ARTMENT OF

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NBS TECHNICAL NOTE 791

Dose Calibrator

Pilot Study
NATIONAL BUREAU OF STANDARDS

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Dose Calibrator Pilot Study

S. B. Garfinkel

Applied Radiation Division

Institute for Basic Standards

National Bureau of Standards Washington, D.C. 20234

G. J. Hine

Veterans Administration

Central Office Washington, D.C. 20420

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U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued August 1973
National Bureau of Standards Technical Note 791

Nat. Bur. Stand. (U.S.), Tech. Note 791, 7 pages (Aug. 1973) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 0.13.46:791). Price $0.30
DOSE CALIBRATOR PILOT STUDY

S. B. Garfinkel and G. J. Hine

Results of measurements of six sources in dose

calibrators used in nuclear medicine facilities

at eight hospitals in the Washington metropolitan

area are given.

Key words; Dose calibrators; indium-113m; molybdenum-99;

nuclear medicine; radiopharmaceuticals; technetium- 9 9m; tin-113.

The radionuclide dose calibrator is an instrument which has become

very important in the assay of radiopharmaceuticals in the clinical

nuclear-medicine laboratory. It is particularly useful for measurements

of 6.0-hour technetium-99m and 104-minute indium-113m, wide availability

of which is made possible by the use of "generators", ion-exchange

columns charged with 66.7-hour mclybdenum-99 or 118-day tin-113 (parents

of the above-named short-lived radionuclides). The dose calibrator is

also used for the assay of many of the other frequently used radiopharmaceuticals. The instrument is composed of an ionization chamber with

a re-entrant well, and an electronic current measuring device, the readout of which is usually of the digital type.

The electronic circuits are designed so that no calculations are required by the operator. Depending on the type of instrument, he

(1) selects a switch position which corresponds to the

particular radionuclide being measured,

(2) sets a multi-turn potentiometer (with a digital-type

dial), or

(3) plugs into the instrument a small module (which actually

contains only a resistor) identified for a given radionuclide.

After having performed one of the above operations, the radioactive sample is placed into the ionization chamber, and the activity,

in micro- or millicuries is displayed on the readout, in a matter of

seconds.

It was considered useful to conduct a pilot study of dose

calibrators that are currently in use in nuclear-medicine facilities

at 8 hospitals in the Washington, D. C., area. Arrangements were made

with the personnel at these laboratories and all measurements were made

on June 2, 1971.

Late Assistant Section Chief, Radioactivity Section, National Bureau of

^Standards, Washington, D. C. 20234

Veterans Administration, Central Office, Washington, D. C. 20420

1
Six sources were used in the study, five of which had been

calibrated at the National Bureau of Standards beforehand. The sixth,

technetium-99m, was obtained at the first hospital visited, and then

calibrated at the National Bureau of Standards on the following day.

Five of the hospitals (D, E, F, G, and H) had instruments made by

the same manufacturer and designated as type "d". Hospital H had a newer version (d-^). Hospitals A, B, and C had instruments made by three

other manufacturers.

The results of the measurements are presented in table 1. The

first five entries in column one identify the National Bureau of

Standards' sources with their respective activities in parentheses

(micrograms for radium, microcuries or millicuries for the four other

sources). The technetium- 9 9m source was 10.8 millicuries at the start

of the day. The second set of data for this same source is given to

show the scale-factor errors on those instruments which have an additional "99mTc x iqii switch position (as most instruments do, but for

^Tc only). It is also interesting to note the small extent of the

nonlinearity (with activity) in the instruments as shown by the differences in the measurements of the two radium-226 sources.

Six of the hospitals had reference sources which are supposed to be

used in conjunction with a calibration-adjustment circuit to correct for

gain changes in the electronics. The entries in the "Hospital-reference

correction factor" row in table 1, show that in hospitals A and G, instruments were out of adjustment by +6.8 and -5.3 percent respectively.

We made no adjustments to the equipment and so the ratio in the first row for each sample reflects differences in the results obtained with

the various instruments used. These differences are possibly due to

initial poor calibration by the manufacturer which should, however, have

been detected by the day-to-day quality-control procedures. The ratio

in the second row for each sample has been calculated to show the relationship of the instrument's reading to that of the National Bureau of

Standards ' value, after having taken into account the reading of the

local reference source.

7 9 fi The unadjusted results, with the exception of those for Ra for

Hospitals A and C, are within +97c to -11% of the NBS values, and the

adjusted results are within +107o to -157 ; adjustment to 407o of the data

showed increased divergence indicating, perhaps, the presence of impurities leading to different instrument response with time, or possibly

that initial reference standard calibrations were in error. This, con- sidering the state of the art and the needs of nuclear medicine

laboratories, is not too unsatisfactory. However, it would appear,

that the development of calibration sources compatible with these

instruments, which would enable the user either to generate his own calibration settings or to correct for instabilities, would be desirable.
From the point of view of simplicity of operation, instrument

type "d" is probably preferable, since it is quickest to set up for

a given radionuclide (it has a 15-position switch; each position

unambiguously labeled). But its accuracy and stability depend, among

other things, on the correct value and quality of the fixed resistors

wired to the switch. If the manufacturer has, for example, not used

an accurate radioactivity standard for a given radionuclide when he

assembled the circuitry, then it is quite inconvenient to change the

appropriate resistors should he find that the instruments in the field

need recalibrating. He can, of course, notify all owners to correct

readings for the given radionuclide by some factor, but this negates

the advantage of having a direct-reading of the activity.

In the case of instrument types "a" and "b" which utilize the

multi-turn digital dial, the recalibration is obviously much easier to achieve. The manufacturer simply notifies his customers to use dial

setting "427" instead of the previously recommended "410" for radionuclide X. Note that these instruments require the operator to read,

from a chart, a different number setting corresponding to each radionuclide. This is considered inconvenient and more subject to error

than types "c" and "d".

which employs the modules, combines advantages

of both. The modules are easily replaced by the manufacturer should

recalibration be necessary, but module insertion and removal are not

as convenient as a multiposition switch.

Since these instruments are used in hospitals, medical laboratories

and research centers throughout the world, it would be advantageous to examine more thoroughly certain characteristics of the different models,

such as stability, linearity, accuracy, geometry effects, temperaturepressure-humidity effects, variation of the time constant, etc. The

development of calibration sources compatible with these instruments

should also be given high priority.
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U.S. GOVERNMENT PRINTING OFFICE: 1973— S42-648/14
form NBS-114A (1-71) 2. Gov't Accession No.

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-791

3. Recipient's Accession Nc

4. TITLE AND SUBTITLE

Dose Calibrator Pilot Study

5. Publication Date August 1973

6. Performing Organization Code

7. AUTHOR(S)

S. B. Garfinkel and G. J. Hine

8. Performing Organization

10. Project/Task/Work Unit No. 2430212

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as No. 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES The work described herein was done at the suggestion of NSI subcommittee N44-3, Nuclear

Medicine, because of the widespread use of dose calibrators in the assay of radiophar

maceuticals in clinical nuclear medicine laboratories

16. ABSTRACT (A 200-word or less factual summaty of most significant information. If document includes a significant bibliography or literature survey, mention it here.)

Results of measurements of six sources in dose calibrators used in nuclear medicine

facilities at eight hospitals in the Washington metropolitan area are given.

17. KEY WORDS (Alphabetical order, separated by semicolons) Dose calibrators; indium-113m; molybdenum-99; nuclear medicine; radiopharmaceuticals;

technetium-99m; tin-113.

18. AVAILABILITY STATEMENT

ryi UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

7

22. Price 30 cents

U5COMM-DC 6624Z.P71

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