The relation between supratentorial irradiation dose and intellectual outcome in 36 children (ages 5 to 15 years) treated for medulloblastoma was evaluated at the Gustave Roussy Institute, Villejuif, France. The standard dose of 35Gy was administered to 13 patients and the dose was reduced to 25Gy for 23 patients. Neuropsychological evaluation performed at a mean of 4.3 years after radiotherapy showed significantly lower scores in children irradiated at the standard dose compared to lower dose. Impaired intellectual functioning involved verbal fluency, word list recall, block design, and fine motor coordination of the dominant hand. 
COMMENT. The dose of cranial irradiation in the treatment of medulloblastoma is critical in terms of intellectual outcome. Both verbal and non-verbal skills are impaired with larger doses of irradiation, and performance IQ may be more impaired than verbal IQ. These deficits may have a major impact on school performance.