Testing re-optimisation strategies in international kidney exchange programmes by the ENCKEP simulator

We tested re-optimisation strategies for international kidney exchange programmes using the simulator developed by the ENCKEP COST Action. Kidney exchange programmes (KEPs) are operating in most of the European countries to facilitate the exchange of kidney donors for the recipients with incompatible living donors. The optimal solutions for national and international KEPs are typically selected in every three months based on the compatibilities estimated on the individual immunological data. However, these estimations are not always accurate, and if a positive crossmatch is found in the laboratory crossmatch tests then the corresponding exchange cycle (or chain) must be cancelled. Depending on the matching process, the coordinators may use different re-optimisation strategies to repair the failed solutions. We examine the effects of using multiple rounds of re-optimisation with different optimisation strategies, such as fixing good cycles in the intermediate solutions or prioritising transplants with negative crossmatch tests in previous rounds. In the context of international KEPs we also consider the possibility of testing and prioritising national transplants in the solutions. We measure the performance of these policies regarding the number of transplants and the number of compatibility tests conducted in a time period. By extending our results presented in [16], we performed simulations for a large number of instances to measure the effects of various re-optimisation policies. Our main findings show a clear trade-off in the number of transplants versus the number of tests and re-optimisation rounds.