Choonsik Lee, Ph.D.
|Organization:||National Cancer InstituteDivision of Cancer Epidemiology & Genetics, Radiation Epidemiology Branch|
|Address:||NCI Shady GroveRoom 7E448|
Dr. Lee received his master's in health physics in 1997 and doctorate in health physics in 2002 from Hanyang University in South Korea, where he was trained in computational human phantom development as well as in advanced dosimetry applications. He subsequently joined the Innovative Technology Center for Radiation Safety in South Korea as a Postdoctoral Fellow. While in the post-doctoral period, he was actively involved in national research projects investigating computational dosimetry of the Korean population. After the 2 years of postdoctoral study, he went to the University of Florida as postdoctoral researcher where he received extensive training in computational medical physics. Throughout both his doctoral studies and postdoctoral training, Dr. Lee has made considerable contributions to the development of anthropomorphic phantoms and to the improvement of the dosimetry calculations for a variety of radiation applications ranging from radiation protection to medical exposures. Dr. Lee was appointed as a tenure-track investigator in REB in May, 2009. Dr. Lee is a Corresponding Member of the DOCAL Task Group of the International Commission on Radiological Protection (ICRP). He regularly reviews manuscripts for numerous journals including Radiology, Medical Physics, Health Physics, Radiation Protection Dosimetry, Physics in Medicine and Biology, and etc. Dr. Lee is also actively involved in the American Association for Physicists in Medicine (AAPM) and Health Physics Society (HPS), participating in their annual meetings.
It is reported by National Council on Radiation Protection and Measurement (Publication 160) that about half of the per capita effective dose from medical exposures in 2006 was due to computed tomography (CT) examinations. The annual number of CT examinations increased from 3.6 million in 1980 to 70 million in 2007 and approximately 10% of all CT examinations in the U.S. are performed in pediatric patients who are at higher risk of radiation-related cancer than adults. Although it is crucial to accurately estimate organ/effective doses for the patients undergoing CT examinations, the existing calculation tools are based on the dated and unrealistic human anatomy developed in 1980s. Dr. Lee’s research goal is to develop a new dose calculation tool including improved anatomical accuracy of patient models and Monte Carlo transport-based CT scanner modeling. He developed a computer program, called National Cancer Institute Computed Tomography (NCICT), based on a comprehensive organ dose database calculated from Monte Carlo simulation. The software is being utilized for the epidemiologic cohort and case-control studies of CT risk in UK. Dr. Lee also plans to collaborate with several CT epidemiologic study groups worldwide to use the NCICT for dosimetry component. The software will be implemented into a website for public use. Dr. Lee is collaborating with the University of Florida to undertake this project.
Although radiation therapy has been routinely and successfully used to treat many types of cancers since the 1920s, there has been an increasing concern about the long-term risk of radiation-induced second cancer among cancer survivors as their life span has been increasing. Although the objective of radiation therapy is to provide the highest radiation dose to tumor volume while delivering the lowest possible dose to normal tissue, it is practically impossible to irradiate the tumor volume without some radiation penetrating through the overlying normal tissues. Numerous epidemiologic studies have demonstrated increased risks of second cancers in children and adults patients who received radiation treatment for cancer. Quantitative estimation of the risk of developing a second cancer related to radiation therapy depends on the quality of the dose estimates to the normal tissues. However, there is substantial difficulty in reconstructing organ doses for epidemiologic follow-up studies of patients who were treated several decades ago. Dr. Lee is developing new dose reconstruction methods by using two different approaches: Monte Carlo transport modeling of radiotherapy machines and radiation treatment planning system (TPS) recently improved by deterministic method. He investigated a use of Monte Carlo model of Co-60 treatment machine for organ dose reconstruction for patients diagnosed with breast cancer after Hodgkin Lymphoma treatment. Dr. Lee is undertaking a feasibility study of using treatment planning system to reconstruct organ dose for patients treated by advanced treatment modalities (e.g. Intensity Modulated Radiation Therapy). He is also collaborating with the University of Pennsylvania proton therapy center for the dose reconstruction of proton therapy patients.
In order to estimate organ doses for patients undergoing radiography examinations, a computer program, PCXMC developed by STUK (Helsinki, Finland), has been utilized for a variety of projects in REB. However, the software has several limitations: outdated x-ray spectra, unrealistic anatomy of human models based on stylized computational phantoms, and long calculation time. Dr. Lee is collaborating with Dr. Steve Simon to develop a new computer program to estimate organ doses of patients undergoing radiography examinations. Dr. Lee is working with a master student Mr. Artem Morgun recruited from Ukraine, to develop a Pearl language-based Monte Carlo transport code by using photon transport algorithm. Dr. Lee is also working with Mr. Brian Moroz, a computer programming expert at the REB, to develop a graphical user interface for the radiography dose calculator in parallel with the Monte Carlo dose calculation engine. Dr. Lee is expecting to finish the two separate components (Monte Carlo engine and graphical user interface) and combine them to establish a user-friendly radiography dose calculation program in 2012.
Since he started a postdoctoral training at the University of Florida in 2005, Dr. Lee has been working on the hybrid pediatric phantoms which are so crucial for realistic dose reconstruction of pediatric population to be done in the future. Recently, the pediatric hybrid phantom series developed by Dr. Lee and Dr. Wesley Bolch’s research team at the University of Florida was accepted to serve as reference pediatric models by the International Commission on Radiological Protection (ICRP) to serve as reference pediatric models. ICRP is planning to publish a series of reference dosimetry data in the near future. Dr. Lee is expanding the 50th percentile reference hybrid phantoms to include different body sizes by using a library of US standard body dimensions. The resulting library of the hybrid phantoms will be substantially used to investigate the effect of body size to organ dose calculations for patients undergoing a variety of medical practices.