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.