What ITV to PTV expansions do you use for free-breathing NSCLC SBRT using CT sim with 4DCT?

5mm concentric PTV margins. Even with daily IGRT and fluoro, I find 3mm to be very tight and adding a little more margin does not change the OAR doses much unless PTV is touching. If 4DCT not available in sim, I do 7mm sup/inf and 5mm in other directions.

I do not specifically add a CTV margin, but do chase all the spiculated GGO around the tumor, which in itself is probably like a 3-5mm CTV margin vs. just contouring the solid component.

To be a stickler for terminology, PTV expansions should be based on uncertainty. My default is 5 mm although would consider 3 mm in certain (limited) circumstances. Discuss with your physicists based on your treatment machine, immobilization, and IGRT strategies. You can consider increasing your PTV margin in cases with higher uncertainty (e.g. significant motion) although it would be better to try and improve your immobilization.

If you have concern for subclinical spread (e.g. lepidic-type aden...

My default expansion from IGTV to PTV is 7 mm concentrically. However, these margins can be customized to as little as 4 mm or as much as 10 mm in certain directions based on several considerations. These include:

(1) proximity of the IGTV to chest wall or critical central structures (typically will not expand more than 4-5 mm into any of these structures)

(2) magnitude of motion of the IGTV or of close by OARs

(3) my confidence in delineating the IGTV depending on spiculations or amount of grou...