Measurement of therapeutic 12C beam in water phantom using CR-39

The motivation of this study was to explore a new method to test the particle spatial distribution for a therapeutic carbon beam. The CR-39 plastic nuclear track detectors (PNTD) were irradiated to a 276.5 MeV/u mono-energy carbon beam at the heavy ion facility in SPHIC (Shanghai Proton and Heavy Ion Center). The spatial distribution of primary carbon beam and secondary fragments in a water phantom were systematically analyzed both in transverse direction (perpendicular to the projection direction of primary beam) and at different depths in longitudinal direction (along the projection direction of primary beam) with the measured tracks on the CR-39 detectors. Meanwhile, the theoretically spatial distribution and linear energy transfer (LET) spectra of primary beam and secondary fragments were calculated using the Monte Carlo toolkit Geant4. The results showed that the CR-39 detectors are capable to provide high lateral resolution of carbon ion at different depths. In the range of primary carbon beam, the beam width simulated with MC is in good agreement with that of experimental measurement. The track size registered in the CR-39 has a good correlation with the particle LET. These findings indicate that the CR-39 can be used for measuring both the particle flux and its spatial distribution of carbon ions.