Stereotactic Bragg Peak Proton Beam Therapy

Abstract

Stereotactic Bragg peak proton beam therapy has been performed in more than 2,000 procedures during the past 25 years at the Harvard Cyclotron Unit. This technique was developed as particle beam surgery, in which the terminal energy peak of protons (Bragg peak) is directed to an intracranial target by the stereotactic method. Proton beams are not electromagnetic radiation but share with it the ability to induce ionization in biologic systems. There is no exit dose of radiation beyond the target. The dose (rad) of a single beam is two to four times greater than the path dose at the Bragg peak [6]. The Bragg peak of the proton beam is biologically more effective than are the plateau portion of the proton beam, cobalt-60 rays, or roentgen rays at the same physical dose [7, 13]. If a number of such beams are converged upon a brain target, the dose within the target may be many times greater than the dose along any path. For example, if 12 proton beams from different directions are focused upon a pituitary tumor, the dose within the tumor is more than 25 times as great as any path dose.