"Enucleation is the historical way of treating ocular melanoma, but radiotherapy has been shown to be as effective as enucleation, and proton-beam therapy is the radiation treatment of choice for ocular melanoma," said Susanna Park, associate professor of ophthalmology and vision sciences. "We're proud to be able to offer this advanced treatment option to patients in our region."
Survival rates for ocular melanoma patients who undergo proton-beam treatment match or exceed those of patients who opt for enucleation, and many proton-beam patients are able to keep their eyesight.
Proton-beam treatments take place in Davis at the UC Davis Crocker Nuclear Laboratory. The laboratory houses the particle accelerator that generates the charged protons used to destroy the tumors. Only six of these machines are in medical use nationwide.
Eye specialists at UC San Francisco have used the UC Davis accelerator to treat ocular melanomas since 1994. This has required proton-beam patients from the Central Valley and inland Northern California to travel to San Francisco for pre-treatment evaluation, preparation, surgery and follow-up. (Surgery is needed prior to proton-beam treatment to stitch small metal rings around the perimeter of the tumor. The rings show up clearly on X-rays and serve as guideposts for the proton-beam treatments.)
Surgery and follow-up are now available at UC Davis Medical Center, thanks to the recent recruitment of Park, a vitreo-retinal surgeon trained in proton-beam therapy at Harvard University/Massachusetts Eye & Ear Infirmary. For now, patients still must make one trip to UCSF for radiation treatment planning and to be fitted with a face mask and bite block. However, these services will also be offered at UC Davis Medical Center as the proton-beam therapy program expands.
Conventional radiation therapy kills cancer cells with gamma rays, which deliver energy to all the tissues they travel through, from the point they enter the body until they exit it. Proton beams, in contrast, drop almost all of their energy on their target. Dosing is so exact that tissue just one-tenth of an inch from the target receives almost no radiation. Because damage to healthy tissue is minimized, doctors can treat cancers with higher and more effective radiation doses. Proton-beam therapy is especially well-suited to treat tumors near delicate structures like the optic nerve or retina.
Although proton-beam therapy dates to 1954, the size and cost of the particle accelerators needed to produce the charged protons have limited its availability, leading the Wall Street Journal last year to call proton-beam radiation "a well-kept secret in the war on cancer."
A 90,000-square-foot building -- bigger than many hospitals -- is needed to house a state-of-the-art proton-beam accelerator. And the machines carry price tags of up to $150 million.
The other five other centers with proton-beam accelerators are Loma Linda Medical Center in Loma Linda, Calif., MD Anderson Cancer Center in Houston, Midwest Proton Radiotherapy Institute in Bloomington, Ind., Massachusetts General Hospital in Boston, and the University of Florida Proton Therapy Institute in Jacksonville. These accelerators are large enough to treat other cancers as well, while the Davis machine treats only eyes.
Scientists at UC Davis Cancer Center and Lawrence Livermore National Laboratory, however, are completing a prototype of a new-generation proton-beam machine that will be capable of treating cancer anywhere in the body at a fraction of the size and cost of existing full-body machines. The first compact proton-beam accelerator will be housed at UC Davis Cancer Center.
For Michael Bone, a Fair Oaks veterinarian who was recently diagnosed with retinal melanoma, the decision to choose proton-beam therapy over enucleation was an easy one.
"I keep my eye," Bone said. "And because the radiation is so controlled, I don't have to worry about collateral damage to healthy eye tissue, so there's very little risk of vision loss."
A few days after his final proton-beam treatment at the Crocker Nuclear Laboratory at UC Davis earlier this year, Bone was waist-deep in the American River, casting flies.
He had no vision loss, and better than a 90-percent chance for a full cure.
UC Davis Cancer Center is the nation's 61st National Cancer Institute-designated cancer center. It cares for more children and adults with eye cancer than any other center in inland Northern California, offering the latest and most advanced medical and surgical treatments available for intraocular melanoma, retinoblastoma and other malignancies affecting the eye.
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