NRC INSPECTION MANUAL NMSS/MSB
PROGRAM APPLICABILITY: 2800
01.01 To verify licensees are using appropriate calibration values for their Strontium-90 (Sr-90) ophthalmic applicators. Specifically, to verify that each licensee using Sr-90 applicators for ophthalmic radiotherapy, have in their possession either the original vendors certificate(s) of calibration for their applicator(s), or a calibration certificate from a calibration laboratory traceable to the National Institute of Standards and Technology (NIST).
01.02 To verify licensees are properly correcting their Sr-90 applicator dose rate(s), obtained from a valid source calibration, for the radioactive decay of the Sr-90 source. Licensees are expected to perform these essential corrections for radioactive decay of the source in accordance with the guidance set forth in NRC Information Notice 96-66, issued December 13, 1996.
In the past few years, the occurrence of Sr-90 eye applicator misadministrations appears to have increased (ten since 1994). These ten reports, each report representing one or more patient misadministrations, involve hundreds of patients with two of the reports involving over 50 patients with overexposure to doses twice the intended treatment doses.
A recent search of the NMED and an IMNS database for Sr-90 eye applicator misadministrations found 13 reports of misadministrations involving over 750 patients. Analysis of these reports revealed that in 3 of these reports, the cause of the misadministrations was attributed to improper calibration of the Sr-90 source and, in 6 more of the reports, the cause was attributed to either failure to correct or improperly correcting the source for radioactive decay.
Taken together these two causes account the majority of all patient misadministration reports arising from ophthalmic radiation therapies using Sr-90 ophthalmic applicators. Calibration errors due to improper source calibrations and/or improper corrections for radioactive decay frequently result in multiple patient misadministrations due to the significant periods of time that often elapses between the error and its discovery.
Since these errors are commonly made by the licensee, self discovery and subsequent correction of such errors occur infrequently. Most are discovered by either NRC inspectors or, less commonly, outside consultants to the licensee. In order to reduce the potentially adverse impact of such errors on patients, the NRC inspection process should focus on reviewing the adequacy of licensee calibration and decay correction data for licensees authorized to perform Sr-90 ophthalmic therapy.
03.01 During routine inspections for all Sr-90 ophthalmic applicator licensees authorized to perform ophthalmic therapy:
a. | Verify that the licensee has in their possession and utilize, a certificate of calibration for each Sr-90 ophthalmic applicator in their possession from either: | ||
1. | The manufacturer/vendor of the Sr-90 applicator; or, | ||
2. | a calibration laboratory with established traceability to NIST for performing Sr-90 ophthalmic applicator calibrations. | ||
b. | Confirm by independent calculation, using either equation F1 or Table 1 (given in NRC Information Notice 96-66), the adequacy of the licensee's corrections for radioactive decay of the Sr-90 source(s). |
At this time, two calibration laboratories are known to be capable of providing the required NIST traceable calibrations of Sr-90 ophthalmic applicators. They are NIST itself and the University of Wisconsin Accredited Dosimetry Calibration Laboratory.
Each region shall document its findings in the field notes.
Within 60 (sixty) calender days of the expiration of this temporary instruction, each region shall send the Office of Nuclear Material Safety and Safeguards (NMSS) the names and address of all licensees that have not been inspected in accordance with this temporary instruction and the total number of licensees inspected. For each licensee inspected, each region shall send the following information:
a. | Make and model of Sr-90 ophthalmic applicator(s) possessed by licensee; | |
b. | Source of calibration data (original vendor or NIST traceable re-calibration) and date of calibration; and, | |
c. | Confirm as to the adequacy of the licensee's corrections for radioactive decay of their Sr-90 source. |
This temporary instruction shall remain in effect until September 1, 2000.
Questions regarding this temporary instruction, particularly those relating to the adequacy of Sr-90 source calibration certificates, should be addressed to the Branch Chief, Materials Safety Branch, NMSS, at (301) 415-7231.
08.01 Organizational Responsibility. The Materials Safety Branch of the Division of Industrial and Medical Nuclear Safety (MSB/NMSS) initiated this temporary instruction.
08.02 Resource Estimate. This inspection will be performed during regularly scheduled inspections.
The estimated onsite inspection time to verify the calibration and accuracy of decay corrections is estimated to be less that 30 minutes per inspection. The time to compile the data and prepare the report for MSB/NMSS containing the final statistics regarding the calibrations and decay corrections is estimated to require less than 16 staff-hours.
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