LAUSR

T Final Rule, implemented in 2000, directs the Organ Procurement and Transplantation Network to “distribute organs over as broad a geographic area as feasible” and to ensure that allocation priority “shall not be based on a candidate's place of listing.” However, substantial geographic disparity in access to liver transplantation among waitlisted patients indicates that the transplant community has failed to comply with this directive. In a new article, Mehrotra and colleagues propose a suite of potential modifications to the existing allocation regime, with the goal of alleviating this geographic disparity. The proposed framework (called “concentric neighborhoods”) features broader sharing at low model of end-stage liver disease (MELD) scores (replacing the current MELD-15 threshold with MELD-18 or MELD-20) and places each donor service area (DSA) within a “concentric neighborhood” of adjacent and nearby DSAs within a specified radius. In some variants, “proximity points” grant local candidates higher allocation priority than nonlocal candidates in the same DSA or region. Several previous proposals have been made by the same research group and others. A notable feature of the “concentric neighborhoods” framework is its flexibility: various tunable parameters (eg, size of the neighborhood, value of proximity points) create a system through which policymakers could, in principle, balance trade-offs (eg, reduced geographic disparity vs the shock of sudden volume loss to centers, which currently benefit from that disparity) with a high degree of precision. However, some caution is warranted. The authors use a simulation tool (LivSim) of their own design, different from the Scientific Registry of Transplant Recipients–produced kidney/ pancreas-simulated allocation model and liver-simulated allocation model, which have been the basis for previous allocation changes. The authors are to be commended for making LivSim open-source, meaning that other researchers will be able to study the tool, to understand its strengths and