MOSFET dose measurements for proton SOBP beam

•Depth-dose in water for proton SOBP beam was measured by ion chamber and MOSFET.•Lower MOSFET outputs were due to electron-hole recombination in the oxide layer.•For a Bragg peak, proton LET was determined from residual range or residual energy.•Dose-weighted correction factor for the SOBP was derived from measured hole yields.•With correction factors, predicted MOSFET outputs agreed well with measured data. The aim of this work was to develop a computational scheme for the correction of the LET dependence on the MOSFET response in water phantom dose measurements for a spread-out Bragg peak (SOBP) proton beam. The LET dependence of MOSFET was attributed to the stopping power ratio of SiO2 to H2O and to the fractional hole yield in the SiO2 layer. Using literature values for the stopping powers of the continuous slowing down approximation and measured fractional hole yields vs. electric field and LET, formulas were derived for the computation of a dose-weighted correction factor of a SOBP beam. Dose-weighted correction factors were computed for a clinical 190-MeV proton SOBP beam in a high-density polyethylene phantom. By applying correction factors to the SOBP beam, which consisted of weighted monoenergetic Bragg peaks, the MOSFET outputs were predicted and agreed well with the measured MOSFET responses. By applying LET dependent correction factors to MOSFET data, quality assurance of dose verification based on MOSFET measurements becomes possible for proton therapy.