DOT/FAA/AM-00/33

Joyce S. Nicholas

Department of Biometry and Epidemiology

Medical University of South Carolina

Charleston, SC 29425

Kyle Copeland

Frances E. Duke

Wallace Friedberg

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

Keran O’Brien III

Department of Physics and Astronomy

Northern Arizona University

Flagstaff, AZ 86011

October 2000

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

Galactic Cosmic Radiation

Exposure of Pregnant

Aircrew Members II Office of Aviation Medicine

Washington, D.C. 20591

U.S. Department

of Transportation

Federal Aviation

Administration
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-00/33

5. Report Date

October 2000

4. Title and Subtitle

Galactic Cosmic Radiation Exposure of Pregnant Aircrew

Members II 6. Performing Organization Code

7. Author(s)

Nicholas, J.S.1, Copeland, K.2, Duke, F.E. 2, Friedberg, W.2, and

O'Brien, K., III3

8. Performing Organization Report No.

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

11. Contract or Grant No.

1

Department of Biometry and Epidemiology, Medical University of South

Carolina, Charleston, SC 29425

2

FAA Civil Aeromedical Institute, P.O. Box 25082, Oklahoma City, OK 73125

3

Department of Physics and Astronomy, Northern Arizona University,

Flagstaff, AZ 86011

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, S.W.

Washington, D.C. 20591 14. Sponsoring Agency Code

15. Supplemental Notes

This work was accomplished under the approved task AM-PHY305.

16. Abstract

In its 1990 recommendation regarding occupational exposure during pregnancy, the International

Commission on Radiological Protection apparently assumed that the equivalent dose to a pregnant woman's

abdomen is reduced by half in traversing the body to the conceptus. This assumption was tested with respect

to galactic cosmic radiation, the principal ionizing radiation to which aircrews are exposed. We calculated

the equivalent dose that would be received at depths of 0, 5, 10, and 15 centimeters in a 30-centimeter

thick, soft-tissue slab phantom, at several locations in the atmosphere and on two air carrier flights, and

found that the dose was almost the same at all the tissue depths studied. Thus, the assumption of

considerable shielding of the conceptus by the woman’s body is not valid with respect to galactic cosmic

radiation. The effective dose of galactic radiation to the mother was found to be a good estimate of the

equivalent dose to the conceptus.

17. Key Words 18. Distribution Statement

Aerospace Medicine, Pregnancy, Galactic Cosmic

Radiation

Document is available to the public through

the National Technical Information Service,

Springfield, Virginia, 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 8

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

iii

ACKNOWLEDGMENT

 We thank Dr. Slavica Vlahovich, Medical Advisor, Radiation Protection Bureau, Health Canada,

for reminding us that galactic cosmic radiation is too penetrating to be reduced by half from the

surface of the mother’s abdomen to the depth of the conceptus.

1

GALACTIC COSMIC RADIATION EXPOSURE OF PREGNANT AIRCREW MEMBERS II

1. INTRODUCTION

This report is an updated version of a previously

published Technical Note in the journal Aviation,

Space, and Environmental Medicine (1). The main

change is that improved computer programs were

used to estimate galactic cosmic radiation. The calculations also cover a greater range of altitudes. Small

differences in the calculated doses were obtained, but

the conclusions are the same.

The International Commission on Radiological

Protection (ICRP) and the Federal Aviation Administration (FAA) consider aircrews to be occupationally exposed to ionizing radiation (2, 3). Although

the United States has no regulations limiting aircrew

exposure to cosmic radiation, the FAA has recommended limits. For pregnant crewmembers, starting

when the pregnancy is reported to management, the

FAA recommends: a) a limit of 1 millisievert to the

conceptus for the remainder of the pregnancy, in

accordance with the ICRP policy/recommendation

(2, 4), and b) a monthly limit of 0.5 millisievert to the

conceptus, as recommended by the National Council

on Radiation Protection and Measurements (NCRP)

(5). Here we address, principally, the ICRP policy.

The stated ICRP policy is that a standard of

radiation protection for any conceptus be broadly

comparable with that provided for members of the

general public, i.e., a yearly limit of 1 millisievert. In

their 1990 recommendations (2), the ICRP indicated

that this standard could be met by limiting the

equivalent dose to the surface of the pregnant woman’s

abdomen to 2 millisieverts for the remainder of the

pregnancy, once declared. They apparently assumed

that the equivalent dose to the conceptus would be

about half the dose to the surface of the abdomen. We

tested this assumption with respect to galactic cosmic

radiation, the principal ionizing radiation to which

aircrews are exposed.

2. METHODS

Using computer program CARI-LF3 (6), we calculated the equivalent dose rate at depths of 0, 5, 10,

and 15 centimeters in a 30-centimeter thick, softtissue slab phantom at several locations in the atmosphere (Table 1) and the equivalent dose, at the same

tissue depths, on two air carrier flights (Table 2).

Table 1. Galactic Radiation Dose Rates at Several Locations in the Atmosphere: Effective Dose Rate

Compared With Equivalent Dose Rate at Various Tissue Depths. *

Geographic Altitude Effective Dose Equivalent Dose Rate (μSv/h) at a Depth of

Coordinates (feet) Rate (μSv/h) 0-cm 5-cm 10-cm 15-cm

_______________________________________________________________________

0o, 20oE 0 0.028 0.029 0.028 0.028 0.028

20,000 0.54 0.52 0.52 0.52 0.52

30,000 1.6 1.5 1.5 1.5 1.5

40,000 3.0 2.8 2.9 2.9 2.9

40oN, 20oE 0 0.037 0.037 0.037 0.036 0.036

20,000 0.76 0.74 0.72 0.71 0.71

30,000 2.3 2.3 2.3 2.2 2.2

40,000 4.7 4.5 4.5 4.5 4.5

80oN, 20oE 0 0.041 0.041 0.040 0.040 0.040

20,000 1.1 1.1 1.1 1.0 1.0

30,000 4.1 4.0 3.8 3.8 3.7

40,000 9.1 8.8 8.6 8.5 8.5

_______________________________________________________________________

* Calculated doses for February 1998. Effective and equivalent dose rates were calculated by CARI-6 and CARI-LF3, respectively.
2

CARI-LF3 uses radiation weighting factors recommended by the ICRP (2). For the same locations in

the atmosphere and the same flights, computer program CARI-6 (7) was used to calculate the effective

dose rates and doses to an adult (Tables 1 and 2).

CARI-6 incorporates fluence to effective dose conversion coefficients calculated by Ferrari et al. (8, 9,

10, 11, 12, 13). See O’Brien et al. (14) for a description of the physics and dosimetry that is the basis of

CARI-LF3 and CARI-6.

3. RESULTS AND DISCUSSION

Results in Table 1 show that, at each of a wide

range of locations in the atmosphere, the equivalent

dose rates from galactic cosmic radiation are almost

the same at 0, 5, 10, and 15 centimeters depth in a 30-

centimeter thick slab phantom. Also, at each location, the effective dose rate is close to the equivalent

dose rates at the various tissue depths.

As additional comparisons, consider two air carrier flights (Table 2): a) a 9.4 hour (time airborne),

high-altitude flight from Athens, Greece, to New

York City and b) a 0.5 hour, low-altitude flight from

Houston, Texas, to Austin, Texas. On the flight from

Athens to New York City, equivalent doses at the

tissue depths studied are 64 or 65 microsieverts and

the effective dose 67 microsieverts. On the flight

from Houston to Austin the equivalent doses at the

various depths are 0.16 or 0.17 microsievert and the

effective dose 0.17 microsievert. Thus, on each of the

two flights, the equivalent doses are almost the same

at all the tissue depths studied, and the effective dose

is close to the equivalent doses.

Results in Tables 1 and 2 indicate that, during air

travel, exposure of the body to galactic radiation is

almost uniform and therefore, as expected, the equivalent dose to any part of the body is close to the

effective dose to the whole person. Thus, for galactic

radiation exposure during air travel, the equivalent

dose to a conceptus can be estimated by the effective

dose to the mother. We used effective dose as an

estimate of the equivalent dose to the conceptus to

obtain the results that follow.

Consider a crewmember who declares pregnancy

after 1 month and continues working 80 airborne

hours per month on the long, high-altitude flight

from Athens to New York City. The monthly dose to

the conceptus would be about 0.57 millisievert, which

would exceed the recommended monthly limit of 0.5

millisievert. The recommended limit to the conceptus of 1 millisievert for the duration of the declared

pregnancy would be reached in less than 2 months. In

contrast, if she were airborne the same number of

hours per month on the short, low-altitude flight

from Houston to Austin, the dose per month would

Table 2. Galactic Radiation Doses Received on Two Air-Carrier Flights: Effective Dose to an Adult

Compared With Equivalent Dose at Various Tissue Depths.*

Effective Equivalent Dose (μSv) at a Depth of

One-Way Flight Dose (μSv) 0-cm 5-cm 10-cm 15-cm

_______________________________________________________________________

Athens, Greece (LGAT)

to New York, NY (KJFK) † 67 65 64 64 64

Houston, TX (KIAH)

to Austin, TX (KAUS) ‡ 0.17 0.17 0.17 0.16 0.16

_______________________________________________________________________

* Calculated doses for February, 1998. Effective and equivalent doses were calculated by CARI-6 and CARI-LF3, respectively.

†

 Air time 9.4 hours, maximum altitude 41,000 feet.

‡

 Air time 0.5 hours, maximum altitude 20,000 feet.
3

be 0.027 millisievert. This is well below the recommended monthly limit; the total dose to the conceptus would not exceed the recommended 1 millisievert

limit, regardless of the number of months flown.

4. CONCLUSIONS

The mother’s body provides no significant shielding for a conceptus from galactic radiation received

during air travel. The effective dose to the mother, as

calculated with CARI-6, is a good estimate of the

equivalent dose to the conceptus from galactic radiation. By restricting occupational exposure to a maximum effective dose of 1 millisievert during her

pregnancy, starting when it is reported to management, a pregnant crewmember will comply with the

recommendation of the FAA and the ICRP regarding

the total radiation exposure of the conceptus. Pregnant crewmembers can minimize occupational exposure to galactic radiation by working on short,

low-altitude, low-latitude flights (15).

REFERENCES AND NOTES

1. Nicholas, J.S., K.A. Copeland, F.E. Duke,

W.Friedberg, and K.O’Brien III (2000). Galactic

Cosmic Radiation Exposure of Pregnant Flight

Crewmembers. Aviation, Space, and Environmental Medicine, 71(6):647-8.

2. International Commission on Radiological Protection (1991). 1990 Recommendations of the ICRP,

ICRP Publication 60, Annals of the ICRP 21(1-

3). New York: Pergamon Press. (For recommended

dose limits for the conceptus, see p. 42, pars. 177-

178 and p. 46, Table 6.)

Equivalent dose (pp. 82-83):

When considering health effects of ionizing radiation, the amount of radiation received by a person is

often expressed in terms of equivalent dose. Equivalent

dose is a measure of the biological harmfulness of

ionizing radiation and takes into account that equal

amounts of absorbed energy from different types of

ionizing radiation are not necessarily equally harmful.

For each type of radiation (e. g., 20 MeV neutrons), the

equivalent dose is the product of the absorbed dose

(which may be different for different tissues/organs

under the same irradiation conditions) and the

appropriate radiation weighting factor. This factor

takes into account the particular type of radiation’s

potential for causing biological harm. For mixed

radiation fields (multiple particle types and/or energies), the resultant equivalent dose is the sum of the

contributions from each of the component radiations.

The international unit of equivalent dose is the

sievert. The sievert replaces the rem:

1 sievert (Sv) = 100 rem

1 sievert = 1000 millisieverts (mSv)

1 millisievert = 1000 microsieverts (μSv)

Effective dose (pp. 6-9):

When irradiation of the body is not uniform, an

additional group of factors called tissue weighting factors are applied to take into account that the risk of

biological harm to a person from stochastic effects of

radiation (specifically: cancer, hereditary effects to all

generations, and length of life lost) depends on the

specific tissues/organs irradiated, as well as the equivalent doses received. The effective dose to an irradiated

person is the sum of the products of equivalent dose and

tissue weighting factor for each irradiated organ. The

unit of effective dose is the sievert.

In the case of a uniform whole-body exposure, the

equivalent dose to each tissue/organ is the same as the

effective dose to the person. This is essentially the case

with galactic cosmic radiation exposure of air travelers

(see Tables 1 and 2 of this report).

3. Federal Aviation Administration (1994). Crewmember Training on In-Flight Radiation

Exposure, Advisory Circular No. 120-61, Washington, DC.

4. International Commission on Radiological Protection (1997). General Principles for the Radiation

Protection of Workers, ICRP Publication 75,

Annals of the ICRP 27(1). New York: Pergamon

Press. (For the recommended dose limit for the

conceptus, see p. 25, par. 124.)

5. National Council on Radiation Protection and Measurements (1993). Limitation of Exposure to Ionizing Radiation, NCRP Report No. 116, Bethesda,

MD. (For the recommended monthly equivalent

dose limit for the conceptus, see p. 38.)

6. CARI-LF3 (computer program). Oklahoma City,

OK: FAA Civil Aeromedical Institute.
4

CARI-LF3 can be used to calculate many dosimetric endpoints, including equivalent dose. It takes

into account changes in altitude and geographic

location during the course of a flight (assumed to

follow a great circle route or a reasonable approximation). Based on the date of the flight, appropriate

databases are used to account for effects of changes in

the earth’s magnetic field and solar activity on galactic radiation levels.

7. CARI-6 (computer program). Oklahoma City, OK:

FAA Civil Aeromedical Institute. (Available at

Web site http://www.cami.jccbi.gov/AAM-600/

610/600radio.html).

CARI-6 calculates the effective dose of galactic

cosmic radiation received by an individual (adult) on

an aircraft flying a great circle route (or a reasonable

approximation) between any two airports in the world.

The program takes into account changes in altitude

and geographic location during the course of a flight.

Based on the date of the flight, appropriate databases

are used to account for effects of changes in the

earth’s magnetic field and solar activity on galactic

radiation levels. The program also calculates the

effective dose rate from galactic radiation at any

location in the atmosphere at altitudes up to 87,298

feet. CARI-6 requires MS-DOS and can be run on

most personal computers.

8. Ferrari A., M. Pelliccioni, M. Pillon (1996). Fluence

to Effective Dose and Effective Dose Equivalent

Conversion Coefficients for Photons From 50

keV to 10 GeV. Radiation Protection Dosimetry,

67(4): 245-51.

9. Ferrari A., M. Pelliccioni, M. Pillon (1997).

Fluence to Effective Dose and Effective Dose

Equivalent Conversion Coefficients for Electrons From 5 MeV to 10 GeV. Radiation Protection Dosimetry, 69(2): 97-104.

10. Ferrari A, M. Pelliccioni, M. Pillon (1997).

Fluence to Effective Dose Conversion Coefficients for Protons From 5 MeV to 10 TeV.

Radiation Protection Dosimetry, 71(2): 85-91.

11. Ferrari A, M. Pelliccioni, M. Pillon (1997). Fluence

to Effective Dose Conversion Coefficients for

Neutrons up to 10 TeV. Radiation Protection

Dosimetry, 71(3): 165-73.

12. Ferrari A, M. Pelliccioni, M. Pillon (1997). Fluenceto-Effective Dose Equivalent Conversion Coefficients for Muons. Radiation Protection Dosimetry,

74(4): 227-33.

13. Ferrari A, M. Pelliccioni, M. Pillon (1998). Fluence

to Effective Dose Conversion Coefficients for

Negatively and Positively Charged Pions. Radiation Protection Dosimetry, 80(4):361-70.

14. O’Brien K., W. Friedberg, H.H. Sauer, and D.F.

Smart (1996). Atmospheric Cosmic Rays and

Solar Energetic Particles at Aircraft Altitudes. Environment International, 22 (Suppl. 1): S9-S44.

15. Friedberg W., K.Copeland, F.E. Duke, K.O’Brien

III, and E.B. Darden Jr. (1999). Guidelines and

Technical Information Provided by the US Federal Aviation Administration to Promote Radiation Safety for Air Carrier Crew Members. Radiation Protection Dosimetry, 86(4): 323-7.