The Morning Call of Allentown, PA, reports about an effort to build a proton therapy center, describing it as “a type of radiation therapy available at only three major medical centers in the country”.
For additional information about the physics of proton therapy we go to IBA, a Belgian company, one of the manufacturers of proton accelerators:
In conventional radiation therapy, photons (standard x-rays) or electrons, the intensity of the beam decreases exponentially with the penetration depth and the beam has no finite depth. However, beam must be delivered into the body in sufficient doses to ensure that enough interactions occur to damage all cancer cells.
Protons are accelerated to specific energies and these energies determine how deeply protons will deposit maximum energy in the body.
When entering the body, the energy of the incident particle is slowly increasing with decreasing velocity until it suddenly reaches a sharp maximum just before the end of the proton range. This point, where the high-dose region of energy release occurs, is called the Bragg peak.
Additionally, with their heavy mass compared to electrons, protons exhibit little lateral deviation when entering matter. Tumor control is therefore further improved in comparison with the large lateral deviation associated to photon beams.
These two major advantages of proton over photons coming from intrinsic physical properties (small angular scattering and localized radiation damage) give proton beams the unequalled advantage of delivering a precise dose of energy directly to the tumor while reducing adverse effects to adjacent normal tissues as experienced by conventional radiation treatment. From a patient’s perspective it makes protons the smartest way for radiotherapy.