Biomedical Engineering Reference
In-Depth Information
The choice of all of these variables, most of which are dictated by
purely clinical considerations, is at the heart of the planning process.
Manual planning is the approach that has been taken since the very
beginnings of radiation therapy more than a hundred years ago. It
takes advantage of:
the memory of previous satisfactory knob settings (that is, of
plans used previously for similar cases) as a starting point;
rules of thumb as to how to set combinations of knobs
e.g.,
“design the aperture so as to have the beam just cover the target
−
volume
1
with a predetermined margin or margins;”
a fast calculation engine to compute, ideally interactively, the
dose distribution resulting from a particular set of knobs;
displays of that dose distribution;
the provision for the planner's inspection of a number of dose-
summarization statistics
−
e.g., dose
−
volume histograms and/or
calculation of the minimum, maximum, and mean tumor dose,
and so forth;
a body of experience that makes a judgment about the overall
acceptability of the plan;
the iteration (a few times) of the process to arrive at the best plan
the planner is able to come up with.
A glimpse of a planner engaged in manual planning is shown in
Figure 8.2. You will surely
observe that this drawing is, on
the face of it, a rather simple
extension of Figure 8.1.
Apparently, all we have to do
is to connect the knobs to a
calculation engine and show
the resulting dose distribution,
and other quantities derived
from it, on a screen. What
Figure 8.2. Planning treatment using
manual planning (see text).
you do not see, because his
1
To avoid lengthy qualifications, I have used the generic term “target volume”
throughout this chapter, without specifying whether the GTV, CTV, or PTV
(see Chapter 3) is meant. Generally, however, the PTV is implied.
