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Age at irradiation had more impact on late effects than radiation dose
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Patients with low-grade glioma who had conformal radiation therapy before they were aged 5 experienced the greater cognitive decline than other age groups. Researchers said age at irradiation played a greater role in cognitive decline than the amount of radiation assigned to the patient.
The researchers monitored 78 children for five years after conformal radiation therapy to determine the effect of treatment on their cognitive function. Mean age at radiation was 9.7 years.
They observed lower Child Behavior Checklist scores for patients who were younger at irradiation; scores dropped 0.6616 points per year of age (P=.0400). Each year of increasing age reduced the decline in IQ by 0.0256 points per month.
The researchers predicted a 10-point decline in IQ five years after radiation therapy for a patient who was 5 at the time of irradiation. Each year of increasing age resulted in significantly improved Child Behavior Checklist scores for externalizing scores (–0.0275 points per month) and internalizing scores (–0.0181 points per month).
“This research demonstrates the importance of age when cognitive effects are estimated,” they wrote. “The effect of age exceeds the effect of radiation dose. This provides guidance regarding selection of patients for treatment, and it additionally demonstrates the overarching influence of age and increasing deficits with time in younger patients.”
Merchant TE. J Clin Oncol. 2009;doi:10.1200/JCO.2008.21.2738.