Trial Information

A Prospective Pilot Study of Surgical Radiation Shielding With Vitrectomy and Silicone Oil Tamponade for the Protection of Radiation-induced Ocular Injury in the Treatment of Choroidal Melanoma With Radioactive Iodine-125 Plaque Brachytherapy

Melanoma arising from the choroid and ciliary body is the most common primary intraocular
cancer.1 The Collaborative Ocular Melanoma Study (COMS) randomized clinical trial of I-125
brachytherapy versus enucleation for medium-sized choroidal melanoma (2.5-10.0 mm in
thickness and ≤ 16 mm in diameter) showed that, for patients who met the eligibility
criteria, there was no statistically significant difference in all-cause mortality between
I-125 brachytherapy and enucleation 5, 10, and 12 years following treatment.2-4 The COMS
trial supported the use of globe-conserving I-125 brachytherapy. Following brachytherapy,
however, visual acuity in the treated eye generally declined at a rate of approximately 2
lines of visual acuity per year and nearly 45% of patients lost ambulatory vision (≤20/200)
in the treated eye by 3 years.5

Adverse effects of plaque brachytherapy include cataract, radiation-associated proliferative
retinopathy, maculopathy and papillopathy. Radiation maculopathy, which may result in
decreased central vision, cystoid macular edema (CME), macular ischemia, and chorioretinal
atrophy, was reported in other series in 18% to 43% of treated eyes within 5 years after
brachytherapy.6, 7 Typical onset occurred 18-24 months following treatment.6, 8 Primary
risk factors for radiation papillopathy and maculopathy were total radiation dose to the
affected structures, proximity of the tumor to the affected structures and systemic
conditions such as diabetes mellitus.7, 9, 10 No treatment for radiation maculopathy or
papillopathy has been proven to be effective in a randomized clinical trial.

Radiation injury to vital structures may be avoided or shielded with the use of materials
such as lead that have a higher effective atomic number and density than tissue. However,
solid metals are not amenable to use within the eye (Figure 1).11

There have been previous efforts to try to use a vitreous substitute in order to protect
intraocular structures from the deleterious effects of radiations.12 In an animal study,
Finger et al, demonstrated that iodinated contrast agents (iophendylate, iohexol, and
iopamidol) could block radiation intraocularly. But these substances were highly toxic and
could not be retained in the eye due to high water solubility.12

The technique of vitrectomy and oil tamponade during plaque brachytherapy has been performed
previously in humans by Dr. Tara McCannel at UCLA. During a paper presentation at the 2010
meeting of the American Society of Retina Specialist in Vancouver, BC, the first series of
10 patients were presented, and no complications of the technique were reported. It is now
a commonly applied technique at this center for treatment of choroidal melanoma (Oncology
Times 2010; 32(14):36, UCLA, Clinical Update 2011; 20(1):1, 4)

In this prospective pilot study the investigators propose that patients will undergo
standard plaque placement for treatment of their ocular melanoma in addition to pars plana
vitrectomy and silicone oil infusion. When patients return for their scheduled plaque
removal one week later, they will also undergo removal of the silicone oil from the eye.
Placement of silicone oil should not alter the radiation dose delivered to the tumor, as
there is no physical space between the tumor and the radioactive plaque for silicone oil to
be present. The reduction in radiation to healthy ocular structures by using the oil
technique may be sufficient to avoid the clinical complications caused by radiation-induced
injury.