Quantification of Neutron-Induced Single-Event Upsets in a Static Random-Access Memory by Clinical High-Energy Photon Beam

The possibility of using calibrated static random-access memory (SRAM) memory for the quantification of neutron fluence in a radiotherapy facility for cancer treatment utilizing a high-energy 15-MV photon beam (Bremsstrahlung) from an electron linear accelerator has been exploited in this work. This has been performed by varying the field size of the photon beam and the positioning of the SRAM memory at three different positions in relation to the isocenter of the beam. The measurements demonstrated that neutrons originating from interactions between the high-energy photons and accelerator parts with high-Z materials are able to induce single-event upsets (SEUs) in the SRAM memory, where the measured SEUs depend on the measurement location. Monte Carlo (MC) simulations have been performed to retrieve the neutron fluence under each investigated measurement condition. Using the simulated neutron fluence differential in energy and the interactions cross sections determined previously, the expected SEUs were computed. The comparison between measured and simulated SEUs normalized to the linear accelerators (linac) output shows acceptable agreement within the experimental uncertainties. As exposure to secondary neutrons poses a risk to all patients, especially the ones with pacemakers or other electronical aids, the feasibility of establishing the neutron fluence through SEU quantification in an SRAM device provides new opportunities to estimate the associated risk in a clinical environment. Further work can be performed to investigate the correlation between the high-Z linac components and the neutron fluence during patient irradiation to better comprehend the variation between different linac types and manufacturers.