It might help you to know that there are all sorts of things that may be making your father act like this: pain, nausea, depression -- he may even be
in an altered state because of chemicals in his system from radiation or chemo. It's possible he may not even know what he's saying or how he's saying it.
Chances are, he's really hurting and he's taking his pain and discomfort out on you. In other words, it's not about you -- it's about him and how awful he feels. Of course, that doesn't make his outbursts okay. And you have to find ways to cope, or you won't be able to continue to care for him.
If you have siblings or anyone else sharing care for your father who is also receiving abuse, it really helps to commiserate with each other. My sister and I used to use baseball terminology and ask each other each day, "So, which ball got thrown at you today? Was it a curve ball or a line drive?" It helps to get it out in the open and talk about it so it's not as personal and you don't feel so hurt.
Another strategy that works well is to give yourself permission to leave the room at any time. You don't have to continue the conversation if it's getting unpleasant. Not only do you give each other some space to cool down, you prevent yourself from reacting and making the situation worse. And you send a signal that you don't want to be talked to like that.
When you come back into the room, start a distraction. Turn on the TV or radio so the focus isn't on the two of you anymore. Or while you're out of the room, call a friend or family member from your cell phone and ask them to call your parent or drop by. This gives your father the opportunity to talk about something else, which can break the vicious cycle of complaints and griping.
You probably have days when you're asking yourself, "Why do I want to care for him? I'm not getting anything out of this. Why should I put up with being treated like this?" When you feel this way, get someone else involved. Have someone take over for a day and give yourself a break.
If you don't have a friend or family member you can call, this is when you want to consider bringing in some paid help, such as a home care nurse or nursing assistant -- at least once in a while. You may also need to enlist a social worker or oncology nurse at the hospital for guidance. It won't serve your long-term relationship with your parent if it deteriorates into abuse, so you may have to involve others to prevent that.