[Freesurfer] ICV for incomplete whole brain coverage

A colleague asked me to look at some T1s for possible Freesurfer analyses. Unfortunately, several subjects do not have whole brain acquisitions (I know, quite unexpected and disappointing). Would it be possible to correct volumes of subcortical structures (which are covered by the acquisition) for ICV in the absence of whole brain coverage? The T1s were acquired in the coronal plane...so typically brain tissue is missing in either the anterior and/or posterior regions.

I reflexively think that whole brain coverage is required for accurate ICV calculated by Freesurfer...but I'm not positive.

Many Thanks for any thoughts you might have, Jenifer