The invention comprises a method and apparatus for using a multi-layer multi-color scintillation based detector element to image a tumor of a patient using a process of determining residual energies of positively charged particles after passing through the patient, the process comprising the steps of: (1) transmitting the positively charged particles at known energies through the patient and into a multi-layer detector element； (2) detecting first and second secondary photons, resultant from passage of the positively charged particles, respectively from a first layer of a first scintillation material and a second layer of a second scintillation material at two respective layer depths, where the first wavelength range differs from the second wavelength range； (4) determining residual energies of the positively charged particles, using output from the step of detecting； and (5) relating the residual energies to body densities to generate an image.
