osteosarcoma: malignant bone tumor; most common in children and young adults where it tends to affect the femur
sarcoma: a usually malignant tumor arising from connective tissue (bone or muscle etc.); one of the four major types of cancer
collimator: optical device consisting of a tube containing a convex achromatic lens at one end and a slit at the other with the slit at the focus of the lens; light rays leave the slit as a parallel beam