We’ve had issues with this when using MV/kV pairs, so all the arms are out at the same time.
Advice from vision RT was that if the arms are blocking the side cameras, then your ROI needs to reflect what the Front camera at the feet looking down the bed can see more than the other cameras. I tried making my ROI bigger initially and all it did was make the area the cameras couldnt see bigger! If it cant see a certain percentage of the ROI, it just gives up!
Try using an ROI that the front camera can see, like an inverted T to include the sternal area, and under the breasts, but dont go around the sides too much where the front camera cant see. Dont go too high up the sternum or the camera cant see the chest dipping away either.
As with most SGRT things, its the ROI thats critical, and especially in these cases varies from patient to patient depending on biody shape and whats being obscured from the cameras
You can also create an imaging ROI so that you only use this when the arms are out, and you can go back to the normal treatment ROI once imaging is completed so your ROI reflects what your actually treating. (when drawing on your ROI, theres an option to ADD SELECTION to achieve this).