Ionizing radiation has enough energy to remove tightly bound electrons from the orbit of an atom—causing that atom to become "ionized." It also has enough energy to cause changes in living cells that can have long-term health implications. While this makes ionizing radiation useful in some medical applications, such as cancer treatment, it can also have negative effects, and there are extensive guidelines and regulations in place to protect Canadians from unsafe levels of exposure to ionizing radiation.
In Canada and elsewhere, current guidelines for exposure to ionizing radiation are based largely on studies of the effects of radiation released in the explosion of nuclear weapons—using the impact of what is usually a brief and very high dose of ionizing radiation to estimate the risk posed by other levels of exposure. As a result, there are significant gaps in what we know about the effects of low doses of ionizing radiation on human health.
With the support of funding through the Government of Canada's Genomics Research and Development Initiative (GRDI), Dr. Vinita Chauhan, Research Scientist in Health Canada's Consumer and Clinical Radiation Protection Bureau, is leading a research project aimed at reducing the knowledge gaps by generating new information on the biological effects of exposure to low-dose ionizing radiation.
Chronic low dose exposures
"This is important when we look at a source of ionizing radiation like radon gas, which can cause lung cancer," says Dr. Chauhan. "Unlike artificial sources of ionizing radiation, such as nuclear energy production or medical devices, radon occurs naturally. In fact, all houses in Canada have radon gas in various concentrations, and there is uncertainty on the risk it may pose in terms of long-term health effects."
Dr. Chauhan adds, "While most people's bodies are able to repair any damage that might be caused by occasional, very low doses of radiation, the effects of chronic exposure to low doses are still not well known. Are there levels of exposure that lead to significant biological effects?"
Gene and protein markers can provide early signs of exposure
To answer this question, Dr. Chauhan and her team are working to identify the early events at the molecular level—using genomics technologies that enable them to spot the early gene/protein changes that signal the beginning of long-term damage from exposure to low doses of radiation.
"By identifying a number of gene/protein-based markers and seeing how they respond to different levels of radiation, using benchmark dose (BMD) modelling, we can begin to establish dose-response relationships," she says. "We can use this knowledge to make a more accurate determination of the doses at which ionizing radiation exposure will lead to activation of genetic pathways that may be associated with adverse outcomes."
Collaboration through GRDI to accelerate progress
Dr. Chauhan, together with co-investigators Dr. Baki Sadi and Dr. Ruth Wilkins at Health Canada (HC) and her collaborators, Dr. Premkumari Kumarathasan at HC, Dr. Sue Twine at the National Research Council of Canada, Dr. Carole Yauk at the University of Ottawa and Dr. Laura Bannister at the Canadian Nuclear Laboratories, are working on three sub-projects simultaneously.
The first involves reviewing existing genomic studies that have assessed the effects of different doses and different types of radiation to see the levels at which the markers have been triggered in a variety of exposure scenarios. In the second sub-project, the team exposes samples of human blood to different levels of ionizing radiation to determine the level at which the gene/protein-based markers are triggered.
The third sub-project also involves looking for the levels at which the gene/protein markers are triggered, this time in laboratory animals that have been exposed to very low doses of radiation from uranium.
Enhancing health and safety
Dr. Chauhan is also a member of the Canadian Organization on Health Effects from Radiation Exposure (COHERE), a recently established joint initiative between Health Canada and the Canadian Nuclear Safety Commission (CNSC) to study potential health impacts from exposure to low doses of radiation.
Kiza Sauvé, Director of the Health Sciences and Environmental Compliance Division at the CNSC, says the research led by Dr. Chauhan offers a much-needed contribution to understanding the effects of low dose radiation.
"Most of what we understand about the effects of low doses of ionizing radiation is based on the assumption that the impacts follow a linear model, according to the dosage," says Ms. Sauvé. "The effects of high doses are well-known, but at the places we regulate, low dose radiation is the concern. So the more we know specifically about the effects of low dose radiation, the more confidence we can have in what we determine to be safe levels of exposure."