Comparing the Safety and Efficacy of Proton Therapy versus Photon Therapy
Radiotherapy is part of the standard treatment for many types of cancer. It is not without consequences, however.
Conventional radiotherapy (or photon radiation) penetrates tumors as well as healthy cells in the path of the X-ray beam. This can be particularly damaging when used to treat brain tumors and is associated with post-therapeutic cognitive deficits. Infants and young children, who are still in early stages of development, are most at risk.
By contrast, proton therapy directs a beam of radiation at a tumor, and the radiation particles stop there. It does not exit the tissue, and is hoped to create far fewer adverse events such as cognitive damage and other complications.
Carol L. Armstrong, PhD, ABPN, and researchers at the Center for Childhood Cancer Research are comparing the efficacy and side effects of proton therapy with pre-existing historical data on conventional (photon) radiotherapy, particularly in the area of cognition.
Cognitive markers of injury are being developed and validated to compare the two types of radiotherapy. Cognitive effects are being assessed with a battery of psychological testing that show that one memory system is easily damaged by radiation, and other memory and cognitive systems are more resistant. This research has revealed a window of recovery for children during the year following radiation.
For infants, an innovative cognitive biomarker called the Conditioned Eye Blink Response is being investigated. Very young children are exposed repeatedly to a tone followed by a gentle puff of air to the eye, and tracked to see how long it takes for them to make the association, anticipate the puff of air after hearing the tone, and develop an adaptive avoidance behavior, i.e., blinking when they hear the tone only in anticipation of the air puff.
The eye blink measurements are performed prior to proton therapy and then afterwards and are tracked longitudinally. Since this eye blink measurement has been performed repeatedly in other research (including non-cancer research such as in premature infants and fetal alcohol syndrome), it has been shown to be an effective learning measurement tool.
This particular measurement is important in understanding cognitive development in the cerebellum. The single most common site of brain tumors in infants and young children is the cerebellum. As the cerebellum develops for a long period of time, it is particularly sensitive and susceptible to damage from many forms of neurological injury.
The findings from this research will contribute to an understanding of the critical windows when cognitive functions are most affected by radiation therapy, and when a period of recovery is expected. This is important because it suggests the best time for cognitive rehabilitation. This research will also contribute to cerebellum-mediated cognition and post-radiotherapy developmental effects.