EP-1697: Does contrast agent influence the prognostic accuracy of CT radiomics based outcome modelling?

Purpose or ObjectiveFirst dose-painting clinical trials are ongoing, even though the largest challenge of dose-painting has not been solved yet: to robustly redistribute the dose to the different regions of the tumor.Efforts to derive dose-response relations for different tumor regions rely on strong assumptions.Without accounting for uncertainty in the assumed dose-response relations, the potential gain of dose-painting may be lost.The goal of this study is to implement an automated treatment planning approach for dose-painting that takes into account uncertainties both in dose-response relations and in patient positioning directly into the optimization.Such that even in the presence of large uncertainties the delivered dosepainting plan is unlikely to perform worse than current clinical practice with homogeneous prescriptions. Material and MethodsDose response relations in TCP (tumor control probability) are modeled by a sigmoid shaped function, using 2 parameters to describe the dose level and cell sensitivity.Each voxel has its own tuple of parameters, and the parameters were assumed to follow probability distributions for which the mean and the variance were known.The expected TCP over all uncertainty distributions was optimized.Random positioning uncertainties were dealt with by convolving the pencil beam kernels with a Gaussian.For systematic geometrical uncertainties, a worst case optimization was implemented, to ensure adequate dose delivery in 95% of the geometrical scenarios.The method was implemented in our in house developed TPS and applied to a 3D ellipsoid phantom with a spherical tumor with a resistant shell and sensitive core and to a NSCLC cancer patient case with 3 subvolumes that were assumed to vary in radio-sensitivity.The effect of different probability distributions for cell sensitivity was investigated. ResultsAs expected, in the absence of dose-response and positioning uncertainties (red line), the dose to the resistant ring of the phantom (light gray in Fig 1) is considerably higher than to the sensitive core (dark gray).However, as the uncertainty in dose response relations increases (blue and green lines), the dose difference between the subvolumes decreases, even though the expected cell sensitivities do not change.Including positioning uncertainties leads to further smearing out of the dose (black line).Fig 2 demonstrates the effect on a real lung patient case with high risk GTV (white), low risk GTV (black), lymph nodes (pink).