Protons vs photons

Both, protons and photons are used in the treatment of cancer by directing beams towards tumors and killing the cancer cells in the tumor when energy is deposited. The main difference between the two methods lies in the way the energy is deposited in the patient's body.
Photons are highly energetic packets of light that travel at the speed of light. As photons enter the patient's body, they deposit most of their energy at the surface of the patient and the energy deposition weakens as the photons travel through the patient's body and finally exits the patient's body.
In contrast, protons are electrically charged particles that upon entering the body, immediately begin slowing down as they deposit their energy. Protons deposit most of their energy immediately before they have given up all of their energy and come to rest. This leads to a peak in energy right before the protons come to rest, called the Bragg peak. The initial energy of protons may be adjusted in such a way that the protons come to rest in the tumor and minimal energy is deposited beyond the tumor. Therefore the healthy tissues that lie beyond the tumor may be spared better when compared with photons. This can be of great benefit to the patient in most cases.
Accelerating protons to energies suitable for treatment of most cancers is technically difficult and expensive. Therefore there are far fewer proton beam therapy facilities available than photon therapy facilities. In some cases the energy deposition difference described above is not of the highest importance and photon therapy may be more beneficial to the patient. Radiation oncologists use scientific evidence to determine which radiation type is best for any given patient and tumor location.

Answered by WGATE

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