Dealing with a Toxic Parent

84 years old.  Always put himself first.  Extreme jealousy over everyone who is doing better than he.  Can't stand to see anyone with an ounce of money.  This is the person who is my father.  He was not always this way.  For a brief time he found God and became a much better person.  That doesn't mean he wasn't strange.  Always believed in witchcraft and voodoo.  Always been a difficult person.  
I was raised in the Catholic church to honor my parents.  My father used it like a weapon--to this day sprouting this scripture.  
Let me ramble on--I see people marrying and divorcing.  No big deal if you don't have kids, but to all that are considering that wonderful man you just met and you're thinking he's cute, and yes he has some problems, but maybe you can get used to them.  Think of your children.  Think of them long after you've divorced that person and moved on with your life.  'Cause, guess what? 
Your kids can't divorce a parent and just move on.
Ever hear about the woman who was charged in neglect because she'd left her 95 year old mother alone?  Well, yes it can happen.  You see, you become responsible for the old geezers when they get old.  You just can't up and leave them.  Think of the headlines,  "Senior Citizen found Home Alone, Living in Squalor, with No one to Care for Him.  Daughter Charged."
This sort of thing has happened.  Once they get in their 80s they become your kid whether you want them or not.  It's even worse, because you can drop a kid off at the police station if you don't want them.  It's cruel, but it's allowable under the law.
Now you take my 84 year-old kid.  He's mentally sound.  He's not going to just let me bundle him up in my car and drop him off at the police station.  Did I mention he still lifts weight and has a six-pack stomach.  We're not talking about some old, feeble guy here.  Yet, when I go into a place of business, people will direct questions to me if he says something strange.  And when he canceled his doctor's appointment for radiation treatment, they called me, like I could change his mind about talking to the doctor.
So he's my responsibility. 
Back to the radiation thearpy.  He was diagnosed with prostate cancer a few months ago.  It's pretty common in his age bracket and most of the time is not life threatening.  Nevertheless, the doctor referred him to a radiologist.  My father refused to go.  And he also forbid me from talking to his doctors.  Under the law he's allowed to do this.  Still, the receptionist called me to ask if it's okay for him to cancel his appointment.  Doubt if she would have done this if he'd been in his 50s or 60s.  Like I said he's my kid, but I don't have any control over him.  
So, I talked to my dad, trying to get him to see the doctor.  I was told to butt out, that he is 84 and it's none of my business.  I was told that I never did anything for him.  And that my late husband didn't want me.  
Still, the law says he's my responsibility.
What I got here is an 84-year old teenager.  I've got the responsibility, but like a teenager, I can't always control him.  
So, what can I do?  Nothing.  Absolutely nothing.  He called yesterday and apologized.  He said he's going to get some medication to control his nerves.  He had a nice, long talk.  I had a nice, long listen.  Then he told me that I've never done anything for him and that I do everything for my grandkids.  I've never done a thing for those grandkids other than loving them and buying them Xmas and birthday presents.
Again, no progress.
So, thanks everyone for reading this rambling journal, but there's no escape for me, other than in the arms of the Good Lord.  Frankly, I would prefer it.