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Posted: 10:36 AM Nov 4, 2006
Targeting Cancer
Treatment technique expands A successful cancer therapy, once used only to treat brain tumors, is now making the move to the rest of the body.
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A successful cancer therapy, once used only to treat brain tumors, is now making the move to the rest of the body.
Kyle Williams has colon cancer that spread to her liver and doctors recently did a practice run leading up to her radiation therapy.
Kyle says, "With the radiation, they feel like they can really just totally destroy it and reduce your chance of it coming back.”
Stereotactic body radiation therapy requires a lot of pre-planning. Doctors program multiple beams of radiation to zap a tumor that could be the size of a pea.
Dr. Robert Timmerman says, "The dose to the tumor is very high and if it’s done right the dose to the normal tissues around it is very low.”
The technology has been used for years to treat brain tumors. The difference is the skull keeps the brain from moving. The body moves a lot.
Dr. Timmerman says, "Your patients need to breathe and they need to have their hearts beating and their bowels will churn whether they want them to or not.”
Body casts are made to keep patients in position during treatments. A compression plate gets them to breathe at the chest instead of the diaphragm.
Dr. Timmerman says, "Instead of having the tumor go up and down with each breath three centimeters, we have it go up and down maybe one centimeter.”
But even if the tumor moves, doctors can adjust the radiation beam to follow it.
Doctors plan and practice the therapy ahead of time on 3-D images of the tumor. Because the radiation is so potent and so precise, patients need fewer treatments.
Kyle Williams says, "They're looking at maybe five treatments over the course of 12 days.”
That's a big improvement over the 30 to 35 treatments needed in the past.
Doctors are using stereotactic body radiation therapy on lung and liver tumors. Studies are needed to see how effective the treatment will be in other parts of the body.
Fast Facts:
Colorectal Cancer
Colorectal cancer is the third most common cancer diagnosis in the U.S. and the second leading cause of cancer death. The American Cancer Society estimates 148,610 new cases will be diagnosed this year. About 55,170 men and women will die of the cancer.
Colorectal cancer is more common in older people – more than 90 percent of cases are diagnosed after 50. Family history of the cancer, personal history of polyps or prior diagnosis of colorectal cancer, personal history of inflammatory bowel disease, a high-fat diet, obesity, lack of physical activity, diabetes, smoking and excessive consumption of alcohol are associated with an increased risk for colorectal cancer.
If colorectal cancer is detected while the disease is in early stages (before it has spread), five-year survival rates are about 90 percent. But only 39 percent of the cancers are diagnosed at this stage. The cancer first spreads (metastasizes) into the lymph nodes, then to other sites of the body. After the lymph nodes, the most common site of metastasis is the liver. In many cases, there are no obvious signs of liver metastases. Symptoms that occur can include: weight loss, jaundice, fever, body sweats or pain in the upper right abdomen.
Treating Liver Metastases
Treatment for liver metastases depends upon the extent of the cancer, the size and location of the tumor(s) and the health of the patient. Sometimes a single tumor can be removed surgically by taking out a portion of the liver. Surgery may also be possible if the cancer is confined to one section of the liver. Chemotherapy (treatment with anti-cancer medication) may also be helpful. Sometimes the chemotherapy drugs can be administered in higher concentrations directly into the site of the tumor through a catheter. Some tumors can also be treated with cryoablation (killing the tumor cells with freezing temperatures), microwave energy or radiofrequency energy.
Stereotactic Body Radiation Therapy
In conventional radiation treatment, small doses of X-ray energy are aimed at the tumor from a source outside the body. Since the treatment damages healthy tissue as well as cancerous tissue, doctors are limited as to how much radiation can be given at one time. Doctors figure out how much radiation is needed to kill the tumor and divide the doses into small amounts. Generally, patients get 30 to 35 treatments over a month to a month-and-a half. Over time, the effects of the radiation are cumulative, adding up to the total dose.
Some physicians are now using a technique called stereotactic body radiation therapy for patients with liver metastases. In this treatment weak beams of radiation are aimed from many different directions. When added together, the tumor receives a large dose of radiation. However, healthy tissues are more protected because the radiation energy is spread over many points of the body.
Stereotactic radiation therapy was first used to treat brain tumors. To keep the tumor as a fixed target, the patient’s head is traditionally placed in a special frame mounted to the skull. The frame keeps the head immobile and provides reference markers for the computer-guided X-ray beams.
Instead of a mounted frame, stereotactic body radiation treatment is typically done by placing the patient in a special cast personally molded to the shape of the body. Bags can also be molded in a similar fashion to conform to the shape of the body. Imaging scans are taken while the patient is in the body mold to determine the precise location of the tumor. The therapists even hold “practice” sessions to make sure everything will go as planned during the actual treatment.
For liver tumors, patients are generally given about five 30-minute treatments over 12 days. Each time the patient comes in for a new treatment, he/she is placed in the personalized body mold. If the patient isn’t in the correct position, the mold will be uncomfortable, causing the person to wiggle into the right position. Doctors also take CAT scans before each treatment to make sure the tumor hasn’t moved. In addition, a compression plate is placed over the abdomen to help patients breathe with the chest muscles instead of the diaphragm – further limiting movement of the tumor and surrounding tissue.
During the treatment, special points around the mold are used for reference as the computer aims the beams at the tumor. Computerized systems can even track and adjust for movement of the tumor during breathing.
Doctors say stereotactic body radiation may be used for liver tumors up to three inches in size. It is also being used to treat tumors of the lung, pancreas, kidneys, endometrium and cervix.
Web Resources
For information on colorectal cancer or liver metastases:
