Proton radiation, represented in this illustration as a beam of light, can reach deep tumors without damaging key tissue. For example, a brain tumor can be treated without damaging cells closer to the surface.

X-rays, on the other hand, lose energy as they pass through healthy tissue. Therefore, to get the same dose at the tumor site, more radiation is required, and this can damage healthy tissue.

What is Proton Therapy?
Proton therapy is a type of radiation treatment similar to standard radiation treatments such as gamma knife radiation, x-ray therapy, brachytherapy, radioactive seed implantation, and so on. The difference is that all of these treatments, except proton radiation, are light waves. These light waves have too much energy for the eye to see, but they behave according to the same rules of physics. If you place the end of a flashlight to your hand, in the dark, you will notice that you can see light through your hand. Most of the energy is absorbed near the source (you can feel heat on the side of the hand close to the flashlight), but some travels through to your eye, and you see it. So it is with x-rays and gamma rays. Most of the energy is deposited near the skin; a small fraction travels deep inside the body to reach the tumor. Protons are sub-atomic particles that behave like light waves when they travel at speeds close to the speed of light. Unlike x-rays, they travel a very precise distance into the body. That means, if there is a critical organ that cannot tolerate radiation, the proton treatment can be designed to deliver a very high dose of radiation to the tumor and miss the organ completely. Also, protons traveling at high speeds do not deposit energy close to the source. So if you could hold your hand up to a "proton flashlight", you would not feel any heat, nor would you be able to "see" the protons coming out the other side. Thus proton radiation is fundamentally different from x-rays and gamma rays. Most of the proton energy is deposited at the site of the tumor.

Because proton therapy can deliver high doses of radiation to a tumor without damaging healthy tissue, it is used most often for tumors that are near critical tissues such as optic nerve, functional centers of the brain, spinal cord, rectum, intestine, heart, and urinary tract. This delivery advantage is especially important for pediatric cases. Treatment of retinablastoma, for example, requires radiation to be delivered through the skull, near the child's eyes. Although the tumor can be successfully treated in almost all cases, the radiation delivered to the growing skeletal bones causes them to grow less than the ones not irradiated. The end result is permanent malformation of the child's face. Proton radiation can not only destroy the tumor, but prevent damage to the child's face. Proton irradiation can also cure optic melanoma without requiring removal of the eye, or loss of vision. The choice of proton therapy can often significantly improve the patient's quality of life while effectively treating even radiation resistant disease.

If proton therapy is so good, why are there so few centers in the USA?
Proton therapy centers are very expensive to build. This is not translated into cost to the patient because proton accelerators have extended lifetimes, and are not expensive to operate. But it is a difficult initial expense, much like purchasing your first home. The cost of an average clinic is about 80 million dollars. There are currently 2 operating proton therapy centers and 3 more under development in the USA.

Is proton therapy experimental?
No. The concept of proton therapy was first developed by Dr. Robert Wilson in 1946. The University of California at Berkeley began treating patients in 1954, following the construction of the cyclotron at Lawrence Berkeley Laboratory. Although the treatments were very effective, the real advantages of proton therapy could not be realized until imaging systems (CT, MRI, PET) were invented that could precisely locate the tumor. The Harvard Cyclotron Facility pioneered modern proton therapy, treating thousands of patients beginning in 1961 and ending in 2002. The Health Care Financing Administration (HCFA), the federal agency that administers Medicare, Medicaid and the State Children's Health Insurance Program, has recently established reimbursement criteria for proton therapy. This indicates that 1) proton therapy is not experimental, 2) Medicare and Medicaid will reimburse hospitals for this treatment, and 3) no insurance company can refuse to reimburse on the basis that this is an experimental treatment.