PURPOSE: In this study factors are analyzed that may potentially influence the 
site of failure in pediatric medulloblastoma. Patient-related, disease-related, 
and treatment-related variables are analyzed with a special focus on 
radiotherapy time-dose and technical factors.
METHODS AND MATERIALS: Eighty-six children and adolescents with a diagnosis of 
medulloblastoma were treated in Switzerland during the period 1972-1991. 
Postoperative megavoltage radiotherapy was delivered to all patients. Simulation 
and portal films of the whole-brain irradiation (WBI) fields were 
retrospectively reviewed in 77 patients. The distance from the field margin to 
the cribiform plate and to the floor of the temporal fossa was carefully 
assessed and correlated with supratentorial failure-free survival. In 19 
children the spine was treated with high-energy electron beams, the remainder 
with megavoltage photons. Simulation and port films of the posterior fossa 
fields were also reviewed in 72 patients. The field size and the field limits 
were evaluated and correlated with posterior fossa failure-free survival.
RESULTS: In 36 patients (47%) the WBI margins were judged to miss the inferior 
portion of the frontal and temporal lobes. Twelve patients failed in the 
supratentorial region and 9 of these patients belonged to the group of 36 
children in whom the inferior portion of the brain had been underdosed. On 
multivariate analysis only field correctness was retained as being significantly 
correlated with supratentorial failure-free survival (p = 0.049). Neither the 
total dose to the spinal theca nor the treatment technique (electron vs. photon 
beams) were significantly correlated with outcome. Posterior fossa failure-free 
survival was not influenced by total dose, overall treatment time, field size, 
or field margin correctness. Overall survival was not influenced by any of the 
radiotherapy-related technical factors.
CONCLUSION: A correlation between WBI field correctness and supratentorial 
failure-free survival was observed. Treatment protocols should be considered 
that limit supratentorial irradiation mainly to subsites at highest risk of 
relapse. Optimized conformal therapy or proton beam therapy may help to reach 
this goal. Treating the spine with electron beams was not deletereous. A 
significant correlation between local control and other technical factors was 
not observed, including those relating to posterior fossa treatment. The use of 
small conformal tumor bed boost fields may be prefered to the larger posterior 
fossa fields usually considered as the standard treatment approach.