Proton beam therapy (or simply “proton therapy”) is a method of treating cancerous tumors that, unlike traditional chemotherapy or radiation treatments, can target the cancerous cells specifically while leaving the surrounding healthy tissue unaffected and with fewer side effects. Proton therapy uses beams of protons sped up through a particle accelerator and beamed through the skin into the affected area.


In 1946, Robert R. Wilson, a pioneer in atomic research and a group leader on the Manhattan Project, published a scientific paper that proposed the idea of using energized protons to treat cancer. Scientists used particle accelerators in Berkeley, California, and Uppsala, Sweden, in the 1950s to prove its effectiveness. In 1961, the Harvard Cyclotron Laboratory reached a working agreement with Massachusetts General Hospital to research and develop methods of proton therapy. When the lab shut down in 2002, other centers around the world either had developed or were on their way to developing proton therapy treatment centers, including the world-famous M.D. Anderson Cancer Center in Houston, Texas.

How it works

Protons are subatomic particles with a positive charge that reside in the nucleus of an atom. Electrons are subatomic particles with a negative charge that orbit around the atom’s nucleus. When beams of protons pass near the electrons, their opposite charges attract and pull the electrons from their orbits and create a net-positive charge in the targeted atoms. This atomic process, known as ionization, changes the structure of the atom and is used as the basis for all radiation therapies. With the altered atomic structure of each atom in the intricate and delicate DNA molecules in each cell, the ability for these cells to heal and reproduce becomes diminished. Since healthy cells are better equipped for self-repair than cancerous cells, the malignant cells die off faster.


As opposed to X-ray-based radiation treatments that spread radiation damage to both cancerous and normal cells alike, proton radiation can treat tumors close to the skin level without dispersing enough to cause problems to healthy cells. Such precision with these beams allows for treatment of cancers that have not yet spread as well as those cancers in more sensitive areas (eyes, prostate, spinal cord) that may suffer severe damage under the same exposure levels with standard radiation treatments. This method has also shown great efficacy in treating cancer in children, who typically would suffer from growth problems and secondary cancers from other forms of radiation therapy.


Like all radiation treatments, one of the major hindrances to proton therapy is the expense involved. The costs involved in developing the required particle accelerator and radiation shielding to surrounding areas can run into hundreds of millions of dollars in construction costs and requires hundreds of tons of material. Also, proton therapy treatment centers are not yet widely available. Less than a dozen centers are currently open in the United States, with another eight to ten expected to go online in the next two years.


In a similar fashion to computer and communication technologies, new companies are developing smaller and cheaper particle accelerators and proton beam machinery. In the future, hospitals may have proton beam systems that fit in one room instead of the building-sized accelerators required today. Such technological growth can only help to serve patients, expand therapeutic methods and reduce treatment costs.



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