Target delineation in resected acoustic neurinoma

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I have a quick question:

What's your institutional policy for target delineation in acoustic neurinoma, which has been incompletely resected?
I've learned to delineate only the residual tumor as CTV and add a PTV-margin to it.

Do you do that even in cases of big (for example 5cm) tumors, where only a small residual tumor of 1cm has been left behind by the surgeon, or do you include high-risk areas into the CTV which go beyond the residual tumor (for example brainstem - resection margin cranially and caudally to the residual tumor)? I am talking about FSRT here, not SRS.

If you think that risk of failure away from residual disease is sufficiently high, it's reasonable to include those areas in CTV. I would not treat a 5 cm in size target 6 Gy X 5 though.

This is an area where direct neurosurgical input is critical. Though you can learn a lot by reading the operative note, it would be very worthwhile to discuss which areas the surgeon feels are highest risk for residual disease.

Thanx for the answers!

I am thinking of making two CTVs

CTV1 = current GTV + high risk areas
CTV2 = current GTV

then, I'll add a 3mm margin to each and prescribe:

PTV1 = 25 x 1.8 Gy
PTV2 = 5 x 1.8 Gy

:-)

I assume the PTV2 dose is a typo.

Originally Posted by Gfunk6

I assume the PTV2 dose is a typo.

First 25 fractions of 1.8 Gy per fraction to the "big" PTV1, which includes PTV2.
Then 5 fractions 1.8 Gy per fraction to the "small" PTV2.

So: 45 Gy to PTV1, then boost 9 Gy to PTV2 for a total of 54 Gy to PTV2.

Think you raise an interesting point. I've typically only treated residual disease when treating other relatively benign intracranial tumors. However, the consequence of failure within the operative bed but outside of the gross disease would be potentially problematic. Surgical salvage would be difficult or impossible and re-irradiation would have risks. Although the study below is not in the postop setting, I guess I would favor a slightly lower dose based on its results.


Int J Radiat Oncol Biol Phys. 2009 Jun 1;74(2):419-26. doi: 10.1016/j.ijrobp.2008.08.028. Epub 2008 Nov 29.
Toward dose optimization for fractionated stereotactic radiotherapy for acoustic neuromas: comparison of two dose cohorts.