Is my brother's cancer in the bones if cancer cells were found on both femur bones?

My brother is 66 and was diagnosed with diffuse Large B-Cell Lymphoma last May. He has had 8 mos of chemo and following another PET Scan found cancer cells on both femur bones and a new knot in the same spot where the first one was removed. He has now gone through 5 weeks of radiation which was 5X weekly. He is complaining of his knees hurting and his back hurting. He cannot sit in a hard chair and tires very easily.