The experimental basis for internal absorbed-dose calculations : recommendations of the National Council on Radiation Protection and Measurements

115 Pages·1985·4.86 MB·English

by  National Council on Radiation Protection and Measurements

NCRP REPORT No. 83
THE EXPERIMENTAL
BASIS FOR
ABSORBED-DOSE
CALCULATIONS IN
MEDICAL USES OF
RADIONUCLIDES
Recommendations of the
NATIONAL COUNCIL ON RADIATION
PROTECTION AND MEASUREMENTS
Issued September 30,1985
National Council on Radiation Protection and Measurements
7910 WOODMONT AVENUE / BE'THESDA, MD. 20814
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Library of Congress Cataloging in Publication Data
National Council on Radiation Protection and Measurements.
The experimental basis for absorbed dose calculations in medical uses of radionuclides.
(NCRP report ; no. 83)
"Issued September 30, 1985."
Bibliography: p.
Includes index.
1. Nuclear medicine-Statistical methods-Evaluation. 2. Radiation dosimetry-
Evaluation. I. Title. 11. Series.
R905.N38 1985 616.07'57 85-7292
ISBN 0-913392-76-6
Copyright 0 National Council on Radiation
Protection and Measurements 1985
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may be reproduced in any form or by any means, including photocopying, or utilized by
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Preface
This report reviews the status of the methods used to estimate the
radiation absorbed doses to humans from internally deposited radio-
nuclides with the emphasis on medical applications.
Interest in and concern about internally distributed radioactive
substances is not new. Most of the attention in this area has been
directed to the problem of occupational exposure with lesser attention
given to fallout and environmental exposure resulting from facilities
using radioactivity. However, the proliferation of nuclear medicine
procedures has resulted in human exposure from a variety of radio-
pharmaceuticals to an increasingly large segment of the population.
The internal emitter exposure may be for therapeutic or diagnostic
applications. In the diagnostic situation, the upper limit of the amount
of radioactivity to be administered must be determined from the
radiation dose estimate. In the therapeutic situation, not only must
the radiation dose necessary for the desired effect be determined, but
the incidental irradiation of other organs must be considered. It is no
longer satisfactory to provide radiation dose estimates for the critical
organ and whole body only, but estimates of the radiation dose to the
eye, the gonads, the bloodforming organs, and other organs may be
needed.
In this report, the emphasis is placed on comparing the results of
direct measurements with calculations based on mathematical models
used to estimate the parameters that enter into dose calculations.
Methods are suggested which may be used to obtain good data.
The history of internal radiation dosimetry is reviewed and the
physical parameters and transport calculations of dosimetry are dis-
cussed. Also discussed are the techniques used to measure the activity
distributions in humans, and the factors which should be considered
in making in-uiuoa bsorbed dose measurements. Comparisons of rneas-
ured and calculated absorbed dose values in phantom animals and
humans are made.
A formalism is included that can be used to quantify the radioactiv-
ity in irregular geometric shapes using an external measurement
technique. Recommendations for further studies are also given.
This report was prepared by Scientific Committee 55 on Experi-
...
111
iv / PREFACE
mental Verification of Internal Absorbed Dose Calculations. Sewing
on the Committee were:
James S. Robertson, Chairman
Department of Energy
Washington, D.C.
Martin J. Berger John W. Poston
National Bureau of Standards Texas A and M
Washington, D.C. College Station, Texas
Jerry P. Jones Kenneth N. Vanek
Ochsner Medical Institutions USAF Medical Center
New Orleans, Louisiana Keesler Air Force Base
Mississippi
Katherine A. Lathrop Robert G. Zamenhof
University of Chicago Tufts New England Medical Center
Chicago, Illinois Boston, Massachusetts
NCRP Secretariut, Thomas Fearon
James T. Walker
E. Ivan White
The Council wishes to express its appreciation to the Committee
members for the time and effort devoted to the preparation of this
report.
Warren K. Sinclair
President, NCRP
Bethesda, Maryland
March 15, 1985
Contents
Preface ...............................................
.
1 Introduction .......................................
1.1 Statement of the Problem ......................
1.2 Purpose and Scope .............................
.
2 Radiation Dose Calculation Methods ................
2.1 Historical Developments .......................
2.2 The Marinelli Method .........................
2.3 TheMIRDMethod .............................
2.3.1 The Loevinger-Berman Formalism '..........
2.3.2 The Ellett-Brownell Absorbed Fraction
Calculations ..............................
2.3.3 Snyder's System of Dosimetry Calculations ...
.
3 Physical Parameters and Transport Calculations in
Dosimetry .........................................
3.1 Radioactive Decay Data .......................
3.2 Gamma-Ray Absorbed Fraction Calculations ...
3.3 Beta-Particle Absorbed Fraction Calculations . .
3.4 Beta-Ray and Electron Dosimetry in Bone ......
3.5 Anthropomorphic Factors ......................
3.6 Modeling .....................................
.
4 In-Vivo Measurements of Radioactivity .............
4.1 Introduction ...................................
4.2 Area Measurements ...........................
4.3 Transverse Section Imaging ...................
4.4 Summary .....................................
.
5 In-Vivo Measurement of Absorbed Dose .............
5.1 Introduction ...................................
5.2 General Requirements .........................
5.3 Dose and Detector Response ...................
5.4 An Example Experiment .......................
5.5 Human Dose Measurements ....................
.
6 Comparison of Measured and Calculated Dose Values
6.1 Absorbed Dose in Phantoms ....................
6.2 Extrapolation of Biokinetic Data from Labora-
tory Animals to Human Beings ...............
i / CONTENTS
6.3 Absorbed Dose in Animals .....................
6.4 Absorbed Dose in Human Beings ...............
.
7 Summary and Conclusions ..........................
.
8 Recommendations ..................................
APPENDIX A: Formalism for the Quantification of Radio-
activity in Irregular Geometric Shapes US-
ing External Measurements ...............
A.l Introduction ...................................
A.2 Assumptions ...................................
A.3 Single Detector Formalism .....................
A.4 Opposed Detector Formalism ...................
A.6 Comparison of Estimated and True Activity ....
A.6 Uniform Source and Exponential Attenuation . .
A.7 Non-Uniform Activity Distributions ............
A.8 Final Remarks ................................
APPENDIX B: Glossary ..................................
APPENDIX C: Symbols, Units and Conversion Factors ....
References ............................................
NCRP .................................................
NCRP Publications ......................................
Index .................................................
1. Introduction
1.1 Statement of the Problem
Concern about the possible radiation haiards from radioactive sub-
stances distributed within the human body dates from the early uses
of radium in therapy. Since the advent of atomic weapons, most of the
attention in this area has been directed to the problems of occupational
exposure and to the real or hypothetical problems posed by fallout and
other environmental sources of radioactive materials. However, the
relatively recent proliferation of nuclear medicine procedures now
adds exposure from a variety of radiopharmaceuticals to the radiation
exposures of an increasingly large segment of the population (Frost
and Sullivan, 1977; Stanford R.I., 1970). Table 1.1 lists some published
estimates of the absorbed doses for a number of current nuclear
medicine procedures. References to the original papers are given in
the review by Robertson (1982). NCRP Report No. 70 also contains
an extensive list (NCRP, 1982). While it is true that individual
radiation doses are at levels regarded as being acceptable, the concept
of radiation safety involves probabilistic considerations, and when
large populations are exposed, even very low individual radiation doses
become important considerations in assessment of potential genetic
effects and in understanding the epidemiology of cancer and congenital
malformations. In addition, multiple exposures of an individual to
small doses are presumed to be cumulative. Accurate estimates of the
radiation absorbed dose are essential for realistic appraisal of the risk-
benefit equation in such situations.
In diagnostic applications the radiation dose estimate is used in
determining the upper limit of the amount of radioactivity that may
be administered. In therapeutic applications there is not only a direct
relationship between the radiation dose and the desired effect, but the
incidental irradiation of other organs may impose restraints on the
procedure. These requirements are reflected in the regulations that
are issued by the various federal, state, and local agencies involved in
the approval of the use of radioactive chemicals in research and for
new clinical procedures. In applications for authorization for such
uses, it is no longer satisfactory to provide radiation dose estimates
1
TABL1E.1 -Radiotion absorbed doses for current nuclear medicine ~rocedures" to
Adminis- Radiation absorbed dose for listed administered activity
tered \
Procedure or organ activity Total Body M",",","W Gonads Other target organs
studies (mCi) ?'
(3.7B xa )1 0' (.01 GY) (.O(1ra Gd) ~ ) (.0(r1a GdY) ) Organ D(o.s0e1 GbaYd)) 2
4
adrenal scan 3.9 (M) adrenal 25 (normal) 8
57 (Gushing's)
IZlI NP-59 0.05 (M) adrenal 1.3 s
blood pool -TC RBC or HSA - heart 1.6 2
bone scan *Tc MDP 0.34 (F) bladder wall 8.8 0
bone marrow scan ="Tc sulfur colloid 0.08 (F) liver 5.1 Z
L13mIcno lloid - liver 4.3
brain scan *Tc DTPA 0.4 (F) bladder wall 12
-Tc glucoheptonate 0.4 renal cortex 4
cardiac infarct -Tc pyrophosphate 0.3 (F) bladder wall 4.8
"'TI chloride 0.38 (M) renal medulla 1.65
cisternogram 'Bgyb DTPA - brain surface 32
dacryoscintig- -TcOi - lens of eye 0.014
raphy
gallium scan
for tumor 67Ga citrate 2.6 5.8 2.8 (F) lower large 9
intestine
for infection d?Ga citrate 1.3 2.9 1.4 (F) lower large 4.5
intestine
kidney scan -Tc DTPA 0.22 - 0.27 (F) bladder wall 7.8
-Tc DMSA 0.08 - 0.11 (F) renal cortex 3.8
lUI Hippuran (+ 10% 0.0063 - 0.010 (F) bladder wall 0.33
la41)
13'1 Hippuran 0.0028 - 0.022 (P) bladder wall 1.6
liver scan ="Tc sulfur colloid 6 0.114 - 0.034 (F) liver 2.0
-Tc HIDA 20 0.18 - 0.28 (F) upper large 8.4
intestine
13'1 rose bengal 0.25 0.08 0.08 0.4 (F) upper large 9
intestine
lung scan lnXe gas 15 0.020 0.026 0.021 (F) lung 0.071
lSXe gas 15 0.021 0.023 0.020 (F) lung 0.165
="Tc microspheres 4 0.032 0.060 0.024 (F) lung 0.84
Meckel's scan BBmT~O; 5 0.060 0.095 0.090 (F) thyroid 1.00
thyroid scan ="TcO; 2 0.020 0.038 0.044 (F) thyroid 0.4
Iz3Ii odide 0.1 0.003 - 0.002 (F) thyroid 1.1
13'1 iodide 0.03 0.014 - 0.004 (F) thyroid 33
venogram BBmTm~ic rospheres 6
whole body scan 13'1 iodide 1.0 0.24 0.14 0.14 (F) stomach wall 1.7
(athyroid pa-
tients)
-
Abbreviations: NP-59, 6-1311-iodomethyl-19-norcholesterRoBl;C , red blood cells; HSA, human serum albumin; MDP, methylene diphos-
phonate; DTPA, diethylene triamine pentaacetic acetate; DMSA, dimercaptosuccinic acid; HIDA, N-(2,6-dimethylphenyl) carbamoylmethyl
iminodiacetic acid.
" Adapted from Robertson (1982).
4 / 1. INTRODUCTION
for the whole body and a critical organ only. Estimates of the radiation
dose to the eye, the gonads, the bloodforming organs, and other organs
may be requested (DHEW, 1978).
There are three general methods for estimating the radiation dose
in human beings. These are (1)d irect measurements, (2) extrapolation
from measured animal or phantom data, and (3) calculations based on
mathematical models. Each of these methods has its own combination
of strengths and weaknesses. In particular, radiation dose calculations
are sensitive to errors in the method used and in the biological and
physical input data.
In human beings, the direct measurement of the absorbed radiation
dose in internal organs presents severe difficulties, and very few such
measurements have actually been made. Some of the problems are
inherent in the physics of the situation. Others are shared by all
mammalian systems, but some are unique to human studies. Most
often either the locations of interest are inaccessible or the methods
that are available to gain access to the site of interest are regarded as
being too invasive to be acceptable. Even the clearly non-invasive
methods, such as external counting, encounter obstacles associated
with inconvenience or discomfort of patients.
In the absence of direct measurements, estimates of the radiation-
absorbed dose from internally distributed radionuclides in human
beings have come to depend on calculation instead of on measurement.
These calculations reflect a complex mixture of experimentally deter-
mined values and theoretical considerations. For calculation of the
radiation dose to one organ from a source of activity in another organ,
many parameters such as the radiation absorption and scattering
characteristics of intervening tissue, as well as the size and shape of
both source and target organ and the biological kinetics of the distri-
bution of the radioactive material have to be considered.
Studies with animals and phantoms are free from some of the
difficulties that are encountered in attempting to measure the radia-
tion dose parameters in human beings, but these studies have other
inherent weaknesses. To the degree that the animal models may
simulate the biochemical and physiological characteristics of human
beings, they are useful in determining some of the parameters of the
kinetics of distribution of a given radioactive substance. In extrapo-
lating such data to human beings, however, a correction for the time
scale usually must be introduced, and the scaling factor may be difficult
to determine. Anthropomorphic phantoms are useful for simulating
the spatial relationships among the body organs, but typically have no
ability to reproduce the kinetic parameters. In phantoms that are to