Proton therapy is a type of particle therapy which uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy is the ability to more precisely localize the radiation dosage when compared with other types of external beam radiotherapy, though it is controversial whether this provides an overall advantage compared to other, less expensive treatments.

Proton therapy is a type of external beam radiotherapy using ionizing radiation. During treatment, a particle accelerator is used to target the tumor with a beam of protons. These charged particles damage the DNA of cells, ultimately causing their death or interfering with their ability to proliferate. Cancerous cells are particularly vulnerable to attacks on DNA because of their high rate of division and their reduced abilities to repair DNA damage.

The first suggestion that energetic protons could be an effective treatment method was made by Robert R. Wilson in a paper published in 1946 while he was involved in the design of the Harvard Cyclotron Laboratory (HCL).

The types of treatments for which protons are used can be separated into two broad categories. The first are those for disease sites that favor the delivery of higher doses of radiation, i.e. dose escalation. In some instances dose escalation has been shown to achieve a higher probability of "cure" (i.e. local control) than conventional radiotherapy. These include (but are not limited to) uveal melanoma (ocular tumors), skull base and paraspinal tumors (chondrosarcoma and chordoma), and unresectable sarcomas. In all these cases proton therapy achieves significant improvements in the probability of local control over conventional radiotherapy.

The issue of when, whether, and how best to apply this technology is controversial. Proton therapy is far more expensive than conventional therapy.

See also:
https://en.wikipedia.org/wiki/Proton_therapy
https://en.wikipedia.org/wiki/Particle_therapy

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