External Radiation

There are several methods of administering external radiation therapy but really only two types of radiation: photon and proton.

The type we all are familiar with is photon radiation which we know as X-rays. Basically photons have no mass, are easily scattered, and release their energy fairly uniformly dependent on the density of the matter the are penetrating. Typically the energy of the photon delivered to the body is about 30% in the first 4 cm and about 3% / cm as the photon travels through the tissue. Therefore, a limited amount of the energy is actually focused on the cancer tumor. External photon radiation includes but is not limited to: X-ray, IMRT, 3D-CRT, and IGRT.

Proton radiation is different in several ways. The proton has mass and therefore it scatters less, it is more directable, it has a finite travel distance depending on the proton speed and the density of the matter it is penetrating, and most importantly, it releases the majority of its energy as it comes to the end of its travel. This phenomenon is called the Bragg Peak. (http://en.wikipedia.org/w/index.php?title=Bragg_Peak&oldid=98689502)

The effectiveness of radiation treatment of cancer tumors is directly dependent on the amount of radiation delivered to the tumor. In fact, many doctors will tell you that virtually every cancer tumor could be destroyed if enough radiation could be delivered to the tumor.

The ability of the proton to deliver more energy to the tumor with less damage to the surrounding tissue is vividly illustrated with the following graph. (http://en.wikipedia.org/w/index.php?title=Image:BraggPeak.png&oldid=32056566)

The graph shows that about 25% of the energy is delivered on entry and a majority of the remaining energy is delivered in the last 2-3 cm of travel.

The result is that proton radiation therapy delivers more of the radiation energy to the cancer tumor which theoretically will result in destroying more cancer cells and therefore achieve a greater cure rate.

An overview of Proton Therapy is available on the Abramson Cancer Center of the University of Pennsylvania’s OncoLink! web site.

Visit the Proton Treatment Center at Loma Linda University Medical Center on line.

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