GPU-accelerated FREDopt package for simultaneous dose and LETd proton radiotherapy plan optimization via superiorization methods. - Damian Borys; Jan Gajewski; Tobias Becher; Yair Censor; Renata Kopec; Marzena Rydygier; Angelo Schiavi; Tomasz Skóra; Anna Spaleniak; Niklas Wahl; Agnieszka Wochnik; Antoni Rucinski (CoRR, 2025)