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Models of Risk From Low-Dose Radiation Exposures: What Does the Evidence Say?

J Bushberg
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D Boreham

B Ulsh

J Bushberg1*, D Boreham2*, B Ulsh3*, (1) UC Davis Medical Center, Sacramento, CA, (2) McMaster University, Ontario, CA, (3)


TU-C-18A-1 Tuesday 10:15AM - 12:15PM Room: 18A

At dose levels of (approximately) 500 mSv or more, increased cancer incidence and mortality have been clearly demonstrated. However, at the low doses of radiation used in medical imaging, the relationship between dose and cancer risk is not well established. As such, assumptions about the shape of the dose-response curve are made. These assumptions, or risk models, are used to estimate potential long term effects. Common models include 1) the linear non-threshold (LNT) model, 2) threshold models with either a linear or curvilinear dose response above the threshold, and 3) a hormetic model, where the risk is initially decreased below background levels before increasing. The choice of model used when making radiation risk or protection calculations and decisions can have significant implications on public policy and health care decisions. However, the ongoing debate about which risk model best describes the dose-response relationship at low doses of radiation makes informed decision making difficult.

This symposium will review the two fundamental approaches to determining the risk associated with low doses of ionizing radiation, namely radiation epidemiology and radiation biology. The strengths and limitations of each approach will be reviewed, the results of recent studies presented, and the appropriateness of different risk models for various real world scenarios discussed. Examples of well-designed and poorly-designed studies will be provided to assist medical physicists in 1) critically evaluating publications in the field and 2) communicating accurate information to medical professionals, patients, and members of the general public.

Equipped with the best information that radiation epidemiology and radiation biology can currently provide, and an understanding of the limitations of such information, individuals and organizations will be able to make more informed decisions regarding questions such as 1) how much shielding to install at medical facilities, 2) at what dose level are risk vs. benefit discussions with patients appropriate, 3) at what dose level should we tell a pregnant woman that the baby's health risk from a prenatal radiation exposure is "significant", 4) is informed consent needed for patients undergoing medical imaging, and 5) at what dose level is evacuation appropriate after a radiological accident. Examples of the tremendous impact that choosing different risks models can have on the answers to these types of questions will be given.

A moderated panel discussion will allow audience members to pose questions to the faculty members, each of whom is an established expert in his respective discipline.

Learning Objectives:
1. Understand the fundamental principles, strengths and limitations of radiation epidemiology and radiation biology for determining the risk from exposures to low doses of ionizing radiation
2. Become familiar with common models of risk used to describe the dose-response relationship at low dose levels
3. Learn to identify strengths and weaknesses in studies designed to measure the effect of low doses of ionizing radiation
4. Understand the implications of different risk models on public policy and health care decisions


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