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

Abstract

The 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.

Measurement of out of field doses in brain proton therapy with GATE simulations

“…NTLE was used to determine neutrons that are part of the secondary dose. [13] Figures 3 and 4 show particle and dose distributions in brain tissue and out off-field global dosimetry.…”

Prompt-gamma track-length estimator with time tagging from proton tracking

“…Among MC variance reduction techniques, track-length estimators are interesting scoring methods to get a fast and accurate MC simulation of rare events, as proposed back in the 80 s in the MNCP code (Forster and Godfrey 1985) and formalized for the evaluation of the photon dose with the Kerma approximation (Williamson 1987). In the past few years, several other variations of the TLE have been proposed, such as the neutron-induced gamma dose tally in GATE for radiotherapy applications (Elazhar et al 2018) and the next-event estimator in Tripoli-4 ® for neutron transport (Hutinet et al 2023). The PG source variation of the track-length estimator (vpgTLE) has also been proposed in GATE by (El Kanawati et al 2015) and a gain of about 1000 in relative uncertainty has been reported for a patient proton therapy treatment plan by (Huisman et al 2016).…”