Organ Dose Measurement Using the Phantom Torso (Torso) measured the amount of radiation that a human received during an extended space flight. The measurements were taken using an anatomical model of a male head and torso that contains different types of radiation sensors. This experiment is important for future human long-duration space exploration.Principal Investigator(s)
Johnson Space Center, Human Research Program, Houston, TX, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration
March 2001 - August 2001Expeditions Assigned
2Previous ISS Missions
One of the most critical risks to humans in space is radiation exposure. Outside the protection of Earth's atmosphere, space crews are exposed to a wide range of particles, including neutrons, that are not normally a threat on Earth. Exposure to radiation found in low Earth orbit (LEO) and beyond can cause cataracts, cancer, damage to reproductive organs and the nervous system, and changes in heredity.
The Organ Dose Measurement Using the Phantom Torso (Torso) employed a model human head and torso (Rando phantom), imbedded with over 350 detectors (thermo-luminescent detectors) and five silicon diode detectors, over five depths to measure absorbed dose to specific organs during shuttle flight. A tissue equivalent proportional detector and a charged particle directional spectrometer were placed within 1.5-feet of the torso during these ISS measurements. This was the first NASA experiment to simulate doses at discrete locations within the body.
The tissue equivalent proportional counter (TEPC) consisted of a spectrometer and cylindrical detector with which to measure external radiation doses. The TEPC measured radiation dose and dose equivalent in complex radiation fields (fields containing a mixture of particle types). The charged particle directional spectrometer (CPDS) measures particle energy and direction inside ISS. Both the TEPC and the CPDS remained within 1 - 1.5 feet (30.48 - 45.72 cm) of Torso during its operation on station.
The Torso experiment will help scientists more accurately predict the radiation exposure astronauts will experience inside their bodies, especially to critical blood-forming organs. No previous experiment has had the capacity to measure radiation doses in multiple, discrete locations in the body. By performing this experiment on board the International Space Station, scientists also will learn how long human beings can remain in space before the body absorbs dangerous levels of radiation. The experiment may lead to protective procedures to safely prolong human exposure to radiation.Earth Applications
There are benefits on Earth, as well. This experiment is teaching scientists more about the use of embedded devices for data collection and how to monitor real-time data. This could prove beneficial to radiation monitoring of commercial airline crews and military flight crews.
The crew was only required to transfer and activate the Torso and equipment, check its status every 7 to 10-days, download data (using the Human Research Facility - 1 laptop) every 7 to-10 days, and to change the battery every 20-days. At the completion of the experiment, the crew disassembled the Torso for its return on STS-105.Operational Protocols
The crew set up the Torso in the U.S. Destiny Laboratory and activated all the associated hardware. Once activated, the Torso, CPDS, and TEPC collected data continuously, without crew intervention. Data downloads were sent to the Telescience Center at Johnson Space Center for distribution to the investigators.
Organ Dose Measurement Using the Phantom Torso (Torso) results were combined with results from various experiments on previous missions to validate NASA's organ dose database for astronauts. Preliminary results suggest that organ dose and dose equivalent can be projected to a +/- 25% accuracy using a combination of dosimetry and radiation transport models. This accuracy envelope is greatly improved relative to the current
accuracy of organ specific cancer risk projections, estimated at +/- 500%. Further analyses and incorporation of these radiation results into operational planning for exploration is ongoing.
Overall, the dose rates measured in Torso were in good general agreement with other measured values and with the models used to predict these values. The largest differences observed between measured data and the simulations were 15%. In addition, a model which considers orbital altitude, attitude, and solar cycle emissions agreed within 25% of the measured data. It was determined that the majority of radiation energy deposited in human tissues (about 80%) was due to galactic cosmic radiation. This is due to spacecraft material providing effective attenuation of the protons trapped in the Earth's magnetic field. The data indicated an average radiation quality factor (a measurement of how damaging a type of radiation is to tissue) of 2.6 and that the quality factors do not appreciably change with depth in the body. Finally, this experiment indicated that the contribution to both skin and organ doses from secondary neutrons is not negligible (Expedition 2 Postflight Report).
In a follow-on analysis, Cucinotta et al. (2008) report results from post mission biodosimetry assessments of chromosomal damage in lymphocyte cells from 19 ISS astronauts. These results were compared with space radiation transport models, irradiation of pre-flight blood samples, and results from the phantom torso experiments. The ISS astronauts sampled include the earliest missions near the solar maximum, and concluding with Increment 15 astronauts, near the solar minimum. During this timeframe, 67 Solar Particle Events occurred. However, the extended solar maximum (particular to this solar cycle) decreased the galactic cosmic ray levels. Average effective doses for a six-month stay on the ISS were 72 mSv. At least 80% of the organ dose equivalents come from galactic cosmic rays. Another important result shows that the models are predictive within about 10%. The authors conclude that many uncertainties about space radiation remain - both levels and types of radiation, and effects inside the spacecraft. Continued research and analyses are required. (Evans et al. 2009)
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