Influence of phantom material on the depth-dose profile and radiation quality factor of 126 MeV antiprotons - a FLUKA Monte Carlo study

Antiprotons hold significant potential for radiotherapy due to their unique annihilation mechanism, which could offer dosimetric advantages. The objective of the present study was to assess how different phantom compositions affect the position of the Bragg peak and the biological effectiveness of antiproton beams in terms of the quality factor. This study investigated on-axis depth-dose profiles and the LET-based quality factor (Q_LET) for a 126 MeV antiproton beam in various phantom materials such as Water, Polystyrene, PMMA, RW1, WE210, Solid Water, and A150 using the FLUKA Monte Carlo code. The study also investigated the influence of elemental compositions of phantom materials on the relative contribution of antiprotons and secondary radiations to the total on-axis depth-dose profile. Additionally, the study discusses the variation in the in-flight annihilation cross-section across different phantom materials. The results show that depending on the phantom material, the position of the Bragg peak ranges from 11.49 to 11.82 g/cm². Furthermore, depending on the phantom material, Q_LET ranged from about 1.78 to 1.91 in the entrance region, from about 2.0 to 2.8 in the dose fall-off region, and from about 6.28 to 7.0 near the Bragg peak position. It is concluded that the study provides the theoretical basis of the understanding of depth dose profiles of antiprotons in various solid phantoms.