Gap Acute - 1: Determine the dose response for acute effects (focusing on effects that are evident at space-relevant doses) induced by SPE-like radiation, including synergistic effects arising from other spaceflight factors (e.g. altered gravity (microgravity), stress, altered immune function, or other) that modify and/or enhance the biological response.
Last Published:  03/29/18 08:54:54 AM (Central)
Responsible Element: Space Radiation (SR)
Status: Open
Description


Initial State of Gap:

The space environment is variable with infrequent and sporadic solar particle events that consist largely of low to medium energy protons with energies up to a few hundred MeV. Acute radiation syndromes (ARS) from solar particle events (SPE) are of concern for manned spaceflight. ARS symptoms can include hematopoietic, gastrointestinal, cutaneous, and neurovascular decrements. However, through careful evaluation of SPE frequency and size probabilities, dose-rates, likely shielding conditions, and dose distribution at specific organs, the likelihood of acute risks is extremely small. There are scenarios, however, during lunar extravehicular activity (EVA), trans-lunar, or Mars transit where acute radiation sickness (ARS) may occur if adequate shielding is not available in a timely manner. The most probable ARS effects from SPE exposure during spaceflight that can potentially affect mis­sion success are the clinical symptoms associated with the prodromal phase. These symptoms of mild hematopoietic syndrome (nausea, vomiting, anorexia, and fatigue) occur within the first 48 hrs following exposure, along with skin injury and depression of the blood forming organs (BFOs).
 

NASA has established short-term dose limits (0.25 Gy-Eq to the BFO and 1.5 Gy-Eq to the skin in a 30-day period) to prevent clinically significant deterministic health effects, including performance decrements in flight. The short-term PELs are essential for mission planning and influence the amount of spacecraft shielding, storm shelter requirements, spacesuit design and timelines for EVAs and their accuracy is critical in order to ensure the health and safety of the astronaut crew.
 

Radiation protection must be provided in the form of shielding and operational dosimetry and monitoring. In addition, medical countermeasures may be necessary in the case of an unavoidable or accidental exposure when traveling outside of the protective magnet­osphere of Earth. Active dosimetry and predictive models support the evaluation of crew risks, operational requirements and decisions, and the efficient design of vehicle shelters to minimize exposures. NASA has developed state-of-the-art SPE models and radiation transport codes that can estimate SPE and galactic cosmic ray doses. These tools were reviewed by the National Research Council (NRC, 2012). The range of organ doses, real-time dosimetry systems, advanced space weather prediction and likely flight rules that will be required for deep space and lunar missions are under development by NASA.


The NSBRI Center for Space Radiation Research (CSRR) completed studies in 2017 examining proton RBEs at doses surrounding NASA’s Permissible Exposure Levels (PELs) for the BFO using rodent models. The CSRR also examined immune system effects, and synergies to the acute risk when combined with simulated microgravity. 

 

  

 Approach:

Ground-based research has resulted in preliminary estimates of proton RBEs and dose-rate modifiers for acute prodromal risks along with preliminary evidence for other spaceflight factors including immune response and simulated microgravity.  Studies are required to assess the accuracy of short-term limits to the BFO and the skin using proton energy distributions and dose-rates simulating an SPE. Studies should include assessment of the relative biological effectiveness (RBE) at lower energy below 10 MeV where protons become high-LET radiation. Research on acute risks related to EVA conditions must factor in the role of dose-rate over an EVA time course, the additional exposure IVA (intra-vehicular activity) for a terminated EVA, and other spaceflight factors that could modify expected dose response models for acute risks.



In addition, there is reasonable concern of a compromised immune system due to high skin doses from an SPE. This impact on the immune system may then increase the risk to the BFO. Therefore, studies addressing the biological effects of inhomogeneous dose distributions are required. Additional spaceflight factors such as weightlessness have also been shown to cause immune dysfunction and there is concern that this may also increase the risk to the BFO.

 

 


Target for Closure

•Estimate RBE and dose-rate modifiers for acute radiation sickness components (nausea, vomiting, fatigue, blood kinetics).

•Determine the clinical spectrum and severity of skin damage from low energy protons and possible concomitant immune system response from skin doses and how this impacts the short term limits to the BFO.

•Determine the effect of simulated microgravity plus protons on acute radiation sickness and immune response.

Mappings
Risk Risk of Acute Radiation Syndromes Due to Solar Particle Events (SPEs)
You are here! Gap Acute - 1: Determine the dose response for acute effects (focusing on effects that are evident at space-relevant doses) induced by SPE-like radiation, including synergistic effects arising from other spaceflight factors (e.g. altered gravity (microgravity), stress, altered immune function, or other) that modify and/or enhance the biological response.
Active
Completed

Documentation:
No Documentation Available