Hi there,
I'm in England,, but I was diagnosed with this nearly three years ago. I had a lot of initial tests, including bone marrow biobsy, blood tests, x rays ans many scans. One they had decided what was wrong, I was told that this is a very slow reacting contition and it is not treated in any way while it is 'idolent' in other words not effecting my lymph glands or any other organs.
It is frightening to be told that you potentially have cancer, and I started having blood tests every 4 months, then 6 months, and now as the results remain stable, I don't need to go back for another year.
So tell your Dad that 6 monthly checks are fine, but if he feels unwell or has any worries, he should tell his doctor. Althought the condition is not effecting the organs and will effect the body and therefore feeling tired is quite normal, you have to remeber that. And he may be more vulnerable to colds, infections etc., so just keep an eye on things.
There is a lot of info on the web about this condition, but be careful not to frighten yourself or your Dad with what you read - it can be scary.
So good luck, and I hope that your father continues to have good results with each blood test.
Maggie