Range measurements using visible scintillation light for proton therapy

Proton beam therapy has certain advantages over that with the photon: a well-defined range, relatively little scattering, and high-energy deposition in the Bragg peak area. The depth dose distribution of proton beams shows a prominent Bragg peak at the end of the range, beyond which the dose rapidly falls to zero. Therefore, proton therapy makes possible to concentrate dose on tumor without increasing exposure on normal tissue. As a tool of daily treatment, an easy-to-use reliable range measurements method is required. We examined a method using visible scintillation light. We recorded visible scintillation light generated by proton irradiation on a block of plastic scintillator, and analyzed the length, shapes and brightness distribution to obtain the range, the magnitude of multiple Coulomb scattering and the depth dose distribution. The precision of the range measurement is 0.7 mm. The relation between proton range in plastic scintillator and that in water shows good linearity, because physical property of plastic scintillator and that of water have some similarity. Estimation of the depth dose distribution by measuring the brightness distribution was possible with a digital video camera. This measurement method is proved to be an easy-to-handle way as a tool for QA/QC of proton therapy. The depth dose measurements within this accuracy provide critical data for testing the treatment-planning program for proton therapy using the GEANT4 code.