Primary outcomes included the amount of time from study entry to disease progression, disease recurrence, death from any cause, or second malignant neoplasm. Researchers compared rates of overall survival (OS), event-free survival (EFS), local failure and distant failure by computing Hazard Ratios (HR) and performing intent to treat analysis.

With a median follow-up of more than six and a half years, reduction in the volume of RT boost to the posterior fossa did not compromise overall or event-free or survival in pediatric patients with A-R medulloblastoma. Overall survival at five years was 84.1 ± 2.8 percent for patients who received the reduced volume with IFRT and 85.2 ± 2.6 percent for patients who received the standard volume with PFRT. EFS at five years was 82.2 ± 2.9 percent for IFRT and 80.8 ± 3.0 percent for PFRT. Rates of local failure also did not vary significantly between treatment arms. Local failure at five years was 1.9 ± 0.1 percent for IFRT and 3.7 ± 1.3 percent for PFRT (p = 0.178).


"This trial -- the largest of its kind to date -- indicates that it is safe to adopt a limited posterior fossa boost for patients receiving radiation therapy for average risk medulloblastoma, and that these children can have similar positive outcomes with lower chances of radiation affecting surrounding brain tissue" said Jeff M. Michalski, MD, MBA, FASTRO, professor of radiation oncology at Washington University in St. Louis and lead author of the study. "Additional data are needed, however, to address the appropriate volume for patients with higher risk disease or those who have metastasis at the time of diagnosis."

While reduced RT volume to the posterior fossa did not impact survival rates, a low dose of craniospinal irradiation was associated with lower rates of event-free and overall survival for the youngest pediatric patients. Overall survival at five years was 78.1 ± 4.4 percent for patients ages three to seven who received low dose irradiation therapy to the CSI versus 85.9 ± 3.8 percent for the standard CSI dose. EFS at five years was 72.1 ± 4.8 percent for the LD-CSI group, compared to 82.6 ± 4.2 percent for SD-CSI. Rates of distant failure did not vary significantly between treatment groups. Isolated distant failure at five years was 12.8 ± 3.2 percent for LD-CSI and 8.2 ± 2.8 percent for SD-CSI (p = 0.115).

"Unfortunately, we were disappointed to find that a lower dose of irradiation therapy was associated with increased rate of failure in the younger children," said Dr. Michalski. "Reducing the treatment by just three fractions from 23.4 Gy to 18 Gy was associated with a higher rate of events and diminished overall survival. Patients with average risk medulloblastoma should continue to receive a standard dose of 23.4 Gy to the craniospinal axis, unless they are enrolled in a clinical trial."

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