Biomedical Engineering Reference
In-Depth Information
Technical data
In the end, an enormous amount of information is involved in fully
defining a plan. Therefore, the concept of
technical data
has re-
cently been formalized (ICRU78, 2007), as pictured in Figure 6.2.
Technical data include: the planning CT scans; the delineated
volumes of interest; the settings of all treatment machine parameters
such as, for example, the possibly time-varying multi-leaf collimator
(MLC) settings, that altogether result in the approved treatment plan;
the resulting 3D or 4D dose distribution(s) and associated dose
statistics; and so forth.
Seen in the larger view, the technical data are an implicit part of the
treatment prescription
. However, they are buried within the confines
of some data management system, available only for computer recall,
whereas, the prescription, almost by definition, has to be able to be
written out and illustrated by sample images of the dose distribution.
R
EPRESENTATION OF
D
OSE
I am now going to make an enormous leap over the actual process of
designing the treatment plan, in order to discuss how one can
visualize the dose distribution that results from a given plan, and then,
in the following section, how the dose distribution can be assessed.
The reason for this leap, of course, is that the appreciation and
evaluation of the dose distribution that results from a plan is an
essential step in the treatment planning loop. One cannot discuss the
design of a plan until having discussed the tools for inspecting one.
The discussion of plan design
per se
is deferred to Chapters 8, 9 and 11.
I will refer here to the display of dose superimposed on CT images, as
CT is the most commonly used imaging modality. However, it could
equally well be, for example, an MR or other imaging study.
4
The dose distribution is part of a multidimensional data set which
includes: the dose that would result from any given plan in all three
spatial directions; anatomic information from one or more imaging
studies; and from structure delineation
possibly including variations
of these data in time. It is challenging, to say the least, to view such a
−
4
At the time I entered the field of radiation oncology, dose distributions
were only available as isodose contours overlaid on hand drawings of the
patient's outer contour and selected internal anatomy and usually only
worked out in a single patient cross-section.
