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.