November 2010

 

OPHTHALMOLOGY NEWS

 

Novel method for eye cancer radiation treatment


by Faith A. Hayden EyeWorld Staff Writer

   

UCLA researchers unveil use of silicon oil may reduce vision loss

Dr. McCannel, M.D., Ph.D., evaluates the use of silicon oil during radiation treatment

Eye cancer patients and the ophthalmologists treating them face an unfortunate reality when battling ocular melanoma: the radiation treatment that may save the patient's life may also cost the patient his eyesight. Vision loss during ocular melanoma treatment "is extremely discouraging to see day in and day out," said Tara McCannel, M.D., Ph.D., assistant professor of ophthalmology, and director, Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles (UCLA). "You know you're doing something, but it seems like we're really blinding these people with radiation."

But hopefully, that won't be the case for much longer. New research by Dr. McCannel and coworkers suggests that 1,000-centistoke (cSt) silicon oil, a material commonly used during retina surgeries, absorbs nearly 50% of the radiation used during treatment.

Incorporating silicon oil into the procedure is fairly simple. During the surgery, the vitreous gel is replaced with silicon oil and flushed away with saline after the radiation plaque is removed. "If you can cut down the radiation exposure by about half, that could be very significant," Dr. McCannel said. During their research, the team tested on autopsy eyes four substances that are already green-lighted for ophthalmic use: 1,000-cSt silicone oil, 5,000-cSt silicone oil, heavy oil, and perfluorocarbon. All of the materials had some blocking effect, but 1,000-cSt silicone oil had the highest with 48%. Dr. McCannel describes the research as a real "shot in the dark" stemming from a back hallway discussion. "We were thinking that maybe these materials have some side property where they block radiation," she explained. "It was really anybody's guess." Luck may have played a role in the discovery but so did ingenuity. Dr. McCannel knew that the damage to the eye was occurring while the radiation treatments were taking place, so it was imperative to come up with a method that could be used upfront. She also wanted to use common materials in order to help as many patients as quickly as possible. "If you design something that is very novel and very helpful, it often takes years before it gets approval," Dr. McCannel explained. "But these are things right off the shelf." "As soon as the concept was developed I realized how important it could be," said Bradley R. Straatsma, M.D., Jules Stein Eye Institute. "First off, it can be done by a skilled surgeon in a relatively short amount of time. It does have a clearly effective therapeutic benefit." Incorporating silicon oil into the procedure only takes an extra 15 or 20 minutes, and its transparency allows both the patient and surgeon to see through it. Most importantly, the oil doesn't interfere with the effectiveness of the radiation. "Tumors continue to shrink despite silicon oil in the eye, and patients tolerate it very well," Dr. McCannel said. Despite all the positives, silicon oil use isn't for everyone, and there are additional complications to consider. Dr. McCannel sees no purpose in adding the extra step for patients whose vision is already poor due to a tumor affecting their macula. She also sees no need to use the new method on patients with small tumors on the periphery of their retina because those patients tend to do well visually regardless. "People who have a higher risk based on where the tumor is located are the good candidates for this," she said. "I think it's going to be selective, but it's one of those incremental advances that improve our ability as ophthalmologists to render safe and effective care," Dr. Straatsma said. Patients need to be aware that because a vitrectomy is performed, they will develop cataracts earlier in life. There's also a risk of retinal detachment. "These patients need a little more follow-up," she said. "Most importantly, they have to understand that this is something that's completely new."

The silicon oil discovery is certainly better than nothing, but Dr. McCannel admits there is more work to be done. Currently, she is working with UCLA chemists and physicists to come up with a novel material that works even better than silicon oil, but due to the long approval process, this will take some time. Also, the patients who have used the silicon oil treatment method need to be followed carefully to see how their vision is affected. "We need to look back at our results in a few years," Dr. McCannel said. "I look forward to reporting on how patients are doing over a period of time. In the first six months, it does look like people are doing well, at least anecdotally. It's a good start, but we need to look at these people more carefully."

Editors' note: Drs. McCannel and Straatsma have no financial interests related to this study.

Contact information

McCannel: 310-206-7484, tmccannel@jsei.ucla.edu
Straatsma: 310-825-5051, ewing@jsei.ucla.edu

Novel method for eye cancer radiation treatment Novel method for eye cancer radiation treatment
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