Hypodense on a non contrast CT fairly often in my experience. Otherwise I'm lining up to the liver as you have alluded to and things have turned out ok
It varies, but yes. Without fiducials you're generally lining up to the liver edge/anatomy close to the lesion. Super reasonable when you've got a lesion right against the edge that's obvious on CBCT, but less so when the lesion is deeper/further away/you have docs that aren't used to checking it.
I use fiducials at times. The simplest alternative is to fuse diagnostic imaging to the CT sim that clearly shows the target. Then you can get a 4DCT and determine if there is a lot of respiratory movement. If not, then treat with appropriate margins. If so, then consider breath hold; nowadays with the speed of VMAT and FFF, the significant majority of patients can tolerate this. The least desirable option is to treat the entire movement path.
Yes. I would do all that, even with fiducials. It’s more about localizing for each treatment.
Anyone doing fiducial-free breath hold with sgrt? On a C arm linac
I’ve played with it. It’s difficult because there’s often discordance between the surface guided breath holds and the fiducial breath holds, ie the fiducials are off and the surface guidance is on/vice versa. It doesn’t give you a ton of confidence, and there’s no good way I’ve found of identifying patients where it works well/doesn't work well prospectively.
