NCRP report no 124 sources and magnitude of occupational and public exposures from nuclear medicine procedures

NCRP REPORT No. 124

SOURCES AND MAGNITUDE
OF OCCUPATIONAL AND
PUBLIC EXPOSURES FROM
NUCLEAR MEDICINE
PROCEDURES
Recommendations of the
NATIONAL COUNCIL O N RADIATION
PROTECTION AND MEASUREMENTS

Issued March 11, 1996

National Council on Radiation Protection and Measurements
I Bethesda, MD 20814-3095
7910 Woodmont Avenue


LEGAL NOTICE
This report was prepared by the National Council on Radiation Protection a n d
Measurements (NCRP). The Council strives to provide accurate, complete and useful
information in its reports. However, neither the NCRP, the members of NCRP, other
persons contributing to or assisting in the preparation of this Report, nor any person
acting on the behalf of any of these parties: (a) makes any warranty or representation,
express or implied, with respect to the accuracy, completeness or usefulness of the
information contained i n this Report, or that the use of any information, method or
process disclosed i n this Report may not infringe on privately owned rights; or
(b) assumes any liability with respect to the use of, or for damages resulting from
the use of any information, method or process disclosed in this Report, under the
Civil Rights Act of 1964, Section 701 et seq, as amended 42 U.S.C. Section 2000e et
seq. (Title VII) or any other statutory or common law theory governing liability.

Library of Congress Cataloging-in-Publication Data
National Council on Radiation Protection and Measurements.
Sources and magnitude of occupational and public exposures from nuclear
medicine procedures / recommendations of the National Council on Radiation
Protection and Measurements.
cm. - (NCRP report ; no. 124)
p.
"Prepared by Scientific Committee 77 on Guidance on Occupational and Public
Exposure Resulting from Diagnostic Nuclear Medicine Proceduresn-Pref.
"Issued March 1996."
Includes bibliographical references and index.
ISBN 0-929600-51-7
1. Nuclear medicine-Safety measures. 2. Radiation-Dosage.
I. National
Council on Radiation Protection and Measurements. Scientific Committee 77 on
Guidance on Occupational and Public Exposure Resulting from Diagnostic
Nuclear Medicine Procedures. 11. Title. 111. Series.
[DNLM: 1. Nuclear Medicine. 2. Occupational Exposure. 3. Radiation
Effects. 4. Risk. 5. Radiation Protection. WN 440 N2765s 19961
RA569.N355 1996
616.9'897-dc20
DNLMfDLC
for Library of Congress
96-690
CIP

Copyright O National Council on Radiation
Protection and Measurements 1996
All rights reserved. This publication is protected by copyright. No part of this publication may be reproduced in any form or by any means, including photocopying, or

utilized by any information storage and retrieval system without written permission
from the copyright owner, except for brief quotation in critical articles or reviews.


Preface
This Report addresses the sources of exposures incurred in the
practice of nuclear medicine and provides the necessary data to
evaluate the magnitude of exposures to those directly associated
with that practice and to those who provide nursing care to the
patients containing radiopharmaceuticals. Exposure to members of
the public are also addressed. The primary emphasis of this Report
is on these individuals and not on the patient, since the patient
receives the direct benefit from the nuclear medicine procedure. I t
is recognized that the patient also receives the bulk of any potential
radiation decrement.
This Report was prepared by Scientific Committee 77 on Guidance
on Occupational and Public Exposure Resulting from Diagnostic
Nuclear Medicine Procedures. Serving on the Scientific Committee
were:

Kenneth L. Miller, Chairman
Pennsylvania State University
Hershey, Pennsylvania
Members

Frank P. Castronovo, Jr.
Brigham & Women's Hospital
Boston, Massachusetts

Martin L. Nusynowitz

University of Texas Medical
Branch at Galveston
Galveston , Texas

Arnold P. Jacobson
University of Michigan
School of Public Health
Ann Arbor, Michigan

Dennis D. Patton
University of Arizona
College of Medicine
Tucson, Arizona

Sheila I. Kronenberger
Stanford University
Stanford, California
Consultant

Edward W. Webster
Massachusetts General Hospital
Boston, Massachusetts


iv

1

PREFACE

NCRP Secretariat
James A. Spahn, Jr., Senior Staff Scientist
Cindy L. O'Brien, Editorial Assistant
The Council wishes to express its appreciation to the Committee
members for the time and effort devoted to the preparation of this
Report.
Charles B. Meinhold
President


Contents
.

1 Introduction ........................................................................
1.1 Scope ................................................................................
1.2 Quantities and Units ..........................
........................
2 Public SigniGcance of Nuclear Medicine .....................
2.1 Nature and Advantages ..................................................
2.2 Size and Growth ..............................................................
3 Radiation Risk in Perspective ........................................
3.1 Introduction .....................................................................
3.2 Risk ................................................................................
3.3 Radiation Risks ...............................................................
3.3.1 Low-Level Radiation Doses .................................
3.3.2 Dose Limits ...........................................................
3.3.3 Radiation Effects a t Low Doses ..........................
3.3.3.1 Hereditary Defects ..................................
3.3.3.2 Developmental Defects ...........................
3.3.3.3 Cancer Induction .....................................

3.3.4 Comparative Risks ...............................................
4 Receipt and Delivery of Radioactive Materials .........
4.1 Introduction ....................................................................
4.2 Shipment of Radioactive Sources ...................................
4.3 Receipt of Radionuclides .................................................
4.4 "In-House" Transportation of Radioactive Materials ...
4.5 Transport of Patients ......................................................
4.6 Transport of Specimens from Nuclear Medicine
Patients ............................................................................
5 Radiation Exposure from Nuclear Medicine
Practice .................................................................................
5.1 Nuclear Medicine Personnel Exposure ..........................
5.2 Radiation Doses to Patients and Persons Nearby and
Members of the Public ....................................................
5.3 Exposure of Nurses and Other Medical Personnel .......
5.4 Exposure of the General Public .....................................
6 Radiopharmaceutical Handling Procedures in
Nuclear Medicine ...............................................................
6.1 Introduction .....................................................................
6.2 Radiopharmaceutical Dosage Preparation ....................

.
.

.

.

.

vi

/

CONTENTS

6.2.1 Commercial Radiopharmacy Unit Dosages ........
6.2.2 "In-House" Radiopharmacy .................................
6.2.3 Generators ............................................................
6.2.4 Chemical Formulation .........................................
6.2.5 Xenon ....................................................................
6.2.6 Nebulizers .............................................................
6.2.7 Iodine (Diagnosis and Therapy) ..........................
6.3 Dosage Calibrations ......................................................
6.4 Radiopharmaceutical Administration ............................
6.5 Imaging ............................................................................
6.6 Contamination Control ........ ..........................................
6.7 Misadministration ...........................................................
6.8 Safety Considerations with Nursing Mothers ...............
6.9 Radioactive Waste Disposal ............................................
7 Radiation Safety Considerations for the Nursing

.

Staff .......................................................................................

7.1 Radiopharmaceutical Administrations ..........................
7.2 Notification of Radiopharmaceutical Administration ...
7.3 When Radioactive Precautions Are Necessary .............

7.3.1 The Patient ...........................................................
7.3.1.1 For Diagnostic Purposes .........................
7.3.1.2 For Therapeutic Purposes ......................
7.3.2 Collection and Handling of Excreta ....................
7.3.2.1 From Diagnostic Dosages .......................
7.3.2.2 From Therapeutic Dosages ....................
7.3.3 Collected Specimens .............................................
Glossary ....................................................................................
References .................................................................................
The NCRP ................................................................................
NCRP Publications ..............................................................
Index .........................................................................................


1. Introduction
1.1 Scope

The medical use of unsealed radioactive materials, generally
referred to as nuclear medicine, subjects four classes of persons to
radiation exposure. These are patients, health care radiation workers, health care nonradiation workers, and members of the general
public who are in the vicinity of these materials before, during or
after their medical use. Considerations of patient exposure have
been included in two previous reports of the National Council on
Radiation Protection and Measurements (NCRP), namely NCRP
Report No. 70, Nuclear Medicine-Factors Influencing the Choice
and Use of Radionuclides in Diagnosis and Therapy (NCRP, 1982)
and NCRP Report No. 73, Protection in Nuclear Medicine and Ultrasound Diagnostic Procedures in Children (NCRP, 1983). Estimates
of the quantities of radionuclides administered to patients in nuclear
medicine procedures together with evaluations of the equivalent
dose to the gonads and effective dose, and their contribution to the

population exposure and dose are included in NCRP Report No. 100,
Exposure of the U.S. Population from Diagnostic Medical Radiation
(NCRP, 1989a). A primary concern is the evaluation and control of
occupational exposures to nuclear medicine and allied health personnel and to members of the public other than the patient. Since the
general public would potentially receive exposure from patients containing radioactive material, t h e radiation levels close t o these
patients are also important.
Many groups of medical personnel may receive radiation exposure
from radioactive materials used in medical practice. The principal
groups are physicians, technologists, radiopharmacists and others
who handle the radioactive material and radioactive waste or provide
care for the nuclear medicine patient. In addition, other physicians,
nurses, x-ray technologists, receiving room personnel, security staff,
those who transport patients within the hospital, operating room
staff, maintenance workers and others, may occasionally be exposed.
Specific radiation protection guidelines for these and other allied
health personnel have been given in NCRP Report No. 105, Radiation Protection for Medical and Allied Health Personnel (NCRP,


2

1

1. INTRODUCTION

1989b). Members of the general public who might receive small
exposures include other patients in waiting rooms, wards or multibed rooms, visitors and persons close to radioactive patients while
in transit or in the home.
Section 2 of this Report addresses the impact of nuclear medicine
on the practice of medicine and on the diagnosis and treatment of
disease. Its ability to image parts or organs of the body or, when

necessary, the whole body and to treat cancers without performing
surgery was a major public health accomplishment. The use of radioimmunoassay techniques was another major accomplishment that
aided in a more complete understanding of diseases and disease
processes. The advent of single photon emission computed tomography (SPECT) and positron emission tomography (PET) have added
to the number and kind of nuclear medicine procedures being
performed.
Section 3 focuses on radiation risk and presents a few comparisons
which will help to improve understanding of risk and provide some
perspective on the importance of comparing risks of radiation exposure to other risks faced by our society. There is a brief discussion
of limits of radiation exposure followed by an equally brief discussion
of radiation effects.
Section 4 traces the path of radioactive materials from receipt at
a facility through delivery of the material to the nuclear medicine
department, preparation of a dosage for administration to the
patient, and dosage of the patient. Since, when the patient receives
the radioactive material, he or she becomes a source of exposure to
others, the patient is then followed through the facility. Another
aspect examined is the movement of specimens from the patient to
the laboratory for examination or testing. This may or may not
represent another source of exposure.
The subject of radiation exposure to individuals is further developed in Section 5. There are three principal sources to radiation
workers-dosage preparation and assay, administration, and
patient imaging or treatment. The details of each of these areas is
analyzed and techniques useful to reduce exposures are examined.
Finally, the exposure of those not involved in administration of radiopharmaceuticals to patients is examined. This group includes
patients other than nuclear medicine patients who may walk through
the halls or share a patient room, waiting room or elevator with a
nuclear medicine patient, nurses or other providers of care to the
patient, and members of the public.
The more detailed examination of the handling procedures used

in nuclear medicine are covered in Section 6. The two areas for
preparation of dosages for administration to the patient are a


1.2 QUANTITIESANDUNITS

/

3

commercial radiopharmacy or the nuclear medicine department. The
exposures from these two sources and the advantages and disadvantages are discussed. The calibration and use of dosage calibrators
are reviewed. The techniques of the administration of the radiopharmaceuticals to the patient by injection, inhalation or oral administration a r e reviewed. The subjects of contamination control,
misadministration and safety consideration for nursing mothers are
discussed. There is also a brief review of radioactive waste disposal.
Section 7 treats the very important topic of radiation safety in the
care of the hospitalized patient. These are generally patients who
have received therapeutic amounts of radionuclides and, at least in
the early times after administration, represent a significant source
of exposure.

1.2 Quantities and Units
In NCRP Report No. 116 (NCRP, 1993a),the NCRP recommended
the use of a new quantity to be known as effective dose. By combining
doses to radiosensitive organs in the body in a manner that accounts
for their relative contributions to the total radiation detriment, the
effective dose provides a single measure of dose that is directly
related to detriment. The unit for this effective dose is sievert (Sv).
Wherever in this Report the term dose is used, unless otherwise
qualified, its meaning is effective dose.

The energy absorbed per unit mass at a point in the human body
exposed to radiation is known as the absorbed dose in tissue. The
unit of absorbed dose is gray (Gy).
For this Report, the quantity air kerma, and its special unit Gy,
will be used in place of the quantity exposure. The two quantities
are not interchangeable as the unit for air kerma is joules per kilogram and the unit for exposure is coulombs per kilogram. Since they
are not interchangeable, the conventional unit name, roentgen, will
not be used but, until such time as radiation detection and survey
meters are calibrated in air kerma, the numerical value of exposure
in roentgens may be assumed to be approximately equal to the
numerical value of air kerma in rads, which is equal to air kerma
in centigray.
For a more complete discussion ofthese concepts see ICRU Reports
33 and 51 (ICRU, 1980; 1993) and for a more complete discussion
of Systeme Internationale (SI) units see NCRP Report No. 82
(NCRP, 1985a).


2. Public Significance of
Nuclear Medicine
2.1 Nature and Advantages
Radiopharmaceuticals (drugs containing radionuclides) a r e
administered to patients in order to make a physiologic measurement, to obtain images of organs or organ systems, or to provide
treatment. Drugs or compounds tagged with specific radionuclides
will deposit within the human body in a predictable manner (both
as to location and amount). The advantages of using these techniques
are that spatial distributions and physiologic behavior may be studied simply, noninvasively, a t low cost and withlow risk to the patient.
As a n example, nuclear medicine imaging of the heart and studies
of function are frequently used to provide information otherwise
obtainable only by cardiac catheterization, an invasive procedure.

The latter usually requires hospitalization and is accompanied by
higher radiation dose, mortality, morbidity and cost. Another example is the determination of whether newly discovered breast cancer
has metastasized (spread) to the bone. The nuclear bone imaging
procedure is the most cost effective method available for making
such a determination. If metastases in bone are found, they provide
information important for developing a n appropriate treatment protocol for breast cancer. Numerous similar applications exist which
illustrate the impact of this technology on clinical decision making
in the management of patient problems.
Although treatment (as distinct from diagnosis) with radiopharmaceuticals is a small part of the practice of nuclear medicine, it is
very effective for certain medical conditions. The dosage administered for therapeutic purposes is 10 to 50 times the dosage administered for diagnostic purposes. The treatment of hyperthyroidism,
(overactivity of the thyroid gland), is a routinely used procedure in
nuclear medicine. In contrast, surgery requires hospitalization and
has higher associated mortality, morbidity and expense.
A third segment of nuclear medicine is radioimmunoassay laboratory testing. Such procedures do not require the administration of
radioactive materials to the patient. In these tests, a biological


2.1 NATURE AND ADVANTAGES

1

5

specimen, usually blood, is analyzed in the test tube usingradioactive
materials for determination of the content of hormones. vitamins,
drugs, enzymes, viral particles or products, cancer antigens or other
chemicals. The methods are sensitive and precise and, since their
advent a few decades ago, have revolutionized the understanding of
disease and disease processes by the medical profession. These tests
employ small quantities of radioactive materials and result in radiation exposures to the technologists involved in their performance

that are so low the technologists need not be considered radiation
workers, if that is their sole source of exposures.
Information on the physical characteristics of commonly used
radionuclides is set out in Table 2.1. The activity of radioactive
materials used in diagnostic nuclear medicine examinations varies
with the particular radionuclide employed and the purpose of the
examination. In general, larger activities are used with radionuclides
of shorter half-life. The range is from kBq for vitamin B-12absorption
tests with 57Co(physical half-life 272 d) to GBq for PET studies of
brain blood flow with 150(physical half-life, 2 min). Typical organ
doses from diagnostic procedures are in the range of 10 to 30 mGy,
and for therapy procedures, can exceed 100 Gy. In vitro radioimmunoassay procedures typically employ about 300 Bq of radioactive
material. Since the tests are conducted in the laboratory on samples,
e.g., blood, that have been removed from the patient, there is no
accompanying radiation dose to the patient.
Federal and state authorities have been involved in the regulation
of nuclear medicine since its inception. All facilities responsible for
medical use of by-product material must be licensed, for radionuclide
use, by the U.S.Nuclear Regulatory Commission (NRC) or by an
TABLE
2.1-Physical characteristics of radionuclides used in nuclear medicine.
Radionuclide

Physical
Half-Life

99mTc
6 h
'=I
13 h

la11
8d
aolll
73 h
67Ga
78 h
l%e
5.3 d
"'In
68 h
82Rb
1.25 min
l50
2.04 min
llC
20.48 min
18F
109.74 min
laN
9.97 min
" k o m an unshielded point source in air.
bFormrad h-I at 1 m from 1 mCi multiply by 0.037.

Air Kerma Rate Constant'
(pGy h-I 100 MBq-I@ 1 mIb

2.0
3.8
5.5
1.2

4.0
1.1
3.4
16.7
15.7
15.7
15.1
15.7


6

/

2. PUBLIC SIGNIFICANCE OF NUCLEAR MEDICINE

agreement state (see Glossary). For accelerator produced or naturally occurring radionuclides, many states regulate their use. Radiopharmaceuticals intended for medical use must be approved by the
U.S. Food and Drug Administration. Major aspects of radiopharmaceutical production, transportation, application and disposal are regulated by various federal and state agencies.

2.2

Size and Growth

NCRP estimated in 1989 that about 100 million procedures using
radioactive materials are performed each year in the United States
for diagnostic and therapeutic medical purposes (NCRP, 1989a).
Approximately 10percent of these procedures involve administration
of radioactive pharmaceuticals directly to patients for diagnostic or
therapeutic procedures. The remaining 90 percent are radioirnmunoassay procedures that involve the use of small amounts of radioactivity in analysis of patient urine, blood, etc.
There are over 150 diagnostic and therapeutic nuclear medicine

procedures involving the administration of radiopharmaceuticals to
patients (AMA, 1991). According to a survey of full-time nuclear
medicine clinics,' only 10 in vivo diagnostic procedures comprised
over 90 percent of all such procedures performed in a typical nuclear
medicine clinic, and only one therapeutic procedure constitutes the
bulk of all nuclear medicine treatments. These results are qualitatively similar to those of Mettler et al. (1986) who showed that in
the early 19809, nine categories of studies accounted for over 90
percent of diagnostic in vivo examinations (see Table 2.2).
Witherspoon and Shuler2 obtained similar results in a survey of
nuclear medicine facilities in the southwestern United States, but
the distribution of studies has shifted significantly over the years.
Cardiac and pulmonary nuclear medicine studies (pathophysiologic
in nature) have doubled their share of total studies, whereas hepatic
94"T~
sulfur colloid imaging has disappeared from the top ten list.
This change reflects two simultaneously occurring trends over the
past decade. Radiologic imaging has significantly improved with the
advent and application of high contrast, high resolution modalities
(computed tomography, ultrasound, magnetic resonance imaging,
'Personal communications (1991) from Martin L.Nusynowitz, University of Texas
Medical Branch at Galveston, Galveston, Texas.
2Unpublished survey (1991) from Lynn Witherspoon and Stanton Shuler of the
Ochsner Clinic, Metairie, Louisiana.


2.2 SIZE AND GROWTH
T

m 2.2-Relative

Procedure

Diagnostic
Bone
Gastric emptying
Heart: Equilibrium
radiocardiography
Heart: Myocardial
perfusion

Hepatobiliary
Kidney

Relative
Fkeauencv of
Procedu&ss
(percent)

740

1.3

40

0.2

110

4.5

mlT1thallous
chloride
99"Tc sestamibi
""Tc teboroxime
99"Tcdisofenin
1311iodohippurate
""Tc pentetate
*mTcmertiatide
99mTc
macroaggregated
albumin
lS%e gas
*Tc pentetate
aerosol
"31Na iodide
'311Na iodide
99"Tc pertechnetate
aG@
'
citrate

110
1,110
1,850

6.3
5.0
8.3

300

15
370
370
110

1.3
0.4
0.6
0.7
0.5

370
740

0.14
1.6

11.8

17.9
2.9

8.2

5.6
3.8
5.7

Activity
Typical

Administered
Dose
per Procedure to Patient
(MBq)
(mGy)

""Tc medronate or
oxidmnate
*Tc sulfur
colloid
*Tc red cells

4.6

7.3

Tumorlinfedion
Other
Therapeuticb
Hyperthyroidism
Thyroid cancer

Radiopharmaceutical

20.6

Lung ventilation

Thyroid (25% uptake
of iodine)

7

frequency of nuclear medicine procedures (1991), typical
activities administered and typical dose.

9.6
Lung perfusion

1

(
{

{
{

15
4
185
190

0.4
0.7
0.7
13.0

1.8
I3lI Na iodide
740

0.2
'311Na iodide
3,700
"Based on an unpublished survey (1991)of nuclear medicine facilities by Martin L.
Nusynowitz, University of Texas Medical Branch a t Galveston, Galveston, Texas.
Treatment for hyperthyroidism and thyroid cancer estimated at 2 per 100 diagnostic procedures.
'Typical dose is meaningless in therapy. Dose to region of concern is the only
consideration because that dose provides the benefit.

and digital subtraction angiography) for anatomic definition, thereby
supplanting the poorer-resolution nuclear medicine techniques in
the detection and definition of pathologic anatomy. On the other
hand, pathophysiologically-oriented nuclear medicine studies
have made significant progress with the availability of newer


8

1

2. PUBLIC SIGNIFICANCE OF NUCLEAR MEDICINE

radiopharmaceuticals (e.g., myocardial perfusion agents, regional
cerebral blood flow agents), instrumentation (e.g.,SPECT), and computers and software (e.g., renal function evaluation).
The number of in vivo nuclear medicine examinations performed
in hospitals in the United States increased about 16 percent from
approximately 6.4 million to 7.4 million from 1980 to 1990 (Mettler
et al., 1993). The projected growth rate of eight percent per year was
not realized over this 10 y period mainly as a result of the virtual
disappearance of 99"Tcpertechnetate brain scintigraphy and %Tc

sulfur colloid liver imaging, which have been replaced by other
modalities, such as computed tomography (CT) and magnetic
resonance imaging. Meanwhile, nuclear cardiology studies have
increased.
As would be expected, the work load and procedure distribution
a t any one facility depends, in large measure, on the size and nature
of the facility, the patient population and on the interests of the
medical community. Nevertheless, for all but small general hospitals, approximately 8 to 10 in vivo diagnostic studies on in- and
outpatients are performed per year per occupied hospital bed. The
relative frequency of performance of these procedures and typical
amounts of radioactivity administered to a n adult are presented in
Table 2.2.
The coming decade will witness further changes as new procedures
and techniques are developed and applied clinically. Likely to be
among these are PET for the spatial mapping of functional parameters of the brain, including brain blood flow, metabolism, receptor
activity, tumor metabolism and response to therapy, and cardiac
flow and metabolism, using radiopharmaceuticals of the positron
emitters "C, 150,
18F,82Rband 13N.Representative dosages and radiation absorbed doses (Kearfott, 1982a; 1982b) are listed in Table 2.3.
TABLE2.3-Radiation absorbed dose for various PET studies
(adapted from Kearfott, 1982a; 1982b).
Radiopharmaceutical

Activity
Administered

"CO
C150

(MBq)

740
1,850

coi50

1,850

H ~ ~ ~ o 1,850
lBF-FDG
82Rb

370
1,850

Organ of
Interest

Spleen, lungs, intestine
Spleen, lungs, intestine
Lungs
Blood, kidneys, liver,
lungs
Bladder
Heart, kidneys

Organ
&sorbed Dose
to Patient
Absorbed Dose
(pGy MBq-')

(PGYMBg-')

14 to 23
4, 3, 4
1.3
3

5.0
0.4
0.4
0.4

120
3.5 to 5

10.5
0.4


3. Radiation Risk in
Perspective
3.1 Introduction

The rapid growth in development and use of radiation and radioactive materials parallels the development of a large body of knowledge concerning the measurement of radiation, its interaction with
matter, and its biological effects. Of special importance in connection
with effects is the evidence that has been obtained from studies of
human populations that have been exposed to radiation (ICRP,
1991a; 1991b; NCRP, 1993a; 1993b; UNSCEAR, 1993; 1994)
There is much information and general agreement about risks
following exposures to large radiation doses. In contrast, there is

very little direct information about the effects on humans of low
absorbed doses of radiation ((0.2 Gy) received by many radiation
workers and the lower doses received by the public. The available
data for humans do not allow direct estimates of risk from radiation
doses below 0.2 Gy.

3.2 Risk

There is no such thing as a risk-free life. For most people, risk is
an inherent and accepted part of daily life. Death is one risk we all
face to some extent every day. The probability of death occurring
ultimately in every person is unity. The risk from one source, exposure to radiation, should therefore be judged in comparison with the
other risks which we face continuously throughout our lives.

3.3 Radiation Risks
3.3.1 Low-Level Radiation Doses

Numerous groups have estimated that medical radiation workers
in the United States receive annual effective doses between 2.5 and


10

/

3. RADIATION RISK IN PERSPECTIVE

5 mSv (NASNRC, 1980; UNSCEAR, 1988). Doses will vary with the
individual and the task. Table 3.1 provides a summary of radiation
doses routinely encountered by the public in various medically

related procedures. It should be noted that the average annual dose
to the public from nuclear power plants is <0.02 mSv. Also, for
comparison, the annual effective dose from natural background radiation is on the order of 3 mSv (NCRP, 1987a).

3.3.2 Dose Limits
The annual occupational dose limits for adults as adopted by the
NRC beginning January 1, 1994, are 50 mSv total effective dose
equivalent, 500 mSv for any individual organ or tissue other than
the lens of the eye, 150 mSv for the lens of the eye and 500 mSv to
the skin or any extremity (NRC, 1991). The limit on radiation dose,
from licensed activities, for individual members of the general public
is 1 mSv per y. (The natural background and exposure of patients
for diagnostic or therapeutic purposes is excluded from these limits.)
The guideline recommended by the NCRP (1993a) for the lifetime
maximum accumulation of effective dose to occupationally exposed
individuals is: cumulative lifetime limit = age in years x 10 mSv.

3.3.3 Radiation Effects at Low Doses
Figure 3.1 summarizes the major events which follow energy
absorption from ionizing radiations. The initial event is the absorption of energy from the radiation by the cells of the exposed person's
body. This energy causes changes to occur in the molecules of protoplasm. Of all the possible molecular damage to irradiated cells,
TABLE
3.1-Average annual effective dose equivalent received by members of the
public as a result of various medically related activities in the United States
(adapted from NCRP, 1 9 8 7 ~ ) .
Average Annual
Effective
Dose Equivalent
Source

Chest x ray
CT (head and body)
Diagnostic x rays
Nuclear medicine procedures
Transportation of radioactive materials
"Per examination.

(mSv)

0.06"
1.108
0.40
0.14
0.0006


3.3 RADIATION RISKS

Energy
Deposition

-

Bimhemical
Changes

/

11

Cellular
) Damage

I

r ) Cancer Induction
Developmental
(other cells)

Defects(Felal)

Giber Medical
Effects(high
doses only)

Fig.3.1. The major events which follow energy absorptionfrom ionizing radiation.

damage to DNA (the genetic material) is considered the most important (UNSCEAR, 1993).
If the absorbed energy causes this chromosomal damage, two
major results can occur:
1. if the damage occurs in the germ cells (in the ovaries or testes),
hereditary defects in subsequent offspring or later descendants
of the exposed person may result, and
2. if the damage occurs in body (somatic) cells of the exposed
individual, it may result in one or more of the late somatic
radiation effects.
After exposure to radiation there is a theoretical increase in the
probability of these effects. The late effects include mutagenic effects,
teratogenic effects and cancer. Of course, repair or repopulation may
mitigate effects.

3.3.3.1 Hereditary Defects. Radiation-induced inherited genetic
effects have been observed in several animal species and in lower
forms of life, but not in humans (NASNRC, 1990). The estimation
of humangenetic risks is based mainly on data obtained in laboratory
experiments using animals. The use of such data introduces the
uncertainty of extrapolation from the laboratory conditions under
which the experiments were conducted and the nature of the exposed
animal to humans. Despite comprehensive studies of the children


12

/

3. RADIATION RISK IN PERSPECTIVE

of the atomic-bomb survivors in Japan, there remains no evidence
for heritable effects in humans (UNSCEAR, 1993).
3.3.3.2 Developmental Defects. Of the somatic effects of ionizing
radiation other than cancer, developmental effects on the embryo or
fetus are of greatest concern. High radiation doses can cause death,
malformation, growth retardation and functional impairment. However, low doses k 0 . 2 Gy) do not appear, in general, to affect the
developmental process. This observation suggests that there may be
a threshold dose below which no effects occur. Threshold doses for
some effects have, in fact, been demonstrated, but these thresholds
vary for different abnormalities (NASLNRC, 1990). An exception to
this generalization may be the recent observation of an increase in
mental retardation among children irradiated in Hiroshima between
weeks 8 and 15 of gestation. This risk appears to be proportional to
dose a t the rate of 0.4 Gy-' (Otake and Schull, 1984)with a threshold

for severe mental retardation of 0.1 to 0.2 Gy (NCRP, 1993a). [See
also NCRP Commentary No. 9 with respect to exposure of the
embryo, fetus and the nursing child (NCRP, 1994).1
3.3.3.3 Cancer Induction. There are data on cancer induction
from high-dose exposures to certain human populations. These data
can be used to estimate the degree of risk to be expected in a similar
population exposed to smaller doses. Statistical methods are available for finding the expected number of cases required in order to
have any chance of detecting an increased risk of cancer in an irradiated population compared to a suitable unirradiated control population. For example, based on riskestimates, Goss (1975)has estimated
that for a dose to adults of 200 mGy and an observation time of a t
least 20 y, [if there were a difference in cancer incidence (at the
95 percent confidence level)], an exposed population of 100,000 persons is required to detect that difference (Land, 1980;Webster, 1981).
Similarly, at an equivalent dose of 200 mGy to the breast and an
observation time of 20 y, a population of more than two million
exposed persons and a similar number of unexposed individuals
would be required to detect an increase in breast cancer if, in fact,
one exists (Goss, 1975; Webster, 1981).The required population size
must be even larger a t doses lower than 200 mGy.
To determine radiation risk, a long observation period for detection
is necessary due to the phenomenon of latency. For cancer induction
by radiation, the latent period is the time between exposure to radiation and the onset of clinically detectable cancer. The minimum
latent period is 10 y for all solid cancers except leukemia and bone
cancers, in which the minimum latent period is 2 y (NCRP, 1993b).


3.3

RADIATION RISKS

1

13

The latent period depends on: (1)methods of detection, (2) ease of
examination, (3)role of cell division in tumor development, (4)degree
of cell survival, ( 5 ) type of cancer, (6) dose to the organ of concern,
and (7) age at exposure (UNSCEAR, 1993).
Cancers arising in various organs and tissues are the principal late
somatic effects of radiation exposure. As a very general guideline,
the BEIR V Report (NASNRC, 1990) suggests a fatal cancer risk
estimate of four cancers per 100 mSv in 1,000 exposed individuals.
At the doses of 2.5 to 5 mSv experienced by nuclear medical personnel
annually, the cancer risk is small. To place this in perspective, if
an unexposed population of 1,000 persons was exposed to doses of
5 mSv y-l for 40 y there could be eight cancers in addition to the
210 cancer deaths that would occur in that population due to the
normal incidence of cancer in the population of the United States.
The dose limits recommended by NCRP, along with the practice of
as low as reasonably achievable (ALARA),which has limited annual
occupational doses to an average of 4 mSv or less (NASINRC, 1990),
should limit any increased risk from radiation exposure in the
work place.
3.3.4

Comparative Risks

Radiation protection philosophy is based on the conservative
hypothesis that some risk is presumed to be associated with even
small doses of ionizing radiation. The philosophy is based also on
comparisons of radiation risks with other hazards of daily life, especially work hazards. However, in general, risks cannot be regarded
as acceptable if they are readily avoidable or not accompanied by a

commensurate benefit. The weighing of risks and benefits calls for
personal value judgments, which can vary widely.


4. Receipt and Delivery of

Radioactive Materials
4.1 Introduction
Following their manufacture, radiopharmaceuticals are handled
several times before reaching their destination in nuclear medicine
clinics and within other medical facilities. At each step, some radiation exposure may be incurred by the persons handling the package
or the radiation source. In this Section the radiation exposure potential is considered during the following phases: delivery to and receipt
within the medical facility, delivery to the end user, exposures in
the course of radiopharmaceutical production and transportation,
and transportation of radioactive specimens from a patient to the
laboratory.

4.2 Shipment of Radioactive Sources
Although a small number of accidents have occurred during the
transportation of radioactive materials by common carrier, such accidents have produced no radiation-related injury and had little economic consequence (ANS, 1986). Transportation accidents involving
even the highest levels of activity of radioactive materials used in
generators, have been determined
nuclear medicine, i.e., 99Mo-99mT~
to be accidents of a low-severity level (Dodd and Humphries, 1988).
The radiological risk of transporting radioactive materials, in general, is low when compared to other nonradiological risks normally
associated with transportation (Humphries and Dodd, 1989).
Essentially all shipments of radioactive materials to medical institutions are transported either by air or land. Radiopharmaceuticals
for diagnostic use usually have short half-lives and, unless the supplier is within a few hours driving distance of the institution, shipment is usually made by air. Numerous studies have been conducted
to determine radiation exposure to air cargo workers (Bradley et al.,
1977; Carter et al., 1982; Failla, 1977; Luszczynski et al., 1978;NRC,

4.4 TRANSPORTATION OF RADIOACTIVE MATEFUALS

1

15

1977;1978;Uselman and McKlveen, 1975).In normal circumstances,
yearly maximum doses were found to be <5 mGy.

4.3 Receipt of Radionuclides

If radionuclides are packaged and shipped according to regulatory
standards, the potential for inadvertent exposure is minimal. It is
rare that a shipment has been improperly packaged or has suffered
damage in shipping. However, it is imperative that, as soon as possible after receipt, all packages of radionuclides are examined and
surveyed for contamination and radiation exposure and that the
results are recorded in a log book according to an approved procedure
(NRC, 1987).Typical dose equivalent rates at the surface and at 1 m
from radiopharmaceutical packages upon receipt are indicated in
Table 4.1.3

4.4 "In-House"Transportation of Radioactive Materials
Table 4.1 indicates that the radiation level at the surface of certain
packages can be substantial. Therefore, good radiation safety practice dictates that contact with the surface of these packages be
avoided whenever possible and that "in-house" transportation be
performed using carts. These carts can be shielded, but in most
cases, the added distance from the source lessens the dose received
by the operator and the public.

The conveyance of radioactive materials for administration to the
patient within the nuclear medicine department or within the hospital should present minimal radiation exposure potential provided
appropriate shielding is employed. Typically, shielded containers
with at least 3.2 mm lead equivalence are sufficient to absorb nearly
TABLE4.1-Typical dose rates from radiopharmaceutical packages.
Radioisatape

99Mo-9"T~generator
1251

1311

Activity
(MBq)

At Surface
(mGy h-I)

16,280
185
3,700

0.26
0.005
0.63

At 1 m
(pGy h-')

0.8

(0.1
2.0

3Unpublished data (1985)from Kenneth L.Miller, Milton S. Hershey Medical Center, Hershey, Pennsylvania.


16

/

4. RECEIPT AND DELIVERY OF RADIOACTIVE MATERIALS

all of the radiation emitted by radionuclides used in diagnostic
nuclear medicine (see Table 4.2). For therapeutic amounts of 1311or
positron-emitting radionuclides used in PET scanning, additional
shielding is normally required. Shieldingshould be adequate to limit
external radiation levels to no more than 20 p,Gy per h. For a
3,700 MBq source of 1311, the shielding required to reduce the dose
rate at the surface of the shield to 20 p,Gy per h is approximately
5 cm of lead equivalence.
It is again emphasized that the use of a cart, in addition to shielding, can greatly reduce radiation exposure during conveyance, and
is particularly important for therapeutic quantities of high-energy
gamma-ray emitters such as 1311.Assuming the diameter of the
shielded container is 20 cm, the dose rate at 1m from its center is.
about 100 times smaller than at the container surface. The transport
of radioactive material in shielded containers is essential to reduce
the exposure of individuals (the cart handler and members of the
public).

4.5 Transport of Patients

The movement within a hospital of patients to whom radiopharmaceuticals have been administered for diagnostic purposes will normally present minimal potential for radiation exposure to those
individuals near the patient. The radiation dose delivered to the
TABLE
4.2-Shielding data for radionuclides used in nuclear medicine.
Radionuclide

Major X- and GammaRay Energies, keV"

Half-Value Layerb
in mm of Lead

27 (71%), 159 (83%)'
0.04
30 (38%),81 (37%)
0.2
7 1 (47%), 167 (11%)
0.23
140 (89%)
0.3
93 (38%), 184 (21%), 300 (17%)
0.66
364 (81%)
3.0
23 (68%),171 (91%),245 (94%)
1.3
511 (192%), 777 (13%)
6.0
150
511 (200%)

5.5
C
511 (200%)
5.5
IBF
511 (194%)
5.0
13N
511 (200%)
5.5
"Emissiondata abstracted from NCRP (1985b).
general, the use of 10 half-value layers will reduce the intensity to 1,000th the
unshielded value.
'Percent (
indicates
I
) number of gamma rays per 100 disintegrations.
1231

135Xe
nrlTl
99mTc
67Ga
1311
lI1In
82Rb

"

4.6 TRANSPORT OF SPECIMENS

1

17

patient following the administration of a radiopharmaceutical is
determined by the physical characteristics of the radionuclide, the
biological characteristics of the pharmaceutical, and by the activity
administered. The dose received by a person nearby is influenced
also by the exposure time and the distance from the patient.
Although the radiation dose rate a t 1m from a typical diagnostic
patient is usually about 10 kGy per h (Pennock et al., 1980), the
same cannot be said of the patient to whom a therapeutic quantity
of radionuclide is administered (Castronovo et al., 1982a; Miller
et al., 1979; Pennock et al., 1980; Vanderlick et al., 1980). For example, the dose rate at 1m from a patient immediately after administration of 3,700 MBq of 1311will be approximately 0.2 mGy per h. Some
of these patients may experience nausea and vomiting following the
administration of the radiopharmaceutical. Therefore, to minimize
the potential for contamination and exposure, it is preferable if large
quantities (>1,000 MBq) of therapeutic radiopharmaceuticals are
administered in the patient's room.

4.6 Transport of Specimens from

Nuclear Medicine Patients
Table 4.3 provides information on the dose rate from blood samples
pertinent to routinely used radionuclides and nuclear medicine procedures. It is evident that the maximum activities in a sample of
blood taken after a short equilibrium period, as well as the dose
rates at the surface of the test tubes, are minimal in most cases.
The highest maximum dose rate in Table 4.3 is for thevery unlikely

case of a blood sample taken from a patient within 1h after the
administration of the usual amount of 1311 used for thyroid cancer
treatment. Compare this 25 p,Gy per min with a derived occupational
dose rate to the fingers of 10 mGy per week, i.e., the maximum
weekly finger dose would be received handling a test tube containing
the sample for 6.7 h. The dose rates for blood samples taken from
patients receiving diagnostic tests are 30 or more times lower and are
usually negligible compared to those from therapy patients. Doses
received when handling blood samples containing radionuclides can
be reduced readily by a factor of three or more through the simple
practice of holding the test tube a t the top above the level of the
blood in the tube.
It is not necessary to shield blood samples unless a large number
are accumulated in one spot. Also, it is not necessary to provide
personnel monitoring for individuals handling such samples. There


18

/

4. RECEIPT AND DELIVERY OF RADIOACTIVE MATERIALS

TABLE4.3-Dose rate from blood samples withdrawn following injection of
radiopharmaceuticals for common nuclear medicine p r o ~ d u r e s . " ~
Maximum Activity Maximum Dose Rate
Procedure

Diagnostic
Bone (WC)

Kidney (9hTc)
Thyroid P T c )
Thyroid ('?I)
Cardiac (9"Tc)
Abscess/tumor (67Ga)
Lung perfusion (=Tc)
Therapeutic
Hyperthyroidisme ("'I)
Thyroid canceP ("'I)

"q
Admlnlsted

in 10 ml Bloodc

(MBq)

a t 1crnd
(pGy min-'1

740
370
185
15
1,110
190
110

1.3
0.7

0.3
0.1
2.0
0.3
0.2

1.6
0.8
0.4
<0.2
2.4
0.6
0.2

740
3,700

1.33
6.66

5.0
25.0

"One minute after injection.
bRadiopharmaceutical administered a s in Table 2.2.
'Based on 5,500 ml total blood volume.
dAssumes 1 cm distance to fingers from 6 cm line source.
'Following absorption into the blood.

is a slight potential for an individual to become contaminated. However, universal precautions, e.g., avoiding contact with fluids, wearing gloves and cleaning up spills immediately, should eliminate this

potential problem. It is good practice to tag, or otherwise label as
radioactive, samples from therapy patients so that subsequent handlers are aware of the radioactivity and can assure that radioactivity
from the patient does not interfere with radioimmunoassay results.


5. Radiation Exposure from
Nuclear Medicine
Practice
5.1 Nuclear Medicine Personnel Exposure

Exposure of nuclear medicine personnel to radiation can arise
from three main activities: dosage preparation and assay, injection,
and patient imaging. The dose received from dosage preparation is
variable, depending on the particular procedure, and is of the order
of 0.2 kGy per dosage preparation (NCRP, 1990). Typical doses to
personnel engaged in preparation and assay in the clinical situation
are in the range of 5 to 6 mGy y-l, and the use of central radiopharmacy facilities tends to reduce doses to personnel engaged in injection
and imaging. A survey by Iyer and Dhond (1980) indicated that doses
averaged 1.95 mGy per 1,000 procedures for personnel in clinics
where the radiopharmacy was supplied versus 3.42 mGy per 1,000
procedures where the technologists eluted generators and prepared
the radiopharmaceuticals in addition to their other activities.
Batchelor et al.(1991) and Williams et aL.(1987) have indicated an
average annual potential dose to the extremities of nuclear medicine
technologists of 118 mGy and maximum doses approaching the
annual limit of 500 mGy. This dose varies depending on the numbers
and kinds of procedures performed, the use of available shielding
devices and the caution exercised in handling and administering the
radiopharmaceutical. Also of concern is the potential for doses to
the fingers from contamination. Barrall and Smith (1976) indicated

doses of up to 100 Gy for a point source of 37 kBq of mTc on the
skin. Newer estimates reported by Kereiakes (1992) indicate the
dose a t closer to 200 Gy for a point source on the skin that is allowed
to remain until total decay. If the activity is spread over 1cm2the
resulting dose would be several orders of magnitude lower (Faw,
1992) and more on the order of 0.07 Gy if allowed to remain until
total decay (Kereiakes, 1992).
The unit dosage is administered to the patient, usually intravenously, using a shielded syringe. Other routes of administration
include intrathecally, orally, by inhalation, by instillation into the