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Introduction: External beam radiation uses high energy photons to
destroy cancer cells within the body. The photons are in many
ways similar to those used in diagnostic x-ray (chest x-ray) or rays
from the sun except they are much higher in energy. The
beams are generated by a device called a linear accelerator and deposit
radiation dose as they pass through a particular portion of the body.
The radiation damages the DNA of cells which ultimately leads to their
destruction. Normal (non cancerous) cells are much better able
to repair this type of damage and therefore survive. Like the light
from a flash light, radiation dose is delivered only when the machine
is on and the patient is not radioactive once the machine is turned
off.
One of the most important advances in the delivery of external beam
radiation therapy has been the development
of three-dimensional conformal therapy. Traditional conventional
radiation therapy is targeted only by the location of bones seen
on plain x-rays which cannot show the actual tumor. These bony
landmarks do not show the unique anatomy of any particular patient.
The fields therefore tend to be large,
square shaped and generic. This results in more unnecessary
radiation to the surrounding tissues.
Conversely,
conformal therapy allows for the customization
of treatment for each particular individual. Every
person has a unique tumor size, shape,
as well as location of nearby
normal organs. Conformal radiation is
the process of accurately determining
this unique anatomy and tailoring the
radiation treatment such that it "conforms" to every
patient. Where conventional therapy
would treat all patients with the same
big square beams, conformal radiation
treats a round tumor by round beams and
an elongated shaped
tumor with an elongated shaped beams. This technology is now applied
to nearly all tumor sites. (Breast/Gastrointestinal/Prostate/CNS/Lung/Gyn)
Conformal treatment is a complex process
which involves three basic components. The first is patient immobilization. Special
body casts are created to improve the
reproducibility of the patients position on the machine. The second
step is computed tomography (CT) assisted organ identification. The
precise location and shape of the tumor as well as the surrounding
tissues is determined. The
final step involves the use of powerful
computer tools to generate the specific beams which will differentially
deliver the radiation to the tumor while sparing the surrounding normal
tissues. Specialized
blocks are created to shape the beams
which have been generated. This
improvement in technology means that the radiation beams can be
made the smallest size possible to safely
treat the cancer while avoiding normal tissues. The less normal
tissue irradiated results in less unwanted side effects.
Simulation: This is the first step of conformal radiation. The
total time needed for this first day is about 90 minutes. A custom
body mold is made that is customized for each particular area of treatment.
By lying in the mold, you will be in the same position on the treatment
table every day - up to 67% more accurately than without the cast. Next
is the CT scan in our department.
Claustrophobia, a fear of close places, is rarely a problem. Contrast
dye is often used during the CT scan to improve the image of the tumor
on the film. Please tell your doctor or nurse if you are allergic
to contrast dye or iodine. Small tattoos the size of a pencil point
are then placed to be used every day for accurate positioning
of the treatment beams. They are permanent but small and in locations
that will likely not be publicly visible.
3-D Treatment planning: This process takes place
behind the scenes over a 1 week period
-you do not need to be present. The
CT scan taken at simulation is examined
by the physician who contours the important body organs which are
then inputted into the computer. The
physician then directs specially trained
physicists and therapists in designing the conformal shape of the
radiation beams. This
is the custom tailoring - the radiation
beams are designed to mimic the shape of the target with the narrowest
margin of normal tissue possible.
Set-up: We check the accuracy of your specific treatment
on the actual therapy machine before starting
radiation.
Radiation Treatments: The time course of conformal radiation
depends on the disease site being treated but in general ranges from
5 to 7 weeks, Monday through Friday, except for major holidays. The
actual time in the treatment room is 10-15 minutes. Please allow 45-60
minutes total each day for parking, dressing and small delays. Treatment
times are flexible from 7:30 - 5:30 - most requests for a specific
time of day can be met.
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