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3-Dimensional Simulation
with 3-Dimensional Treatment Planning
Simulation is the process of mapping out the location of
the tumor and placing marks on the external skin surface
for external beam radiation therapy. OncoLogics utilizes
a Picker PQ 2000 spiral CT simulator that was specifically
designed for radiation oncology. The patient is placed on
the CT table and the radiation therapist scans the prescribed
area. The images acquired from the scanner are loaded into
a computer called the FocalSim workstation. The physician
reviews the 3-D images and determines the exact location
of the tumor. They contour (outline) the tumor on the CT
images, which allows the radiation therapist to draw the
skin markings precisely where the tumor is located on the
patient.
3-D Treatment planning is the process where a dosimetrist
reviews the prescription written by the physician defining
the treatment technique, beam energy, and contoured images
from the CT simulation. The dosimetrist designs a radiation
field arrangement that covers the tumor contoured by the
physician. This arrangement is plotted on a paper and is
called an isodose plan. The isodose plan shows the radiation
beam arrangement, the tumor, and dose volumes around the
tumor as well as the normal structures around the tumor.
The purpose for the 3-D isodose plan is to limit the radiation
dose to the normal structures, which decreases radiation
side effects while delivering a high dose to the tumor. The
3-D isodose plan designed by the dosimetrist is the guide
that the radiation therapist uses daily to deliver the treatment
to the patient.
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