Emily Whittington, a radiation therapist at Vanderbilt-Ingram Cancer Center, pulls down a mask intended to guide radiation beams into patients with head and neck cancer. Emily Siner/NPR hide caption

itoggle caption Emily Siner/NPR

Japan Aerospace Exploration Agency astronaut Aki Hoshide makes a space walk outside the International Space Station in 2012. NASA/Getty Images hide caption

itoggle caption NASA/Getty Images

Radiation therapist Jean Etienne holds a range compensator, which shapes the depth to which the proton beam enters a patient's body to target a tumor. Rebecca Davis/NPR hide caption

itoggle caption Rebecca Davis/NPR

This illustration shows a device made by MammoSite used to deliver targeted doses of radiation as part of brachytherapy. Courtesy Radiological Society of North America hide caption

itoggle caption Courtesy Radiological Society of North America