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Proton Therapy is a form of radiation therapy used to target tumors and cancerous cells. Proton therapy is used in the same form as therapeutic x-ray radiation treatment. According to companies specializing in proton beam therapy around the world “proton beam therapy is the most precise, painless and noninvasive form of radiation therapy used today to treat cancer and other benign conditions.”

The positively charged particles named protons are 1,800 times larger then photons allowing to control the radiation dose in three dimensions. According to Optivus Proton therapy, “As protons travel through the body interacting with tissues, their velocity slows until reaching the intended target “the tumor” where the bulk of the energy is released in a sharp burst (ionization), followed by a rapid decline in dose energy. Virtually no radiation is expended beyond this point.” In proton beam therapy there is very minimal radiation on entry, surrounding the target and exiting the target, making this a very efficient form of radiation therapy.

As a proton is a positively charged particle, when it comes in contact with or pass by the targets electrons, the proton pulls the electrons out of orbit. This ionization damages the targets molecules and in particular the molecules DNA. By destroying the DNA and the molecules the tumor starts to get destroyed due to the permanent damage caused to the cell. This is how proton beam therapy and x-ray therapy work, but being proton therapy less post target radiation and surrounding radiation of healthy tissue occurs.

In proton beam therapy, the protons are accelerated to a certain velocity via a cyclotron. These velocities determine the depth that the proton will release its energy. In a cyclotron a hydrogen molecule (H2) is hit by a large electric arc producing a negatively charged hydrogen ion (H-) that is basically a proton nucleus with two electrons. By applying an electromagnetic field the ion is accelerated in the particle accelerator. The ion then passes through a stripper removing the electrons, projecting the proton beam.

Varian includes information about there 250 MeV Isochronous Superconduction Cyclotron that uses a powerful magnet and electrical fields of alternating polarities to create accelerated beams of protons. These high MeV energies allow for deep delivery. The continuous and stable proton beam for increased dose rates and precise control, and excellent reliability due to high beam extraction rate that maximizes the availability and facilitates preventive maintenance. Using bending and focusing magnets and different measurements the proton beam can be directed to the desired location from the cyclotron to the treatment room.

References

- Imaging Economics “Proton Therapy Center offers Glimpse of Things to Come.”http://www.imagingeconomics.com/techedge/2010-04-28


- Varian Medical Systems “Proton Therapy” http://www.varian.com/us/oncology/proton/


- Optivus Proton Therapy http://www.optivus.com/proton-therapy.html


- The National Association for Proton Therapy “how it works” http://www.proton-therapy.org/howit.htm

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