Biomedical Engineering Reference
In-Depth Information
need to combine information from all these elements, using clinical
experience and expertise.
Before launching into a description of the various imaging techniques,
I want to present the nomenclature which is used for various volumes
of interest as some of these are referred to in what follows. The
primary goal of imaging is, in fact, to deduce these volumes.
V
OLUMES OF
I
NTEREST
(GTV,
CTV,
PTV, OAR
ETC
.)
The International Commission on Radiation Units and Measurement
(ICRU) has done us all a great favor in developing and standardizing
a terminology for describing a number of volumes of interest. The
ideas were first presented in ICRU50 (1993), and have been clarified
and refined in subsequent reports (ICRU62, 1999; ICRU71, 2005; and
ICRU78, 2007). I refer you to these publications for the details, and
present here a brief summary of the main terms and their acronyms.
Tumor-related terms
Figure 3.1a shows schematically the terms associated with tumor
definition. They are:
gross tumor volume
GTV
gross palpable, visible, or
clinically demonstrable
disease
clinical target volume
CTV
GTV
plus
an extension for
subclinical (microscopic)
malignant disease
internal target volume
ITV
CTV
plus
an internal margin
(IM) for expected
physiological movements and
temporal variations in size,
shape and position of the
CTV
planning target volume
PTV
ITV
plus
a setup margin (SM)
for uncertainties in patient
positioning and alignment of
the therapeutic beams
