Not any easy case you are having there. We have only minor experience of multi-iso DIBH treatments. Still we remember something about those cases. We imaged patient normally with the first isocenter and performed the couch shifts if there was any. Hopefully after the shifts done in the online match we were still inside DICOM_BH, because it was easy to treat the second isocenter with DICOM_BH by just performing the planned couch isocenter shifts (based on plan values) after the first isocenter was treated with the same couch vertical as previous isocenter. If we treated the first isocenter with VRT_BH surface, we used that surface as a tool to achieve similar kind of position and breath hold for the second isocenter. So after the first isocenter was treated we went to treatment room and asked patient to take a breath in to the first isocenter VRT_BH surface. When BH was inside thresholds we changed the second isocenter on the AlignRT screen, did the planned couch shifts (based on plan values), acquired reference capture in the second isocenter BH_DICOM surface- view (without necessarily setting monitoring on) and finally let the patient breath again. Imaging was not performed in between the isocenters. There may be different kind of workflows but that was something like ours. Hope this helps.
Regards RTT Marko and RTT Turkka