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3D-CRT stands
for 3-dimensional conformal radiation therapy and is
sometimes called conformal radiotherapy. This prostate
cancer radiation treatment is a modified form of electron
beam radiation therapy (EBRT) and is designed to be
more accurate and deliver higher radiation doses.
Currently, 3D-CRT is the most common
prostate cancer radiation treatment in the United States,
but some doctors predict that the majority of centers
will soon switch to intensity modulated radiation therapy
(IMRT). 3D-CRT uses a Computer Tomography (CT) scan
and a software program to image the pelvic region and
form the shape of the beam. The accuracy of the electron
beam is increased. While avoiding the healthy tissue
of the neighboring organs, the beam is able to deliver
a higher dose of prostate cancer radiation.
What happens before 3D-CRT?
The planning stage is the most part of external prostate
cancer radiation treatments: the more precise the beam,
the higher the dose of radiation, the better the chances
of ablating all of the malignant tissue. In addition,
higher precision in the electron beams means less severe
and fewer side effects for the patient.
The patient is asked to strip from
the waist down and given a towel or gown to cover himself.
He is then placed in an immobilization device. The device
may be a thermoplastic cast, a bag filled with a liquid
that turns to Styrofoam, or a bag of Styrofoam pellets
from which area is removed. The immobilization device
is customized to his shape to prevent involuntary movements
during treatment. Once the patient is immobilized, the
radiation oncologist will use a CT scan to take 30 to
40 pictures of pelvic region from 3 centimeters below
the prostate gland to 3 centimeters above the upper
tips of the seminal vesicles.
What happens during 3D-CRT?
The malignant tissue of the prostate gland is identified
in each individual image slice. The healthy tissues
are also identified so the beam can avoid them. Using
these images, a computer reconstructs a 3-dimensional
model of the patient’s pelvic region. 3D-CRT delivers
a larger number of beams than EBRT with each day of
treatment. The conformal beams are also shaped to the
targeted area so the dose is higher. An automated computer
controls a multileaf collimator (MLC) which automatically
conforms the beam to the specific shape, no matter how
irregular the treated area appears.
The patient does not see or feel
anything. Patients should not feel any pain. Prostate
cancer radiation treatment is a noninvasive procedure
which is commonly prescribed for patients who are not
physically able to undertake a more invasive and more
demanding procedure. The patient will hear the whirring
sound of the machines as the beam is launched. The treatment
should not take longer than 45 minutes. External prostate
cancer radiation treatment is administered Monday through
Friday for 5 to 9 weeks depending on the doctor’s
prescription.
What happens after 3D-CRT?
As patients enter the final weeks of treatment, they
are likely to experience fatigue. Some patients experience
gastrointestinal side effects such as nausea or diarrhea.
Others may even experience proctitis which is an irritation
of bowels. To read more about the side effects of prostate
cancer radiation therapy, please click
here.
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