Metastatic Brain Tumors - Patient Information

Information for Physicians
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Definition

Many cancers metastasize. Metastasis is the spread of cancer from one part of the body to another. The original location is called the primary tumor. Metastatic tumors are tumors that arise at sites away from the original location.

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Cancer cells from the primary site can break away and enter the body's circulatory system blood stream [arteries and veins], lymph system or spinal fluid [Spinal fluid is the liquid that flows between the layers of the meninges. It circulates around the brain and spinal cord.] and travel to distant locations. Stray cancer cells are often destroyed by the immune system. But, if the number of stray cells is too large, the immune system may be overwhelmed and allow some cancer cells to survive. Those cells will grow at another site. The most common pathway for metastasis to the central nervous system is via the blood stream.

Many variables determine where metastatic tumors grow. Often, the metastatic location is the nearest cluster of small blood vessels found by the circulating cancer cells. Thus lung cancer commonly metastasizes to the brain; colon cancer commonly metastasizes to the liver. Or, the cancer may have a preferred site of metastasis. The brain is a preferred site for melanoma and small cell lung cancer. A metastasis of a metastasis may develop as well a colon cancer may metastasize to the liver which in turn may metastasize to the lung which may in turn metastasize to the brain.

Tumors in the brain are the most common form of central nervous system metastasis. There may be single or multiple tumors. Metastatic brain tumors often have distinct characteristics that can be observed on scans and help distinguish them from primary brain tumors [Primary brain tumors originate in the brain; metastatic brain tumors originate elsewhere in the body]. However, an exact determination of the type of tumor can usually be made only after a sample of the tumor is examined under the microscope.

How does Gamma Knife treat metastatic brain tumors?

The gamma knife is a radiation delivery tool that is dedicated exclusively for the treatment of skull-based tumors and malformations. As such, it is very accurate - with sub-millimeter precision (<.3mm)- less than half the width of a human hair. So healthy tissue is spared while a cancer-destroying dose is delivered to the tumor.

What makes a gamma knife so accurate and effective? The head is fixed in a frame that keeps the brain stable and unmoving. This head frame resembles that of a 'halo' apparatus used in neck injury patients. It goes on without much discomfort while the patient feels some pressure sensation once it is affixed.

The other factor that aids in accuracy is the fixed isocenter of radiation - 201 sources of Cobalt -60 radiation that focus at a single point (fixed isocenter). The Gamma Knife of Spokane can reach multiple metastases, tumors found deep in the brain and tumors that are near critical structures in the brain with one single dose (thus the term 'radiosurgery' versus 'radiotherapy'). A patient can also be treated multiple times should new tumors arise over the course of treatment for systemic disease.

So you have access to a $5 million, 45,000 pound cancer-killing machine that can, in less than a few hours, deliver a dose of radiation that can stop the growth of most tumors and even eliminate other tumors altogether. You or your loved one will be treated in the morning, admitted overnight, and in most cases can go home the next morning.

If you have any questions about your treatment, call our nurse coordinator, Jill Adams, at 509.473.3800.

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