A discrete event simulator for policy evaluation in deceased-donor liver allocation in Eurotransplant

We present the ELAS simulator, a discrete event simulator built for the Eurotransplant (ET) Liver Allocation System (ELAS). Eurotransplant uses ELAS to allocate deceased-donor livers in eight European countries. The simulator is publicly available; this provides transparency concerning the models used by Eurotransplant to evaluate liver allocation policies, and facilitates collaborations with policymakers, scientists, and other stakeholders in evaluating alternative liver allocation policies. This paper describes the design and modules of the ELAS simulator. One of the included modules is the obligation module, which is instrumental in ensuring that international cooperation in liver allocation benefits all ET member countries.
By default, the ELAS simulator simulates liver allocation according to the actual Eurotransplant allocation rules. Stochastic processes, such as graft offer acceptance behavior and listing for a repeat transplantation, are approximated with statistical models that were calibrated using data from the Eurotransplant registry. We validate the ELAS simulator by comparing simulated waiting list outcomes to historically observed waiting list outcomes between 2016 and 2019.
The modular design of the ELAS simulator gives end users maximal control over the rules and assumptions under which Eurotransplant liver allocation is simulated, which makes the simulator useful for policy evaluation. We illustrate this with two clinically motivated case studies, for which we collaborated with hepatologists and transplantation surgeons from two liver advisory committees affiliated with Eurotransplant.