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

Population from Diagnostic Medical Radiation occupational exposures to nuclear medicine and allied health person- nel and to members of the public other than the patient.. Section 4 tra

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

791 0 Woodmont Avenue I Bethesda, MD 2081 4-3095

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

[DNLM: 1 Nuclear Medicine 2 Occupational Exposure 3 Radiation Effects 4 Risk 5 Radiation Protection WN 440 N2765s 19961

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 Martin L Nusynowitz

Galveston , Texas

Arnold P Jacobson Dennis D Patton

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 t h e Committee members for t h e 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 a s nuclear medicine, subjects four classes of persons to radiation exposure These are patients, health care radiation work- ers, 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

and Use of Radionuclides in Diagnosis and Therapy (NCRP, 1982)

sound 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

occupational exposures to nuclear medicine and allied health person- nel and to members of the public other than the patient Since the general public would potentially receive exposure from patients con- taining 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, Radia- tion 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 multi- bed 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 radio- immunoassay techniques was another major accomplishment that aided in a more complete understanding of diseases and disease processes The advent of single photon emission computed tomogra- phy (SPECT) and positron emission tomography (PET) have added

to t h e 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 expo- sure 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 a t

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 devel- oped 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 radio- pharmaceuticals 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 a r e a

1.2 QUANTITIESANDUNITS / 3 commercial radiopharmacy or the nuclear medicine department The exposures from these two sources and the advantages and disadvan- tages are discussed The calibration and use of dosage calibrators are reviewed The techniques of the administration of the radiophar- maceuticals to the patient by injection, inhalation or oral administra- tion 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 kilo- gram 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 measure- ment, 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 stud- ied 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 exam- ple 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 pro- tocol 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 radiophar- maceuticals is a small part of the practice of nuclear medicine, it is very effective for certain medical conditions The dosage adminis- tered for therapeutic purposes is 10 to 50 times the dosage admin- istered 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 labora- tory testing Such procedures do not require the administration of radioactive materials to the patient I n 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 radia- tion 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-12 absorption

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

of nuclear medicine since its inception All facilities responsible for medical use of by-product material must be licensed, for radionuclide

TABLE 2.1-Physical characteristics of radionuclides used in nuclear medicine

Physical Air Kerma Rate Constant' Radionuclide Half-Life (pGy h-I 100 MBq-I @ 1 mIb

" k o m an unshielded point source in air

bFor mrad h-I at 1 m from 1 mCi multiply by 0.037

6 / 2 PUBLIC SIGNIFICANCE OF NUCLEAR MEDICINE

agreement state (see Glossary) For accelerator produced or natu- rally occurring radionuclides, many states regulate their use Radio- pharmaceuticals intended for medical use must be approved by the U.S Food and Drug Administration Major aspects of radiopharma- ceutical production, transportation, application and disposal are reg- ulated 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 10 percent of these procedures involve administration

of radioactive pharmaceuticals directly to patients for diagnostic or therapeutic procedures The remaining 90 percent are radioirnmuno- assay procedures that involve the use of small amounts of radioactiv- ity in analysis of patient urine, blood, etc

There are over 150 diagnostic and therapeutic nuclear medicine procedures involving the administration of radiopharmaceuticals to

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 qualita-

the early 19809, nine categories of studies accounted for over 90

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

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 1 7

T m2.2-Relative frequency of nuclear medicine procedures (1991), typical

activities administered and typical dose

Procedu&ss Radio- per Procedure to Patient Procedure (percent) pharmaceutical (MBq) (mGy)

Diagnostic

Bone 20.6 ""Tc medronate or 740 1.3

oxidmnate Gastric emptying 4.6 *Tc sulfur 40 0.2

colloid Heart: Equilibrium 11.8 *Tc red cells 110 4.5

7.3 { *Tc pentetate 740 1.6

aerosol Thyroid (25% uptake "31 Na iodide 15 0.4

Hyperthyroidism 1.8 I3lI Na iodide 740 -

Thyroid cancer 0.2 '311 Na 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 diagnos- tic 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 t h e 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 com- puters 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 a s a result of the virtual disappearance of 99"Tc pertechnetate brain scintigraphy and %Tc sulfur colloid liver imaging, which have been replaced by other modalities, such a s computed tomography (CT) a n d 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 hospi-

tals, 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 i n Table 2.2

The coming decade will witness further changes a s new procedures and techniques are developed and applied clinically Likely to be among these are PET for the spatial mapping of functional parame- ters 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, 82Rb and 13N Representative dosages and radia- tion absorbed doses (Kearfott, 1982a; 1982b) are listed in Table 2.3

TABLE 2.3-Radiation absorbed dose for various PET studies

(adapted from Kearfott, 1982a; 1982b)

Radio- Administered Organ of Absorbed Dose to Patient pharmaceutical (MBq) Interest (pGy MBq-') (PGY MBg-')

"CO 740 Spleen, lungs, intestine 14 to 23 5.0

C150 1,850 Spleen, lungs, intestine 4, 3, 4 0.4

very little direct information about the effects on humans of low

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, expo-

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 t h e public i n 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 radi-

ation is on the order of 3 mSv (NCRP, 1987a)

The annual occupational dose limits for adults a s 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 t h e major events which follow energy absorption from ionizing radiations The initial event is the absorp- tion of energy from the radiation by the cells of the exposed person's body This energy causes changes to occur in the molecules of proto- plasm Of all t h e 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

Nuclear medicine procedures 0.14

Transportation of radioactive materials 0.0006

"Per examination

Giber Medical Effects (high doses only)

Fig 3.1 The major events which follow energy absorption from ionizing radiation

damage to DNA (the genetic material) is considered the most impor- tant (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 How- ever, 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 t h e 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 avail- able for finding the expected number of cases required in order to

have any chance of detecting an increased risk of cancer in a n irradi- ated population compared to a suitable unirradiated control popula- tion 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 per- sons is required to detect that difference (Land, 1980; Webster, 1981) Similarly, a t 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 radia- tion 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,

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

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

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, espe- cially 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 radia- tion exposure may be incurred by the persons handling the package

or the radiation source In this Section the radiation exposure poten- tial 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 acci- dents have produced no radiation-related injury and had little eco- nomic consequence (ANS, 1986) Transportation accidents involving even the highest levels of activity of radioactive materials used in nuclear medicine, i.e., 99Mo-99mT~ generators, have been determined

to be accidents of a low-severity level (Dodd and Humphries, 1988) The radiological risk of transporting radioactive materials, in gen- eral, is low when compared to other nonradiological risks normally associated with transportation (Humphries and Dodd, 1989) Essentially all shipments of radioactive materials to medical insti- tutions are transported either by air or land Radiopharmaceuticals for diagnostic use usually have short half-lives and, unless the sup- plier is within a few hours driving distance of the institution, ship- ment 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 possi- ble 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

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 a t the surface of certain packages can be substantial Therefore, good radiation safety prac- tice dictates t h a t 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 hospi- tal should present minimal radiation exposure potential provided appropriate shielding is employed Typically, shielded containers with a t least 3.2 mm lead equivalence are sufficient to absorb nearly

TABLE 4.1-Typical dose rates from radiopharmaceutical packages

16 / 4 RECEIPT AND DELIVERY OF RADIOACTIVE MATERIALS

all of the radiation emitted by radionuclides used in diagnostic

positron-emitting radionuclides used in PET scanning, additional shielding is normally required Shielding should be adequate to limit external radiation levels to no more than 20 p,Gy per h For a

rate at the surface of the shield to 20 p,Gy per h is approximately

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 radiopharma- ceuticals have been administered for diagnostic purposes will nor- mally 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

Major X- and Gamma- Half-Value Layerb Radionuclide Ray Energies, keV" in mm of Lead

"Emission data abstracted from NCRP (1985b)

general, the use of 10 half-value layers will reduce the intensity to 1,000th the unshielded value

'Percent (indicates number of gamma rays per I ) 100 disintegrations

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 1 m 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 exam- ple, the dose rate at 1 m from a patient immediately after administra- tion of 3,700 MBq of 1311 will 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 pro- cedures I t 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 1 h 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 TABLE 4.3-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

"q in 10 ml Bloodc a t 1 crnd Procedure A d m l n l s t e d (MBq) (pGy min-'1

Thyroid canceP ("'I) 3,700 6.66 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 How- ever, universal precautions, e.g., avoiding contact with fluids, wear- ing gloves and cleaning up spills immediately, should eliminate this potential problem I t is good practice to tag, or otherwise label as radioactive, samples from therapy patients so that subsequent han- dlers 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

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

personnel engaged in preparation and assay in the clinical situation

macy facilities tends to reduce doses to personnel engaged in injection

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 a n average annual potential dose to the extremities of nuclear medicine technologists of 118 mGy and maximum doses approaching t h e 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

the fingers from contamination Barrall and Smith (1976) indicated

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 1 cm2 the 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 intrave- nously, using a shielded syringe Other routes of administration include intrathecally, orally, by inhalation, by instillation into the

20 1 5 RADIATION EXPOSURE FROM NUCLEAR MEDICINE

eyes, bladder or rectum, or into body cavities (peritoneal, pleural or pericardial cavities) The administration is usually performed in an

"injection" area in the nuclear medicine department, but it is done sometimes in the patient's room

After administration, the patient may be studied almost immedi- ately, or the study may be delayed several hours or several days depending upon the procedure During this delay an inpatient may

be returned to bed, while an outpatient may occupy a waiting room

or resume ordinary activities while waiting for the study to com-

mence In the former case, hospital personnel (e.g., nurses, transport-

ers) receive some exposure; in the latter case, other patients, hospital employees and members of the general public are exposed (see Sec- tions 5.2, 5.3 and 5.4)

The remaining components of dose received by nuclear medicine personnel are due to their proximity to the patient for positioning

of the patient and performance of the imaging procedure Typically

Upon completion of the study, patients are returned to rooms or wards, or they leave for their homes and work places where other medical workers (nurses, hospital personnel) and other patients or the general public, including families, are exposed to the radiation emitted by the patient

5.2 Radiation Doses to Patients and Persons Nearby and

Members of the Public

The dose to a patient following the administration of a radiophar- maceutical is determined by the physical characteristics of the radio- nuclide, the physiological specificity of the pharmaceutical and the amount of radioactivity administered The dose received by a person nearby is influenced by these same factors, but is determined by the exposure time and distance from the patient The dose received by

a person near the patient will be much smaller than that received

by the patient because the exposure time is typically only minutes

to hours, the radiation is partially absorbed by the patient's body and distance from the patient lowers the dose rate

by its physical decay and by excretion primarily in the urine or feces, and therefore, the dose rate to both patient and those nearby will

5.3 EXPOSURE OF NUFLSES AND OTHER MEDICAL PERSONNEL 1 21 fall with time Table 5.1 provides radiation dose rate information for 99"Tc MDP patients from the time of injection to 24 h after injection (Castronovo, 1991) Table 5.2 lists the dose a t skin surface, 0.5 m

and 1 m from a patient receiving the procedures listed in Table 2.2

This is the maximum dose that could possibly be received by an individual remaining a t the distance specified until there is total decay of the radionuclide in the patient

5.3 Exposure of Nurses and Other Medical Personnel

Although nuclear medicine procedures contribute approximately

15 percent of the average dose to t h e United States population (NCRP, 1989a) this is essentially all exposure to the patients under- going the procedures and deriving benefit from the exposure The report of the Committee on the Biological Effects of Ionizing Radia- tions [BEIR I11 (NASNRC, 1980)l indicates that the film badges of

40 percent of monitored hospital personnel indicate undetectable doses, and, a s measured individual doses increase, the number of exposed individuals decreases in an exponential fashion The aver- age dose for medical personnel performing x-ray and nuclear medi-

is some indication that the dose for nuclear medicine personnel may

Hendee and Edwards (1990) found that approximately 53 percent

of those occupationally exposed in medicine receive less than a

TABLE 5.1-Dose rates from patients injected with 740 MBq 99mTc MDP

Injection Patient - Patients Projections" (mGy h-'1 - (mGy h-') (mGy h-'1

5 min Patients with and 16 anterior 0.09 0.03 0.009

without bone 16 posterior 0.09 0.04 0.01

22 / 5 RADIATION EXPOSURE FROM NUCLEAR MEDICINE

TABLE 5.2-Common nuclear medicine procedures, patient doses and calculated

external dose at selected distances

Patient Skin Dose Dose Surface to Total to Total Dose Decay at Decay at Procedure Radiopharmaceutical (mGyY 0.5 mb (@Gy) 1.0 mb (@Gy)

Diagnostic

oxidronate Gastric emptying -Tc sulfur colloid 0.1 7 3

Heart: Equilibrium *Tc red cells 1.7 146 48

T c pentetate aerosol 0.6 52 17

Thyroid (25% lBI Na iodide 0.1 11 4

uptake of iodine) "'I Na iodide 0.3 23 7

-Tc pertechnetate 0.3 23 7 Tumorfinfedion 'j7Ga gallium citrate 4.9 42 1 139

Hyperthyroidism 13'1 Na iodide 15.7 1,361 450

Thyroid cancer 1311 Na iodide 78.7 6,803 2,249

aFor patient dose see Table 2.2

bFrom surface of patient

measurable exposure and the majority, approximately 88 percent, receive <1 mGy per y They also found that fluoroscopy was the

medical procedure most responsible for the higher occupational expo- sures Hospital personnel who have only occasional contact with nuclear medicine patients receive only a fraction of the dose received

by the nuclear medicine personnel who handle the patients as well

as the radioactive materials and tagged radiopharmaceuticals that are used in diagnosis and treatment of these patients As can be

seen from Table 5.3, non-nuclear medicine personnel's dose from the

nuclear medicine patient is expected to be only a small percentage

of that received by the nuclear medicine technical personnel The

5.4 EXPOSURE OF THE GENERAL PUBLIC / 23 TABLE 5.3-Estimated dose of persons exposed to nuclear medicine patients

wr Procedure wr Year

Nuclear medicine technical personnel - 4,000 Non-nuclear medicine hospital personnel - 100

from the patient The short amount of time normally required to attend to these patients, results in total doses to hospital personnel that are low There might be situations that deviate from this that

care for high activity radioiodine thyroid cancer patients In general, personnel monitoring along with training in good radiation safety practice and adherence to radiation safety protocols, such as those described in NCRP (198913) will be adequate to keep the exposure

of hospital personnel fi-om nuclear medicine patients to acceptably low levels

5.4 Exposure of the General Public

The potential exposure of nuclear medicine and other hospital personnel to radiation fiom nuclear medicine patients is low There- fore, the potential for exposure to members of the public from these

to members of the public from diagnostic nuclear medicine patients Assuming that an individual remained at a distance of 1 m from the patient from the time of injection until the radionuclide had decayed,

ing from a few p.Gy to 0.21 mGy A more realistic approach assumed

that the individual remained a t a distance of 1 m for the entire first hour after injection In this second situation, the doses were considerably lower than the doses calculated for the extreme situa- tion and represented only a small portion of the radiation received annually from natural background radiation

24 / 5 RADIATION EXPOSURE FROM NUCLEAR MEDICINE

skin surface of outpatients receiving a variety of radiopharmaceuti- cals in order to estimate the population dose from nuclear medicine studies They found that for exposure of co-workers and family, doses

radiopharmaceuticals (see Table 5.3) Doses per procedure to nurses, orderlies, transporters, etc., would be somewhat less than these val- ues because of shorter exposure times and their total annual effective dose would be less than that of nuclear medicine technical personnel Approximately 10 million patient procedures are performed yearly A,conservative dose to a member of the general public of 10 pGy per procedure is assumed for a population of 250 million and the average

per person per y Table 5.3 summarizes the results described in this Section

6 Radiopharmaceutical

Handling Procedures in Nuclear Medicine

6.1 Introduction

In nuclear medicine there are various procedures that require direct handling of radioactive materials These include compounding and dispensing in a radiopharmacy, calibration of stock vials and dosages for administration, and administration to the patient for diagnosis or therapy Each of these procedures, from receipt

to administration, represents the potential for contamination and exposure of the nuclear medicine department staff Following administration, the patient is also a potential source of exposure

exposure and contamination are presented in this Section

6.2 Radiophamnaceutical Dosage Preparation

Radionuclides for patient dosages may be received by the nuclear medicine department from a commercial radiopharmacy or from an internal (hospital) radiopharmacy as "unit doses," i.e., the dosage for a single patient (unit dose), as generator eluates (see Glossary),

or as multidose radiopharmaceuticals

6.2.1 Commercial Radiopharmacy Unit Dosages

The commercial radiopharmacy obtains radionuclides in large quantities, elutes generators, compounds various chemical forms, conducts quality-assurance procedures, and prepares prescribed dos- ages for delivery to nuclear medicine departments within its geo- graphical area The most commonly supplied unit dosages are

in individual shielded syringes or in capsules (1231, 1311)

26 / 6 RADIOPHARMACEUTICAL HANDLING PROCEDURES

6.2.2 'Yn-House" Radiopharmacy

"In-house" radiopharmacies perform the same function as commer- cial radiopharmacies, but on a smaller scale The commercial phar- macies are likely to have more elaborate shielding, additional remote handling devices, and more complex techniques than the nuclear medicine department In one study (Ahluwaliaet al., 1981), the mean quarterly dose per nuclear medicine technologist was reduced from 2.0 mGy to 0.70 mGy when unit dosages were received from the commercial radiopharmacy; or a reduction of dose per person from

4.5 kGy per unit dosage to 1.2 hGy The reduction of 3.3 kGy per

person per unit dosage is due to the elimination of generator elution and unit dosage preparation in the nuclear medicine department

6.2.3 Generators

A generator consists of a parent radionuclide adsorbed on a column

from which a shorter-lived decay product is eluted by passing a suitable solvent (or air in gaseous generators) through the column Additional shielding placed around the generator after receipt from the supplier is usually required to reduce personnel exposure, partic- ularly ifit is located in a small, crowded area Elution of the generator has a potential for contamination due to release of droplets of the eluate upon removal of the collection vial Nuclear medicine person- nel must follow rigid precautions as described in the package insert that accompanies generators Failure to do so can lead to less than optimal yields, significant personnel contamination, and unneces- sary exposure

6.2.4 Chemical Formulation

Some radiopharmaceuticals are administered in the chemical form

in which they are received, and may require only a volume adjust- ment to obtain the correct patient dosage as measured with a dose calibrator Examples are sodium 1311 iodide, ZOITl chloride and "Ga citrate Capsules of sodium lZ3I iodide are administered as received Most radiopharmaceuticals require only minimal formulation such

as the addition of 99mTc pertechnetate (eluted from the generator or received from a radiopharmacy) to a shielded commercial kit vial of reactants, e.g., methylene disphosphonate (MDP), oxidronate and pyrophosphate, and mixing or shaking of the contents Some radio- pharmaceuticals require more extensive handling One method of preparation of 99"Tc sulfur colloid requires the vial containing the

6.2 RADIOPHARMACEUTICAL DOSAGE PREPARATION 1 27

reaction mixture to be boiled in a water bath To reduce external exposure, the water bath should be shielded Contamination by air- borne release may occur if the water bath is allowed to boil dry and the vial ruptures

An example of a complex formulation is the preparation of lilIn labeled white cells The ll1In requires extensive handling while label- ing the separated white cells from a patient's blood Reaction vials, tubes and syringes should be shielded to reduce external exposure, and care should be taken to avoid contamination of the work area during transfers of active material, particularly in view of the 67 h physical half-life of lllIn Measurements of personnel exposures have indicated receipt of doses of 3.8 pGy during cell labeling for a

100 MBq dosage Because a large hospital may perform 100 to 200 such procedures per year, the cumulative dose to radiopharmacy personnel from these procedures could reach 0.5 mSv per y.4 The annual occupational dose limit is 50 mSv (NCRP, 1993a)

In preparing unit dosages, excessive external exposure can occur unless shielding is provided for both the stock vial and the syringe

to be used for administration of the radiopharmaceutical Exposure rates up to 200 mGy h-l have been measured a t the surface of unshielded syringes containing 740 MBq of 99mTc However, if a syringe shield is used, the exposure rate is reduced by a factor of about 50 (Barrall and Smith, 1976)

Xenon-133 is available in a unit dosage gaseous form requiring special storage and transfer devices Shielded 133Xe traps containing effluent air contamination monitors are available commercially Releases to the atmosphere should be known so that exposures can

be controlled by replacing the traps and so that derived reference air concentrations (DRACs) are not exceeded (NCRP, 1993a) In addition, because of adsorption of the xenon from the saline onto the syringe barrel and plunger, as much as 45 percent of the dosage may remain in the syringe after delivery if the syringe is stored for

6 h after initially drawing up the dosage, and 60 percent can remain

if the storage time is 24 h Therefore, the "empty" syringe, if unshielded, is a potential source of external exposure to nuclear medicine personnel For these reasons all xenon containers, both pre- and post-administration, should be stored in a well-ventilated

Wnpublished data (1982) from Sheila I Smith, Stanford University (WHO24 Hazards Evaluation), Stanford, California

28 1 6 RADIOPHARMACEUTICAL HANDLING PROCEDURES

fume hood to avoid exceeding the DRAG of 13%e for controlled areas (also see Sections 6.4 and 6.5)

6.2.6 Nebulizers

One technique for visualizing the lungs involves inhalation by the patient of a mist (aerosol) generated by nebulizing mTc DTPA Although the patient inhales from 75 to 185 MBq (McGraw et al.,

19921, the nebulizer typically contains 740 to 1,100 MBq of *Tc DTPA and must be carefully shielded Widespread contamination can occur (McGraw et al., 1992) by inadvertent misassembly of the nebulizer which can result in the venting to the air of appreciable quantities of the 99"Tc DTPA Care must be taken to assemble the nebulizer according to the manufacturer's instruction Also, care must be taken to ensure that techniques are used that will minimize airborne contamination and worker dose (Crawford et al., 1992)

6.2.7 Iodine (Diagnosis and Therapy)

Radioactive iodine has been noted for its volatility and therefore its potential for causing internal radiation dose in nuclear medicine personnel Early (1987) and Miller et al (1979) reported that two to three percent of the liquid 1311 activity escaped when the cap of the bottle ofliquid oral solution was removed a s compared to 0.01 percent

of the activity lost for iodine in capsular form Carey and Swanson (19791, Jackson and MacIntyre (1979), and Luckett and Stotler (1980) have investigated the effect of increased pH, buffers, antioxi- dants and stabilizers in reducing the radioiodine volatilization Solu- tions of sodium iodide (Na1311) for therapeutic use are now available

a s a stabilized aqueous solution Miller and Erdman5 have measured volatilized activities ranging from 0.15 to 0.36 percent with liquid solutions listed as "stabilized." Therefore, prior to administration, the radioactive iodine solution vial should be uncapped and vented (Early, 1987) in a fume hood (preferably with an activated charcoal filter) for a few minutes to remove any iodine present in the vial air space The vial should then be recapped, the activity measured in a dosage calibrator and transported to the patient for administration The hospital room used for therapy patients should be prepared for contamination control by covering objects and areas potentially a t

'Unpublished data (1992) from Kenneth L Miller and Michael C Erdman collected

at Milton S Hershey Medical Center, Hershey, Pennsylvania

6.3 DOSAGE CALIBRATIONS / 29

risk such as night stands, the telephone mouthpiece, television con- trols, toilet areas, light switches, etc., with plastic or absorbent paper (Miller et al., 1979) Disposable eating utensils should be treated a s

radioactive waste and t h e linens should be monitored prior to releases to the general laundry

Safety guidelines for the release of radioactive patients from the hospital have been issued (NCRP, 1970; 1995; NRC, 1994a; 1994b) For radioiodine therapy patients these guidelines consider the poten- tial exposure to family members and members of the public from the discharged patient and provide guidelines for the patient to minimize exposure to family members and members of the public

released radioiodine patients ranging from 1.7 p,Gy d-l to 1.3 mGy d-'

and thyroid dose equivalents from uptake by family members that ranged from 0.04 mGy to 13.3 mGy Federal regulations (NRC,

residual activity is below 1,110 MBq However, a proposed change

and eliminates the 1,110 MBq criteria (NRC, 1994b) Although the regulations indicate the patient can be released a t or below these levels, they do not say that the patient must be released a t this level The nuclear medicine physician should consider the home situation,

i.e., the exposure of family members after the patient is released and the radiation safety precautions to be issued to the patient upon discharge [see NCRP Commentary No 11 (NCRP, 1995) for further information]

6.3 Dosage Calibrations

The activity of radiopharmaceuticals must be measured prior to administration to the patient This is done i n a dosage calibrator by removing the syringe containing the dosage from its syringe shield and placingit in the chamber ofthe calibrator The calibrator controls are set to the radionuclide involved and the activity is shown andl

or printed out automatically The unshielded syringe is then removed from the chamber and replaced in the syringe shield Gloves should

be worn to avoid contaminating hands if the syringe is handled directly Tongs should be used to both place and remove the syringe

to avoid excessive exposure

Also, the dosage calibrator must be periodically calibrated (NRC, 1987) and checked daily with reference sources These reference

30 6 RADIOPHARMACEUTICAL HANDLING PROCEDURES

sources should be shielded when not in use and handled with tongs

to minimize exposure

6.4 Radiopharmaceutical Administration

Care must be taken during dosage administration to prevent con- tamination and undue exposure A dosage administration area is usually set aside in the nuclear medicine clinic for those patients who are ambulatory For those patients who are not ambulatory, the dosage is administered to the patient on the gurney, or on the imaging table, or in their hospital room if the study requires appre- ciable delays before imaging In order to minimize exposure, the radiopharmaceutical should be taken to the patient in a shielded syringe in a lead transport container Both the dosage administration area and the technologist's hands should be monitored for contami- nation immediately after administration of the radiopharmaceutical Any radioactive waste that is generated during the dosage adminis- tration process, including the empty syringe, should be put into a shielded radioactive waste container (See Section 6.6 for procedures

to follow if contamination is detected.)

6.5 Imaging

Most imaging is performed in the nuclear medicine department However, for certain patients, such as those in intensive care units,

t h e imaging is performed i n t h e patient's room using portable

imaging systems Following injection, the patient is a source of exter-

nal exposure and, during imaging, individuals should maintain a reasonable distance from the patient Radiation exposure rates a t the edge of imaging tables have been measured a s 0.2 mGy h-l from 59.2 MBq 'OIT1 chloride, 0.015 mGy h-' from 185 MBq 99mTc HSA (human serum albumin) and 0.025 mGy h-I from 740 MBq 99mTc MDP

(Syed et al., 1982)

6.6 Contamination Control

Numerous studies (Barrall and Smith, 1976; Crawford et al., 1992; Early, 1987; Jackson and MacIntyre, 1979; Luckett and Stotler, 1980; Miller et al., 1979; Nishiyama and Lukes, 1982; Nishiyama

6.6 CONTAMINATION CONTROL 1 31

et al., 1980; Serrano et al., 1991) have indicated significant potential for contamination of air, surfaces and personnel as a result of nuclear medicine practices These findings re-emphasize the importance of conducting such activities in a manner that minimizes the potential for contamination, detects and removes contamination immediately when it happens, and identifies effective methods to prevent or mini- mize the possibility of a recurrence

Routine and frequent monitoring of all activities that can lead

to contamination is essential There are three areas that require particular attention:

1 Air Exposure to airborne contamination from procedures, such

as radioiodine diagnosis and therapy, the use of aerosols and the use of radioactive inert gases can lead to intake and expo- sure Each of these procedures must be carefully evaluated to ensure that the risk of exposure is minimal The procedures used by personnel should be routinely evaluated to identify slippage or inadvertent change from good safety practice (NRC, 1987; 1992b) Deficiencies should be corrected immediately Incidents that lead to contamination or exposure should be investigated and corrected immediately and evaluated to see

if changes can be made that will minimize the likelihood of recurrence

2 Surfaces Surface contamination can occur easily and unexpect- edly in nuclear medicine Areas such as those used for dosage preparation, calibration and administration routinely become contaminated and require frequent radiation protection sur- veys (NRC, 1987) Other areas such as imaging rooms, waste storage areas, patient waiting areas and corridors also need to

be monitored routinely The areas with a high potential for contamination should be surveyed for contamination after each procedure that could lead to contamination and at the end of each day Areas with lower potential for contamination can be surveyed after each procedure or on a weekly basis In general, the frequency with which contamination is found will indicate the frequency of required surveying

3 Personnel Contamination of personnel employed in nuclear

medicine can occur frequently and unexpectedly Although the hands are the most likely area to become contaminated, any part of the body and the clothing is a t risk Skin contamination can lead to external exposures, and can be a source of internal exposure through ingestion and skin absorption (Miller et al., 1985) Therefore, monitoring of the hands after each radionu- clide handling procedure is a necessary radiation safety practice

32 1 6 RADIOPHARMACEUTICAL HANDLING PROCEDURES

(NRC, 1987) The remainder of the body, including shoes, should

be monitored frequently and especially before leaving t h e nuclear medicine area

Prompt attention must be given to any incident that leads to contamination in nuclear medicine so that corrective procedures can

be instituted and personnel exposure evaluations can be performed

In the event that such contamination could have led to internal contamination, appropriate bioassay should be performed to assess the internal dose (NCRP, 1987b; NRC, 1991)

6.7 Misadministration

The misadministration of radiopharmaceuticals to patients causes unnecessary exposure and subjects the patient to risk of injury, especially in the case of therapeutic misadministration The misad- ministration rate in nuclear medicine is low, approximately 1 per 10,000 procedures (NCRP, 1991) I t has been estimated that diagnos- tic misadministration represented less than 0.04 percent of the total effective dose of 32,100 person-Sv for all diagnostic nuclear medicine procedures performed in 1982 (NCRP, 1991) When amisadministra- tion occurs, an immediate investigation should be initiated to dis- cover the cause, to estimate the dose, to take the steps necessary to prevent its recurrence, and to provide appropriate counseling of the patient and the patient's referring physician Recent NRC regula- tions have redefined the term "misadministration" and have added

a new classification, "recordable event" (NRC, 1992a)

6.8 Safety Considerations with Nursing Mothers

Various radionuclides, including most used i n nuclear medi- cine practice, will concentrate i n t h e milk of lactating females

(Assimakopoulos et al., 1989; Dydek and Blue, 1988; Gattavecchia

et al., 1989; Hedrick et al., 1986; 1989; Mountford et al., 1984; NCRP, 1994; Ogunleye, 1983; Pittard et al., 1982; Romney et al., 1989; Rubow and Klopper, 1988; Rumble et al., 1978; Sharma et al., 1984;

Siddiqui, 1979) The length of time that this source of radioactivity poses an exposure potential for a nursing infant depends on the effective half-life of the radiopharmaceutical The chemical form and the radionuclide should be taken into consideration by the nuclear medicine physician i n counseling the nursing mother With ""Tc

6.9 RADIOACTIVE WASTE DISPOSAL 1 33

tagged compounds, breast feeding can usually resume within a few to 72 h ; whereas, with therapeutic radionuclides, such a s

"P and 1311 the period is extensive and might warrant cessation

of nursing

In addition to the exposure potential from radionuclides excreted

in milk, there exists a potential for exposure to infants held in close contact with a patient who has undergone a nuclear medicine proce- dure (Mountford, 1987; Mountford et al., 1991; NCRP, 1994) This exposure pathway is especially important for patients who have been administered therapeutic dosages The nuclear medicine physician should consider this contact dose potential when counseling the patient Because evidence suggests that infants may be somewhat more sensitive to radiation t h a n adults, radionuclide therapy patients should be counseled to take a conservative approach in handling or interacting with infants (NCRP, 1993b; 1994) [See NCRP Commentary No 9 (NCRP, 1994) for a discussion on protect- ing the embryo, fetus or nursing child.]

6.9 Radioactive Waste Disposal

Nuclear medicine departments generate low-level radioactive waste, mostly of the dry type, in the form of empty vials, syringes, disposable gloves, absorbent paper, gauze pads, items from therapy patient care (bed linens, disposable eating utensils, etc.), partially decayed radioactive markers, and other standard calibration and check sources Disposal of this radioactive waste is usually accom- plished by one of four different routes, depending on the facility's capacity for waste storage:

sources are often r e t u n e d to the vendor for disposal Many regional radiopharmacies have also agreed to accept radioactive unit dose syringes and multidose vials from their customers on

a daily basis

levels in a reasonably short period of time, usually less than

2 y, can be allowed to decay in storage for a minimum of 10 half- lives where space permits Prior to disposal a s normal trash, the radioactive status of the waste must be determined to ascertain that it is indistinguishable from background with a n appro- priate survey instrument, and all radioactive material labels must be removed or obliterated

34 / 6 RADIOPHARMACEUTICAL HANDLING PROCEDURES

3 Transfer to a licensed low-level radioactive waste disposal facil-

items that have half-lives beyond those that can conveniently

be stored for decay should be transferred to a licensed facility

Radioactive wastes must be collected in containers that are clearly labeled and kept in areas where they are secure and adequately shielded Housekeeping staff must be trained to identify such con- tainers readily and instructed not to empty them inadvertently with the normal trash