Pencil beam scanning couples this unique property of the proton beam with an electronically guided scanning system that delicately and precisely moves a beam of pencil point sharpness back and forth across each layer of the tumor’s thickness to paint the tumor with radiation in three dimensions while eliminating dose to the normal tissues on the other side of the cancer. This ultra precision makes pencil beam scanning an ideal treatment for irregularly shaped tumors that are located next to critical tissues and organs, such as tumors of the prostate, brain or eye. - See more at: http://www.itnonline.com/content/pencil-beam-scanning-increases-precision-proton-therapy#sthash.moN2KIxP.dpuf