Focal irradiation of perforating eye injuries

Animal models of radiation retinopathy - From teletherapy to brachytherapy

Radiation retinopathy is a serious vision-impairing complication of radiation therapy used to treat ocular tumors. Characterized by retinal vasculopathy and subsequent retinal damage, the first sign of radiation retinopathy is the preferential loss of vascular endothelial cells. Ensuing ischemia leads to retinal degradation and late stage neovascularization. Despite the established disease progression, the pathophysiology and cellular mechanisms contributing to radiation retinopathy remain unclear. Clinical experience and basic research for other retinal vasculopathies, such as diabetic retinopathy and retinopathy of prematurity, can inform our understanding of radiation retinopathy; however, the literature investigating the fundamental mechanisms in radiation retinopathy is limited. Treatment trials have shown modest success but, ultimately, fail to address the cellular events that initiate radiation retinopathy. Animal models of radiation retinopathy could provide means to identify effective therapies. Here, we review the literature for all animal models of radiation retinopathy, summarize anatomical highlights pertaining to animal models, identify additional physiological factors to consider when investigating radiation retinopathy, and explore the use of clinically relevant tests for studying in vivo models of radiation retinopathy. We encourage further investigation into the mechanistic characterization of radiation retinopathy in the hope of discovering novel treatments.

Proton Beam Irradiation for Neovascular Age-Related Macular Degeneration

OBJECTIVE

To evaluate safety and visual outcomes after proton therapy for subfoveal neovascular age-related macular degeneration (AMD).

DESIGN

Randomized dose-ranging clinical trial.

PARTICIPANTS

One hundred sixty-six patients with angiographic evidence of classic choroidal neovascularization resulting from AMD and best-corrected visual acuity of 20/320 or better.

METHODS

Patients were assigned randomly (1:1) to receive 16-cobalt gray equivalent (CGE) or 24-CGE proton radiation in 2 equal fractions. Visual acuity was measured using standardized protocol refraction. Complete ophthalmological examinations, color fundus photography, and fluorescein angiography were performed before and 3, 6, 12, 18, and 24 months after treatment.

MAIN OUTCOME MEASURE

Proportion of eyes losing 3 or more lines of vision from baseline. Kaplan-Meier statistics were used to compare cumulative rates of vision loss between the 2 treatment groups.

RESULTS

At 12 months after treatment, 36 eyes (42%) and 27 eyes (35%) lost 3 or more lines of vision in the 16-CGE and 24-CGE groups, respectively. Rates increased to 62% in the 16-CGE group and 53% in the 24-CGE group by 24 months after treatment (P = 0.40). Radiation complications developed in 15.7% of patients receiving 16 CGE and 14.8% of patients receiving 24 CGE.

CONCLUSIONS

No significant differences in rates of visual loss were found between the 2 dose groups. Proton radiation may be useful as an adjuvant therapy or as an alternative for patients who decline or are not appropriate for approved therapies.

Experimental Posterior Perforating Ocular Injury in Rabbit Eyes: Effects of Radiotherapy with or without Intravitreal Cyclosporin on Vitreous Proliferation

Double perforating ocular injuries were made in 30 rabbits and the effects of radiotherapy (RT) alone or in combination with cyclosporin (CS) on vitreous proliferation investigated. Thirteen rabbits in group 1 received RT alone (600 cGy), and 13 rabbits in group 2 received RT combined with 100 microg of intravitreal CS. No treatment was given to 4 rabbits in the control group (group 3). All animals were ophthalmologically examined on the 1st, 3rd, 7th, 14th and 28th days following the injury and the clinical findings scored; they were sacrificed on the 28th day, and histopathological scoring was made. The median histopathological score of the RT group (4.0; range: 0-8) was significantly higher than that of the CS + RT group (1.0; range: 0-5; p = 0.018). We conclude that intravitreal CS may be used as an adjunctive agent to RT to inhibit intraocular proliferation following penetrating ocular injury in rabbits.

Results of radiotherapy of subfoveal neovascularization with 16 and 20 Gy

PURPOSE

In a nonrandomized, prospective study the efficacy of radiotherapy with 16 and 20 Gray (Gy) for subfoveal neovascularization in age-related macular degeneration (ARMD) was analysed.

MATERIAL AND METHODS

From 1996 to 1998, 63 eyes were irradiated with 16 Gy and 38 eyes with 20 Gy for exudative ARMD. A total of 12 eyes had classic ARMD, 89 eyes occult ARMD, median baseline visual acuity (VA) was 6/30 (range: 3/60-6/9.5), median age was 78 years. Risk factors (type of ARMD, baseline VA) were evenly distributed in both groups. Median follow-up was 1.3 years (range: 4 months-4.7 years). VA of +/-1 line or better and unchanged size and activity of the membrane in fluorescein angiography were defined as stable. Actuarial methods were used.

RESULTS

Median loss of VA was -3 lines (range: -14 to +5), neovascularization remained unchanged or decreased in size and activity in 35 eyes. At 18 months, the probability of stabilized VA was 0.4 (95% confidence interval (CI): 0.3-0.5), at 24 months 0.3 (95% CI: 0.2-0.4). Radiation dose, type of ARMD or baseline VA had no significant impact on outcome of VA and membrane size and activity (P>0.05). Side effects were mild and transient increased tearing.

CONCLUSION

In this study, the results after radiotherapy were comparable to the natural course of the disease. An impact of radiation dose (16 vs 20 Gy) on stabilizing visual acuity and subfoveal neovascularization could not be shown. The results of studies on dose escalation using very small fields and high radiation doses should be awaited.

Palladium-103 plaque radiation therapy for macular degeneration: results of a 7 year study

AIM

To report 7 year results of ophthalmic plaque radiotherapy for exudative macular degeneration.

METHODS

In a phase I clinical trial, 30 patients (31 eyes) were treated with ophthalmic plaque irradiation for subfoveal exudative macular degeneration. Radiation was delivered to a mean 2 mm from the inner sclera (range 1.2-2.4) prescription point calculated along the central axis of the plaque. The mean prescription dose was 17.62 Gy (range 12.5-24) delivered over 34 hours (range 18-65). Early Treatment Diabetic Retinopathy Study (ETDRS) type standardised visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a non-randomised and unmasked fashion.

RESULTS

At 33.3 months (range 3-4), 17 of 31 (55%) eyes had lost 3 or more lines of vision on the ETDRS chart, five (16%) had improved 3 or more lines, and the remaining nine (29%) were within 2 lines of their pretreatment visual acuity measurement. Overall, 45% of patients were within or improved more than 2 lines of their initial visual acuity. Five eyes developed macular scars, eight developed subsequent neovascularisation or haemorrhage, and three progressed through therapy. Two patients were lost to follow up. The most common finding of patients followed for 6 or more months (n=18 of 29 (62%)) was regression or stabilisation of the exudative process. No radiation retinopathy, optic neuropathy, or cataracts could be attributed to irradiation.

CONCLUSION

Ophthalmic plaque radiation can be used to treat exudative macular degeneration. At the dose and dose rates employed, most patients experienced decreased exudation or stabilisation of their maculas. No sight limiting radiation complications were noted during 7 year follow up. Owing to the variable natural course of this disease, a prospective randomised clinical trial should be performed to evaluate the efficacy of plaque radiation therapy for exudative macular degeneration.

Review Article. New treatments in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of legal blindness in individuals 50 years and older in the developed world. Choroidal neovascularization (CNV) in exudative AMD is responsible for the majority of severe vision loss. Until recently, laser photocoagulation was the only well-established and widely accepted treatment for CNV. However, it is beneficial only for a small subset of patients, has a high rate of CNV persistence and recurrence and results in iatrogenic, collateral damage to the overlying retina. These issues make it difficult to recommend in the case of subfoveal lesions. Consequently, numerous experimental therapeutic interventions are under investigation with the common objective of destroying the CNV but leaving the foveal neurosensory retina intact. Treatment modalities can be grouped into five major categories: photodynamic therapy; radiotherapy; transpupillary thermotherapy; anti-angiogenic and angiostatic agents; and surgical intervention. The present review aims to explain the rationale behind these new treatments, analyse the evidence for their safety and efficacy, determine their stage of development and indicate in which patients they are potentially useful.

External beam radiotherapy for subretinal neovascularization in age-related macular degeneration: is this treatment efficient?

PURPOSE

Control of the natural course of subretinal neovascularization (SRNV) in age-related macular degeneration (AMD) is difficult. Only a subset of patients is suitable for laser coagulation. This prospective study aimed to determine the efficacy and individual benefit of external beam radiotherapy (EBRT).

METHODS AND MATERIALS

The prospective trial included 287 patients with subfoveal neovascularization due to AMD which was verified by fluorescein angiography. Patients have been treated between January 1996 and October 1997. All patients received a total dose of 16 Gy in 2-Gy daily fractions with 5-6 MeV photons based on computerized treatment planning in individual head mask fixation. This first analysis is based on 73 patients (50 women, 23 men, median age 74.3 years), with a median follow-up of 13.3 months and a minimum follow-up of 11 months.

RESULTS

All patients completed therapy and tolerability was good. First clinical control with second angiography was performed 6 weeks after irradiation, then in 3-month intervals. Eighteen patients with SRNV refusing radiotherapy served as a control group and were matched with 18 irradiated patients. After 7 months median visual acuity (VA) was 20/160 for the irradiated and 20/400 for the untreated patients. One year after radiotherapy final median VA was 20/400 in both groups.

CONCLUSION

These results suggest that 16 Gy of conventionally fractionated external beam irradiation slows down the visual loss in exudative AMD for only a few months. Patients' reading vision could not be saved for a long-term run.

Radiation therapy for age-related macular degeneration

Neovascular age-related macular degeneration is the most common cause of severe irreversible blindness in the Western world in people older than age 50. Laser photocoagulation is the only proven treatment for this disease; however, fewer than 20% of patients are eligible for this treatment because the majority of choroidal neovascularization membranes are not visible by ophthalmoscopy or angiography. In addition, many patients elect not to undergo this treatment because laser treatment of subfoveal neovascular membranes results in immediate and permanent central visual loss. Several treatments are under investigation, including external-beam radiation therapy. There are multiple publications of early trials using radiation therapy, but to date there is only one randomized published study. This article reviews these trials and summarizes the status of radiation therapy as a treatment for macular degeneration.

Ophthalmic plaque radiotherapy for age-related macular degeneration associated with subretinal neovascularization

PURPOSE

To evaluate ophthalmic plaque radiotherapy for the treatment of subretinal neovascularization associated with age-related macular degeneration.

METHODS

In a prospective phase I clinical trial, we treated 23 patients (23 eyes) with ophthalmic plaque radiotherapy for subfoveal exudative macular degeneration. Palladium 103 ophthalmic plaque brachytherapy was delivered to a retinal apex dose of 1,250 to 2,362 cGy (rad). Early Treatment Diabetic Retinopathy Study type visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a nonrandomized and unmasked fashion.

RESULTS

Patients were followed up for a mean (+/-SD) of 19 +/- 10.7 months (range, 3 to 37 months). Six months after radiation therapy, three (16%) of 19 eyes had lost 3 or more lines of best-corrected visual acuity; 12 months after radiation therapy, four eyes (31% of 13 eyes), and 24 months after radiation therapy, only two (22% of nine eyes) lost 3 or more lines of visual acuity. No eye suffered sudden irreversible loss of central vision. No radiation retinopathy, optic neuropathy, or cataract could be attributed to radiotherapy within this follow-up period.

CONCLUSION

Ophthalmic plaque radiotherapy can be used to treat neovascular age-related macular degeneration. In contrast to external beam radiotherapy, ophthalmic plaque radiotherapy is a unilateral treatment, which allows a larger dose to be delivered to the macula with less irradiation of normal ocular structures. We have found no sight-limiting complications at the doses, dose rates, and follow-up evaluated in this study.

Treatment options In subfoveal choroidal neovascularization secondary to age-related macular degeneration

Laser photocoagulation of the entire area of the neovascular lesion is the only proven treatment for subfoveal choroidal neovascularization secondary to age-related macular degeneration with a poor natural history. However, there are some limiting factors such as patient eligibility, a significant decline in visual acuity after treatment, and a very low possibility of a final vision of 20/100 or better. Although no large benefit of other treatment modalities, such as indocyanine green videoangiography-guided laser photocoagulation, surgical removal of neovascular membranes, and radiation therapy, has yet been proven, carefully selected patients may be suitable candidates for such treatments. This article reviews the status of treatment modalities for subfoveal choroidal neovascularization secondary to age-related macular degeneration, including laser photocoagulation of the entire area of the neovascular lesion, and discusses factors prognostic of visual outcome in these treatment options.

Strontium plaque irradiation of subfoveal neovascular membranes in age-related macular degeneration

PURPOSE

To determine the effect of focal strontium-90 plaque radiotherapy on subfoveal choroidal neovascularization in patients with age-related macular degeneration.

METHODS

Twenty patients with age-related macular degeneration, presenting with a recent subfoveal neovascular membrane, were treated with local episcleral radiotherapy using a strontium-90 applicator. The applicator was applied to the sclera under the macular region and held there tightly for 54 min to obtain a dose of 15 Gy at a depth of 1.75 mm. The main parameters evaluated at follow-up after 3, 6 and 12 months were visual acuity and changes in fluorescein angiography. Twelve untreated patients with the same criteria were followed as controls.

RESULTS

Early effects of radiation could be seen at 3 months, but became more obvious after follow-up for 6 and 12 months. At 6 months, regression of the choroidal neovascularization was detected in 14/19 patients (74%) as a decrease in the size of the lesion or as diminished leakage in late-phase fluorescein angiography. Likewise, in 14/19 patients (74%) at 12 months the neovascular membrane was partially or totally occluded. In all patients showing regression of the choroidal neovascular membrane, the neurosensory detachment had also dried. Visual acuity was unchanged (within 1 line) or improved in 11/20 (55%) and 9/20 (45%) treated patients after 6 and 12 months, respectively. In the controls, the choroidal neovascularization had increased in size in 9/12 patients (75%) at the last follow-up (mean 12.0 months). Visual acuity was unchanged in 3/12 patients (25%).

CONCLUSION

Local low-energy beta irradiation with a strontium-90 applicator can induce regression of choroidal neovascularization. The effect of irradiation is seen as a decrease in the size of the choroidal neovascular membrane and disappearance of the neurosensory detachment and exudates.

[Radiotherapy and age-related macular degeneration: a review of the literature]

Macular degeneration is a major health problem. Less than 10% of the cases can be successfully treated by laser therapy. Low dose radiation therapy (in the range of 20 Gy) appears to decrease neovascularisation. These early results need to be confirmed through a randomized trial.

Radiation therapy for subretinal neovascularization

PURPOSE

To evaluate low-dose external beam irradiation and plaque radiotherapy for the treatment of subretinal neovascularization.

METHODS

The authors treated 137 patients with radiation therapy for subretinal neovascularization. Herein, they examine a subset of 75 patients with exudative age-related macular degeneration who were treated with (4- or 6-MV photons) external beam irradiation at a dose of 1200 to 1500 cGy to the affected macula. In addition, six patients were treated with palladium 103 ophthalmic plaque brachytherapy to an equivalent retinal apex dose of 1200 to 1500 cGy. The authors compared the intralesional, intraocular, and intracranial radiation dose distributions of each treatment modality. Early Treatment Diabetic Retinopathy Study-type visual acuity determinations, ophthalmic examinations, and angiography were performed before and after treatment. Clinical evaluations were performed in a nonrandomized and unmasked fashion.

RESULTS

Episcleral plaque brachytherapy was found to provide a higher average radiation dose within the neovascular tissues while delivering less radiation to most normal ocular (both eyes) and all intracranial structures. Both forms of radiotherapy were associated with decreased hemorrhages, exudates, and leakage of neovascular membranes. Ten (13 percent) patients receiving external beam radiotherapy had transient epiphora and ocular irritation.

CONCLUSION

Observation and laser photocoagulation of subfoveal neovascularization have been associated with poor visual outcomes. Pilot experience suggests that low-dose radiotherapy offers a method to treat subretinal neovascularization without destroying the overlying retina. Although the authors' radiation distribution studies favored plaque radiotherapy, additional factors such as relative efficacy, expense, convenience, and safety must be investigated.

Treatment of age-related subfoveal neovascular membranes by teletherapy: a pilot study

This investigation was designed to determine whether low dose radiation to the macular region could influence the natural course of age-related subfoveal neovascularisation. Nineteen patients with subfoveal membranes due to age-related macular degeneration (ARMD) were treated with 10 or 15 Gy of 6 MV photons and seven patients who declined treatment were followed up as controls. Six controls and all treated patients had completed follow up times of at least 12 months. Visual acuity was maintained or improved in 78% and 63% of treated patients at their 6 and 12 month follow up examinations respectively. By contrast visual acuity showed steady deterioration in six of seven controls. Significant neovascular membrane regression, as measured by image analysis, was recorded in 68% and 77% of treated patients at 6 and 12 months post-radiation, whereas the membranes in all seven control patients showed progressive enlargement. This study suggests that low doses of radiation can maintain central vision and induce regression of subfoveal neovascular membranes of ARMD in a significant proportion of patients. We now believe it appropriate to proceed to a prospective randomised study to test this hypothesis further.