Proton therapy is a medical treatment that sends a beam of protons into the body to destroy infected tissue, typically cancerous tissue. It uses ionizing radiation and a particle accelerator to direct the proton beam at the cancerous tumor. This helps to better protect the nearby healthy tissue while destroying the cancer, most often cancer of the brain, eyes, spine, lungs, head, neck or prostate. Cancer treatment remains its main use in the early 21st century, but proton therapy also is being studied for its potential benefit in the treatment of such medical conditions as macular degeneration.
By bombarding cancerous tissue with protons, proton therapy destroys the deoxyribonucleic acid (DNA) of the cells. Many cells have the ability to repair their damaged DNA. Cancer cells reproduce so quickly that they are less able to make those repairs before the defective genes are passed on or before the damaged cells simply die.
This type of particle therapy, which has been used as a medical treatment since the 1950s, is chosen over other types of radiation therapy for one of two reasons, depending on the type and location of the cancer the patient has. First, because of the nature of energized protons, proton therapy radiation can be given in larger doses. The protons can only go a certain distance into the body according to the amount of energy they have. Sending higher amounts of radiation at the tumor works, because the protons are too localized to do much damage to surrounding cells. Other types of radiation have to be given at lower thresholds because they cannot be controlled the way proton therapy can.
Second, the radiation can be given in a normal dose but in a narrower beam so it is not likely to harm neighboring tissues and organs. Sometimes an inadequate treatment dose doesn’t worry a doctor as much as the treatment’s potential to damage other cells. By having the ability to narrow the stream to a microbeam of protons focused on a particular area, doctors can minimize damage elsewhere.
There are different types of proton therapy from which doctors can choose the most effective for a particular type of cancer. Each type of charged-particle therapy works similarly, but with differences in the charged protons and the injected materials used. Boron neutron capture therapy is a therapy that was being tested in early 2011. It involves boron being injected into the tumor and then shot with a beam of neutrons. The neutrons cause the boron atom to split, destroying the cell completely with almost no effect on nearby cells and healthy tissues. Fast-neutron therapy works in a similar way, but uses injected beryllium as the target instead of boron.