Table Of ContentNCRP REPORT No. 68
RADIATION PROTECTION
IN PEDIATRIC RADIOLOGY
Recommendations of the
NATIONAL COUNCIL ON RADIATION
PROTECTION AND MEASUREMENTS
Issued November 1, 1978
- .- -- - .
First ~ebrintinJu~ly 31, 1989
Second Reprinting April 30,1993
Third Reprinting June 30,1994
National Council on Radiation Protection and Measurements
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Preface
The purpose of this report is to make available a source of practical
information regarding the manner in which radiologic examinations in
children should be conducted to reduce the radiation dose to these
patients and those responsible for their care. The emphasis is on
radiologic examinations as they affect children, although some addi-
tional material of more general interest is included for completeness.
The report. is mainly for the use of pediatricians, radiologists, radiologic
technologists, and other physicians and medical practitioners who
order or use radiological methods in examining children.
It is recognized that there are many approaches to the reduction of
dose in the radiologic examination of children. The guidelines in this
report are intended as assistance in the reduction of unnecessary
radiation exposure and should not be construed as specific regulations.
The Council has noted the adoption by the 15th General Conference
of Weights and Measures of special names for some units of the
Systeme International #Unit& (SI) used in the field of ionizing
radiation. The gray (symbol Gy)h as been adopted as the special name
for the SI unit of absorbed dose, absorbed dose index, kenna, and
specifice nergy imparted. The becquerel (symbol Bq)h as been adopted
as the special name for the SI unit of activity (of a radionuclide). One
gray equals one joule per kilogram; and one becquerel is equal to one
wond to the power of minus one. Since the transition from the special
- -
units currently employed rad and curie to the new special names is
expected to take some time, the Council has determined to continue,
for the time being, the use of rad and curie. To convert from one set of
unite to the other, the following relationships pertain:
1 rad = 0.01 J kg-' = 0.01 Gy
1c urie = 3.7 x 101Os-l= 3.7 x 10'' Bq (exactly).
iv / PREFACE
Serving on Scientific Committee 51A on Radiation Protection in
Pediatric Rsdiology during the preparation of this report were:
ANDREWK . POZNANSICU hahm
Radiologist in Chief
Department of Radiology
Children's Memorial Hospital
Chicago, Illinois
Members
SColT DUNBAR WIUIAM MCSWEENI~Y
Director of Radiology Chairman of Radiology
Children's Hospital Medical Center Children's Hospital
Cincinnati, Ohio National Medical Center
Washington, D.C.
ELEXMAN GROSS~UN
Director of Pediatric Radiology LEsrsR WE~SS
Duke University Medical Center Chairman of Pediatrics
Durham,N orth Carolina Henry Ford Hospital
Detroit, M i c w
JOHNA. KIRKPATRICK
Radiologist in Chief
Department of Radiology
Children's Hospital Medical Center
Boston. Mmaachusetts
-
NCRP Seeretarkt T'O~'EAFESA RON
The Council wishes to express its appreciation to the members of
the Committee for the time and effort devoted to the preparation of
this -report.
Warren K. Sinclair
President, NCRP
Bethesda, Maryland
December 1,1980
Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Objectives of Radiation Protection ....................
1.2 Tissues at Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 A Common Sense Consideration of Risk . . . . . . . . . . . . .
1.4 Differences Between Adults and Children ..............
1.5 Maximum Permissible Dose Equivalent . . . . . . . . . . . .
.
2 General Concepts of Reduction of Exposure to Medical
Radiation in Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Should the Examination be Done? . . . . . . . . . . . . . . . . . . .
2.2 Training of Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Examination Rooms ................................
2.4 Means of Minimizii Radiation Exposures from Exam-
. .
lnations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Minimizing the Need for Repeat Examinations .........
2.6 Diminution of Radiation Dose in Radiography . . . . . . .
2.7 Diminishing Fluoroscopic Dose . . . . . . . . . . . . . . . . . . . . .
2.8 Minimizing Radiation Outside the Area Examined . . . .
2.9 The Pregnant Girl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Gonadal Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Indications .........................................
3.2 Means of Gonadal Protection . . . . . . . . . . . . . . . . . . . . . .
.
4 Protection of Personnel and Parents . . . . . . . . . . . . . . . .
4.1 Immobilization of Patients ...........................
4.2 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Fluoroscope Design and Radiation to Personnel . . . . . . .
4.4 Eye Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Monitoring Dose ...................................
. 4.6 Pregnant Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 Immobilization of Children ............................
5.1 Indications .......................................
5.2 Methods of Immobilization ...........................
.
6 Equipment Consideration in Pediatric Radiology ......
6.1 Radiographic Units ..................................
6.2 Imaging Systems ..................................
v
vi / CONTENTS
6.3 Grids ............................................... 43
6.4 Processing .......................................... 43
6.6 Fluoroscopic Equipment ............................. 44
6.6 Cineradiography .................................... 46
6.7 Computed Tomography (C.T.) ........................ 46
6.8 Dental Radiography ................................. 48
.
7 Special Problems of Mobile Equipment ................ 50
7.1 General ............................................ 50
7.2 Radiography in Operating Rooms ..................... 52
7.3 Mobile Fluoroscopy ................................. 52
Appendix A .D oses from Various Examinations in Pedi-
atric Radiology .......................................... 55
.
Appendix B Method for Estimating Selected Organ Doses
for Projections Commonly Used in Pediatric Radiology . . 65
.
Appendix C Glossary ................................... 111
References . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ................ 114
The NCRP ................................................ 122
NCRP Publications ........................................ 128
Index .............................................. 139
Introduction
1.1 Objectives of Radiation Protection
The major objective of radiation protection is the protection of
people exposed, future generations, and the maintenance of the collec-
tive dose to mankind as a whole at a low level, while still allowing the
necessary activities from which radiation exposure may result. Protec-
tion is required to minimize somatic and hereditary effects. Somatic
effects are those that become manifest in the exposed individual.
Hereditary effects are those that become manifest in the exposed
individual's subsequent progeny. Of these effects, there are two types
that are considered The first is stochastic, for which the probability of
an effect occurring, rather than its severity, is regarded as a function
of dose without apparent threshold. Non-stochastic effects are those
in which the severity varies with the dose and for which a threshold
may occur. Hereditary effects and, at the doses of interest here, most
somatic effects are stochastic. Carcinogenesis is the chief somatic effect
at low doses and, therefore, is a significant reason for maximal radiation
protection. Other clinically significant somatic effects of postnatal
irradiation require doses far greater than those usually involved in
medical diagnostic radiology. Another somatic effect of concern in
radiological practice is teratogenesis as a consequence of the exami-
nation of pregnant women with resultant exposure of the embryo or
fetus in utero. This effect may be a low threshold phenomenon or
stochastic in nature. The goal of radiation protection is to prevent
detrimental, non-stochastic effects and to limit the probability of
stochastic effects to levels deemed acceptable. In medical applications
of radiation, the decision about the acceptability of the level of risk is
usually dependent upon the potential benefit that the patient may
derive from the study. The problem with this approach is that it is
very difficult to quantitate the benefit; therefore, a qualitative judg-
ment must be made.
In general, the following criteria should be considered for the use of
medical diagnostic radiation:
1) When a new diagnostic imaging procedure using ionizing radia-
tion is introduced, it should produce a benefit that is expected to
outweigh the risk from irradiation.
1
2) Exposure should be kept to the minimum necessary to gain the
needed diagnostic information.
3) The recommended maximum permissible dose limits for the
general public or radiation workers do not apply to the patient's
radiation dose from medical procedures. There is no maximum per-
missible dose for medical radiation.
4) The exposure to other individuals in the vicinity of the patient
being examined should be kept as low as reasonably achievable and
should not exceed the limits recommended by the NCRP (NCRP,
1971).
1.2 Tissues at Risk
In the past, much concern was given to the concept of critical organs
and tissues, particularly the gonads and active bone marrow. Recent
evidence suggests that other tissues may also be susceptible to the
induction of cancer and that some, particularly the female breast, have
a higher risk of radiogenic cancer than does the bone marrow. The
risk factors will be discussed in connection with each tissue. Most of
the data available for risk estimates deal with mortality from cancer.
In some situations other riskti, such as benign tumors of the thyroid,
may be important. Estimates of risk mortality are available (ICRP,
1977, UNSCEAR 1977, and NAS 1972) (Table 1.1). According to
TABL1E.1 -Radiogenic cancer mortcrl3y risk estimates for low-LET radiations
(Deatha per 10' persons per rad)
ICRP (1977) UNSCEAR (1977) BEIR (NAS 1972)'
N-
RiaL per 106 per red Risk per 106 per rad Rink per 10" per rad
Bone Cancer 5 2-5
Lung Cancer 20 25-50
Thyroid Cancer 5 5-15
Breast Cancer 25 10 (Japan)
60 45
Leukemia 20 20-50 250 (in uterolb
100-125 (in utero) 50 (G9 Y ) ~
25 (10 + y)b
W Other Cancers 50 2.0
All Cancers 100 100 250 (in ~tero)~
2w250 (in utero) 30 (G9 Y ) ~
150 (10 + vlb
' BEIR eatimates (NAS. 1972). were originally given an deaths per 10' persons per
year per rem. They are converted to deaths per 106 person per rad since we are dealing
with I radiation. They are mukiplied by duration of the plateau region (period of
manifeet excess incidence) to obtain the figures given in this table.
Age at the time of radiation exposure in parenthesis.
1.2 TISSUES AT RISK / 3
NCRP Report No. 64 (NCRP, 1980) the effect of x radiation at very
low doses and/or dose rates may be smaller than the linear projections
given in the other reports cited above, perhaps % to %o of those values.
1.2.1 Bone Marrow
The active bone marrow is the tissue at risk for radiation-induced
leukemia. Data from studies on populations irradiated as the result of
the atomic bomb explosions at Nagasaki and Hiroshima, as well as
data from patients who have received radiation therapy, suggest that
the risk of death from leukemia is approximately 20 to 50 deaths per
lo6 per rad. The incidence of radiation-induced leukemia reaches its
peak within a few years after irradiation and returns to pre-irradiation
levels after about 25 years (ICRP, 1977). The risk appears to be about
twice as great after irradiation of children as it is after irradiation of
adults, and the risk after in utero irradiation is probably even higher.
Impairment of the bone marrow function is not a significant factor in
most forms of diagnostic radiology since an exposure of 2000 R given
during radiation therapy over a lifetime does not appear to impair the
hemopoietic function (ICRP, 1977).
1.2.2 Breast
During reproductive life, the breast seems to be among the body
tissues more susceptible to radiogenic cancer. The risk factor for breast
cancer is of comparable magnitude to that for leukemia. The mortality
risk estimate given by the ICRP (1977) is 25 per lo6 persons per rem;
UNSCEAFt (1977) gives values of 10 per lo6 persons per rem from
Japanese data and 60 per lo6 person per rem from other data for
females. The risk in children before maturity is not known. Boice et
al. (1979) suggest that girls 10-19 years of age have the greatest risk of
breast cancer based on the best available human epidemiological data.
For doses in the usual diagnostic range, this predicted excess risk from
radiation is stitl very small as compared with the risk of spontaneous
(nonradiogenic) breast cancer.
1.2.3 Thyroid
There is a greater chance per rern of radiation induction of thyroid
cancer than of leukemia. However, since thyroid cancer is usually
controllable, the overall mortality is much less than that from leuke-
mia. ICRP (1977) gives a risk of 5 per lo6 person per rem for thyroid
cancer mortality. The absolute risk of thyroid nodularity is 12.3 per
lo6 person per rem per year and the absolute risk of thyroid cancer in
children is 4 3p er 1$ person per rern per year (Maxon et al., 1977).
1.24 Other Organs
Some of the risks of death for various organs are given in Table 1-1.
ICRP (1977)a nd UNSCEAR (1977)g ive the overall lifetime mortality
risk from cancer as about 1 per LO4 per rem of whole body irradiation.
Therefore, a large population would be needed to detect any increase
in incidence of cancer for the dose levels used in diagnostic radiology.
Since the overall risk of fatal cancer is only 1 per 10' per rem or less,
it is not surprising that in a follow-up study of 1,480 children who had
multiple cardiac fluoroscopies, no increase of cancer was found (Birch
and Baker, 1960). Obviously, one would need a much larger population
to detect any increase in incidence of cancer for the dose levels used in
those examinations.
The main concern in irradiation of the gonads is the hereditary
(genetic) effects on the descendants. The human gonads have a low
sensitivity to the induction of cancer. Impairment of fertility is also
not a concern for the exposure levels used in diagnostic radiology since
it does not occur as a result of doses less than 300 rads in young women
(ICRP, 1977). This is much larger than doses used in diagnostic
radiology. Similarly, although sperm count may be depressed tempo-
rarily by an absorbed dose of 25 rads delivered at a high dose rate, the
absorbed dose rate required to cause permanent sterility is larger by
at least one order of magnitude (ICRP, 1977). Ash (1980) reportd
similar data.
It appears that at low doses and/or dose rates the frequency of
dominant and sex-linked disorders, as well as chromosomal diseases,
increases in direct proportion to the dose, although there are few
substantiating data available at low doses in man. The genetic defects
resulting from paternal radiation are more often dominant mutations
and unbalanced translocations, whole chromosomal trisomies are more
commonly the result of maternal radiation (Lewis,1 975). The mortality
risk of hereditary disease within the first two generations following the
radiation of either parent is considered to be about 4 x 1W'p er rem
(ICW, 1977).
