From our clinical experience, not more than 25 mm at
level of point A could be covered by an intracavitary approach
alone taking into account the dose–volume constraints
for OAR. At the level of the ring, this maximum
adaptation results in a distance of not more than 35 mm.
The improvement gained by using interstitial needles is
not limited to extension of the treated volume but also
allows for dose shaping in case of unfavorable topography,
where a standard dose distribution leads to high exposure
for bladder or rectum, but the lateral extension remains
within 20 mm from the tandem axis. With the presented
approach, the unique pear-shaped dose distribution is maintained
in general and adapted only by source positions with
limited dwell weight (20%). Rules of typical interstitial
treatments as in head and neck or breast are not applicable,
because the character of the resulting isodose remains always
comparable to intracavitary treatments. Classical parameters
for interstitial treatments such as mean central
dose, conformity index, and so on are therefore not useful.
For our MRI-based intracavitary brachytherapy approach,
we still report to point A and could show that D90, prescribed
dose, and point A dose are very similar (1). For the
combined intracavitary/interstitial approach, point A is often
not applicable, because it is too close to the needles.
However, classical point A tradition is still maintained by
starting our treatment planning process with a standard plan
normalized to point A and adapting very carefully by adding
needle positions with much lower dwell times. On the other
hand, treatment planning and reporting are now mainly
based on DVH parameters from the 3D image–based concept