Analysis of the production of 11C fragments mainly by projectile fragmentation of a stable monodirectional and monoenergetic primary 12C beam in different decelerating materials are presented and the optimal target choice have been identified to obtain the highest possible beam quality of decelerated 11C beam at arbitrary energies and therapeutic ranges. The optimal 11C-generating target is made of hydrogen preferably followed by a digitally variable decelerator of a hydrogen rich compound, such as polyethylene, to maximize the quality of the 11C beam.