Neutron track length estimator for GATE Monte Carlo dose calculation in radiotherapy

International audienceThe out-of-field dose in radiation therapy is a growing concern in regards to the late side-effects and secondary cancer induction. In high-energy x-ray therapy, the secondary neutrons generated through photonuclear reactions in the accelerator are part of this secondary dose. The neutron dose is currently not estimated by the treatment planning system while it appears to be preponderant for distances greater than 50 cm from the isocenter. Monte Carlo simulation has become the gold standard for accurately calculating the neutron dose under specific treatment conditions but the method is also known for having a slow statistical convergence, which makes it difficult to be used on a clinical basis. The neutron track length estimator, a neutron variance reduction technique inspired by the track length estimator method has thus been developped for the first time in the Monte Carlo code GATE to allow a fast computation of the neutron dose in radiotherapy. The details of its implementation, as well as the comparison of its performances against the analog MC method, are presented here. A gain of time from 15 to 400 can be obtained by our method, with a mean difference in the dose calculation of about 1% in comparison with the analog MC method

Light particle spectroscopy using CR-39 detectors: An experimental and simulation study

International audienceCR-39 detectors have been irradiated with both 241 Am alpha particles and protons in the energy range of 1.0–5.5 MeV and 0.8–2.8 MeV, respectively. The proton irradiation has been achieved through two different techniques: Rutherford Backscattering (RB) and Nuclear Reaction (NR). The detectors were chemically etched in a hot KOH solution for periods ranging from 0.5 h to 3 h for alpha particles and 2.5 to 5.5 h for protons. The track diameter variation as a function of particles energies and etching time has been studied. A new predictive model based on experimental track parameters has been developed for the studied particles and for variable bulk track etching velocities. This predictive model is based on a single parameter β determined by fitting our experimental data