PURPOSE: To assess the potential influence of improved dose distribution with 
proton beams compared to conventional or intensity-modulated (IM) X-ray beams on 
the incidence of treatment-induced secondary cancers in pediatric oncology.
METHODS AND MATERIALS: Two children, one with a parameningeal rhabdomyosarcoma 
(RMS) and a second with a medulloblastoma, were used as models for the purpose 
of this study. After defining the target and critical structures, treatment 
plans were calculated and optimized, four for the RMS case (conventional X-ray, 
IM X-rays, protons, and IM protons) and three for the irradiation of the spinal 
axis in medulloblastoma (conventional X-ray, IM X-rays, protons). Secondary 
cancer incidence was estimated using a model based on Publication No. 60 of the 
International Commission on Radiologic Protection. This model allowed estimation 
of absolute risks of secondary cancer for each treatment plan based on 
dose-volume distributions for the nontarget organs.
RESULTS: Proton beams reduced the expected incidence of radiation-induced 
secondary cancers for the RMS patient by a factor of >or=2 and for the 
medulloblastoma case by a factor of 8 to 15 when compared with either IM or 
conventional X-ray plans.
CONCLUSIONS: The potential for a significant reduction in secondary cancers with 
pediatric cancers after using proton beams (forward planned or IM) in the 
treatment of RMS and MBD in children and adolescents represents an additional 
argument supporting the development of proton therapy for most radiotherapy 
indications in pediatric oncology.