Requirements for Space Radiation Dosimetry Walter Schimmerling, Francis A. Cucinotta, and John W. Wilson

Transcription

1 Requirements for Space Radiation Dosimetry Walter Schimmerling, Francis A. Cucinotta, and John W. Wilson Workshop on Radiation Monitoring for the International Space Station Farnborough, UK 3-5 November 1999

2 Primaries and Secondaries Inside 5 g/cm 2 of Aluminum (all energies) 21 Z 28 24% C3H10T1/2 Cell Death Proton 13% Alpha 24% C3H10T1/2 Cell Transformation 11 Z 20 16% 21 Z 28 13% Proton 35% 11 Z 20 22% 3 Z 10 17% Dose Equivalent to Skin 21 Z 28 21% Different Biology Proton 21% 3 Z 10 14% Alpha 22% 11 Z 20 15% 21 Z 28 15% Harderian Gland Proton 32% 11 Z 20 24% 3 Z 10 15% Alpha 19% 3 Z 10 12% Alpha 26% 2

3 Annual Dose Equivalent Behind 5 g/cm 2 of Aluminum (1977 Solar Minimum) dh / d(ln E) dh / d(ln E) E, MeV/amu Protons Alphas Z Z Z 28 Proton 3 Z Protons Alpha Z Alpha Z Z Z 10 Protons 2 Alpha E, MeV/amu BFO SKIN H(<E) (csv) H(<E) (csv) Proton Alpha Z Proton Alpha 11 Z Z 28 3 Z E, MeV/amu Proton Alpha Z Z 20 Proton 15 Alpha 10 Alpha Proton 21 Z 28 3 Z E, MeV/amu

4 LET vs. Range Range, cm 4 50 A MeV 100 A MeV 200 A MeV 400 A MeV 650 A MeV 800 A MeV 1200 A MeV 2000 A MeV max RBE Iron Chromium Argon Silicon Magnesium Oxygen Carbon Alpha Proton LET, kev/µm

5 Critical Questions Related to Space Dosimetry Space Radiation Environment For a given mission, what are the fluxes of GCR in interplanetary space as a function of particle energy, LET, and solar cycle? What is the solar cycle dependence of space radiation? What is the trapped radiation flux as a function of time, magnetic field coordinates and geographical coordinates? What are the doses related to heavy ions in deep space? Nuclear Interactions What are the yields for nuclear interactions of HZE particles in tissue and space shielding materials? How are radiation fields transformed as a function of depth in different space materials? What are the optimal ways of shielding humans in space? Atomic Interactions What is the precise energy deposition of heavy ions? What are the yields and energy spectra of electrons? Human Radiation Protection What should be the radiation dose limits for manned deep space missions? What is the risk associated with each crew member at any time during a given mission? 5

6 Critical Questions Related to Space Dosimetry Space Radiation Environment For a given mission, what are the fluxes of GCR in interplanetary space as a function of particle energy, LET, and solar cycle? What is the solar cycle dependence of space radiation? What is the trapped radiation flux as a function of time, magnetic field coordinates and geographical coordinates? What are the doses related to heavy ions in deep space? Nuclear Interactions What are the yields for nuclear interactions of HZE particles in tissue and space shielding materials? How are radiation fields transformed as a function of depth in different space materials? What are the optimal ways of shielding humans in space? Atomic Interactions What is the precise energy deposition of heavy ions? What are the yields and energy spectra of electrons? Human Radiation Protection What should be the radiation dose limits for manned deep space missions? What is the risk associated with each crew member at any time during a given mission? 6

7 Critical Questions Related to Space Dosimetry Space Radiation Environment For a given mission, what are the fluxes of GCR in interplanetary space as a function of particle energy, LET, and solar cycle? What is the solar cycle dependence of space radiation? What is the trapped radiation flux as a function of time, magnetic field coordinates and geographical coordinates? What are the doses related to heavy ions in deep space? Nuclear Interactions What are the yields for nuclear interactions of HZE particles in tissue and space shielding materials? How are radiation fields transformed as a function of depth in different space materials? What are the optimal ways of shielding humans in space? Atomic Interactions What is the precise energy deposition of heavy ions? What are the yields and energy spectra of electrons? Human Radiation Protection What should be the radiation dose limits for manned deep space missions? What is the risk associated with each crew member at any time during a given mission? 7

8 Critical Questions Related to Space Dosimetry Space Radiation Environment For a given mission, what are the fluxes of GCR in interplanetary space as a function of particle energy, LET, and solar cycle? What is the solar cycle dependence of space radiation? What is the trapped radiation flux as a function of time, magnetic field coordinates and geographical coordinates? What are the doses related to heavy ions in deep space? Nuclear Interactions What are the yields for nuclear interactions of HZE particles in tissue and space shielding materials? How are radiation fields transformed as a function of depth in different space materials? What are the optimal ways of shielding humans in space? Atomic Interactions What is the precise energy deposition of heavy ions? What are the yields and energy spectra of electrons? Human Radiation Protection What should be the radiation dose limits for manned deep space missions? What is the risk associated with each crew member at any time during a given mission? 8

9 Radiation Protection Model Radiation Limits (Dose Equivalent, proportional to acceptable risk) Operational and Flight Rule Limitations (ALARA) CURRENT KNOWLEDGE PREDICT RISK ALARA? N Y SPACE FLIGHT SUCCESS Reduce Risk DOSIMETRY: Measure Monitor Record Forecast Warn GROUND-BASED RESEARCH 9

10 Risk Prediction Model Space Radiation Dosimetry Current A-bomb survivors γ-rays Quality Factor (LET) cancer, neutrons (ICRP 60,1990) genetic effects acute effects Low-LET radiobiology D, D, DREF, (LET), risk age, gender (UNSCEAR, BEIR V) PPA, LBL, BNL (USA) ϕ(a,z,ω,m,b, ) RBE cancer, CNS, GSI(Germany), HIMAC(Japan) cataracts, etc. Future Space radiation environment shielding, risk radiation biology countermeasures 10 7

11 Risk Issues Related to Space Dosimetry What is risk? a priori vs. a posteriori probabilities probability of defined effect (e.g., excess leukemia) architecture-dependent (trip duration, spacecraft, EVA's, etc.) Prospective risk assessment: radiation monitoring identify radiation in sufficient detail to understand results, i.e., spectral information may be required in addition to ionization chambers; area monitors to define radiation field risk assessment vs. risk estimate architecture issues Archival risk assessment: legal evidence of causation (or lack of causation) of an effect by exposure to space radiation medical history acute effects: treatment, record late effects: how? epidemiological evaluate effects of cumulative population exposures 11

12 Risk Issues Related to Space Dosimetry What is risk? a priori vs. a posteriori probabilities probability of defined effect (e.g., excess leukemia) architecture-dependent (trip duration, spacecraft, EVA's, etc.) Prospective risk assessment: radiation monitoring identify radiation in sufficient detail to understand results, i.e., spectral information may be required in addition to ionization chambers; area monitors to define radiation field risk assessment vs. risk estimate architecture issues Archival risk assessment: legal evidence of causation (or lack of causation) of an effect by exposure to space radiation medical history acute effects: treatment, record late effects: how? epidemiological evaluate effects of cumulative population exposures 12

13 Risk Issues Related to Space Dosimetry What is risk? a priori vs. a posteriori probabilities probability of defined effect (e.g., excess leukemia) architecture-dependent (trip duration, spacecraft, EVA's, etc.) Prospective risk assessment: radiation monitoring identify radiation in sufficient detail to understand results, i.e., spectral information may be required in addition to ionization chambers; area monitors to define radiation field risk assessment vs. risk estimate architecture issues Archival risk assessment: legal evidence of causation (or lack of causation) of an effect by exposure to space radiation medical history acute effects: treatment, record late effects: how? epidemiological evaluate effects of cumulative population exposures 13

14 Detector Considerations Accuracy Signal-to-noise ratio Calibration, pre-experiment testing Detection artifacts Timing and location Precision Sensitivity adequate for statistically significant results Geometry factors and acceptance Dynamic range Spectrum of particles and energies Spectrum of LET Doses, dose rates and flux Data acquisition On-line vs. off-line Stability of data, especially for integrating detectors Availability of records 14

15 Detector Considerations Accuracy Signal-to-noise ratio Calibration, pre-experiment testing Detection artifacts Timing and location Precision Sensitivity adequate for statistically significant results Geometry factors and acceptance Dynamic range Spectrum of particles and energies Spectrum of LET Doses, dose rates and flux Data acquisition On-line vs. off-line Stability of data, especially for integrating detectors Availability of records 15

16 Detector Considerations Accuracy Signal-to-noise ratio Calibration, pre-experiment testing Detection artifacts Timing and location Precision Sensitivity adequate for statistically significant results Geometry factors and acceptance Dynamic range Spectrum of particles and energies Spectrum of LET Doses, dose rates and flux Data acquisition On-line vs. off-line Stability of data, especially for integrating detectors Availability of records 16

17 Detector Considerations Accuracy Signal-to-noise ratio Calibration, pre-experiment testing Detection artifacts Timing and location Precision Sensitivity adequate for statistically significant results Geometry factors and acceptance Dynamic range Spectrum of particles and energies Spectrum of LET Doses, dose rates and flux Data acquisition On-line vs. off-line Stability of data, especially for integrating detectors Availability of records 17

18 TLD Efficiency(*) (*) R.H. Thomas,Passive Detectors. In: Advances in Radiation Protection and Dosimetry In Medicine (R.H. Thomas and V. Perez-Mendez, Eds.) Plenum Press, New York, 1980, p

19 Separating Species 1500 Ions with differing M, Z, and E can have similar de/dx over a substantial portion of their paths. Need good energy calibration (< 3% or so) and information from many detectors. Measure efficiencies of triggers Using these efficiencies, apply corrections AMeV Fe 295AMeV Cr 320AMeV Mn Detector Number 19

20 Radial Energy Deposition 20

21 Biodosimetry Biological monitoring of radiation exposure: record accumulated radiation exposure for individuals supplement area monitors weigh components of environmental radiation according to their biological efficacy desired goal: predict risk Different types: intrinsic biological dosimeters: biomarkers for genetic or metabolic changes extrinsic biological dosimeters/indicators for radiation and other genotoxic substances and agents 21

22 Biomarker Requirements sensitivity to the levels of radiation exposure of concern unequivocal: not sensitive to confounding factors (high signal-tonoise ratio) accuracy of predictions predict risk and health care decisions at a well-defined level of confidence specificity of prediction plausible causal relationship based on testable mechanisms of radiation action, rather than just a contingent correlation with radiation exposure precision: the results are not significantly distorted by individual or circumstantial variations in radiation response lead to diagnostic procedures that are: practical under actual circumstances of exposure rather than only under highly restricted laboratory conditions cost-effective, to screen large populations where required 22

23 Biomarker Requirements sensitivity to the levels of radiation exposure of concern unequivocal: not sensitive to confounding factors (high signal-tonoise ratio) accuracy of predictions predict risk and health care decisions at a well-defined level of confidence specificity of prediction plausible causal relationship based on testable mechanisms of radiation action, rather than just a contingent correlation with radiation exposure precision: the results are not significantly distorted by individual or circumstantial variations in radiation response lead to diagnostic procedures that are: practical under actual circumstances of exposure rather than only under highly restricted laboratory conditions cost-effective, to screen large populations where required 23

24 Biomarker Requirements sensitivity to the levels of radiation exposure of concern unequivocal: not sensitive to confounding factors (high signal-tonoise ratio) accuracy of predictions predict risk and health care decisions at a well-defined level of confidence specificity of prediction plausible causal relationship based on testable mechanisms of radiation action, rather than just a contingent correlation with radiation exposure precision: the results are not significantly distorted by individual or circumstantial variations in radiation response lead to diagnostic procedures that are: practical under actual circumstances of exposure rather than only under highly restricted laboratory conditions cost-effective, to screen large populations where required 24

25 Biomarker Requirements sensitivity to the levels of radiation exposure of concern unequivocal: not sensitive to confounding factors (high signal-tonoise ratio) accuracy of predictions predict risk and health care decisions at a well-defined level of confidence specificity of prediction plausible causal relationship based on testable mechanisms of radiation action, rather than just a contingent correlation with radiation exposure precision: the results are not significantly distorted by individual or circumstantial variations in radiation response lead to diagnostic procedures that are: practical under actual circumstances of exposure rather than only under highly restricted laboratory conditions cost-effective, to screen large populations where required 25

26 Biomarker Requirements sensitivity to the levels of radiation exposure of concern unequivocal: not sensitive to confounding factors (high signal-tonoise ratio) accuracy of predictions predict risk and health care decisions at a well-defined level of confidence specificity of prediction plausible causal relationship based on testable mechanisms of radiation action, rather than just a contingent correlation with radiation exposure precision: the results are not significantly distorted by individual or circumstantial variations in radiation response lead to diagnostic procedures that are: practical under actual circumstances of exposure rather than only under highly restricted laboratory conditions cost-effective, to screen large populations where required 26

27 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 27

28 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 28

29 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 29

30 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 30

31 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 31

32 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 32

33 Single Instrument Specifications ϕ(a,z, LET, ), D(LET), QF(LET), Particle identification: Positive charges vs. neutrons, electrons, γ-rays (1,1) (A,Z) (56,26) [p to Fe] Z/Z 0.2] A/A 1 Energies: 10 ε HZE 1000 MeV/nucleon 10 kev ε n 100 MeV 700 kev ε x,γ,β 10 MeV LET range: 0.1 LET 2000 kev/µm Acceptance Solid angle (statistics) 2 detection efficiency 10% ø/ø (angular resolution) 3 Rate Dependence R 10 5 particles/sec; N 10 4 particles/cm µgy/min D/ t 1 Gy/min Localization Portability» Personnel dosimetry» Area monitoring Shielding: traceable to mass distributions Data acquisition and recording Telemetry and on-board readout Coincidence and correlation w/other instruments Autonomy > 90 days Availability and distribution < 30 days Stability: 50 yrs 33

34 When is a dosimeter not a dosimeter? Not every measurement is ISS dosimetry Have the instruments been calibrated at a recognized facility?» How accurately does the calibration site simulate the component of space radiation for which the instrument is designed? Can the results of the measurement be interpreted in terms of other measurements?» Has an intercomparison been performed with other dosimetry instruments?» Have previous flight data been published in refereed journals? Not every ISS dosimetry measurement will necessarily be used for implementing ALARA Are the data available during the mission?» Are they available in real time?» Are they available to the crew in flight?» Is privacy of individual data safeguarded?» Is there a protocol for use by mission operations? Are the data available after the mission?» Is there a protocol for incorporation into medical records?» Is there a protocol for interpretation of the data in terms of crew member radiation history?» Can the data be interpreted in terms of crew member risk? 34

35 When is a dosimeter not a dosimeter? Not every measurement is ISS dosimetry Have the instruments been calibrated at a recognized facility?» How accurately does the calibration site simulate the component of space radiation for which the instrument is designed? Can the results of the measurement be interpreted in terms of other measurements?» Has an intercomparison been performed with other dosimetry instruments?» Have previous flight data been published in refereed journals? Not every ISS dosimetry measurement will necessarily be used for implementing ALARA Are the data available during the mission?» Are they available in real time?» Are they available to the crew in flight?» Is privacy of individual data safeguarded?» Is there a protocol for use by mission operations? Are the data available after the mission?» Is there a protocol for incorporation into medical records?» Is there a protocol for interpretation of the data in terms of crew member radiation history?» Can the data be interpreted in terms of crew member risk? 35

36 Space Radiation Research Program Road Map Uncertainties Environment Shielding Basic Knowledge ROBOTIC PRECURSOR MISSIONS operational shielding biomedical Countermeasures Relative Biological Efficiency Doses and Dose Rates ACCELERATOR EXPOSURE FACILITIES protons HZE Validate Flight Rules Loma Linda Brookhaven Ground Research: Simulate Space Radiation Determine Biological Factors of Risk Enable Human Presence in Space 36