Leak Test Failure on a Sealed Source
A nuclear medicine department uses a 1.85 GBq (50 mCi) Co-57 flood source for daily uniformity checks. The quarterly wipe test shows 2,000 Bq of removable contamination on the source housing, above the 185 Bq limit. The technologist wipes the source, repeats the test, and gets 150 Bq. She wants to return the source to service. A patient was imaged the same morning with the same camera. The RSO must decide whether to (a) return the source to service, (b) take the source out of service and investigate, or (c) notify the regulator and survey personnel.
1. What is the significance of the initial 2,000 Bq wipe result and what should be done?
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A removable contamination level of 2,000 Bq on a sealed source exceeds the 185 Bq (5 nCi) limit and indicates the source has failed the leak test. The source must be removed from service and not used until it is decontaminated and re-tested, or disposed of. The fact that a repeat wipe after cleaning gives 150 Bq does not automatically clear it: the first wipe may have removed the loose contamination, but the source may still be leaking. The RSO should (1) take the source out of service, (2) survey the camera, the room, and personnel for contamination, (3) perform a second independent wipe test after a suitable interval to confirm it is not a false positive or a continuing leak, (4) document. If the source is confirmed leaking, it must be removed from service and the regulator notified per the license.
2. What about the patient imaged that morning and the personnel?
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The patient was imaged with a flood source used for uniformity, not administered the source, so the patient is not contaminated. The concern is contamination of the camera and the room. The RSO should survey the camera head, collimator, and floor, and check personnel with a survey meter and wipe tests. If contamination is found, decontaminate and re-survey. The RSO should also review whether the source was used before the leak test result was known and document the investigation. Notification to the regulator is required if the source is confirmed leaking; the RSO should follow the license condition and the state's reporting requirements.