Radiation therapy, alone or in combination with other treatment, is an important treatment for many cancers. More than half of all cancer patients receive one or more courses of radiation therapy as part of their treatment. Intense amounts of energy are directed at cancer cells to destroy the genetic material that controls cell growth. Both healthy and cancer cells are affected by radiation, so the goal is to try to target only the bad cells as much as possible.
X-rays (photons) are the energy source in conventional radiation therapy. However, an X-ray radiates everything in its path, in front of and behind the target. So X-ray doses need to be reduced from the optimal therapeutic dose to protect surrounding normal tissues from harm.
In proton therapy, energy comes from protons, the positively charged parts of an atom. Protons are generated by a powerful machine called a particle accelerator. Unlike an X-ray, the proton stops after striking the target. A proton beam can be much more finely controlled, in both its width and its depth, so higher doses of radiation can be more safely delivered to tumors, with less risk to healthy tissues.
Mayo's program will employ the next generation of proton therapy — intensity-modulated proton beam therapy, using pencil beam scanning, which "paints" small groups of protons back and forth through a tumor. The protons fill the depth and contour of the tumor, allowing greater control of radiation doses, shorter treatment times and reduced side effects, compared with most other proton therapy systems.
Proton therapy has been shown to be beneficial in the treatment of many kinds of tumors, including head and neck, eye, central nervous system, lung, sarcomas, gastrointestinal, prostate, and many pediatric cancers. The precision of pencil beam scanning makes it especially beneficial in treating tumors adjacent to critical and sensitive organs, such as the brain, eye and spinal cord.
Benefits of pencil beam proton therapy include:
Children with cancer stand to benefit the most from proton beam therapy. Children suffer the greatest long-term harm from conventional X-ray therapy since their organs are still growing and developing. Some delayed effects of X-ray therapy in children include arrested bone growth, low IQ, hearing loss, hypothyroidism, pituitary dysfunction, radiation-induced cancers and coronary artery disease.