Biomedical Engineering Reference
In-Depth Information
Dose difference display
Another interesting way of comparing a pair of plans is to display the
difference
in dose for the two plans, overlaid on a CT image and using
a color scale that permits the coding of both positive and negative
differences. In such a display it helps greatly if small differences that
are not considered to be clinically important are suppressed (i.e., not
shown in color). When analyzing such an image, the size and
location of the dose differences can be readily seen - whereas, when
comparing DVHs as discussed immediately below, the
location
of
any differences is not observable. However, the information as to the
absolute dose level is lost. A 10 Gy dose difference between 75 and
85 Gy has an entirely different significance than the same difference
between 5 and 15 Gy. For this reason, one should always inspect
dose-difference displays in conjunction with a display of the dose
distribution of at least one of the plans being compared. Such a
difference display is shown in Figure 11.6 of Chapter 11.
Overlaid DVHs
Figure 6.11: DVHs for several VOIs, with the curves for the three
plans overlaid. Figure courtesy of G. Goitein, PSI, CH.
An often-used way of comparing plans is to display a number of
panels, one for each volume of interest, and in each panel show the
DVHs for the plans being compared. Figure 6.11 portrays DVHs for
