The aim of this treatment planning comparison study was to explore different 
spinal irradiation techniques with respect to the risk of late side-effects, 
particularly radiation-induced cancer. The radiotherapy techniques compared were 
conventional photon therapy, intensity modulated x-ray therapy (IMXT), 
conventional electron therapy, intensity/energy modulated electron therapy 
(IMET) and proton therapy (IMPT).CT images for radiotherapy use from five 
children, median age 8 and diagnosed with medulloblastoma, were selected for 
this study. Target volumes and organs at risk were defined in 3-D. Treatment 
plans using conventional photon therapy, IMXT, conventional electron therapy, 
IMET and IMPT were set up. The probability of normal tissue complication (NTCP) 
and the risk of cancer induction were calculated using models with 
parameters-sets taken from published data for the general population; dose data 
were taken from dose volume histograms (DVH). Similar dose distributions in the 
targets were achieved with all techniques but the absorbed doses in the 
organs-at-risk varied significantly between the different techniques. The NTCP 
models based on available data predicted very low probabilities for side-effects 
in all cases. However, the effective mean doses outside the target volumes, and 
thus the predicted risk of cancer induction, varied significantly between the 
techniques. The highest lifetime risk of secondary cancers was estimated for 
IMXT (30%). The lowest risk was found with IMPT (4%). The risks associated with 
conventional photon therapy, electron therapy and IMET were 20%, 21% and 15%, 
respectively. This model study shows that spinal irradiation of young children 
with photon and electron techniques results in a substantial risk of 
radiation-induced secondary cancers. Multiple beam IMXT seems to be associated 
with a particularly high risk of secondary cancer induction. To minimise this 
risk, IMPT should be the treatment of choice. If proton therapy is not 
available, advanced electron therapy may provide a better alternative.