261 Dosimetric considerations in the outcome of medulloblastoma

Abstract

Seventy-three patients aged 2 to 48 years were treated for medulloblastoma (MB). Chang staging was: 7% T1, 42% T2, 16% T3a, 27% T3b, 8% T4. Thirty-three percent of patients had spinal axis (SAX) staging. Median radiation doses were posterior fossa (PF) 52 Gy, whole brain (WB) 40 Gy, and SAX 35 Gy. Fraction sizes ranged 0.5–3 Gy (median 1.7 Gy WB, 1. 7 Gy SAX, 1.8 Gy PF). The 5-year overall and disease-free survival are 67% and 59%, respectively. PF control was better for patients receiving>50 Gy to the PF (86% vs 42%, P = 0.0007). PF dose >50 Gy gave improved actuarial and disease-free survival. PF control was improved when patients were treated with fraction ≥ 1.7 Gy/day to the brain and spine (84% vs 51%, P = 0.0006). When PF was controlled, neuroaxis control was better if >30 Gy to the SAX (97% vs 71%, P = 0.05). WB dose did not have an impact on neuroaxis control, but few patients received ≤30 Gy WB. Incidence of extra-CNS metastases is 13% and 20% at 5 and 10 years, respectively. Patients with continuous PF and neuroaxis control have an extra-CNS relapse rate of 10%. Our data confirm a dose response >50 Gy for PF control in MB. SAX dose of >30 Gy is necessary for neuroaxis control. Fraction size >1.7 Gy appears to improve local control. Ten percent of patients develop extra CNS metastases despite CNS control.