Samei is the director of the Carl E. Ravin Advanced Imaging Laboratories, and the director of Duke University’s Center for Virtual Imaging Trials (CVIT), which has been developing advanced, realistic human phantoms for use in virtual clinical trials for radiation oncology and radiology. NASA asked if his team could use their technology to assess the actual dangers to humans in deep space once they leave the powerful magnetic fields of the Earth that protect the planet from extremely high doses of radiation from the sun and other cosmic sources. To date, there has been little research in this area, but as manned space missions now look at long-term exploration of the Moon and Mars, that data down to dose levels per organ is essential to understanding potential health impacts and survivability of these missions.

The Artemis I mission was a major step forward as part of NASA’s lunar exploration efforts, and these radiology phantom computational models will play a key role in the next steps in manned space flight beyond Earth's orbit.

"Imagine the astronaut as a patient and you want to understand how much radiation dose they will receive," Samei explained. "We need to know the magnitude of the radiation and if they will be passing some safety threshold and how concerned do we need to be."

His research lab does a lot of radiation dosimetry for radiation oncology research. Organ specific dosimetry is the best measure because some organs are more radiosensitive than others. The NASA phantom astronauts they built, both female and named Helga and Zohar, are made of materials that have the same radio density, or Hounsfield units, as actual human tissue. Implanted inside these virtual organs are thousands of radiation sensors that recorded data during the Artemis I mission. The flight of that first mission went well beyond the moon and further into deep space so that measurements of radiation level well outside the influences of the Earth and Moon could be made. These data are now being analyzed by the Duke team for a report to NASA. The outcomes of the report may be far reaching for how to proceed with safety measures and shielding on future Artemis missions. 

"This is a big project with multiple partners and it is really remarkable because it is really the first time we are getting very detailed, granular information on the organ dose of astronauts," Samei said. 

The cost to send these phantoms into space and to interpret the information they gathered likely make this one of the most expensive clinical trials for radiation dose ever undertaken. He explained that every ounce of weight for people or cargo taken into space has a very high cost, so it is remarkable that they could dedicate two seats on the spacecraft to this science experiment. 

"This is a significant financial investment, but will provide definitive data that we have never had before," Samei said. "The radiation levels are not insignificant. NASA has some concern whether the cognition of the astronauts will remain viable at high levels. You have heavy ions in space and you don't have heavy shielding. You can't have heavy shielding because everything has a weight cost. So that is why it is so important to have a much more precise assessment."

He said this is particularly true for females, whose bodies are more sensitive to radiation than males. That is why the two phantom astronauts are females. Samei said by estimating dosimetry for the female models, he said the numbers will then be an overestimation for male, so the male measurements can be calculated from there.

There are two phantoms that were aboard the Artemis I mission Orion capsule because one acted as a control, and the second was fitted with a special radiation protection suit. The difference between the radiation measures between the two phantoms will help determine the level of protection the shielding suit provides. 

Samei said back on Earth, this detailed phantom technology Duke developed was actually designed to be used in virtual clinical trials. He said the technology can help better assess safety in humans before using new treatments in an actual person. The hope is to offer more realistic bench testing and to help speed pre-clinical work to get new therapies to patients faster. 

He spoke in a session at the  Radiological Society of North American (RSNA) 2022 meeting on the topic of virtual clinical trials using this phantom technology. He took time during RSNA to speak with Health Imaging for this interview. At the time of the interview, his phantoms in Artemis I were on the far side of the Moon more than 260,000 miles away.