The methods used to calculate the risk of cancer differ in their area of application and have differing benefits and drawbacks. The “cumulative risk assessment method” is, however, more favoured. This was the conclusion drawn by Luana Hafner, radiation protection expert at ENSI, and epidemiologist Linda Walsh as part of a scientific study published by the Journal of Radiological Protection.
In the paper, published by the Journal of Radiological Protection, entitled “Valid versus invalid radiation cancer risk assessment methods illustrated using Swiss population data” Luana Hafner, a member of staff at ENSI, and epidemiologist Linda Walsh compare two different methods for calculating cancer risk: the collective dose method and the cumulative risk assessment method.
In the collective dose method, the mean effective dose is multiplied by the number of affected persons to calculate the collective dose. Based on this collective dose, the number of possible deaths caused by cancer is then calculated using a risk factor, drawing on the assumptions of the linear non-threshold model (LNT).
In contrast, the cumulative risk assessment method calculates an average cancer risk for a certain population, for a certain exposure age and gender by means of integrating over the age reached and takes account of various other factors (age of exposure, type of cancer, gender, etc.) in the calculation. The specific factors applied are appropriately communicated when publishing the results. However, it should be borne in mind that this does not relate to the cancer risk of a particular individual where other factors such as genetics, personal radio sensitivity or lifestyle would also have to be taken into account.
In their study, Hafner and Walsh weigh up the respective advantages and disadvantages and define the appropriate areas of application for the two methods. The authors conclude that the cumulative risk assessment method is more conclusive than the collective dose method. As a result, the authors advocate using only this method to assess the risk of cancer. In general, only those methods permitted from a scientific point of view should be used in the intended areas of application.
The study also picks up on risk assessment in different dose ranges and the uncertainties inherent in any calculation. To illustrate the topics and methods used more practically, Hafner and Walsh used examples based on data drawn from the Swiss population.
Moreover, the authors state that, due to the high level of uncertainty, there is insufficient evidence of a causal relationship between cancer and radiation when assessing the risk of radiation exposure for doses less than 100 millisievert (mSv). “Nevertheless, the linear non-threshold model (LNT) is still of practical importance for doses less than 100 mSv,” says Rosa Sardella, Director of the Radiation Protection Division at ENSI. “With this LNT model, radiation protection specialists have a safety-related tool at their disposal for modelling dose-dependence in everyday work.”
Making sense of a complex topic
In the wake of the Fukushima Daiichi reactor accident, there has been a sharp increase in public interest in radiation-induced cancer risks and their calculation methods. These topics from the fields of epidemiology, medicine and radiation protection are diverse and extensive.
Currently, there are now various calculation methods with different areas of application. This paper from Luana Hafner and Linda Walsh provides an overview of these methods and will help to prevent confusion, misapplication or the misinterpretation of studies and their results.