What margins do you use for GBM volume delineation?

There is an ASTRO consensus guidelines committee currently working on guidelines for glioblastoma. One of the key questions facing the committee is the optimal target volumes for potentially curative radiation therapy. Issues include treatment of FLAIR/T2/edema followed by a boost to the T1 enhancin...

This conversation is much more useful than the newly published ASTRO guideline in Practical Radiation Oncology:

http://www.practicalradonc.org/article/S1879-8500(16)30003-0/abstract

The entire discussion of target volume margins was reduced to a hedged commentary with one self-citation. Both this guid...

Great comments above. I have found it quite interesting that there are quite a lot of differences in the way that GBM volumes are done. Interestingly, if you look at the Canadian recommendations (Mason et al., PMID 17593983, they recommend treating only the T1post area of disease, with no considerat...

Interesting discussion and something I struggle with on a regular basis.

It is peculiar that what was a margin to block edge got transformed into a PTV margin. A 2 cm margin to block edge is more akin to a 1.5 cm margin expansion.

We know there are tumor cells in the edema as @Dr. First Last pointed o...

@Dr. First Last - These responses are from 2014 - 2017. Have practices changed by 2024?

Great discussion from 2014. Six years later, is there a consensus?

Great discussion. I will also add that POF analysis from our own institution suggests that long term survivors in the TMZ era are at higher risk for distant failure. Again, this is food for thought for the residents but to me that suggests that RT-TMZ is increasingly effective in controlling disease...

This is a terrific discussion. At my institution, we have begun an arduous retrospective study along with Dr. Li at MD Anderson to attempt to compare failure patterns and clinical outcomes in patients treated with larger RTOG volumes vs tighter margins in a large pooled analysis. We hope that this w...

As someone trained at the institution where Dr. Kelly did the initial biopsy studies leading to our inclusion of the edema in the target volume, I will present a slightly different view. The original biopsy study confirmed high-grade glioma cells are present (not just low-grade tumor, as secondary G...

For standard fractionation schemas:

Our current philosophy is Flair + 5 mm to CTV/5 mm PTV

If using anisotropy maps then area of anisotropy + 5 mm/5 mm PTV

For accelerated courses, I agree with @Dr. First Last - we focus on enhancement.

As for the reference to Pat Kelly's work, as a neurosurgeon mys...

Thanks for the really useful comments.

This is another recent and hopefully useful reference that also nicely summarises recent developments in target volume delineation and imaging techniques in gliomas.

Whitfield et al., PMID 24824451

Great question, and great timing! I was thinking of writing up a blog post on this topic because NCCN recommends much wider margins - with no data to back it up. In addition to the data listed above, here is an Italian study

Minniti et al., PMID 20855119

Here's another re: the need to include edema in...

Fascinating discussion thread, thanks for everyone's comments. Indeed the Kelly paper was key, although I personally struggle to reconcile the findings that many places, across the pond and above the border, only cover T1post with no differences in outcomes (examples below). One note for the Kelly p...

Excellent discussion, thanks @Dr. First Last and @Dr. First Last for your insights and some reading to look forward to.

As a community doc, my issue has been that the BTSG/RTOG definitions haven't correlated well to the evolution being explained above. My particular concern is that NCCN, which many n...

Indeed - if anyone can find more references on things like the 46 Gy dose origin, send them along. I will ask Ed Shaw...

Thank you everyone for the interesting discussion. Apparently, there was a small randomized trial that compared the RTOG volumes vs more modest volumes that reported an OS advantage with a smaller PTV. The abstract was presented at SNO but I haven't seen a publication with the details. Slide 17 for ...