A non Gaussian model for the lateral dose evaluation in hadrontherapy: development and Treatment Planning System implementation

Challenging issues in Treatment Planning System for hadrontherapy are the accurate calculation of dose distribution, the reduction in memory space required to store the dose kernel of individual pencil beams and the shortening of computation time for dose optimization and calculation. In this framework, the prediction of lateral dose distributions is a topic of great interest because currently, a Double Gaussian parametrization is typically used as approximation although other parameterizations are also available. The best accuracy for this kind of calculations can be obtained by Monte Carlo (MC) methods, at the expense of a long computing time. As alternative, we propose a flexible model based on the full Molière theory for Coulomb multiple scattering. The use of the original equations of the theory allows to remove free parameters for the electromagnetic inter action with the advantage of full accuracy with a reasonable increase in the computing time. The contribution of the nuclear interactions are also fully taken into account with a two-parameters fit on FLUKA simulation and this part is added to the electromagnetic core with a proper weight. The Model has been inserted in a research Treatment Planning System CERR - A Computational Environment for Radiotherapy Research, to compare its result against the ones obtained with the currently used Double Gaussian parametrization to evaluate the lateral energy deposition. A quantitative comparison has been done to evaluate the difference between a treatment plan obtained using the Double Gaussian parametrization and a treatment plan obtained using the model calculation, in the cases of a single beam and a full treatment plan in homogeneous water phantom and also a plan is performed in presence of inhomogeneities.