Biomedical Engineering Reference
In-Depth Information
The second approach is what I call
computer-driven planning
. By
this is meant that decisions about a plan's worth are made by
computer. This is done out of necessity, because in computer-driven
planning a huge number of plans are tried out. Computer-driven
planning usually, but not necessarily, has as its goal the development
of intensity-modulated radiation therapy and virtually always uses the
optimization techniques discussed in Chapter 9.
P
LANNING BY
H
AND
Figure 8.1 depicts a planner
sitting in front of a console
that has a large number of
knobs and wanting to decide
on the setting of each knob
in order to arrive at an
acceptable treatment plan.
How is this poor guy to
adjust all the knobs so as to
arrive at even a good, let
alone optimal, plan?
The knobs, of course, are the
treatment
machine
controls
Figure 8.1. The problem of planning
therapy: so many “knobs” (treatment
variables) to tweak! How can the
planner decide how to set them so as to
deliver a passable, let alone optimal,
treatment?
variables that can be adjusted.
The following is a partial list
of those variables:
the type of therapy (external beam, intracavitary or interstitial
implant, intraoperative
−
or, some combination of these). If exter-
nal beam therapy, then:
the modality of any external radiation beams (e.g., X-rays, elec-
trons, protons etc.) and the characteristics (e.g., the energy) of the
chosen modality;
the location of the patient and the tumor and organs of interest
within the patient in both space and time
−
including measures to
control, or to make allowance for, uncertainties in organ and
patient location relative to the treatment beams;
the number of external radiation beams;
the angulation and aiming point of each beam;
the shape of each beam;
the weight and intensity profile of each beam;
