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Let’s start with the definition
•
ICRU 83
:
In earlier ICRU documents, the possibility of
compromising
the
margins of the PTV if they encroached on
OAR
was suggested (ICRU,
1999; 2004; 2007), but is
no longer recommended
. To reduce the
CTV-to-PTV margin has always been a temptation. As an example,
the CTV-to-PTV margin between the prostate and rectum is often 1
cm, except in the anterior – posterior direction for which it is
reduced to spare the rectum
To ensure accurate reporting of absorbed dose to the PTV in cases for
which the PTV encroaches or overlaps another PTV, OAR, or PRV, it
is now recommended that the delineation of the primary PTV
margins should not be compromised. Developments in treatment-
planning software now make it possible to achieve sufficient dose
sparing of the OAR by
using priority rules in optimizer
planning
systems (see Section 2). Alternatively, subdivision of the PTV into
regions with different prescribed absorbed doses (so-called
PTV-subvolumes
, PTVSV) may be used.
The PTV 2017 - D. Verellen