Gentry*, Sommer (NYU Grossman School of Medicine)

Sommer Gentry

Dr. Sommer Gentry
Professor of Population Health
Professor of Surgery
NYU Grossman School of Medicine
550 1st Ave., New York, NY 10016

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Faster, Safer, Healthier: Adventures in Operations Research

While mathematical advances of all sorts have impacted our world for the better, operations research is a branch of mathematics that is expressly focused on applying advanced analytical methods to help make better decisions.  Operations researchers have eased traffic jams by closing selected streets, and gotten packages to you more quickly by planning U.P.S. routes with fewer left turns.  Operations researchers have shown which personal decisions are the leading causes of death, and planned maintenance schedules to minimize bridge collapses.  The mathematical tools of operations research, like using random numbers to simulate a range of outcomes when some data are unknown, or finding clever algorithms that shortcut the need to try every possible decision in order to find the best one, can be recycled to solve problems everywhere in our world.  In this talk, I will describe some of my O.R. forays into far-flung fields, and tell my favorite stories about O.R.

These days, I am using O.R. to increase the supply of kidneys available for patients who need a transplant.  In a kidney exchange, one patient and his incompatible donor is matched with another patient and donor in the same situation.  Patient-donor pairs can be drawn as the vertices of a graph, with an edge between two vertices if a kidney exchange is possible. A maximum matching on that graph is an arrangement in which the largest number of people can receive a transplant.  We used operations research techniques to prove the impact of kidney exchange on the organ shortage, which motivated the U.S. Congress to pass a law allowing hospitals to arrange these transplants.


Redistricting U.S. Liver Allocation to Save Lives and Mitigate Inequity

In some areas of the U.S., the sickest liver transplant candidates have an 82% chance of dying within 90 days, versus an 14% chance of dying within 90 days in some other areas, because of extreme disparities in the availability of livers for transplant.  Some members of the transplant community continue to resist allocation changes that might resolve these disparities, 15 years after the Final Rule required that geography must not be a major determinant of access to a transplant. Candidates for deceased donor livers are prioritized in order of decreasing disease severity, as measured by the MELD (Model for End-stage Liver Disease) score.  However, historical precedent dictates organ sharing within a hierarchy of 50 small areas grouped into 11 regions, and these regions have very different ratios of eligible liver donors to liver transplant candidates. 

We designed novel regions for liver allocation by partitioning the set of donor service areas according to an integer program redistricting model.  Our work directly addressed the paramount clinical and ethical concern about geographic equity in MELD at transplant.  Also, we validated our optimally redistricted maps using the clinically detailed Liver Simulated Allocation Model that is the gold standard for testing allocation policy proposals, to compensate for the necessarily simplified and aggregated picture of liver allocation in an integer program. 

Some of the unusual aspects of this work are: the requirement to formulate redistricting as a transparently interpretable model, to reassure stakeholders; the quandary of evaluating a solution by a different metric than the optimization objective; and the high-stakes group negotiation and tactics employed by some likely losers in the battle to reapportion livers.


Education & Background

  • Ph.D. Electrical Engineering and Computer Science, Massachusetts Institute of Technology
  • M.S. Operations Research, Stanford University
  • B.S. Mathematical and Computational Sciences, Stanford University

Sommer Gentry is a Professor of Mathematics at the United States Naval Academy, and is also on the faculty of the Johns Hopkins University School of Medicine. She is a senior investigator with the Scientific Registry for Transplant Recipients. She has a B.S. in Mathematical and Computational Science and an M.S. in Operations Research, both from Stanford University, and a Ph.D. in Electrical Engineering and Computer Science from MIT. She designed matching optimization methods used for nationwide kidney paired donation registries in both the United States and Canada, and is now redistricting liver sharing boundaries to help the Organ Procurement and Transplantation Network reduce geographic disparities in transplantation. Her work has attracted the attention of major media outlets including Time Magazine, Reader’s Digest, Science, the Discovery Channel, and National Public Radio. Gentry has received the MAA’s Henry L. Alder award for distinguished teaching by a beginning mathematics faculty member.