An apparatus 900 for determining a position of a tumor 720 in a patient 730 in a treatment room using positively charged particles. Apparatus 900 comprising: a synchrotron sequentially transporting positively charged particles into the patient 730； and an imaging system comprising: first and second sheets 760,770 each comprising a light emitting element； a first detector 812 that generates a first signal in response to imaging first photons emitted when a first positively charged particle passes through the light emitter of first sheet 760； and a second detector 814 forming a second signal on imaging second photons emitted the first positively charged particle passes through the light emitter of second sheet 770； and a controller determining a first segment V1a of a beam path of the first particle using the first signal and the second signal. The imaging system may comprise a third sheet 780 with a light emitting element to yield a third signal due to the first particle； and a scintillation plate 710 of a tomography system to generate a fourth signal due to the first particle where the controller determines segments of the beam path of the first particle using the first, second, third and fourth signals.
