What CTV expansions do you use for NSCLC with conventional chemoradiation and do you do different expansions based on specific histologies?   

We do 5 mm for all chemoRT cases and do not alter based on histology.

I currently use 0 mm for all thoracic XRT cases. This is whether prescribing SBRT, Hypofx RT, Conventional RT, or CRT. I'm comfortable omitting a CTV as we have a state-of-the-art CT simulation system showing a lot of historically invisible fuzz. I make sure to include "all the fuzz" around a tumor ...

CTVs are cool things IMO. They aren't so easy to derive and are a mix of pathologic data and patterns of failure (if they are data-driven in their derivation). It's one of the few things that AI won't easily do for us since it's not radiomics per se... but I digress. :) The best paper is the pa...

We also use 5 mm expansions for all cases regardless of histology. 

Interesting discussion. Thanks to all who have weighed in already. I don't think you can discuss CTV expansion out of context without considering the PTV expansion, IGRT method, 3D vs 4D sim, 3D vs 4D couch corrections, etc.  For example, a larger PTV expansion will make up for a smaller CTV ...

I tend to split the difference and do 7 mm if not using a 4D CT to draw an ITV.

Also, Cui et al., PMID 36764460: A prospective phase II randomized study, randomizing to CTV creation or no CTV creation supports lower toxicity and equal control and survival without creation of CTV. I generally avoid it in large-volume tumors but in small tumors where we will achieve reasonable lu...

Are we talking GTV to CTV or CTV to PTV?