I'm 45..no children, peri-menopausal, no period in 3 months, fibroids biggest 8 cm. can i insist on not having a hysterectomy?

Yes and No: Doctors have rights too! If you and your doctor disagree, you can certainly ask for a hysterectomy but you can't force your doctor to operate. (Insisting on something that is against your surgeon's better judgement could be hazardous to you.) Its better to get a second opinion or look for another doctor whose treatment plan corresponds more closely to your desires. Best wishes!

Of course, you can: Since most fibroids are benign muscle tumors which can remain asymptomatic and unchanged till the menopause when they tend to shrink, you should indeed "Insist" on obtaining a clear description of your risks, benefits, alternatives etc. and on the medical-gynecological indications for a hysterectomy in order to make an informed decision that you feel comfortable with (surgery as your last resort.)