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Radiation Oncology: An Overview of the Treatment
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Q: How is radiation treatment
different for patients with primary and
metastatic brain tumors?
A: Primary brain tumors with only a few exceptions are a local problem and
rarely spread to other parts of the body or nervous system. There are rarely
tumor cells more than inch away from the visible tumor. Every effort is
therefore directed at killing the tumor cells in this local area. A high dose
of radiation is required which can take up to six and one-half weeks of
treatment to administer. The treatment generally concentrates on the entire
visible tumor and any microscopic extensions for 2 to 3 centimeters around it.
Metastatic tumors may appear in many different parts of the brain
simultaneously or at different times. Therefore, radiation is often
administered to the entire brain at one time in order to treat multiple tumors
that are visible as well as other sites that are currently invisible on the
brain scan. In the past ten years an additional type of treatment called
radiosurgery has also been performed. This concentrates the radiation on a
very small marble-sized area while sparing brain tissue around it. If there
are only a few visible tumors, radiosurgery alone may be used without whole
brain treatment with a single concentrated dose. In many cases, however, new
tumors will appear later and require additional treatment either with more
radiosurgery or whole brain radiation.
Q: Does the treatment of brain
tumors with radiation therapy require
specialized equipment?
A: Modern radiotherapy is performed with a machine called a linear
accelerator. These machines produce high energy x-rays and a separate type of
radiation called electron beam. By using the type of radiation best suited to
the location of the patient's tumor and often treating from several different
directions, the treatment can be concentrated in the area at risk while
sparing as much of the normal brain tissue as possible. In addition, special
radiation planning computers can use the information from CT and MRI scanners
to plan the radiation and the optimal number of treatment directions and
angles for each individual patient. Another treatment machine called the Gamma
Knife is utilized for performing radiosurgery. Unlike a linear accelerator,
which treats areas throughout the body, the gamma knife is dedicated to the
treatment of tumors and other abnormalities within and adjacent to the brain.
Q: What are the side effects
from radiation therapy?
A: Side effects are caused by irritation of the tissues that receive the
radiation. There are no direct effects on the rest of the body. Effects are
divided into immediate effects, which are common and long-term effects that
are not. Even doing the treatment slowly, some irritation builds up. This
results in redness and irritation on the scalp as well as hair loss.
Irritation of the brain tissue can sometimes result in nausea or headaches,
but medication can prevent this. Patients may also feel fatigue and
drowsiness. If the ear must be included in the treatment, there is often an
inflammation of the ear canal and a feeling of a "stopped-up" ear. Depressions
of the blood counts or effects on the immune system are unusual. Most early
reactions will subside one to two weeks after the treatments are completed.
Although brain tissue tolerates radiation well, very high doses are required
to destroy most brain tumors. Therefore, treatment can result in late
problems, which occur a few to many months after the treatments. Brain cells
in the treated area can be damaged, causing problems with thinking ability or
memory. Occasionally, patients will have more persistent tiredness. Hair loss
can occasionally be permanent at least in spots. If the pituitary gland is
within the area of irradiation, its functioning can slow down requiring
hormone replacement. In children, there can also be growth disturbances both
within the brain tissue and the bones of the skull and face.
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Q: Are there new techniques in
Radiation therapy that impact on brain tumor treatment?
A: Advances in computer technology have resulted in very powerful
computers for planning radiation therapy. Three-dimensional planning is
accomplished by inputting images from CT scans. From this, a computer model of
the tumor and surrounding brain can be constructed. This enables the physician
to construct a plan using radiation from multiple directions and sometimes of
multiple types to best encompass the tumor given its specific size and
location. Special lead alloy blocks can be constructed from the computer plan
to further protect the normal surrounding brain tissue. A variant of
three-dimensional planning called intensity modulated therapy is currently
under continuing development and not widely available. It also treats the
tumor in three dimensions while sparing normal brain tissue and is best
utilized on smaller tumors.
Radiosurgery is a technique that focuses the radiation on a very small spot
creating a small marble-sized area of strong radiation on that spot. While
multiple marbles of treatment can be added together to treat a larger and more
irregular area, radiosurgery is most effective on tumors that are 3 cm or less
in size. It is best used as a way of boosting or administering additional
radiation to a primary tumor or in treating metastatic tumors. It is also used
to treat some benign brain tumors and diseases such as meningiomas and
arteriovenous malformations.
Q: How does a patient decide
on a treatment facility and a radiation oncologist?
A: The treatment facility should offer a number of treatment options. It
should have linear accelerators that are capable of producing different types
and energies of radiation. A three-dimensional planning computer should be
available for the radiation planning. The ability to perform radiosurgery
while not essential for all patients could be helpful for some. In addition,
the facility should be affiliated with radiation oncologists, medical
oncologists and neurosurgeons who specialize in the treatment of brain tumors
since optimum treatment often requires the joint effort of multiple
specialists.
The choice of a radiation oncologist is extremely important. This person both
plans and directs your treatment. He should be board-certified in radiation
oncology, meaning that he has passed both written and oral examinations in
this field and been certified by the American Board of Radiology in this
specialty. You must feel comfortable with your physician and he/she should
spend time with you explaining the treatment and answering all of your
questions.
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