Reinforcement Learning in Healthcare: A Survey (1908.08796v4)

Abstract: As a subfield of machine learning, reinforcement learning (RL) aims at empowering one's capabilities in behavioural decision making by using interaction experience with the world and an evaluative feedback. Unlike traditional supervised learning methods that usually rely on one-shot, exhaustive and supervised reward signals, RL tackles with sequential decision making problems with sampled, evaluative and delayed feedback simultaneously. Such distinctive features make RL technique a suitable candidate for developing powerful solutions in a variety of healthcare domains, where diagnosing decisions or treatment regimes are usually characterized by a prolonged and sequential procedure. This survey discusses the broad applications of RL techniques in healthcare domains, in order to provide the research community with systematic understanding of theoretical foundations, enabling methods and techniques, existing challenges, and new insights of this emerging paradigm. By first briefly examining theoretical foundations and key techniques in RL research from efficient and representational directions, we then provide an overview of RL applications in healthcare domains ranging from dynamic treatment regimes in chronic diseases and critical care, automated medical diagnosis from both unstructured and structured clinical data, as well as many other control or scheduling domains that have infiltrated many aspects of a healthcare system. Finally, we summarize the challenges and open issues in current research, and point out some potential solutions and directions for future research.

Overview of Reinforcement Learning in Healthcare

The paper, "Reinforcement Learning in Healthcare: A Survey" by Chao Yu, Jiming Liu, and Shamim Nemati, presents a comprehensive review of the application of Reinforcement Learning (RL) techniques in healthcare. It offers a detailed examination of how RL can be used to address the complexities and dynamic nature of medical treatment and diagnosis, emphasizing the unique advantages of RL over traditional learning methods.

Theoretical Foundations and Techniques

The paper begins by outlining the core theoretical foundations of RL, distinguishing it from traditional supervised learning by its focus on sequential decision-making without predefined labels. Emphasis is placed on the agent's capacity to interact with the environment through trial-and-error to learn optimal policies. The technical discussion recognizes both model-based and model-free RL methods, highlighting Dynamic Programming (DP) techniques such as Value Iteration (VI) and Policy Iteration (PI), and their reliance on a complete model of the environment.

Key advances in RL efficiency, such as experience replay, Batch RL (BRL), and function approximation, are discussed. These techniques facilitate more stable learning, essential in the healthcare domain where data may be sporadic or costly to obtain. The survey also reviews the integration of deep learning with RL, producing what is now known as Deep Reinforcement Learning (DRL), which significantly enhances the capability to handle complex, high-dimensional states.

Applications in Healthcare

Dynamic Treatment Regimes (DTRs)

A significant portion of the survey examines the application of RL in developing Dynamic Treatment Regimes for chronic diseases such as cancer and diabetes, as well as critical care scenarios. The review of RL in chemotherapy and radiotherapy for cancer illustrates its potential to personalize treatment strategies without requiring exhaustive computational models of the disease and patient physiology. Similar applications in diabetes treatment highlight RL's capacity to adapt insulin dosage in real-time according to patient-specific characteristics.

Critical Care

In critical care, RL's application extends to managing sedation levels, heparin dosing, and mechanical ventilation. The inherent challenges of these applications, such as noise in data and variance among individual patient responses, are addressed through robust BRL and DRL techniques.

Automated Medical Diagnosis

RL is also applied to automated medical diagnosis, utilizing structured data (e.g., images) and unstructured data (e.g., text narratives) to enhance diagnostic accuracy and decision-making. The integration of RL with natural language processing and computer vision allows for more adaptive and intelligent diagnostic tools, potentially reducing human diagnostic error rates.

Challenges and Future Directions

The paper outlines several challenges in applying RL to healthcare, such as defining suitable reward functions, handling partial observability, managing exploration-exploitation trade-offs, and ensuring the interpretability of learned policies. It calls for more research into safe exploration methods and robust policy evaluation techniques suitable for the high-stakes nature of healthcare.

Moreover, the authors envision future developments in RL that include enhanced interpretability of strategies, integration of domain-specific knowledge, handling of sparse data, and deployment in real-time adaptive systems. The potential for RL to function within ambient intelligence systems highlights a forward-looking perspective, envisioning RL's role in pervasive and intelligent health monitoring environments.

Implications

In conclusion, the survey underscores RL's potential to transform healthcare by providing adaptive, personalized treatments and improving clinical decision-making processes. Theoretical advancements and practical implementations of RL can have far-reaching impacts, contributing to more efficient, safer, and patient-centered healthcare systems in the future.