I believe this is a question for your doctor because largely it depends on your treatment.
I had field radiation to both sides of my head as well as throat and my main salivary glands were basically nuked. Now, 4.5 years later I have an extremely dry mouth and my diet is restricted because of it.
At first I got quite angry about it but I have learned to live with it. I must have the healthiest kidneys around because of all the water I drink! It is one of the radiation gifts which I just have to live with, but I am very happy to be a survivor.
I do hope that your saliva loss is temporary. Love from Helen