According to an article published in The Lancet in June, 2012, CT scan radiation triples the risk of brain tumors or leukemia in children. Look at this URL: http://naturalsociety.com/ct-scan-radiation-triples-brain-tumor-risk-in-children/
Also, the same article mentions that dental X-rays significantly increase the risk of brain tumors, and the risk is even greater for children than for adults.