Biomedical Engineering Reference
In-Depth Information
fluence within any one beam need not be uniform across the PTV.
The non-uniformity of each beam is driven by anatomic features
specific to the patient and allows a better sparing of nearby normal
tissues than is possible with uniform-intensity radiation therapy.
IMRT was developed independently by Cormack (1987) and Brahme
(1988) . IMRT has become widely accepted as a worthwhile
1
approach for patient treatments. Palta
et al
. (2003) and Bortfeld
et al.
(2006) offer extensive accounts of IMRT, and Bortfeld (2006)
provides a short overview of IMRT with references to many of the
important papers.
IMRT allows one to deliver only low doses to all or part of selected
normal structures. In particular, one can create a concave irradiated
volume that can spare much of an invaginating OAR, whereas
uniform-intensity radiation therapy inherently creates convex irradi-
ated volumes and cannot achieve such OAR sparing. This difference
is illustrated in Figure 9.1.
Figure 9.1. Illustration of why IMRT, but not uniform-intensity
radiation therapy, can generate concave dose distributions (see text).
Uniform-intensity radiation therapy is illustrated in the left hand side
panel. A beam that covers the target volume with a uniform flux of
radiation cannot avoid irradiating an OAR invaginating the target
volume. This is true of each beam. The irradiated volume is the
intersection of the tissues irradiated to high dose in each of the beams.
1
Pedroni (1981) had earlier used intensity modulation in the context of
π
-meson therapy.
