Proton beam irradiation of subfoveal choroidal neovascularisation in age-related macular degeneration

PURPOSE

To assess the safety and potential toxicity of proton beam radiation in the treatment of subfoveal choroidal neovascular membrane (CNVM) due to age-related manner degeneration (ARMD) in a prospective, non-randomised study.

METHODS

Forty-eight eyes of 46 consecutive patients with subfoveal CNVM due to ARMD, not amenable to laser photocoagulation, were treated prospectively with a single proton beam exposure. Two dose regimens were evaluated: 8 CGE (Cobalt Gray Equivalent) and 14 CGE. Patients were followed for an average of 22.1 months after proton beam treatment.

RESULTS

At the 12 month follow-up, 44% of eyes in the 8 CGE group and 75% of the eyes in the 14 CGE group had stabilized or improved visual acuity. Complex size in the 8 CGE group as measured on standard fluorescein angiography (FA), decreased or had no change initially but showed less effect over time, while the eyes treated with 14 CGE maintained decreased leakage over the follow-up period of 12 months. However, 11 eyes in the 14 CGE group experienced radiation retinopathy, with the onset between 3 and 30 months. Seven of these 11 eyes have demonstrated some visual loss but only 1 eye developed severe visual loss at 15 months after proton treatment.

CONCLUSIONS

To date, 14 CGE has suggested a favourable influence on visual function and growth inhibition of CNVM. Proton beam irradiation appears to inhibit CNVM growth. The 14 CGE dose regimen appears to have a longer effect of CNVM growth than does 8 CGE, with overall stabilisation of visual function and growth inhibition. Radiation retinopathy has developed over time, but severe visual loss has been limited. On the basis of the incidence of radiation retinopathy, adjustments in the total radiation dosage and/or fractionation of the dosage should be considered.

Treatment of macular degeneration with proton beams

Subfoveal neovascular membranes (SNVMs) are a leading cause of severe visual loss in the elderly in the United States. Previously, the only treatment that could halt progression of this disease was laser photocoagulation, which was, however, accompanied by immediate reduction in visual acuity. A single narrow proton beam was used to irradiate 45 patients to either 8 or 14 Cobalt Gray Equivalent. The alignment technique and dosimetry of these treatments are described. The proton beam direction, range, and modulation were planned with the assistance of an eye-specific planning program. A single anterior beam was used, with patients looking nasally toward a blinking fixation light at an angle of 30 degrees. Patients were aligned using a light field projected through a slit collimator. Patients' positions were monitored during treatment with a short-focal-length camera. Depth dose in a flat phantom was measured with a small-diameter parallel plate ionization chamber. Lateral profiles were measured at several depths with silver halide film. Each treatment session lasted 15 min, of which 1 min consisted of beam delivery. The proton beam stopped in the orbital cavity, delivering no primary proton dose to the brain. Dose to the center of the lens of the involved eye was less than 0.5% of the dose delivered to the macula. Treatments of SNVMs with proton beams require only a short visit to the hospital, little immobilization effort, and a minimal amount of treatment room and beam time. Compared to previous treatment trials using x-ray beams, the dose to nonocular tissues is reduced significantly.

Phase I/II study of proton beam irradiation for the treatment of subfoveal choroidal neovascularization in age-related macular degeneration: treatment techniques and preliminary results

PURPOSE

Age-related macular degeneration is the prevalent etiology of subfoveal choroidal neovascularization (CNV). The only effective treatment is laser photocoagulation, which is associated with decreased visual acuity following treatment in most patients. This study assessed both the response of subfoveal CNV to proton beam irradiation and treatment-related morbidity. We evaluated preliminary results in patients treated with an initial dose of 8 Cobalt Gray Equivalents (CGE) using a relative biological effectiveness (RBE) of 1.1.

METHODS AND MATERIALS

Twenty-one patients with subfoveal CNV received proton irradiation to the central macula with a single fraction of 8 CGE; 19 were eligible for evaluation. Treatment-related morbidity was based on Radiation Therapy Oncology Group (RTOG) criteria; response was evaluated by Macular Photocoagulation Study (MPS) guidelines. Fluorescein angiography was performed; visual acuity, contrast sensitivity, and reading speed were measured at study entry and at 3-month intervals after treatment. Follow-up ranged from 6 to 15 months.

RESULTS

No measurable treatment-related morbidity was seen during or after treatment. Of 19 patients evaluated at 6 months, fluorescein angiography demonstrated treatment response in 10 (53%); 14 (74%) patients had improved or stable visual acuity. With a mean follow-up of 11.6 months, 11 (58%) patients have demonstrated improved or stable visual acuity.

CONCLUSION

A macular dose of 8 CGE yielded no measurable treatment morbidity in patients studied. Fluorescein angiography demonstrated that regressed or stabilized lesions were associated with improved visual acuity as compared with MPS results. In the next phase, a dose of 14 CGE in a single fraction will be used to further define the optimal dose fractionation schedule.

Treatment of idiopathic macular holes by induced posterior vitreous detachment

PURPOSE

To determine if an expansile gas bubble can relieve vitreofoveal traction without vitrectomy by inducing a posterior vitreous detachment (PVD) in eyes with an idiopathic impending or full-thickness macular hole (stages 1-3). The status of the impending and full-thickness macular holes after gas injection and tamponade also was studied secondarily.

METHODS

Eighteen patients participated in this pilot study. Eleven patients with an impending macular hole (stages 1A and 1B) and seven patients (8 eyes) with a full-thickness macular hole (stages 2 and 3) received gas injections and prospectively were followed for an average of 15.6 months (range, 3-42 months).

RESULTS

A complete PVD was achieved in 18 of 19 eyes without a prior PVD within 2 to 9 weeks after gas injection. Ten of the 11 impending holes (all 7 had stage 1A holes; 3 of 4 had stage 1B holes) resolved after gas injection. After gas tamponade, three of six early full-thickness (stage 2) macular holes closed. None of the stage 3 macular holes closed after gas injection. The mean best-corrected visual acuity of the successful eyes was 20/32. There were no major complications.

CONCLUSION

An expansile gas bubble consistently can induce a PVD in aging eyes. The ability of an expansile gas bubble to induce a PVD with minimal morbidity and expense may have clinical applications for macular hole therapy. Impending macular holes may resolve and some early full-thickness (stage 2) macular holes may close after gas injection and tamponade without vitrectomy. The efficacy and safety of this procedure may be evaluated further in the context of a carefully designed prospective and randomized study for selected patients with an idiopathic impending or early macular hole.

Immunohistochemical comparison of transscleral continuous wave 1064-Nd:YAG laser retinopexy and cryoretinopexy

BACKGROUND

Transcleral retinopexy may be applied with either a cryoprobe or the newer contact laser delivery systems. Tissue responses to these modalities are studied.

METHODS

Transcleral 1064-nm continuous wave neodymium-ytrium-aluminum garnet (CW Nd:YAG) laser retinopexy lesions were compared with retinopexy lesions produced by a cryoprobe in a pigmented rabbit model. Equatorial transcleral CW Nd:YAG laser retinopexy or cryoretinopexy was applied. Rabbits were killed 1 day, 3 days, 1 week, or 1 month after treatment. Hematoxylin and eosin stains and immunohistochemical studies were conducted to determine the level of retinal damage and glial reaction. Antibodies against Müller cells (vimentin and glial fibrillary acidic protein), astrocytes (glial fibrillary acidic protein and S-100 protein), retinal pigment epithelial (RPE) cells (cytokeratin 8, 18, and 19 [5D3]), and macrophages (HAM 56) were used.

RESULTS

Lesions produced by cryotherapy showed significant overlying retinal destruction with intravitreal RPE cell (5D3 positive) migration. Lesions produced by transcleral CW Nd:YAG laser showed reaction primarily at the level of choroidal melanocytes and RPE. Marked expression of both glial fibrillary acidic protein and vimentin epitopes with a normal expression of S-100 was seen in the chronic lesion made with cryotherapy and with less intensity in lesions made with CW Nd:YAG laser.

CONCLUSION

Although less inner retinal destruction and no intravitreal RPE migration was observed in lesions formed by transcleral CW Nd:YAG laser, similar deep retinal Müller cell reaction occurred in lesions formed by both cryotherapy and laser as demonstrated by immunohistochemical studies.