A neutron is made of up, down, down quarks, and a proton is made of up, up, down. An antineutron would be antiup, antidown, antidown, and the ups and antiups and the downs and antidowns would annihilate if it was in the same atom as a proton.

Surgeons are guided by imaging devices like PET, CT and MRI scanners. You can use contrast agents to show areas of greater glucose metabolism, for instance, as cancer cells use energy faster than others for respiration and blood vessel construction, and draw a contour around that to be used in surgery and radiotherapy.