Newer radiation therapy techniques could reduce the harmful adverse effects of brain radiation therapy in children. For children who undergo brain radiation therapy, permanent neurocognitive adverse effects are a significant risk. These risks arise because the radiation often encounters healthy tissue, which reduces the formation of new cells, particularly in the hippocampus. The hippocampus is the part of the brain involved in memory and learning.
The newer techniques use proton beams. While traditional x-ray radiation and electron radiation pass right through the body and so have the potential to harm healthy tissue, the energy in a proton beam can be varied so that it reaches a predetermined depth. The protons can be concentrated to the actual tumor with a minimum dose to healthy tissue, which reduces the risk of adverse effects.
A model study tested how the harmful adverse effects could be reduced by using newer techniques. The study was based on a number of pediatric patients who had undergone conventional radiation treatment for medulloblastoma, which is a form of brain tumor that almost exclusively affects children. The study simulated treatment plans using proton therapy techniques and newer proton therapy techniques.
Four techniques were compared: standard opposing fields, intensity-modulated radiotherapy, intensity-modulated arc therapy, and intensity-modulated proton therapy. While maintaining at least 95% of the prescribed dose in 95% of the whole-brain target volume, the mean dose to the hippocampus and subventricular zone could be limited to 88.3% with intensity-modulated radiotherapy, 77.1% with intensity-modulated arc therapy, and 42.3% with intensity-modulated proton therapy. These newer techniques reduced the estimated risks for developing memory impairment to less than half that with standard opposing fields.
The study concluded that these techniques are feasible, and that they lower the risk of long-term neurocognitive adverse effects. Intensity-modulated proton therapy achieved the most sparing of the hippocampus and subventricular zone, so it is an attractive option to be tested in a prospective clinical trial.
“This could mean a better quality of life for children who are forced to undergo brain radiation therapy,” says Malin Blomstrand, first author and doctoral student at the Sahlgrenska Academy at the University of Gothenburg. This study is published in Neuro-Oncology (2012; doi:10.1093/neuonc/nos120).