You didn’t know, and you weren’t told. You are not a doctor and you depended on your doctor/urologist to give you the proper guidance.
I do not know all the particulars of your case, but surgery on a 78 yr old is usually NOT the first option. It’s an option but not one often chosen by men close to 80 years of age.
Were you even told of radiation? Did you get a second opinion from someone who wasn’t a surgeon?
It’s water under the bridge at this point but your current condition might have been prevented if you had more information before you made your decision.