Choonsik Lee, Ph.D.

Biography

Dr. Lee received a Ph.D. degree in health physics in 2002 from Hanyang University in South Korea. He subsequently joined the Innovative Technology Center for Radiation Safety in South Korea as a postdoctoral fellow and later completed extensive training in computational medical physics as a postdoctoral researcher at the University of Florida. Dr. Lee joined the Radiation Epidemiology Branch (REB) as a tenure-track investigator in 2009, and was awarded scientific tenure and promoted to senior investigator in 2016, and named Head of REB’s Dosimetry Unit. Dr. Lee is a full member of two task groups of the International Commission on Radiological Protection (ICRP). In 2021, he was appointed to the ICRP Committee 2 (Doses from Radiation Exposure) and delivered the prestigious Dade Moeller Lectureship at the Health Physics Society annual meeting. He also serves on the editorial board of Radiation Protection Dosimetry.

NCI Dose Tools: Radiation Dosimetry Tools

A collection of medical radiation dosimetry tools developed by radiation physicists in the Radiation Epidemiology Branch. 

Research Interests

Dr. Lee develops methods and tools to estimate radiation dose from medical exposures, including treatment and diagnostic tests, in order to generate reliable data for use in epidemiological studies of ionizing radiation and cancer risk. 

Computational Human Phantoms

There are two broad approaches to determine organ doses to portions of the human body exposed to ionizing radiation: measurement and calculation. Although measurement can provide dose estimates in actual radiation exposure settings, it is not practical to perform a large number of measurements for all study subjects in epidemiologic studies, because the process is usually time-consuming, expensive, and inflexible.

Alternatively, organ doses can be calculated using a computer simulation of the human body (called a computational human phantom) and radiation exposure scenarios combined with Monte Carlo radiation transport techniques. Dr. Lee has developed a series of computational human phantoms that are crucial for realistic, individualized dose reconstruction. His pediatric series of phantoms has been adopted by the ICRP as the international reference model. To estimate more accurate doses, Dr. Lee, in collaboration with the University of Florida, has expanded the computational phantoms include non-reference body sizes utilizing a library of body dimensions representative of the U.S. population. Learn more about the phantoms.

Dosimetry for Therapeutic Radiation Procedures

Quantitative estimation of the risk of developing second cancers related to radiotherapy relies on the quality of the dose estimates to normal tissues. However, there are substantial difficulties in reconstructing organ doses for a large cohort of patients treated years ago. Dr. Lee initiated a research consortium with several universities and clinical centers to develop new dose reconstruction methods for external radiotherapy using Monte Carlo simulation of radiotherapy machines coupled with his computational human phantoms. He calls this combination the National Cancer Institute dosimetry system for Radiation Treatment (NCIRT). Dr. Lee is applying NCIRT to multiple epidemiological studies of second cancers in radiotherapy patients in collaboration with REB epidemiologists as well as the research consortium. He is also extending NCIRT to include dosimetry methods for proton therapy patients, in particular the Pediatric Proton and Photon Therapy Comparison Cohort.

Dosimetry for Diagnostic Radiation Procedures

Dr. Lee develops computational dosimetry methods and software tools for a broad range of diagnostic radiation procedures. These include the National Cancer Institute dosimetry system for Computed Tomography (NCICT), the NCI dosimetry system for Nuclear Medicine (NCINM), and the NCI dosimetry system for Radiography and Fluoroscopy (NCIRF). These tools combine Monte Carlo radiation transport with computational human phantoms to estimate organ doses for patients of different ages and body sizes. They are used in epidemiological studies and are also made available to the scientific and medical communities to support radiation dose assessment and optimization. More information about these tools, documentation, and software resources is available at NCI Dose Tools Github Pages.