Biomedical Engineering Reference
In-Depth Information
several VOIs in which the DVH curves for three plans which are
being compared are shown. (The three plans, in fact, feature the three
different proton beam delivery techniques illustrated in Figure 11.13
of Chapter 11.) The DVHs are very valuable in helping one assess
the dosimetric differences between the plans and, hence, between the
techniques.
Commonly, two or more DVH curves cross one another
although
this is not the case in Figure 6.11. One then needs to know which of
−
two crossing curves is better, and by how much. This matter is
touched upon in Chapter 8.
Comparison of dose statistics and biophysical models
Table 6.1. Side-by-side, dose statistics for the same three plans as are illus-
trated in Figure 11.13. Table courtesy of G. Goitein, PSI, CH.
scattered
protons
scanned
protons
IMPT
Target volume (PTV)
dose to 98% of volume, D
98%
49
50
49
median dose, D
50%
55
55
55
dose to 2% of volume, D
2%
56
55
56
relative volume receiving 95% of the
prescribed dose, V
95%
93
93
92
Right femoral head
relative volume receiving 20% of the
prescribed dose, V
20%
54
50
27
relative volume receiving 50% of the
prescribed dose, V
50%
50
40
10
relative volume receiving 80% of the
prescribed dose, V
80%
35
10
2.3
dose to 2% of volume, D
2%
(near-
maximum dose)
102
98
85
Intestines
…
Body outline minus PTV
mean dose outside the PTV, D
mean
7.2
5.9
5.6
To compare dose statistics for two or more plans, it is very helpful to
lay out the information so that the data for the plans lie side-by-side.
An example of such a table is shown in Table 6.1. It is extremely
helpful in such a table to include in an additional column the
constraints imposed by the prescription, so that one can judge how
well they have been met, and whether one plan does a better job than
