Energy dependency of dose response function of a Gd2O2S scintillator detection system for spot-scanning carbon-ion and proton radiotherapy

Abstract To ensure quality assurance (QA) of scanning proton and carbon-ion therapy doses, an efficient and reliable method to measure the energy dependency of the dose response function (DRF) of an optical scintillator detection system (OSDS), is required. We present a calibration process that corrects the non-linear sensitivity of the imager's electronic readings into linear light intensities. After calibration, a digital readout of green colored stimulated-light emission (SLE) are converted to nominal SLE (N_SLE). The slope of N_SLE as a linear function of dose is labelled as K-factor. The K-factors for 7 energies of carbon-ion and proton have been measured. For the highest (424.89 MeV/u) and lowest (97.87 MeV/u) energies of carbon-ion, the K-factors are 0.96 and 0.76 N_SLE/Gy. For the highest (218.56 MeV) and lowest (53.04 MeV) energies of protons, the K-factors are 0.96 and 0.86 N_SLE/Gy. The variation of K-factor for its energy dependence are 18% and 11% between lowest and highest energies of carbon-ion and proton beam respectively. Similar trending of the K-factor was seen for the red and blue colors with respect to the green color channel, although the signal magnitude was lower for the red channel. The OSDS dose response is weakly dependent on the energy of the carbon-ion and proton beams regardless of color channel. The energy-dependency of DRF and interactive capability of OSDS can be used to create efficient dosimetry tools to measure data for spot-scanning carbon-ion and proton radiotherapy.