How does imaging frequency and soft tissue motion affect the PTV margin size in partial breast and boost radiotherapy?

A boost or partial breast PTV margin of ∼10 mm, is possible with zero imaging dose and workload, however, patients receiving boost radiotherapy may benefit from a margin reduction of ∼4 mm with imaging doses from 0.4 cGy to 25 cGy using an eNAL protocol. PTV margin contributions from deformation errors are likely to be small in comparison to other sources of error, i.e., set up or delineation.