Framebased-Frameless_DV_2017

Let’s start with the definitions

•

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. Alternatively, subdivision of the PTV

into regions with different prescribed absorbed doses (so-called

PTV-

subvolumes

, PTV

) may be used.

SBRT 2017 - D. Verellen