Has anyone had hipocampal sparing whole brain radiation?

Hi everyone,
I have HER2 positive breast cancer with many brain metastases.  I've had Gamma Knife treatment in the past but new lesions keep developing so now I have been offered hippocampal sparing whole brain radiation as my only treatment option.  From reading all the posts about whole brain radiation, I am very reluctant to go ahead with this procedure, hippocampal sparing or not.    I currently have no symptoms but I will soon be unwell according to my oncologist.
Has anyone had this treatment and what side effects, short-term and long term, did they experience?
Thank you very much,
N x