SU-E-T-257: Risk of Radiogenic Second Cancer after Photon and Proton Craniospinal Irradiation

To compare proton and photon therapies in terms of the risks of second cancers for a pediatric medulloblastoma patient receiving craniospinal irradiation (CSI).

Two CSI treatment plans with 23.4 Gy or Gy (RBE) prescribed dose were computed for a 4-year-old boy withmedulloblastoma: a three-field 6-MV photon therapy plan and a four-field proton therapy plan. The primary doses for both plans were determined using a commercial treatment planning system. Stray radiation doses for proton therapy were determined from Monte Carlo simulations, and stray radiation doses for photon therapy were determined from measured data. The dose-risk model based on Biological Effects of Ionization Radiation VII report was used to estimate risk of second cancer.

Baseline predictions of the relative risk of each organ were always less for proton CSI than for photon CSI after various follow-up years for the patient. The lifetime risks of the incidence of second cancer after proton CSI and photon CSI were 7.7% and 92%, respectively, and the ratio of lifetime risk was 0.083. Uncertainty analysis revealed the qualitative findings of this study were insensitive to any plausible changes of dose-risk models and mean neutron radiation weighting factor.

Proton therapy confers lower predicted risk of second cancer for the pediatric medulloblastoma patient compared with photon therapy.