Comparing second cancer risk for multiple radiotherapy modalities in survivors of hodgkin lymphoma

Objectives: To assess if Excess Absolute Risk (EAR) of radiation-induced solid cancer can be used to rank radiotherapy plans for treatment of Hodgkin Lymphoma (HL) in a statistically significant way. Methods: EAR models, calibrated with data from the Life Span Study and HL survivors, have been incorporated into a voxelised risk-calculation software, which is used to compare four treatment modalities planned for five virtual HL patients. Organ-specific parameters are generated repeatedly in a Monte Carlo fashion to model their uncertainties. This in turn enables a quantitative estimation of the EAR uncertainties. Results: Parameter driven uncertainties on total EAR are around 13%, decreasing to around 2–5% for relative EAR comparisons. Total EAR estimations indicate that Intensity Modulated Proton Therapy decreases the average risk by 40% compared to the Intensity Modulated Radiation Therapy plan, 28% compared to the Volumetric Modulated Arc Therapy plan whereas the 3D Conformal Radiation Therapy plan is equivalent within the uncertainty. Conclusions: Relative EAR is a useful metric for distinguishing between radiotherapy plans in terms of second cancer risk. Advances in knowledge: Relative EAR is not dominated by model or parameter uncertainties and can be used to guide the choice of radiotherapy for HL patients.