Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation by Committee for Evaluation of Space Radiation Cancer Risk Model

Author:Committee for Evaluation of Space Radiation Cancer Risk Model
Language: eng
Format: epub
Tags: ebook, book
Publisher: The National Academies Press
Published: 2012-12-14T00:00:00+00:00

Non-Targeted Effects in the NASA Model

Section 5 of the 2011 NASA report (Cucinotta et al., 2011) also discusses the possibility of modifying the NASA model by adding a term for non-targeted effects, considered to be biological responses in cells that are not directly irradiated. The existence of such effects in cell culture systems has been widely documented for both high- and low-LET radiations (e.g., reviewed in NRC, 2006; UNSCEAR, 2008; Held, 2009), and the potential relevance of NTEs to space radiation biology has been discussed (Cucinotta and Durante, 2006; Held, 2009). However, there are also published studies in which the effect could not be demonstrated (e.g., Fournier et al., 2009). The existence of NTEs in vivo is less well documented, and the relevance to cancer risk is not known with any degree of certainty. Section 5 of the NASA report presents a clear discussion of the manner in which NTEs could be incorporated mathematically into the proposed risk model, and based on current knowledge, the approach seems reasonable. Furthermore, the section summarizes a recent study (Cucinotta and Chappell, 2010) in which the NTE-containing model, when compared with the so-called targeted effect (TE) model, was shown to improve the fit to data on cancer induction in the Harderian gland (data of Alpen et al., 1993) by a range of heavy charged particles. However, the NTE component is not incorporated into the final version of the proposed NASA risk model because the NASA report authors believe that insufficient data are available to lead to an understanding of the importance of NTEs in cancer risks at this time. The committee endorses the decision that an NTE component not be included in the NASA model at this time.

However, the committee points out that, although it is appreciated that the inclusion of considerations of NTEs in the 2011 NASA report was done to indicate potential future enhancements of NASA’s proposed model, such an extensive discussion in the 2011 NASA report seems distracting for an element that is then not incorporated into the final version of the proposed model.

Another issue to consider relates to NTEs with HZE, since delta rays may crossfire into neighboring cells and need to be taken into consideration when defining bystander cells, especially as the energy deposition events due to the delta rays may extend several hundred microns or more. The committee believes that continued research on NTEs and their potential impact on cancer risk projections is highly warranted.

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