Gauging the risk from prolonged low-level radiation

Dec 7 2004

Everyone knows that high doses of radiation are dangerous, but the effects of long-term exposure to low-level radiation is poorly understood. RISC-RAD, a new European Union backed research project, seeks to identify our tolerance threshold so as to optimise protective measures.

Ionising radiation – radiation given off by radioactive materials – has a bit of the Dr Jekyll and Mr Hyde about it. In hospitals, for instance, it is used to treat cancer. But prolonged exposure to low doses can cause the killer disease to form. For this reason, the safety precautions for exposure to such radiation are extremely strict.

“Radio-protection standards are set to limit the amounts of radiation to which workers and the general population are exposed in order to protect them from the harmful effects of radiation,” explains Laure Sabatier, head of the Department of Radiobiology and Oncology at France’s Commissariat à l’Energie Atomique (CEA).

“These standards are based on the extrapolation to low doses of effects observed at high exposure levels, and so are not in themselves correlated with measurable health hazards.”

The effects of high doses have been closely studied and are well known. However, the long-term impact of prolonged exposure to low doses has only been inferred. But such statistical extrapolations are “controversial” because they assume that radiation will behave proportionately the same at all concentrations. “What we need are new biological approaches for sounder risk assessment,” Sabatier notes.

In addition, risk estimates are based largely on a statistically “average” individual in an exposed population. “But clinical observations of adverse reactions to radiotherapy show large differences among individuals,” she points out.

It was with this in mind that the four-year EU-backed RISC-RAD (Radiosensitivity of Individuals and Susceptibility to Cancer induced by ionizing RADiations) project was launched earlier this year. With €10 million in EU funding, the pioneering project brings together 29 research teams from 11 European countries. They have joined forces to build a thorough understanding of the long-term effects of low-dose ionising radiation and how it causes cancer.

The project will plot the various steps in the multi-stage evolution of radiation-induced DNA-damage and subsequent tumours. “Understanding the mechanisms that increase the risk of cancer 30 years later is a major challenge,” observes Sabatier, who coordinates RISC-RAD.

RISC-RAD aims ultimately to pave the way to the setting of realistic safety standards and procedures that reflect the actual risks involved.