Abel Sapirstein

Abel Sapirstein

PhD Student in Operations Research
NDSEG and Former TJ Watson Fellow

Posts by Collection

portfolio

publications

Geographic disparities in liver supply/demand ratio within fixed-distance and fixed-population circles

Published in American Journal of Transplantation, 2007

Recent OPTN proposals to address geographic disparity in liver allocation have involved circular boundaries: the policy selected 12/17 allocated to 150-mile circles in addition to DSAs/regions, and the policy selected 12/18 allocated to 150-mile circles eliminating DSA/region boundaries. However, methods to reduce geographic disparity remain controversial, within the OPTN and the transplant community. To inform ongoing discussions, we studied center-level supply/demand ratios using SRTR data (07/2013-06/2017) for 27 334 transplanted deceased donor livers and 44 652 incident waitlist candidates. Supply was the number of donors from an allocation unit (DSA or circle), allocated proportionally (by waitlist size) to the centers drawing on these donors. We measured geographic disparity as variance in log-transformed supply/demand ratio, comparing allocation based on DSAs, fixed-distance circles (150- or 400-mile radius), and fixed-population (12- or 50-million) circles. The recently proposed 150-mile radius circles (variance = 0.11, P = .9) or 12-million-population circles (variance = 0.08, P = .1) did not reduce the geographic disparity compared to DSA-based allocation (variance = 0.11). However, geographic disparity decreased substantially to 0.02 in both larger fixed-distance (400-mile, P < .001) and larger fixed-population (50-million, P < .001) circles (P = .9 comparing fixed distance and fixed population). For allocation circles to reduce geographic disparities, they must be larger than a 150-mile radius; additionally, fixed-population circles are not superior to fixed-distance circles.

Recommended citation: Haugen, C.E., Ishaque, T., Sapirstein, A., Cauneac, A., Segev, D.L., and Gentry, S. (2019). Geographic disparities in liver supply/demand ratio within fixed-distance and fixed-population circles. American Journal of Transplantation 19, 2044�2052. https://doi.org/10.1111/ajt.15297.
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Toward Expanded Access to Cancer Care with Cost Awareness: An Optimization Modeling Analysis of Rwanda

Published in Journal of Clinical Oncology: Global Oncology, 2024

Cancers are a growing cause of mortality especially in low- and middle-income countries in Africa. Rwanda is no exception. Two cancer centers currently provide care to the public, but there are both political and human interest in expanding access to tertiary cancer care. Improved geographic access could lead to both better patient outcomes and a better understanding of the existing cancer burden across Rwanda. To identify cost-aware ways of expanding geographic access, we adopt an optimization approach and identify expansion plans that minimize the average travel time to a cancer center across the country while remaining under a given monetary budget. Three additional hospitals could reduce average travel times by 40%, with the largest decrease in travel times observed in populations with long travel times. However, such an expansion would require a 50% increase in the number of in-country oncologists. We find that oncologist scarcity, as opposed to monetary constraints, is likely to be a limiting factor for improved access to cancer care. We present an array of expansion plans and suggest that further modeling approaches that incorporate oncologist scarcity can help deliver better policy recommendations.

Recommended citation: Sapirstein, A., Steimle, L.N., and Stefan, D.C. (2024). Toward Expanded Access to Cancer Care With Cost Awareness: An Optimization Modeling Analysis of Rwanda. JCO Glob Oncol, e2400022. https://doi.org/10.1200/GO.24.00022.
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Geographic disparities in liver supply/demand ratio within fixed-distance and fixed-population circles

Published in American Journal of Transplantation, 2025

Recent OPTN proposals to address geographic disparity in liver allocation have involved circular boundaries: the policy selected 12/17 allocated to 150-mile circles in addition to DSAs/regions, and the policy selected 12/18 allocated to 150-mile circles eliminating DSA/region boundaries. However, methods to reduce geographic disparity remain controversial, within the OPTN and the transplant community. To inform ongoing discussions, we studied center-level supply/demand ratios using SRTR data (07/2013-06/2017) for 27 334 transplanted deceased donor livers and 44 652 incident waitlist candidates. Supply was the number of donors from an allocation unit (DSA or circle), allocated proportionally (by waitlist size) to the centers drawing on these donors. We measured geographic disparity as variance in log-transformed supply/demand ratio, comparing allocation based on DSAs, fixed-distance circles (150- or 400-mile radius), and fixed-population (12- or 50-million) circles. The recently proposed 150-mile radius circles (variance = 0.11, P = .9) or 12-million-population circles (variance = 0.08, P = .1) did not reduce the geographic disparity compared to DSA-based allocation (variance = 0.11). However, geographic disparity decreased substantially to 0.02 in both larger fixed-distance (400-mile, P < .001) and larger fixed-population (50-million, P < .001) circles (P = .9 comparing fixed distance and fixed population). For allocation circles to reduce geographic disparities, they must be larger than a 150-mile radius; additionally, fixed-population circles are not superior to fixed-distance circles.

Recommended citation: Haugen, C.E., Ishaque, T., Sapirstein, A., Cauneac, A., Segev, D.L., and Gentry, S. (2019). Geographic disparities in liver supply/demand ratio within fixed-distance and fixed-population circles. American Journal of Transplantation 19, 2044�2052. https://doi.org/10.1111/ajt.15297.
Download Paper

talks

Improving Equity in Healthcare Access Through Network Design: A Case Study of Specialist Cancer Care in Rwanda

Published:

Cancer is a growing cause of death in Rwanda. Addressing inequity in access to cancer care requires policy solutions that consider cost, demand for care, provider availability, and barriers to healthcare access. In this talk, we consider an important barrier to access - poor road conditions that lead to long travel times to access specialist cancer care in Rwanda. We formulate a network design problem that considers road improvements and facility expansion simultaneously. We parameterize the model using publicly available data and propose solutions that align with the objectives of government and NGO partners.

Paving the Way for More Accessible Cancer Care in Low-Income Countries with Optimization

Published:

Cancers are a growing cause of morbidity and mortality in low-income countries. Geographic access plays a key role in both timely diagnosis and successful treatment. In areas lacking well-developed road networks, seasonal weather events can lengthen already long travel times to access care. Expanding facilities to offer cancer care is expensive and requires staffing by skilled medical professionals, which are often in short supply. In this article, we propose a mathematical model to improve geographic access to cancer care by jointly considering expansions to care facilities and improvements to the road network. We model this as a multi-period stochastic facility location network design problem. In each period, a decision maker must simultaneously choose a set of facilities at which to add tertiary cancer services and a set of roads to improve while facing demand and travel time uncertainty. Once demand for cancer care and weather events are realized, patients observe road conditions and use the transportation network to travel towards the closed facility with available cancer services. We create a new path-based formulation of this problem and develop a new branch-price-and-cut algorithm with acceleration techniques that take advantage of this formulation’s structure. We demonstrate our approach using Rwanda as a case study and show that the reductions in travel time to cancer care that are directly attributable to the road network improvements can be as high as 1 hour.

teaching

Teaching experience 2

Workshop, University 1, Department, 2015

This is a description of a teaching experience. You can use markdown like any other post.

Classroom Based Undergraduate Research

CURE, Georgia Tech, Center for Teaching and Learning, 2025

This is a description of a teaching experience. You can use markdown like any other post. (link)[https://ctl.gatech.edu/project/teaching-statistics-using-facility-location-modeling-a-course-based-undergraduate-research-experience/]