Figure. DR. ROGER J. PACKER RESPONDS:
A Standard X-ray therapy, in which radiation is “scattered,” is often used when a tumor's edges are ill defined. Conversely, proton-beam X-rays provide greater ability to limit radiation to a well-defined tumor.
Standard X-ray therapy uses photon particles to deliver radiation to the affected tissue. This results in both an entry beam—the path of the beam entering the targeted tissue—and an exit beam—the path of the beam when it leaves the tissue—as well as some scatter radiation to the surrounding tissue. When the tumor is ill defined, scatter radiation is desirable because it may get the leading edge of the tumor.
Proton-beam therapy uses proton particle radiation to target affected tissue. Although there is an entry beam, there is no exit beam, which provides a greater ability to target the radiation to a specific area. The proton beam has a significant advantage when the tumor is located at the periphery of the brain, because all the radiation can be aimed toward the tumor without affecting surrounding organs.
The side effects of proton beam radiation are similar to the side effects of any form of external radiation. The brain is exposed to essentially the same dose of radiation therapy and, as a result, the long-term effects on cognitive functioning—thinking, memory, and executive function, such as attention—may be the same regardless of the type of radiation used. However, since the proton beam can be a bit more focused, it may spare other sites, such as the inner ear, causing less hearing deficits.
Parents and caregivers should discuss their options with treating physicians and with the radiation oncologist available in the patient's community. If proton-beam therapy is determined to be a better option, patients should visit a facility that is experienced in the delivery of proton-beam therapy, especially in pediatric brain tumors. Go to www.proton-therapy.org to learn more.