Organ Dose Measurement Using the Phantom Torso (Torso) - 09.17.14
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Organ Dose Measurement Using the Phantom Torso (Torso) measures the amount of radiation that a human received during an extended space flight. The measurements are 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.
Science Results for Everyone
The Phantom of the ISS – Phantom Torso, that is. This model of a male head and torso contains sensors that measure the radiation supposedly absorbed by the body during extended space flight. The data suggest that organ radiation dose and dose equivalent can be projected to within 25 percent accuracy, an improvement to the current plus-or-minus 500 percent accuracy of cancer risk projections. About 80 percent of radiation energy deposited in human tissues seems to come from galactic cosmic radiation, most likely because the spacecraft effectively deflects the protons trapped in Earth's magnetic field. Many uncertainties about space radiation remain, and more research and analyses are needed. The Phantom may ride again.
Johnson Space Center, Human Research Program, Houston, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
March 2001 - August 2001
Previous ISS Missions
- This experiment uses a synthetic human torso, embedded with over 300 strategically placed dosimeters (radiation sensors), to determine the levels of cosmic radiation absorbed by specific organs in the human body during space flight.
Two types of sensors are used:
- passive sensors will quantify the total amount of radiation absorbed in various body parts throughout the entire flight.
- active sensors will give real time data describing how much radiation is absorbed at varying times during ISS orbit.
- Real time data will focus on the brain, thyroid, colon, and stomach.
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 helps 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 aboard the International Space Station (ISS), scientists also learns 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.
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.
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.
Torso results are 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 is a great improvement relative to the current accuracy of organ-specific cancer risk projections. Further analyses and incorporation of these radiation results into operational planning for exploration is ongoing. Overall, the dose rates measured in Torso are in good general agreement with other measured values and with the models used to predict these values. So far, the largest difference observed between measured data and the simulations is 15%. In addition, a model that considers orbital altitude, attitude, and solar cycle emissions agrees within 25% of the measured data. It is determined that the majority of radiation energy deposited in human tissues (about 80%) was due to galactic cosmic radiation. This is because of spacecraft material providing effective reduction from the protons trapped in the Earth's magnetic field. Finally, this experiment indicated that the contribution to both skin and organ doses from secondary neutrons is not negligible. Radiation assessments from chromosomal damage in lymphocyte cells of 19 ISS crew members were conducted as a follow-on study. These results were compared with space radiation transport models, irradiation of pre-flight blood samples, and results from the phantom torso experiments. The ISS crew members 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 6-month stay on the ISS were 72 mSv. At least 80% of the organ radiation exposures 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 (Cucinotta 2008).
Cucinotta FA, Cucinotta FA, Kim MY, Willingham V, George KA. Physical and Biological Organ Dosimetry Analysis for International Space Station Astronauts. Radiation Research. 2008 July; 170(1): 127-138.
Ground Based Results Publications
Edwards AA. RBE of radiations in space and the implications for space travel. Physica Medica: European Journal of Medical Physics. 2001; 17 Suppl 1: 147-152.
Kolomensky AV, Kuznetsov VG, Laiko IA, Bengin V, Shurshakov VA. The model of radiation sheilding of the service module of the International Space Station. Aviakosmicheskaia i Ekologicheskaia Meditsina (Aerospace and Environmental Medicine). 2001; 35(6): 39-43.
Yasuda H. Effective Dose Measured with a Life Size Human Phantom in a Low Earth Orbit Mission. Journal of Radiation Research. 2009.
Badhwar GD. Shuttle radiation dose measurements in the international space station orbits. Radiation Research. 2002; 157(1): 69-75.
Berger T, Hajek M, Hajek M, Schoner W, Fugger M, Vana N, Noll M, Ebner R, Akatov YA, Shurshakov VA, Arkhangelsky VV. Measurement of the depth distribution of average LET and absorbed dose inside a water-filled phantom on board space station Mir. Physica Medica: European Journal of Medical Physics. 2001; 17 Suppl 1: 128-130.
Wilson JW, Shinn JL, Tripathi RK, Singleterry Jr. RC, Clowdsley MS, Thibeault SA, Cheatwood FM, Schimmerling W, Cucinotta FA, Cucinotta FA, Badhwar GD, Noor AK, Kim MY, Badavi FF, Heinbockel JH, Miller J, Zeitlin C, Heilbronn L. Issues in deep space radiation protection. Acta Astronautica. 2001; 49(3-10): 289-312.
Badhwar GD, O'Neill PM. Response of silicon-based linear energy transfer spectrometers: implication for radiation risk assessment in space flights. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2001; 466(3): 464-474.
Badhwar GD, Atwell W, Badavi FF, Yang TC, Cleghorn TF. Space radiation absorbed dose distribution in a human phantom. Radiation Research. 2002; 1571(1): 76-91.
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NASA Image: ISS002E5952 - Image of the Torso on ISS during Expedition 2.
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Torso is an anatomical model of a torso and head containing more than 300 radiation sensors. Image courtesy of NASA.
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