Thanks Mary, there does seem to be no harm in asking him about it so will do that.
Actually i have rheumatoid arthritis and one thing that I found interesting during my mom's treatment were the common drugs used between PCNSL and RA. Though RA being an autoimmune disease i suppose that's natural. I've been taking MTX for years, of course very small doses, and then i read that rituxan is also given in RA. My drs also never prescribed rituxan to me but in my case its evident why. I haven't been given any biologics and rituxan is only given when other biologics have failed.
So anyway i went off the tangent there, actually in our country there's really not much of a culture of patients questioning dr's choices so i don't how he'll react but it's my mom's life and we need to be sure that she's getting what's best for her. I'm sure the onc has his reasons and he shouldn't mind telling us what they are.