sentences:  Both CT and MRI can be used to follow response to radiation and/or chemotherapy.Bone scintigraphy can also be used to follow tumor response to therapy.In the group of malignant small round cell tumors that includes Ewing's sarcoma, bone lymphoma, and small cell osteosarcoma, the cortex may appear almost normal radiographically, while permeative growth occurs throughout the Haversian channels.