Introduction.

The idea and implementation of Proton radiation is not new. The birth of the idea of using Proton Radiation as medical therapy was in 1946. You may find it’s interesting history here.
The use of this form of radiation therapy is gaining widespread use. If one is faced with the unfortunate situation of undergoing cancer treatment, especially radiation, the inevitable search on Google may lead to the term Proton radiation. This brief post intends to give the reader some basic understanding of Proton Radiation.

Various kinds of radiation in Medical use.

There are many ways to classify radiation modalities. The most useful and basic starting point of classifications seems to be based on the kind of radiation employed. Three common ones used nowadays are:

• Photons
• Electrons
• Protons

Photons and electrons based on their physical properties are used widely for various cancers. For example, electrons deliver most of their energy as they hit the surface of the skin and thus are useful for superficial tumors.

Radiation with Photons.

This is currently the most commonly used form and based on modifications of use, many different forms are available such as conventional radiation , 3D conformal radiation, Intensity Modulated Radiation, brachytherapy, GammaKnife and CyberKnife to name just a few.
Essentially a Photon beam is delivered to pass through the body and within the path of the beam lies the tumor. Think of the picture below representing a section of the body containing tumor (red mass) and the radiation beam (arrow) has to pass through the normal tissue, hit the tumor and the pass beyond it through normal tissue again. The beam damages the tissues in the entirety of its path. Normal tissue may get more damaged than the tumor itself.

source, modified

A modification of methodology is to give smaller intensity beams from various angles with these beams intersecting at the tumor. The greatest effect is thus in the tumor rather than the normal tissue. Imagine this as a sunray pattern as depicted in the picture below.

source

Radiation with Protons.

There are many differences between photon wave properties and the properties of a heavy particle like a proton which is carrying a charge. The important property of Proton radiation that makes it unique lies in the way it loses energy. This is called Bragg peak.

What is Bragg peak?

A Bragg curve is simply a graphic representation of the energy loss of radiation. A proton as it travels through the body slowly loses energy thus delivering very little radiation to the tissue. It then suddenly loses a lot of energy at once as it comes to a halt. So most of the radiation given off is at the point just before it comes to a rest. This is graphically represented as the Bragg peak.

source

In the above diagram, you can clearly see the difference between a photon (in red) energy loss and a proton (in yellow) energy loss pattern.

Proton Radiation utilizes Bragg Peak to target tumors.source

Protons are generated from a Hydrogen canister. Protons are then passed through a vacuum tube into a linear accelerator and accelerated to reach an energy of 7 million electron volts. As they enter the synchrotron they are accelerated further to an energy of 70- 250 million electron volts. This is needed to get them into the body wherever desired. They are shot via beam control mechanisms and modified nozzles to the target tissue.
Controlling many factors and with intense computations, you can very precisely control where the Bragg peak will occur in the body. When made to occur in the tumor, the tumor suffers the most damage with very little damage to the surrounding tissue.

Commentary.

Proton therapy provides precision minimizing collateral damage. Thus the utility of it can be imagined when radiation is needed in vital brain areas or structures near eyes or other important areas. There is thus far a paucity of randomized controlled trials that show absolute superiority of Proton radiation vs Photon radiation in every situation. Yet based on physics alone, Proton radiation touts it’s benefits. It has become increasingly popular. My post is simply educational. The post makes no claims of superiority of one modality of radiation vs another. Those decisions are best left to a treating radiation oncologist.