SU-E-T-283; Risks of Cardiac Toxicity in Pediatric Patients Receiving Photon Or Proton Radiotherapy

Abstract

Purpose: To compare the predicted risk of developing radiogenic cardiac toxicity after photon versus proton radiotherapies for a pediatric patient with Hodgkin disease (HD) and a pediatric patient with medulloblastoma (MB). Methods: In the treatment plans, each patient heart was contoured in fine detail, including substructures of the pericardium and myocardium. Risk calculations took into account both therapeutic and stray radiation doses. We calculated the relative risk (RR) of cardiac toxicity using a linear risk model and the normal tissue complication probability (NTCP) values using relative seriality and Lyman models. Uncertainty analyses were also performed Results: The RR values of cardiac toxicity for the HD patient were 7.27 (95% confidence interval (CI), 3.09 to 27.12) (proton) and 8.37 (95% CI, 3.46 to 31.70) (photon), respectively; the RR values for the MB patient were 1.28 (95% CI, 1.09 to 2.18) (proton) and 8.39 (95% CI, 3.46 to 31.78) (photon), respectively. The predicted NTCP values for the HD patient were 2.17% (proton) and 2.67% (photon) for the myocardium, and were 2.11% (proton) and 1.92% (photon) for the whole heart. The predicted ratios of NTCP values (proton/photon) for the MB patient were much less than unity. Uncertainty analyses revealed that the predicted ratio of risk between proton and photon therapies was sensitive to uncertainties in the NTCP model parameters and the mean radiation weighting factor for neutrons, but was not sensitive to heart structure contours. The qualitative findings of the study were not sensitive to uncertainties in these factors. Conclusion: We conclude that proton and photon radiotherapies confer similar predicted risks of cardiac toxicity for the HD patient and that proton therapy reduced the predicted risk for the MB patient relative to photon therapy.