A system for radiation therapy includes a radiation planning system. The radiation planning system includes a data processor that is adapted to receive information concerning an intended radiation treatment region of a body, receive a calculated initial energy released per unit mass for a plurality of locations within the body, compute a radiation dose at a plurality of locations within the radiation treatment region based on the calculated initial energy released per unit mass and including radiation dose contributions due to scattering from other locations within the body, and determine radiation therapy parameters for providing radiation treatment to the intended radiation treatment region based on the radiation dose computed at the plurality of locations within the radiation treatment region. Including radiation dose contributions due to scattering from other locations within the body take into account density discontinuities in the body.
