How Does Your Doctor Plan Your Treatment?
How Long Does the Treatment Take?
What Happens During Each Treatment Visit?
Newer Forms of External Radiation Therapy
How Does Your
Doctor Plan Your Treatment?
Choosing the type of radiation to use depends on your cancer
and where it is located.
After a physical exam and a review of your medical history
and test results, your doctor will pinpoint the area to be treated.
This is done a few days before starting radiation therapy in a process
called simulation.
You will be asked to lie still on a table while the radiation therapist
uses a special x-ray machine to define your treatment field
(also called treatment port). This is the exact place on your body
where the radiation beam will be aimed.
To be sure the radiation beam is aimed correctly, special
molds or casts of parts of your body may be made to help you be still
during your treatment. The radiation therapist may mark the treatment
field with freckle-sized dots of semi-permanent ink. The marks will
likely fade away over time, but they are needed until your treatment is
completed. Don’t use soap on or scrub these marks. Sometimes the area
may be marked with permanent dots like a tattoo.
Based on the simulation, other tests, and your medical
diagnosis, your doctor will decide how much radiation is needed, how it
will be given, and how many treatments you should have.
External radiation therapy is usually given with a machine
called a linear
accelerator (linac), which is described below.
How
Long Does the Treatment Take?
Usually, the total dose of radiation needed to be effective
against a tumor can’t be given all at once. This is because it is very
hard to give radiation therapy without affecting at least some normal
cells nearby. A dose of radiation given all at once can cause more side
effects than giving the same dose over many treatments.
Because of this, the total dose of external radiation therapy is
usually divided into smaller doses called fractions. The most common
way to give it is daily, 5 days a week (Monday through Friday) for 5 to
8 weeks. Weekend rest breaks allow time for normal cells to recover.
The total dose of radiation and the number of treatments can vary,
based on:
- the size and location of your cancer
- the type of cancer
- the reason for the treatment
- your general health
- any other treatments you are receiving
Other radiation schedules may be used in certain situations. For
example, radiation therapy may last only a few weeks (or less) when
it’s being given to relieve symptoms, because the overall dose of
radiation is lower. In some situations, radiation might be given as 2
or more treatments each day (called hyperfractionated
radiation therapy). Or it might be given as split-course therapy, which
allows for several weeks off in the middle of treatments to allow the
body time to recover while the cancer shrinks.
What Happens
During Each Treatment Visit?
External radiation treatments are painless. The experience is
like having a regular x-ray. The treatment itself takes only a few
minutes. But each session can last 15 to 30 minutes because of the time
it takes to set up the equipment and place you in the correct position.
Depending on the area being treated, you may need to undress, so wear
clothes that are easy to take on and off. You will be asked to lie on a
treatment table next to the radiation machine (linear accelerator or
linac). The machine has an arm that extends over the table through
which the radiation comes out. The machine can move around the table to
change the angle of the radiation, if needed.
The radiation therapist may put special shields between the machine and
parts of your body that are not being treated to help protect normal
tissues and organs.
Once you are in the correct position, the radiation therapist will go
into a nearby room to operate the machine and watch you on a TV
monitor. You will be able to talk with the therapist over an intercom.
You will be asked to lie still during the treatment. You do not have to
hold your breath -- just breathe normally.
The radiation therapy machine will make clicking and whirring noises
and may sometimes sound like a vacuum cleaner as it moves to aim the
radiation beam from different angles. The radiation therapist controls
the movement and checks to be sure it is working properly. If you are
concerned about anything that happens in the treatment room, ask your
therapist to explain. If you feel ill or uncomfortable during the
treatment, tell your therapist right away. The machine can be stopped
at any time.
Newer
Forms of External Radiation Therapy
Today, scientists have developed newer, more precise ways of
giving external radiation therapy. These approaches allow doctors to
focus the radiation more directly on the tumors.
These newer forms of radiation do less damage to normal
tissues, and this allows doctors to use higher doses directed only at
the tumors. These methods though are still fairly new, and their
long-term effects are still being studied.
Newer machines allow doctors to conform the shape of the
radiation beam to match the shape of the tumor. With conformal radiation,
a special computer uses imaging scans (such as CT scans) to map the
location of the cancer in the body from 3 directions (3 dimensional or
3-D). Radiation beams can then be directed to conform to the shape of
the cancer. This helps to better protect the parts of the body in
between the radiation beam and the cancer.
Three-dimensional
conformal radiation therapy (3D-CRT) delivers shaped
beams at the cancer from different directions. Patients are fitted with
a mold or cast to keep the body part still so the radiation can be
aimed more accurately. By aiming the radiation more precisely, it may
be possible to reduce radiation damage to normal tissues and better
fight the cancer by increasing the radiation dose to the cancer.
Intensity
modulated radiation therapy (IMRT) is a newer method
similar to 3D-CRT. It conforms to the tumor shape like 3D-CRT, but also
allows the strength of the beams to be changed to lessen damage to
normal body tissues. This provides even more control in reducing the
radiation reaching normal tissue while delivering a higher dose to the
cancer. It may result in even fewer side effects.
A newer form of IMRT, known as helical tomotherapy,
uses a linear accelerator inside a large "donut" that spirals around
the body while you lie on the table during treatment. It can deliver
radiation from many different angles around the body. This may allow
for even more precisely focused radiation.
Conformal proton
beam radiation therapy is similar to conformal therapy but
it uses proton beams instead of x-rays. Protons are parts of atoms that
cause little damage to tissues they pass through but are very good at
killing cells at the end of their path. This means that proton beam
radiation may be able to deliver more radiation to the cancer while
reducing side effects on nearby normal tissues. Protons can only be put
out by a special machine called a cyclotron or synchrotron. Installing
this machine costs millions of dollars and requires expert staff.
Because of this, proton beam therapy can be expensive. As of late 2007,
fewer than half a dozen treatment centers in the United States offer
it, although new proton machines are scheduled to be in place in 2008
and 2009. More studies are needed to determine whether proton produces
better results in specific cancers than the usual radiation (photon)
treatment.
Intraoperative
radiation therapy (IORT) delivers radiation directly to
the tumor or tumors during surgery. While the patient is under anesthesia
(asleep), the surgeon locates the cancer. Normal tissues can be moved
out of the way and protected during surgery, so IORT reduces the amount
of tissue that is exposed to radiation. This allows a higher dose of
radiation to reach the cancer. IORT is usually given in a special
operating room lined with radiation-shielding walls.
Stereotactic
radiosurgery is not really surgery but a type of radiation
treatment that delivers a large, precise radiation dose to a small
tumor area in a single session. It is most commonly used for brain
tumors and other tumors inside the head. First, a head frame is
attached to the skull to help precisely aim the radiation beams. Once
the exact location of the tumor is known from the CT or MRI scans,
radiation from a machine called a Gamma Knife can be focused at the
tumor from hundreds of different angles for a short period of time.
A similar approach uses a movable linear accelerator that is
controlled by a computer. Instead of delivering many beams at once, the
machine moves around to deliver radiation to the tumor from different
angles. Several machines do stereotactic radiosurgery in this way, with
names such as X-Knife, CyberKnife, and Clinac. Another technique uses
particle beams of protons or helium ions to deliver the radiation to
the tumor in this way.
Stereotactic radiosurgery typically uses a single session to
deliver the whole radiation dose, though it may be repeated if needed.
Sometimes doctors give the radiation in several treatments to deliver
the same or slightly higher dose (fractionation).
This is sometimes called fractionated radiosurgery or stereotactic
radiotherapy.
Clinical trials are under way to study how well stereotactic
radiosurgery and stereotactic radiotherapy work alone and when used
with other types of radiation therapy.
Revised: 10/02/2007
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