This gives radiation oncologists the ability to deliver a full dose of radiation to the entire structure of a tumor while reducing the risk of damage to surrounding normal tissues, according to Ronald W. Thompson, M.D., Director of Radiation Oncology at Cedars-Sinai. While stereotactic radiation is used in other parts of the body, it is especially valuable in treating tumors in the brain and near the spinal cord.
Stereotactic radiation therapy directs precise dose of radiation to the tumor from a variety of preselected angles. No single "path" to the tumor is exposed to a large dose of radiation, sparing the normal tissues, but the tumor is bombarded by radiation from multiple directions. Critical structures, such as the brain stem and optic nerves, are protected from exposure.
The Radionics® ConforMAX Mini-Multileaf Collimator (mMLC(tm)), approved for use by the Food and Drug Administration earlier this year, is a device that attaches to a linear accelerator to focus and direct the radiation beam generated by the accelerator.
The mMLC can be used in traditional radiation therapy conducted over a period of days or weeks to expose a tumor to repeated doses of radiation. It also can be used to perform radiosurgery, which may be accomplished in a single visit, usually on an outpatient basis. Unlike traditional surgery, the surgeon uses the convergence of radiation beams to destroy a tumor, rather than a scalpel to remove it. Therefore, the tumor may be obliterated without "open" surgery and the associated recovery time and risk of complications.
The mMLC functions in conjunction with Radionics' Xplan® treatment planning software. Because tumors vary greatly in size, density, shape and location, the computer program is able to view each tumor as a three-dimensional object, takes into consideration nearby vital tissues and structures, and the various angles and doses of radiation are rapidly calculated and displayed for review.
The mMLC's capabilities are perfectly suited to the needs of Tim Evans, a 52-year-old patient from Las Vegas who was among the first to be treated with the new system at Cedars-Sinai, said Dr. Thompson. In 1991, Evans had undergone surgery to remove a choroid plexus papilloma, a slow-growing benign tumor that was located near his brain stem. That operation was performed at the University of California Los Angeles by neurosurgeon Keith Dr. K. Black.
Because of the tumor's location, Dr. Black removed nearly all the tumor without damaging the brain stem but informed Evans that the tumor would probably return in 8-10 years. About a year ago, Evans began to notice excessive fatigue and an unusual lack of energy. Magnetic resonance imaging confirmed that the tumor had grown back and a second tumor had developed near his optic nerve.
Evans and his wife, Noreen, came to Cedars-Sinai because Dr. Black now directs the hospital's Maxine Dunitz Neurosurgical Institute and because the mMLC technology and expertise are not available in the Las Vegas area. "Their HMO was very cooperative in allowing him to be treated here," said Dr. Thompson.
Dr. Black and Dr. Thompson prescribed a 26-treatment radiation course, which started on July 28. With the mMLC, full doses of radiation can be directed at both tumors while protecting the brain stem and the optic nerve.
"This is a fantastic way of doing things versus having them open up your brain and go inside and cut the tumors out," said Evans.
While other stereotactic radiosurgery devices use gamma rays, Radionics' system employs X-ray radiation and is highly adaptable and effective in treating a variety of benign and malignant tumors within the brain and along the spinal cord.
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