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, FL (652379)

Objectives: 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. Methods: Activity 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. Conclusions: 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 Zevalin.

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 that:
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.