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Irradiation therapy for the brain cancer medulloblastoma is more likely to impair IQ and reading skills of younger children than older children even if the dose of radiation is reduced, according to results of the largest study of its kind, conducted by investigators at St. Jude, Texas Children’s Cancer Center (Houston) and Royal Children’s Hospital (Melbourne, Australia).
The researchers found that the greatest rates of decline in IQ and reading skills occurred in patients who were younger than 7 years old at diagnosis. Patients who were at either high risk (HR) or average risk (AR) of treatment failure suffered significant loss of reading skills over time following treatment.
The study also allowed the researchers to develop a way to predict the number of IQ points that would be lost by both HR and AR patients depending on whether they were older or younger than 7 years at time of diagnosis and treatment.
The study used “risk-adapted” radiation therapy in which the dose of radiation was adjusted. Patients in the study were classified as HR (37 patients) or AR (74 patients) according to whether the patient’s cancer had already spread and how much tumor was left following initial surgery to remove the cancer. HR patients were considered more likely to experience treatment failure and therefore received higher doses of radiation.
The loss of reading and spelling skills among both AR and HR children apparently is caused by impairments of the fundamental cognitive processes that are critical to the early development of these skills in a child, according to Amar Gajjar, MD, Hematology-Oncology. Gajjar is senior author of a report on the study published in the August 20 issue of Journal of Clinical Oncology.
The investigators are now using results of this study to identify and help children in need of special training to enhance their cognitive functioning following treatment for medulloblastoma.
The study followed a larger number of patients than any previous such investigation; and the investigators conducted neurocognitive testing of children for up to six years after diagnosis—that is, both before and after treatment. Moreover, no other such previous prospective study (a study following patients over the course of time) has compared the outcome of children receiving risk-adapted radiation therapy doses.
Other St. Jude authors of the study include the late Raymond K. Mulhern, PhD, Shawna Palmer, PhD, and Vida Tyc, PhD, Behavioral Medicine; Larry Kun, MD, and Thomas Merchant, DO, PhD, Radiological Sciences; and James Boyett, PhD, Dana Wallace and Mehmet Kocak, Biostatistics.
Last update: September 2005