diag tongue base cancer / has mechanical heart valve

My 53 yr old brother was recently diagnosed with base of tongue cancer.  He has a St Jude mechanical valve and takes coumadin.  I am worried about the effects of chemo and radiation on the heart and blood.  I can't seem to find any info on this.  The ENT has stressed the dangers of the biopsy.  He is going for the PET, MRI/CT tomorrow so we don't know how far advanced anything is yet.  I would appreciate any word from anyone that has a mechanical valve and has had cancer treatment.  Thanks, worried sis!