A SINGLE DOSE CALIBRATOR
DIAL SETTING ACCURATELY MEASURES Y-90 IBRITUMOMAB TIUXETAN ACTIVY.
J.A. Siegel*, B.E. Zimmerman, K.
Kodimer, M.A. Dell, W.E. Simon, President & CEO, Nuclear Physics
Enterprises, Cherry Hill, NJ; National Institute of Standards and
Technology, Gaithersburg, MD; Syncor International Corporation, Woodland
Hills, CA; Capintec, Inc., Ramsey, NJ; Sun Nuclear Corporation, Melbourne,
Accurate dose calibrator activity measurement of pure
beta-emitting radionuclides is potentially a challenge for all Nuclear
Regulatory Commission and Agreement State licenses. This investigation
examined the potential use of a single dose calibrator dial setting for
activity measurement of the beta-emitting radionuclide Y-90 and the
necessity for volume correction factors when measuring activity
prescriptions for Y-90 ibritumomab tiuxetan, A U.S. Food and Drug
Administration approved agent for the treatment of non-Hodgkin’s lymphoma.
Y-90 ibritumomab tiuxetan is supplied to medical facilities from a
commercial radiopharmacy as a unit dosage in a 10 cc syringe up to a maximum
activity of 1184 MBq (32 mCi) in volumes ranging from 3 to 9 cc, dependent
upon the required activity prescription for an individual patient.
measurements of either Y-90 ibritumomab tiuxetan or Y-90 in saline were
independently made in the 10 cc syringe geometry with 31 dose calibrators at
four different facilities (Capintec, National Institute of standards and
Technology, Sun Nuclear, and Syncor) with activity ranging from 81.4 MBq
(2.2 mCi) to 1184 MBq (32 mCi) over the volume range of 3 cc to 9 cc.
Different dose calibrator models of the pressurized argon well reentrant
design, both new and used, from three different manufacturers, Capintec,
Nuclear Associates and Sun Nuclear) were used.
Results: The accuracy of the Y-90 dose calibrator
activity measurement, using the recommended calibration setting resulting
from this study, was estimated to be better than 95.2%. The volume
dependence (i.e., volume correction factor variation) in a syringe was found
to be at most 0.21% per cc, between the range of 3 and 9 cc.
This study, conducted at four separate facilities,
demonstrated that only a single dose calibrator dial setting is required for
accurate dose calibrator measurement for all Y-90 ibritumomab tiuxetan
activity prescriptions, with no correction required for differing volumes.
Medical facilities need only to use this manufacturer-approved calibration
dial setting and simply measure and record the activity of Y-90 ibritumomab
tiuxetan, if supplied by a licenses radiopharmacy as a unit dosage,
regardless of the volume in the supplied syringe.
July 21, 2003
A TECHNICAL NOTE TO
ATOMLAB DOSE CALIBRATOR USERS, REGARDING Y-90.
The typical Atomlab Dose calibrator dial
setting for Y-90 activity in a 10 cc plastic syringe is 375. This value can
be used as a starting point for initial measurements. However, it is
recommended that the dial setting used for clinical measurements be
determined from the first dose of Zevalin received from the radiopharmacy,
as outlined below. Follow on doses should then be compared to the
radiopharmacy doses for constancy.
A sampling of Atomlab Dose Calibrators has
been tested with a NIST traceable Y-90 activity in a 10 cc plastic syringe
geometry with volumes ranging from 3-9 cc. A Dial setting range for Y-90 was
determined to be 363 to 394 for an accurate activity measurement. The
average volume dependence for this sampling of Atomlab Dose Calibrators was
determined to be 0.13%/cc, using 3, 4, 5, 6, 7, 8, and 9 cc in the 10 cc
plastic syringe. Therefore, the volume dependence is negligible and the same
dial setting can be used for all volumes as distributed by IDEC for Y-90
The Y-90 recipient, using an Atomlab dose
calibrator, should determine the correct dial value from the first Y-90 dose
that they receive from a commercial radiopharmacy. This is determined by
selecting the OTHER key and adjusting the dial setting until the displayed
activity agrees with the decay corrected Y-90 syringe activity as stated by
the commercial radiopharmacy. If the adjusted dial setting falls within the
range of 363 to 394, then use that dial setting.
If it falls outside the range, then verify
a) there is a well liner in place
b) a hook style dipper is used
c) the annual accuracy and daily constancy tests results are acceptable
If these criteria are met, then determine the
percent difference of the new dial value with respect to the nearest range
limit value (363 or 394), i.e, Dial Value Error (DVE). Add this percent to
the Change in Constancy Percent Error (CCPE). If the sum of the errors is in
the range of -2% to +2%, then the new dial value should be used. If not,
contact Biodex technical support. The user may also want to contact the
radiopharmacy to determine if a calibration error may have occurred.
(The CCPE is the percent change from
calibrator installation of the constancy measurement, where CCPE = "Today's"
Constancy Percent Error – "Installation's" Constancy Percent Error. The
Constancy Percent Error is the measurement error with respect to the decay
corrected source activity. A change down in the Atomlab calibrator constancy
will cause a change up in the dial value required to compensate the change
in constancy, and visa-a versa. Thus the CCPE will have the opposite sign as
the DVE, so adding them should cancel to within 2%.)
For example, a new dial value for Y-90 is
found to be 400. This falls outside the range and is +1.5% higher than 394.
The constancy measurement shows a -2.5% change since the dose calibrator was
installed. Their sum is (+1.5%) + (-2.5%) = -1.0%, which is within -2% and
+2%. The dial value of 400 should be used.
For all dose calibrator models, the well liner must be installed before
making measurements. The well liner provides attenuation for the Y-90 betas
that would otherwise enter the chamber and cause high readings.