beam-hardening effect on wedge factors in photon fields

It is known experimentally that a wedge transmission factor depends upon the field size and depth of measurement in particular. Dependence of the transmission upon depth has been attributed to a hardening of the incident beam through the filter, which preferentially absorbs the low-energy photon of the bremsstrahlung component of that beam. We have attempted to separate this hardening effect from that of increased phantom scatter due to dose gradient induced by the wedge filter. Using an experimental wedge machined from cerrobend, the filter transmission at depth is measured and redefined relative to an "equally hardened" beam, obtained by filtering through a flat slab of equal thickness at the center of the wedge. Results of the Co-60, 4-, and 8-MV wedged beams indicate that nearly half of the increase in the transmission at depth is due to the effect of dose-gradient scatter in polystyrene phantom. Based on a simple relationship between primary and scattering radiation, an algebraic presentation is indeed in support of the dose gradient resulting in apparent increase in the wedge factors, at depth.

Stereotactic radiosurgery of the brain using the first United States 201 cobalt-60 source gamma knife

The first United States 201 cobalt-60 source gamma knife for stereotactic radiosurgery of brain tumors and arteriovenous malformations became operational at the University of Pittsburgh on August 14, 1987. Four and one-half years of intensive planning, regulatory agency review, and analysis of published results preceded the first radiosurgical procedure. Installation of this 18,000-kg device and loading of the 201 cobalt-60 sources posed major challenges in engineering, architecture, and radiophysics. In the first 4 months of operation, we treated 52 patients (29 with arteriovenous malformations, 19 with extra-axial neoplasms of the skull base, and 4 with intra-axial malignant tumors). Most patients either had lesions considered "inoperable" or had residual lesions after attempted surgical resection. Neither surgical mortality nor significant morbidity was associated with gamma knife radiosurgery. As compared with treatment by conventional intracranial surgery (craniotomy), the average length of stay for radiosurgery was reduced by 4 to 14 days, and hospital charges were reduced by as much as 65%. Based on both the previously published results of treatment of more than 2,000 patients worldwide and on our initial clinical experience, we believe that gamma knife stereotactic radiosurgery is a therapeutically effective and economically sound alternative to more conventional neurosurgical procedures, in selected cases.

First United States 201 source cobalt-60 gamma unit for radiosurgery

Installation of the first United States 201-source 60Co gamma unit for stereotactic radiosurgery was completed at the University of Pittsburgh in May, 1987. Despite a very favorable 19-year experience in Stockholm, introduction of this technology into the US proved to be a formidable task. Extensive internal and government regulatory review by the Health Systems Agency, the Food and Drug Administration and the Nuclear Regulatory Commission ultimately resulted in approval of marketing and use of the gamma unit. Clinical use and radiobiological research has begun.