Rejected eluate, failed MDP kit, and a pediatric bone scan booked in two hours

No dose from this eluate or this kit may be given. All three results fail.

Test	Result	Limit	Verdict
Mo-99 breakthrough	0.19 microCi/mCi	0.15 microCi/mCi (0.15 kBq/MBq)	Fail
Al3+ breakthrough	12 microg/mL	10 microg/mL	Fail
MDP radiochemical purity	87%	at least 90%	Fail

Why each matters:

• Mo-99 has a 66 h half-life versus 6 h for Tc-99m, so its relative contribution grows with time since the last elution. It delivers high-energy beta and gamma emissions that raise patient dose and degrade image quality, and it is a reportable failure.
• Aluminum causes flocculation and particle aggregation in diphosphonate kits, with altered biodistribution (reduced bone uptake, hepatic or pulmonary activity) and inconsistent labeling.
• RCP of 87% means excess free pertechnetate: thyroid, salivary, gastric and renal activity that degrades a bone scan and adds unnecessary dose.

The 'only slightly over' argument is exactly the reasoning that produces a reportable event. Before accepting the numbers, though, confirm them: assay geometry (a 5 mL vial versus a 1 mL standard can bias the result), the correct Mo-99 setting and shield attenuation correction, and the age of the chromatography strip. Repeating the tests takes 20 minutes; injecting a failing eluate cannot be undone.

Root cause. A 63-hour weekend ingrowth period on a 6-day-old generator is the classic setting for breakthrough: eluate that sits allows Mo-99 to accumulate relative to Tc-99m, and a loaded column sheds aluminum. The three failures are probably linked - a degraded column/eluate produces both breakthrough and poor labeling.

A key point: re-eluting this generator will not fix it. Because Tc-99m decays faster than Mo-99, a second elution drawn shortly afterward has an even higher Mo-99/Tc-99m ratio. The generator is unusable until the Mo-99 has decayed (roughly 2 weeks), or must be replaced.

Actions:

1. Quarantine the bulk eluate and the MDP kit; label them 'do not use'; segregate the waste.
2. Document the event per your licensee's written procedures and notify the RSO and the generator vendor.
3. Verify the backup generator's own Mo-99, aluminum and RCP before use - do not assume it is good.
4. Re-sequence the day: start the six adults at 10:00 with the backup eluate; consider moving the pediatric patient to the sister site or later in the day rather than cancelling, since she has osteosarcoma and the study affects staging.
5. Debrief: Monday-morning elution should be scheduled and assayed with enough lead time to source an alternative, and weekend elution policy should be reviewed.

Backup eluate: 260 mCi in 4.0 mL at 08:30 (Tc-99m half-life 6.02 h; decay factor 0.5^(t/6.02)).

Adult dose, 25 mCi at 10:00 (1.5 h after assay): 260 x 0.5^(1.5/6.02) = 260 x 0.841 = 219 mCi in 4.0 mL = 54.7 mCi/mL, so 25/54.7 = 0.46 mL.

Pediatric dose, 9.0 mCi at 11:00 (2.5 h after assay): 260 x 0.5^(2.5/6.02) = 260 x 0.750 = 195 mCi in 4.0 mL = 48.8 mCi/mL, so 9.0/48.8 = 0.18 mL.

Practical issues:

• A 0.18 mL volume is hard to measure accurately; dilute the aliquot or use a 1 mL syringe with a syringe shield and have a second technologist verify.
• Activity is not the constraint; concentration late in the day is. Six adults at 25 mCi plus 9 mCi at 11:00 is about 159 mCi drawn by 11:00 from 195 mCi remaining, which works but leaves little margin. Draw the later adult doses last, or plan a second elution of the fresh generator in the afternoon.
• Question the prescription: 9.0 mCi for a 7-year-old of about 23 kg is roughly 0.39 mCi/kg, close to double the usual pediatric weight-based activity (about 0.2 mCi/kg, with a minimum activity). Confirm with the ordering physician before injecting - a low-activity pediatric bone scan with poor count statistics is a preventable repeat study.