Protection of iodine-125 brachytherapy brain injury in the rat with the 21-aminosteroid U-74389F

Advances in radiotherapy of brain tumors: radiobiology versus reality

Radiotherapy still remains the most effective adjunctive therapy for malignant gliomas following surgery and provides useful local control for some benign tumors. Research efforts have been directed towards several aspects of the radiation therapy of tumors. The results of clinical trials undertaken in the last decade offer some basis for optimism in the management of patients with malignant brain tumors, although cure is still not a realistic objective. This review focuses on the rationale and radiobiological basis for recent developments in the radiotherapy of adult brain tumors. The salient issues are discussed from a neurosurgeon's perspective.

Stereotactic Radiosurgery: Adjacent Tissue Injury and Response after High-Dose Single Fraction Radiation—Part II: Strategies for Therapeutic Enhancement, Brain Injury Mitigation, and Brain Injury Repair

IN THE FIRST part of this series, we reviewed the histological, radiographic, and molecular data gathered regarding the brain parenchymal response to radiosurgery and suggested future studies that could enhance our understanding of the topic. With this article, we begin by addressing methods of potentiating the effect of radiosurgery on target lesions of the central nervous system. Much of the work on potentiating the effects of cranial radiation has been performed in the field of whole-brain radiotherapy. Data from Phase III trials evaluating the efficacy of various agents as radiosensitizers or radioenhancers in whole-brain radiotherapy are reviewed, and trials for investigating certain agents as enhancers of radiosurgery are suggested. The roles of gene therapy and nanotechnology in enhancing the therapeutic efficacy of radiosurgery are then addressed. Focus is then shifted to a discussion of strategies of protecting healthy tissue from the potentially deleterious aspects of the brain's response to radiosurgery that were presented in the first article of this series. Finally, comments are made regarding the role of neural progenitor or stem cells in the repair of radiation-induced brain injury after radiosurgery. The importance of both the role of the extracellular matrix and properly directed axonal regrowth leading to appropriate target reinnervation is highlighted.

Stereotactic radiosurgery: adjacent tissue injury and response after high-dose single fraction radiation: Part I--Histology, imaging, and molecular events

Radiosurgery is now the preferred treatment modality for many intracranial disease processes. Although almost 50 years have passed since it was introduced as a tool to treat neurological disease, investigations into its effects on normal tissues of the central nervous system are still ongoing. The need for these continuing studies must be underscored. A fundamental understanding of the brain parenchymal response to radiosurgery would permit development of strategies that would enhance and potentiate the radiosurgical treatment effects on diseased tissue while mitigating injury to normal structures. To date, most studies on the response of the central nervous system to radiosurgery have been performed on brain tissue in the absence of pathological lesions, such as benign tumors or metastases. Although instructive, these investigations fail to emulate the majority of clinical scenarios that involve radiosurgical treatment of specific lesions surrounded by normal brain parenchyma. This article is the first in a two-part series that addresses the brain parenchyma's response to radiosurgery. This first article analyzes the histological, radiographic, and molecular data gathered regarding the brain parenchymal response to radiosurgery and aims to suggest future studies that could enhance our understanding of the topic. The second article in the series begins by discussing strategies for radiosurgical therapeutic enhancement. It concludes by focusing on strategies for mitigation and repair of radiation-induced brain injury.

Intravitreal triamcinolone acetonide for acute radiation papillopathy

OBJECTIVE

To evaluate intravitreal triamcinolone acetonide for patients with visually symptomatic acute radiation-induced papillopathy.

METHODS

In a prospective, nonrandomized, single-center case series, intravitreal triamcinolone acetonide (4 mg/0.1 mL) was injected through the pars plana using sterile technique in 9 patients with radiation papillopathy after plaque radiotherapy for choroidal melanoma. Status of radiation papillopathy and final visual acuity were the main outcome measures.

RESULTS

At the time of diagnosis of the choroidal melanoma, visual acuity was 20/20 to 20/40 (n = 6), 20/60 (n = 2), and 20/100 (n = 1). The mean radiation dose to the optic disk was 6,175 cGy (median, 5,994 cGy; range, 3,571-12,760 cGy). Radiation papillopathy developed a mean of 18 months (median, 17 months; range, 6-33 months) after plaque radiotherapy. In all cases, the choroidal melanoma was regressed, and there was no retinal detachment or neovascularization of the retina, optic disk, or iris. Concomitant radiation maculopathy was found in 8 eyes manifesting as macular edema (n = 8), intraretinal dot hemorrhages (n = 6), intraretinal exudation (n = 6), or nerve fiber layer infarction (n = 3). The radiation papillopathy findings included optic disk hyperemia (n = 9), edema (n = 9), and circumpapillary hemorrhage (n = 8). At the time of diagnosis of radiation papillopathy, visual acuity was 20/70 (n = 1), 20/100 (n = 4), 20/200 (n = 1), and counting fingers (n = 3). At 1 week after injection of triamcinolone acetonide, visual acuity improvement was found in seven patients, and resolution of optic disk hyperemia and edema was noted for four and three patients, respectively. At a mean follow-up of 11 months (median, 9 months; range, 6-19 months), visual acuity was stable or improved in 7 patients, and resolution of optic disk hyperemia and edema was found in all 9 patients. The mean time to improvement in visual acuity by > or =2 lines was 3 weeks (median, 1 week; range, 1-12 weeks). The mean time to complete resolution of radiation papillopathy was 4 months. The two patients with worse final visual acuity also had macular hole and central retinal vein obstruction. The only complication of this therapy was possibly related cataract in three patients.

CONCLUSION

During short-term follow-up, acute radiation-induced papillopathy appears to respond rapidly to intravitreal triamcinolone acetonide injection with resolution of optic disk hyperemia and edema and modest return of visual acuity. The long-term effects remain unknown.

Experimental Radiobiological Investigations into Radiosurgery: Present Understanding and Future Directions

LARS LEKSELL BEGAN radiobiological investigations to study the effect of high-dose focused radiation on the central nervous system more than 5 decades ago. Although the effects of radiosurgery on the brain tumor microenvironment are still under investigation, radiosurgery has become a preferred management modality for many intracranial tumors and vascular malformations. The effects and the pathogenesis of biological effects after radiosurgery may be unique. The need for basic research concerning the radiobiological effects of high-dose, single-fraction, ionizing radiation on nervous system tissue is crucial. Information from those studies would be useful in devising strategies to avoid, prevent, or ameliorate damage to normal tissue without compromising treatment efficacy. The development of future applications of radiosurgery will depend on an increase in our understanding of the radiobiology of radiosurgery, which in turn will affect the efficacy of treatment. This article analyzes the current state of radiosurgery research with regard to the nature of central nervous system effects, the techniques developed to increase therapeutic efficacy, investigations into the use of radiosurgery for functional disorders, radiosurgery as a tool for investigations into basic central nervous system biology, and the additional areas that require further investigation.

Beneficial effects of the radioprotectant 21-aminosteroid U-74389G in a radiosurgery rat malignant glioma model

PURPOSE

To evaluate the radioprotectant effects of the 21-aminosteroid U-74389G on the rat C6 glioma model after stereotactic radiosurgery. Because radiosurgery causes both tumor cytotoxicity, as well as regional brain edema, we hypothesized that this drug might exhibit advantageous or deleterious effects on healthy and neoplastic tissue.

METHODS

Rats were implanted with 10(6) C6 glioma cells into the right frontal brain and randomized to a Control Group (n = 18), radiosurgery on Day 14 (50% isodose = 35 Gy) (n = 15), or radiosurgery preceded by a single 15 mg/kg intravenous dose of 21-aminosteroid (n = 27). All animals were killed by 90 days and evaluated for survival, tumor size, the presence or absence of regional parenchymal edema, or radiation-induced vasculopathy.

RESULTS

After tumor implantation, median survival in the Control Group was 23 days. Significant improvements in median survival were noted after RS alone (median, 31 days; p = 0.02), and RS plus 21-aminosteroid (median, 59 days; p < 0.0001). In the Control Group, mean tumor diameter was 5.4 mm. After RS alone, the mean diameter was 3.2 mm (p = 0.002), and after RS plus 21-aminosteroid, 2.9 mm (p = 0.0002). In the Control Group, the tumor grew as a hypercellular, compact mass. Only 3 of 18 animals had peritumoral edema. In contrast, 7 of 15 animals in the RS group had evidence of edema (p = 0.006), but rats that received 21-aminosteroid showed no increase compared to controls (p = 0.38). Similarly, 6 of 15 animals that had radiosurgery alone showed evidence of vasculopathy (p = 0.005) compared to no animals in the control group and only 2 of 27 aminosteroid-treated animals.

CONCLUSIONS

The 21-aminosteroid U-74389G exhibits a radioprotectant effect on normal brain tissue, but does not appear to protect the tumor in an in vivo rat radiosurgery model. We believe that the observed beneficial effects on healthy brain led to significant prolongation of animal survival; perhaps, by limiting the adverse effects of high-dose radiosurgery. This radioprotectant should now be evaluated in randomized clinical trials in patients with malignant brain tumors.

Effect of implant dose/volume and surgical resection on survival in a rat glioma brachytherapy model: implications for brain tumor therapy

OBJECTIVE

This study sought to investigate the effects of implant dose/volume and surgical resection on survival in a rat glioma brachytherapy model. Two doses were investigated to determine a suitable therapeutic range.

METHODS

We performed two experiments. Three treatment groups and one control group of male F-344 rats bearing 9L brain tumors 12 days after tumor inoculation were used in the first experiment. Day 12 tumors were an average of 4 to 6 mm in diameter. Animals treated with brachytherapy received a tumor dose of 80 Gy delivered to a 5.5-mm-radius volume. Total macroscopic tumor removal was achieved by microsurgical techniques. A subsequent experiment compared the survival of tumor-burdened rats treated with an implant dose of 60 Gy delivered to a 5.5-mm-radius volume with a control group.

RESULTS

Surgery alone produced an increased life span of 28.6% over control animals treated with sham surgery and dummy seed implants, a statistically significant increase in survival (P = 0.0023, log-rank test). Brachytherapy alone produced the most significant increase in survival over control animals (P = 0.0001, log-rank test; median survival not attained with an implant dose of 80 Gy delivered to a 5.5-mm-radius volume; and P = 0.0001, increased life span 121% with an implant dose of 60 Gy delivered to a 5.5-mm-radius volume). This was not improved by the addition of surgical tumor removal.

CONCLUSION

We have demonstrated a relationship between implant dose/volume and survival of tumor-burdened rats in this model that is not improved by the addition of tumor removal. Implications for brain tumor brachytherapy are discussed.

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.

The protective effect of dexamethasone against radiation damage induced by interstitial irradiation in normal monkey brain

OBJECTIVE

The protective effect of dexamethasone against radiation damage is unclear. We examined the effect of early treatment of high-dose dexamethasone on iridium-192-induced damage to normal brain tissue.

METHODS

Brain damage induced by interstitial irradiation with iridium-192 was evaluated with sequential magnetic resonance imaging and proton magnetic resonance spectroscopy in 11 adult monkeys, with or without short-term high-dose dexamethasone treatment. Dexamethasone (1 mg/kg of body weight/d) was administered intramuscularly to five irradiated animals every 24 hours, beginning 2 days before and ending 7 days after irradiation. Magnetic resonance imaging and proton magnetic resonance spectroscopy were performed 1 week, 1 month, and 3 months after irradiation.

RESULTS

Magnetic resonance imaging performed 1 week after irradiation revealed marked edema in five nontreated animals. In dexamethasone-treated animals, the volume of edema was reduced significantly, compared to that of nontreated animals, 1 week and 1 month after irradiation. The volume of ring enhancement in dexamethasone-treated animals was also reduced significantly, compared to that of nontreated animals, 3 months after the irradiation. Proton magnetic resonance spectroscopy spectra revealed that N-acetylaspartate and choline peaks were reduced 1 week after irradiation in both groups. However, there were no statistically significant differences between the two groups at any time points.

CONCLUSION

These results suggest that dexamethasone treatment may have an antiedema effect at an early stage and may modify subsequent development of vascular and inflammatory changes but may have no effect of preventing radiation-induced necrosis and the reduction of N-acetylaspartate after brachytherapy.

Tirilazad does not protect rat brain from brachytherapy-induced injury

BACKGROUND

Acute and chronic brain injury are common sequelae of high-dose focused radiation, as in radiosurgery and brachytherapy. Development of protectors of radiation injury, which would work in brain but not in tumor, would help enhance the therapeutic ratio of focused-radiation therapy.

METHODS

Radiation protection by a clinically available 21-aminosteroid, Tirilazad, was studied in a rat brain brachytherapy model, both in tumor and non-tumor bearing animals. For the tumor model, 9L Glioma/SF line cells were implanted stereotactically into the right frontal lobe of F-344 rats and grew to a sphere of 5.0-mm diameter after 12 days. Animals received a standard brachytherapy dose of 80 Gy to a 5.5-mm radius volume administered by a high-activity removable iodine-125 seed. Radiation damage was evaluated 24 hours after removal of the seeds in all animals and again at 3 months in non-tumor-bearing animals, by T1-weighted gadolinium-enhanced and T2-weighted magnetic resonance imaging (MRI) on a 1.5-T unit. Treated animals received Tirilazad 5 mg/kg intravenously 15 minutes prior to implant, 1 hour after implant, every 6 hours for the duration of the implant, and for 24 hours after removal of the seed. Control animals were administered vehicle only.

RESULTS

In both non-tumor-bearing and tumor-bearing rats, no difference in the volume of lesions on enhanced T1 or T2 MRI was seen between the Tirilazad-treated and control groups. In the non-tumor-bearing rats, volume of both T1 enhanced and T2 MRI lesions was significantly reduced at 3 months compared to the values at 24 hours.

CONCLUSIONS

In the present model, Tirilazad failed to reduce the volume of radiation brain injury from brachytherapy as seen on MRI, studied acutely in tumor-bearing and non-tumor-bearing animals and also at 3 months in non-tumor-bearing rats.

The lazaroid U74389G protects normal brain from stereotactic radiosurgery-induced radiation injury

PURPOSE

To test an established model of stereotactic radiosurgery-induced radiation injury with pretreatments of either methylprednisolone or the lazaroid U74389G.

METHODS AND MATERIALS

Nine cats received stereotactic radiosurgery with a linear accelerator using and animal radiosurgery device. Each received a dose of 125.0 Gy prescribed to the 84% isodose shell to the anterior limb of the right internal capsule. One animal received no pretreatment, two received citrate vehicle, three received 30 mg/kg of methylprednisolone, and three received 5 mg/kg of U74389G. After irradiation, the animals had frequent neurologic examinations, and neurologic deficits developed in all of them. Six months after the radiation treatment, the animals were anesthetized, and had gadolinium-enhanced magnetic resonance (MR) scans, followed by Evans blue dye perfusion, euthanasia, and brain fixation.

RESULTS

Magnetic resonance scans revealed a decrease in the size of the lesions from a mean volume of 0.45 +/- 0.06 cm(3) in the control, vehicle-treated, and methylpredniosolone-treated animals to 0.22 +/- 0.14 cm(3) in the U74389G-treated group. The scans also suggested the absence of necrosis and ventricular dilatation in the lazaroid-treated group. Gross pathology revealed that lesions produced in the untreated, vehicle-treated, and methylprednisolone-treated cats were similar and were characterized by a peripheral zone of Evans blue dye staining with a central zone of a mature coagulative necrosis and focal hemorrhage. However, in the U74389G-treated animals, the lesions were found to have an area of Evans blue dye staining, but lacked discrete areas of necrosis and hemorrhage.

CONCLUSION

These results suggest that the lazaroid U74389G protects the normal brain from radiation injury produced by stereotactic radiosurgery.

Influence of the 21-aminosteroid U74389F on ischemia-reperfusion injury in the rat

We examined the effects of the administration of 21-[4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl]-pregna-1,4,9( 11)-triene-3,20-dione, monomethansulfonate (U74389F), a 21-aminosteroid and so-called lazaroid, that is characterized by an inhibitory activity against iron-dependent lipid peroxidation, on ischemia-reperfusion renal injury in a rat model. After either 60 or 90 min of ischemia, plus 2 or 24 h of reperfusion, kidneys were assayed for glutathione, adenine nucleotides and lipid peroxidation products. 60 min of ischemia produced too little oxidative stress and/or too much spontaneous recovery to allow visualization of the protective effect of the drug. 90 min of ischemia followed by reperfusion induced significant glutathione oxidation, the free oxidized glutathione to total glutathione redox ratio (%) being enhanced from 4.6 +/- 0.7% before kidney clamping to 11 +/- 1 and 8.6 +/- 1.4% at 2 and 24 h reperfusion, respectively. Treatment with the lazaroid provided significant protection against this oxidation (4.9 +/- 1.05% at 24 h reperfusion). Results of lipid peroxidation confirmed the antioxidant effect of the lazaroid. In conclusion this study provides evidence for a protective role of the tested lazaroid against ischemia-reperfusion renal injury in the rat.

Enhanced magnetic resonance imaging of the rat brain using a stereotactic device with a small head coil: technical note

A stereotactic device (SDM) was developed for performing consistent magnetic resonance imaging (MRI) of the rat brain. The SDM was developed by adapting a radiofrequency transmit/receive head coil of 4.4 cm inner diameter (quadrature birdcage head coil), and utilizing partial acrylic construction for the positioning elements. The small head coil provides improved resolution and accuracy of the image, while the stereotactic holder permits repeatable and accurate imaging of identified brain structures. This system provides several advantages over existing experimental MRI devices. The SDM ensures that the head is always placed in the center of the coil in a uniform fashion. Standardized positioning of the skull optimizes image quality and provides a consistent orientation of the brain. In addition, a widely-utilized coordinate system described by Paxinos and Watson can be employed to assist in the identification of structures and to facilitate surgical planning. The SDM is compatible with a recently-developed stereotactic device for radiosurgery with the Gamma Knife, thus permitting the planning and performance of experimental radiosurgery using the same coordinate system. The SDM also provides the ability to perform MRI and radiosurgery at different times, thus avoiding the need for prolonged anesthesia during an experimental study. Finally, the SDM allows repeated MRI of the same, identifiable positions in the brain during longitudinal experimental studies. The utility of this device is demonstrated here by examining the time course of cerebral damage that evolved within a radiosurgical focus after gamma irradiation.

Brachytherapy for recurrent malignant astrocytoma

PURPOSE

To assess the efficacy of interstitial brachytherapy in the treatment of patients with recurrent malignant astrocytoma.

METHODS AND MATERIALS

Forty-six patients with recurrent malignant astrocytoma were treated with stereotactic high-activity temporary iodine-125 implants between September, 1986 and October, 1992. All patients had been initially treated for malignant astrocytoma (44) or low-grade astrocytoma (2) with surgery and external fractionated radiation. The median time between initial diagnosis and recurrence treated with brachytherapy was 12.5 months. Twenty-five patients received chemotherapy prior to brachytherapy.

RESULTS

All but four patients have died; median survival time following brachytherapy is 46 weeks. Twelve patients underwent reoperation for radiation necrosis at a median interval of 6.5 months after treatment (26%). Five patients incurred complications directly due to brachytherapy (11%). Forty-four patients are evaluable regarding pattern of failure following brachytherapy. Six of these 44 patients (13.6%) recurred at a distance from the treatment volume (4 in brain and 2 in spinal subarachnoid space).

CONCLUSION

Brachytherapy confers modest but meaningful prolongation of survival in selected patients with recurrent malignant astrocytoma, but complications are significant, reoperation frequently required, and recurrence outside the treatment volume common.

On radiation damage to normal tissues and its treatment. II. Anti-inflammatory drugs

In addition to transiently inhibiting cell cycle progression and sterilizing those cells capable of proliferation, irradiation disturbs the homeostasis effected by endogenous mediators of intercellular communication (humoral component of tissue response to radiation). Changes in the mediator levels may modulate radiation effects either by assisting a return to normality (e.g., through a rise in H-type cell lineage-specific growth factors) or by aggravating the damage. The latter mode is illustrated with reports on changes in eicosanoid levels after irradiation and on results of empirical treatment of radiation injuries with anti-inflammatory drugs. Prodromal, acute and chronic effects of radiation are accompanied by excessive production of eicosanoids (prostaglandins, prostacyclin, thromboxanes and leukotrienes). These endogenous mediators of inflammatory reactions may be responsible for the vasodilatation, vasoconstriction, increased microvascular permeability, thrombosis and chemotaxis observed after radiation exposure. Glucocorticoids inhibit eicosanoid synthesis primarily by interfering with phospholipase A2 whilst non-steroidal anti-inflammatory drugs prevent prostaglandin/thromboxane synthesis by inhibiting cyclooxygenase. When administered after irradiation on empirical grounds, drugs belonging to both groups tend to attenuate a range of prodromal, acute and chronic effects of radiation in man and animals. Taken together, these two sets of observations are highly suggestive of a contribution of humoral factors to the adverse responses of normal tissues and organs to radiation. A full account of radiation damage should therefore consist of complementary descriptions of cellular and humoral events. Further studies on anti-inflammatory drug treatment of radiation damage to normal organs are justified and desirable.