Can the donor hair be taken from the sides of the head. I don’t want to thin the back of the head any further.

It is best to ask your surgeon about operative issues as each doctor has their unique regimen.  Your doctor also needs to examine you to make sure what you are asking is possible.

When treating hair loss with FUE and FUT techniques hair can be harvested from both the back and the sides of the scalp. 

The donor hair can be harvested from the horseshoe which consists of the occipital and parietal scalp (back and sides). There is a limit to harvest of approximately 10-15% of the available follicles in order to avoid thinning at the donor site.As always, discuss your concerns with a board certified plastic surgeon (ABPS) with experience in hair restoration.