Biomedical Engineering Reference
In-Depth Information
DVHs have become widely adopted as a tool for dose summarization
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particularly when plans must be compared, as discussed below.
However, they share the problem of all data abstractions in that
information is lost. In the case of a DVH, one loses all spatial
information about the dose within the VOI whose dose it summarizes.
One cannot tell, for example, whether low doses in the DVH come
from one subvolume of the VOI, or are distributed across many sub-
volumes. Moreover, particularly with large VOIs, the sheer volume
of tissue may make it easy to miss small hot or cold spots. For all
these reasons, I judge it very unwise to rely on DVHs alone to analyze
a dose distribution;
DVHs should always be looked at in conjunction
with graphical representations of the dose distributions
.
As between differential and cumulative DVHs, while the former have
their value, they are in practice little used. A major reason for
preferring cumulative DVHs is that a number of useful dose statistics
can be directly read off them, as indicated in Figure 6.8.
Figure 6.8. Demonstration of how a number of dose statistics
can be read off a cumulative DVH. Reproduced with
permission from ICRU78 (2007).
0D dose and dose-volume statistics
The “0” in 0D indicates that dose statistics are scalar quantities; they
have magnitude but not direction. In describing dose-volume
relationships, the following nomenclature has been established, for
example, in ICRU78 (2007):
