A new hybrid next-event estimator for photon-based Monte Carlo dose rate calculations

This work describes the implementation of a deterministic-like straight-line transport routine inside the $$\hbox {TRIPOLI-4}^{\circledR }$$ Monte Carlo code, aimed at developing a hybrid estimator that can speed up the MC calculation while retaining its precision. The algorithm is based on the exponential track length estimator or eTLE, a next-event estimator that has already been investigated for medical applications. In this implementation, the eTLE is paired with a forced detection algorithm. We describe the implementation of the method in $$\hbox {TRIPOLI-4}^{\circledR }$$ , then we present the first results obtained over some test cases and compare them with the classic track-length estimator already implemented in $$\hbox {TRIPOLI-4}^{\circledR }$$ . These results show that the forced detection technique drastically improves the eTLE performance.