The biological effectiveness of charged-particle beams depends not only on dose but also on radiation quality. The radiation quality of charged-particle beams has been most commonly represented by the linear energy transfer (LET) in radiation biology studies. We investigated a new therapeutic technique of charged-particle therapy in which two or more ion species are delivered in one treatment session for optimizing the dose and LET distributions in a patient. We refer the therapeutic technique as an Intensity Modulated composite PArtiCle Therapy (IMPACT). Helium, carbon, oxygen and neon ions are considered as ion species for the IMPACT. To demonstrate the effectiveness of the IMPACT for simultaneous optimization of dose and LET distributions, an IMPACT plan was made for a prostate case. In accordance with the prescriptions, LETs in prostate, planning target volume (PTV), and rectum could be adjusted at 80 keV/μm, at 50 keV/μm, and below 30 keV/μm, respectively, while keeping the dose to the PTV at 2 Gy uniformly. The IMPACT enables the optimization of the dose and the LET distributions in a patient, which will maximize the potential of charged-particle therapy by expanding the therapeutic window.