Do you always use the same CTV and PTV expansions when defining fields for lumpectomy bed boost?  

If using electron beams, we expand by 2 to 2.5 cm (based on electron energy) around the lumpectomy cavity. If using photons, then we use 1 cm for CTV and 3 mm for PTV. 

No argument with 1cm from seroma/clips to CTV (carving out skin rind/air and pec/chest-wall if not invaded); however, having practiced in a variety of centers with varying technology, I'd say the PTV expansion necessarily depends upon the image guidance techniques and motion control/monitoring syste...

As a follow-up to the other answers - is there an evidence-based rationale for adding a CTV margin to the lumpectomy cavity/seroma in the boost setting after WBI? I can somewhat understand a CTV margin for APBI given concerns for the marginal miss, but is the process of adding a CTV margin to the lu...