ESTRO 2025 - Abstract Book

S3570

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

Material/Methods: Clinically relevant treatment plans were created for a phantom case with a centrally-situated target, simulating the treatment of pituitary gland-like targets with two proton fields. DD and LET d distributions were investigated as a function of the angular separation of the employed beam. In addition, distributions for proton plans employing between two and eight fields were calculated in ten pituitary gland patient cases to include effects of anatomical heterogeneity. The resulting distributions were analysed in terms of mean and maximum DD and LET d to organs at risk. Results: Ionisation density features increased for smaller angular separation of the proton beams, especially for centrally situated structures like the brain stem (Figure 2). Most sensitive to variations in DD was a shell situated between 0.6 0.9 cm around the target illustrating the region where the maximum DD deposition occurs. In patient plans, maximum LET d per plan decreased with increasing number of beams, however the maximum LET d per field was relatively constant, showing that at least one field has a large LET d contribution, albeit at a lower dose.

Conclusion: This study offered insights into the variation of plan- and beam-specific ionisation density parameters for planning approaches, as well as the potential of various planning approaches to mitigate risk aspects related to ionisation density in proton plan optimisation.

Keywords: Proton Therapy, LET, RBE