Ben Clasie, Research Fellow in MGH's Department of Radiation Oncology, explains how pencil-beam scanning proton therapy uses the narrow unmodified beam from the beam line, steering it magnetically in scanning patterns to paint the dose throughout the target.

"The scanning beam is deployed clinically here at MGH and the patients that we have treated thus far have benefited from the superior dose distributions, and hence have reduced side effects," says Clasie.

If you enjoyed this video, then you may want to watch this film about the history of the MGH and its approach to cancer therapy.