Biomedical Engineering Reference
In-Depth Information
remaining volume at
risk
RVR
The volume which is:
(a) within the imaged part of
the patient, and (b) outside all
delineated PRVs (or OARs)
and outside the PTV(s)
With regard to these definitions:
It is desirable that every OAR should have an associated PRV,
but it is not required.
The RVR is always defined, if only implicitly. The reporting of
the dose to the RVR, as well as to delineated OARs, is strongly
encouraged.
Other terms
Other useful terms are:
Volume of Interest
VOI
any volume which one wishes
to define. VOI may be used
generically to describe
particular volumes such as the
PTV, OAR, etc.
Surface of Interest
SOI
the surface of a feature or a
plane or curved plane
Point of Interest
POI
any point in space
I strongly encourage you to follow the ICRU terminology. We now
turn to the question of how these volumes are determined - or,
speaking more generally, to the mapping out of the patient's anatomy.
3D
AND
2D
I
MAGES
The patient is intrinsically multi-dimensional, having multiple pro-
perties which are of interest such as X-ray absorption coefficients,
T1 and T2 magnetic resonance (MR) decay times and so forth. These
properties are distributed throughout the three spatial dimensions and
may vary in time The display of any particular property is therefore
at least three-dimensional and potentially four-dimensional. At any
given time, three spatial dimensions suffice. Thus, to fully represent
a region of interest within a patient, one needs to have anatomic
information in at least three dimensions. This information may be of
many forms. Typically, in CT and MRI for example, some property
