Biomedical Engineering Reference
In-Depth Information
8.
Simulate the selected plan to ensure that it is deliverable and that
all parameters have been correctly established.
Deliver the treatment, and verify that the delivery is correct,
in many fractions over many weeks.
10.
Re-evaluate the patient during the course of treatment to ensure
that the plan remains appropriate (e.g., weight loss or tumor
regression have not affected the treatment geometry unduly) and,
if it does not, return to step 5, or even 2, to re-plan the remainder
the treatment.
9.
11.
Document and archive the final treatment plan.
12.
Review the treatment plan at the time of patient follow-up or
possible recurrence.
I have used up a lot of paper and ink here to emphasize one simple
but important point, namely, that
these steps are identical to the
planning steps outlined in Chapter 6 with the exception of steps 5 and
6
. That is, there is a great deal of work which is common to manual
planning and computer-driven planning. I will confine myself for the
rest of this chapter to discussing those aspects that are unique to the
latter.
There are numerous tried and true mathematical techniques which are
designed to search in a large space of variables for the set of values of
those variables that maximizes the value of some function of those
variables; that is, which maximizes the score. Since the search for an
IMRT plan uses such so-called optimization techniques, it is often
referred to as a process of
optimization
. As I shall explain at the end
of this chapter, I don't like this term. Nevertheless, I bow to common
usage and employ it here.
The following is a breakdown of steps 5 and 6 in the preceding list.
The italicized items are ones that require human input:
a)
Design those aspects of the plan that you do not plan to optimize-
for example, choose the beam directions.
b)
Establish the goals of the optimization process (deduced from
the planning aims) - for example, the score function you wish
to optimize, and the constraints and their importance factors, if
any.
c)
Set any parameters needed by the search algorithm, if any.
d) Provide starting values for all variables that will be set in the
search process - many search algorithms do this for you, auto-
matically and invisibly.
