Information Notice No. 93-10: Dose Calibrator Quality Control

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                              February 2, 1993

Information Notice No. 93-10:  DOSE CALIBRATOR QUALITY CONTROL


All Nuclear Regulatory Commission medical licensees.


This notice is provided to alert recipients to problems concerning dose
calibrator quality control tests, identified by NRC inspectors during
inspections of medical programs, and also to emphasize the importance of
quality control procedures for equipment used to assay patient doses.  It is
expected that licensees will:  review this information for applicability to
their programs; distribute this notice to those responsible for radiation
safety and medical quality assurance, including technologists; and consider
actions to preclude similar situations from occurring at their facilities. 
However, the suggestions contained in this notice do not constitute any new
NRC requirements, and no written response is required.  

Description of Circumstances

During recent NRC inspections of medical facilities, inspectors found
deficiencies and irregularities in the performance and recording of dose
calibrator quality control tests.  The most frequently occurring deficiencies
involve the constancy checks and linearity tests.  However, there have also
been citations for failure to perform accuracy tests and determine geometric
independence.  In some instances, the licensee did identify a malfunctioning
dose calibrator, but no corrective action was taken even though the error or
deviation exceeded allowable limits.  Other problems included:  failure to
instruct supervised individuals in the proper use of the dose calibrator;
failure to perform constancy checks when emergencies required the dose
calibrator to be used during non-routine periods such as weekends and
holidays; and failure to analyze the data, as required.  


Quality control checks of dose calibrators used to assay patient dosages are
essential to ensure that the dosage administered to a patient is the same as
the prescribed dosage.  Medical personnel administering dosages should be
aware of the applicable NRC regulations (10 CFR 35.50) and any specific
related license conditions.  Licensees are encouraged in Regulatory Guide
10.8, Rev. 2, to develop procedures that provide an even higher level of
confidence that the correct dosage is administered.  For example, Regulatory
Guide 10.8, provides a model procedure for meeting the requirement.  The guide
proposes a smaller percent deviation as a trigger level, so the licensee can 


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take action before the regulatory limit is reached.  However, if it committed
to the regulatory guide procedures as part of a license application, the
licensee must comply with the more restrictive requirement.  Licensees are
responsible for the instruction and supervision of individuals to ensure that
they know and follow the proper procedures for dose calibrator checks.  

1.  Constancy Checks

Constancy means reproducibility in measuring the activity of a known source
over a long period of time.  The dose calibrator is required 
(10 CFR 35.50(b)(1)) to be checked for constancy with a dedicated check source
at the beginning of each day of use.  This includes weekends and holidays, if
radiopharmaceuticals are administered to a patient.  During recent NRC
inspections, inspectors determined that licensees had failed to perform these
required checks because part-time technologists who worked only on weekends or
staff technologists called in on weekends had not been properly instructed by
the licensee and did not know that these checks were to be performed on

The reference source used for the constancy check must be assayed at a
frequently used setting.  Regulatory Guide 10.8 suggests using two or more
sources with different photon energies and activities, although one source
meets the requirement.  The rule requires that the licensee determine the
constancy of the dose calibrator under an actual condition of use.  Since most
medical licensees use technetium-99m for patient-dosage administrations more
frequently than any other isotope, such licensees should check the technetium-
99m setting, on each day of use, with a dedicated check source.  It is
recommended that dose calibrators having both pre-adjusted controls (i.e.,
push buttons) and variable potentiometers be tested on both the variable
potentiometer technetium-99m (or other frequently used isotope) setting and
the pre-adjusted control.   Discrepancies or fluctuations between the two
controls, when tested for constancy with the same check source, may be
indicative of equipment malfunction.  Licensees must plot or log 
(10 CFR 35.50(e)(1)) the measured activity of each source and compare it to
the calculated activity, based on decay of the dedicated check source.  If the
error between the two values exceeds 10 percent, the dose calibrator must be
repaired or replaced (10 CFR 35.50(d)).

2.  Accuracy Test

The accuracy test ensures that the activity is within 10 percent of a given
calibrated reference source whose activity has been determined by the
manufacturer to be within 5 percent of the activity stated by the National
Institute of Standards and Technology (NIST) or by the supplier who has
compared that source to a source that was calibrated by NIST.  At least two
sealed sources with different principal photon energies, one of which has a
principal energy between 100 keV and 500 keV, must be used to determine
accuracy upon installation, and at least annually thereafter 
(10 CFR 35.50(b)(2)).  The regulations require that the activity is at least
10 �Ci for Ra-226 and 50 �Ci for any other photon-emitting radionuclide.  For
best accuracy, the lower energy reference standards should be in vials of
similar thickness to those for actual samples.  As with the constancy check 

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and linearity tests, Regulatory Guide 10.8 suggests a trigger level of 
5 percent difference but the requirement states that if the error exceeds 
10 percent then the dose calibrator must be repaired or replaced.

3.  Linearity Tests

The linearity test ensures that the dose calibrator can indicate the correct
activity over the range of use between the highest dose that will be
administered to a patient and 10 microcuries.  The dose calibrator is to be
tested for linearity upon installation and at least quarterly thereafter 
(10 CFR 35.50(b)(3)).  Licensees have frequently not determined linearity over
the entire range of use.  Technetium-99m is most frequently used for the
linearity test because of its availability and short half-life, and it is
relatively inexpensive.  If the percent deviation exceeds 10 percent, dosage
readings must be mathematically corrected.  Regulatory Guide 10.8 suggests a
trigger level of +5 percent but unless the licensee commits to this level in
the license application, the requirement allows for a 10 percent variation.  

4.  Geometry Dependence

Testing for geometry independence ensures that the indicated activity does not
change with volume or configuration.  This test must be performed, upon
installation, over the range of volumes and volume configurations for which it
will be used (10 CFR 35.50(b)(4)) and, as suggested in Regulatory Guide 10.8,
should be done using a syringe that is normally used for injections. 
Licensees who use generators and radiopharmaceutical kits should also do the
test using a vial similar in size, shape, and construction to the
radiopharmaceutical kit vials normally used.  Geometry testing performed by
the manufacturer may be acceptable, provided that the manufacturer has
included all volumes and volume configurations for which the dose calibrator
will be used at the licensee's facility and the licensee keeps a record of
this test.  

Licensees are also required (10 CFR 35.50(c)) to perform appropriate checks
and tests following adjustment (e.g., a constancy check after battery
replacement) or repair of the dose calibrator.  Whereas it is not necessary to
check geometry dependence if the dose calibrator is physically relocated
within the department or following minor repairs to the instrument panel, it
is appropriate to do the geometry check if repairs are done that might affect
the response of the chamber.  It is appropriate to conduct linearity and
accuracy tests following any repairs to the dose calibrator.  

It is the responsibility of the Radiation Safety Officer (RSO) and Radiation
Safety Committee (RSC) to ensure that these checks are performed.  Licensees
are reminded that 10 CFR 35.21 requires that an RSO be responsible for
implementing the radiation safety program and ensuring that radiation safety
activities are being performed in accordance with approved procedures and
regulatory requirements in the daily operation of the licensee's byproduct
material program.  In addition, 10 CFR 35.22 requires that an RSC perform
periodic reviews, to oversee the use of byproduct material. 

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No written response is required by this information notice.  If you have any
questions about this matter, please contact the appropriate NRC regional
office or this office.  

                                               ORIGINAL SIGNED BY

                                          Richard E. Cunningham, Director
                                          Division of Industrial and
                                            Medical Nuclear Safety
                                          Office of Nuclear Material 
                                            Safety and Safeguards

Technical contact:  Patricia K. Holahan, NMSS
                    (301) 504-2694

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