PhD | Personal online dosimetry of astronauts using computational methods

Exposure to ionizing radiation is one of the most important health risks for astronauts in space. For future missions beyond Low Earth Orbit (LEO) to the Moon or Mars, radiation will become an even more challenging issue. Therefore, radiation protection for astronauts is of fundamental importance, and dosimetry is an important part of this. Currently, personal dosimetry of astronauts is performed by physical personal dosimeters. These have several important drawbacks such as an imperfect response for the complex radiation field encountered in space consisting of electrons, neutrons, photons, protons and heavier ions up to extremely high energies. Also from a practical point of view, it is difficult to use passive dosemeters, as these need to be send back to earth for processing, but also active dosemeters are not straightforward as they generally are quite bulky. Furthermore, personal dosimetry with a physical dosemeter is always limited to measurement at one position on the body, and as such does not give information on doses to all organs. These issues could be avoided by a novel approach, namely using cameras for tracking of the astronaut movements, modelling the spacecraft and its radiation field and then computing the worker radiation doses by Monte Carlo radiation transport simulations.

In the International Space Station (ISS) the personal doses of the astronauts are currently being monitored by passive personal dosimeters that are based on the combination of thermoluminescent detectors (TLDs) and track etch detectors. Recently, both NASA and ESA started testing new active personal dosimeters based on silicon and direct ion storage detectors. However, even with these state-of-the-art active personal dosimeters, the dose assessment in the complex space radiation field comes with a large uncertainty and is limited to a single dose value at the position of the dosimeter. This information is not sufficient for an accurate assessment of the associated health risk for the astronaut. Accurate risk assessment requires evaluation of the absorbed dose in the different organs of the astronaut together with information about the radiation quality. This is only possible by replacement of the physical personal dosimeters by computational dosimetry. The recent H2020 PODIUM (Personal Online DosImetry Using computational Methods) project coordinated by SCK CEN demonstrated the feasibility of this innovative dosimetric approach for application in interventional radiology and neutron workplace fields. An important input for computational dosimetry is the radiation source. In literature there exist already several well established and validated models of the main sources of cosmic radiation, namely Galactic Cosmic Radiation (GCR), Solar Particle Events (SPEs) and the Van Allen radiation belts. Furthermore, Monte Carlo radiation transport codes like PHITS and GEANT4, dedicated for complex and high energy radiation fields, can be used to simulate how this primary cosmic radiation is modified by the spacecraft. By using existing realistic numerical anthropomorphic phantoms it is even possible to simulate the absorbed doses and radiation quality in the different organs of the astronauts for any position and posture in the spacecraft. However, even with the availability of these models and simulation codes, the computational dosimetry technology developed within the PODIUM project cannot simply be translated for application in space. Several important scientific and technological challenges first need to be overcome.

The goal of this PhD is to further elaborate and demonstrate this computation dosimetry technology specifically for application of personal dosimetry of astronauts in space and develop augmented reality software based on this technology to allow the astronauts to visualize the radiation field.

In PODIUM dedicated 3D cameras were used for tracking of the radiation workers. However, installation and operation of additional hardware in spacecraft is not straightforward due to very stringent mass, materials and power consumption restrictions. Also specific tracking algorithms will be required dedicated to the special situation of spacecraft.

The geometry of a spacecraft is very complex. It will be investigated how the spacecraft can be modelled efficiently in Monte Carlo radiation transport simulations codes such as GEANT4 or PHITS.

Besides the geometry also the radiation field in spacecraft is very complex. It is influenced by many parameters such as the spacecraft orbit, position in the orbit, solar activity, local shielding within the spacecraft and position and orientation of the astronauts. During this PhD it will be evaluated how the radiation field can be modelled sufficiently realistically (cosmic radiation source models, Monte Carlo radiation transport simulations, …) and which input data (radiation detectors within the spacecraft or on-board other spacecraft or satellites, cosmic neutron monitors on earth, …) will be required.

Finally, it will be investigated how all these different elements can be combined and what simplifications or computational techniques will be required to allow real-time follow-up of the personal astronaut doses and visualization of the radiation field for the astronauts through the application of augmented reality. Different techniques and combinations of those techniques such as Monte Carlo radiation transport simulations (GEANT4, PHITS), deterministic ray tracing radiation transport simulations (HZETRN), artificial intelligence and machine learning algorithms and databases of pre-calculated dose rate maps will be evaluated.