Hey Lauren! All of our DIBH electron boost patients are planned off of their Free Breathe CT scan. This eliminates the need for DIBH on an electron breast boost. We set up using VRT and then put the cone on and treat. We have had an electron patient (not breast) with a bigger cone where the cameras actually read through the gaps.
If dosimetry is set on planning off DIBH scan then I would extend the ROI to cover both sides like you said. Then cameras will have enough information to pick up even if one camera gets blocked.