Scintillator-based measurement of off-axis neutron and photon dose rates during proton therapy

Dose rates, especially from photons and neutrons, inform safety procedures in any radioactive environment. A method for measuring dose rates from both particles with one device will simplify current methods for surveying dose fields. We have developed a technique using organic scintillators that is based on the definition of effective dose, extracted from energy deposited in the detector. Using pulse shape discrimination, energy deposited from either neutrons or photons can be separated. Radiation weighting factors are applied to obtain effective dose from neutrons and photons concurrently. This method was previously demonstrated for organic scintillators with a californium-252 source; this work presents measurements of off-axis secondary particle dose rates from a sub-clinical strength proton beam incident on various tissue-equivalent targets. The experiment was modeled using the Monte Carlo code MCNPX-PoliMi. Measured proton beam secondary neutron dose rates agree reasonably well with simulated results. The comprehensive analysis of this dose rate technique demonstrates the possibility for a dual particle dosimeter to be used in a variety of applications, including surveying, room monitoring, and shielding analysis. Enhancing and simplifying dose rate monitoring will allow for a safer and more productive radiation work environment.