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Risk of Radiogenic Second Cancer After Photon and Proton Craniospinal Irradiation

R Zhang

R Zhang1,2*, R Howell3, A Giebeler3, P Taddei3, A Mahajan3, W Newhauser1,2, (1) Mary Bird Perkins Cancer Center, BATON ROUGE, LA, (2) Louisiana State University, BATON ROUGE, LA, (3) UT MD Anderson Cancer Center, Houston, TX

SU-E-T-257 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

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

Methods: Two CSI treatment plans with 23.4 Gy or Gy (RBE) prescribed dose were computed for a 4-year-old boy with medulloblastoma: 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.

Results: 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.

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

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