The hot lab decides whether a nuclear medicine department runs on time. A practical guide to one-way workflow, bench shielding, dose calibrator siting, contamination control, decay storage and ventilation.
The hot lab is the smallest room in a nuclear medicine department and the one that decides whether the rest of it runs to time. A camera that images a patient in twenty minutes is worth nothing if the dose was not dispensed when the patient was ready, and the reason a dose is late is almost never the generator. It is the layout: somebody is walking across the room to reach the dose calibrator, the shielded carrier is on the wrong bench, and the previous patient's waste is still on the dispensing surface.
A hot lab is a workflow problem with radiation protection constraints attached. Design it in that order.
Everything moves one way. Clean items never cross back over dirty ones. In a room of realistic size you achieve that by dedicating surfaces and directions rather than by adding doors.
Draw that sequence on the floor plan as a line before you place any furniture. If the line crosses itself, the layout is wrong, and no amount of shielding fixes it.
Work is done seated, behind an L-block with a lead glass window, with hands kept behind the shielding and long handled forceps used to move vials. That single sentence dictates most of the furniture: bench height suited to seated work, knee space under the bench, the L-block placed so the operator looks through the glass rather than over it, and enough clear surface either side that a vial never has to be lifted over the shield.
Departments spend a long time selecting a dose calibrator and about five seconds deciding where to put it. The instrument measures the activity in its well plus whatever the room is contributing, and the room contribution changes through the day as the generator is eluted and the stock is drawn down.
The commonest error in a small hot lab is a constancy check performed with the generator standing a metre away. The background is different every morning, the constancy result wanders, and the department either chases a fault that does not exist or, more often, stops believing the check. Site the calibrator with shielding between it and the stored activity, keep that geometry fixed, and record background at the start of each session.
The test set is standard and worth writing into your procedure explicitly.
| Test | Frequency | What it establishes |
|---|---|---|
| Constancy | Every day of use | That the reading has not shifted since yesterday, measured with a long lived reference source in a fixed geometry |
| Accuracy | At the interval set in your procedure | That readings agree with certified reference sources across the range of energies you use |
| Linearity | Periodically, usually by following a decaying source | That the instrument reads correctly from the highest activity you dispense down to the lowest |
| Geometry | At installation, and after any repair | That the reading does not change with sample volume or container shape |
| Background | Each session | That the room contribution is known and subtracted rather than assumed |
Keep the reference source, its certificate and its own log together, and treat the certificate as a controlled document. An accuracy check against a source whose certificate cannot be found is not evidence of anything.
Contamination in a hot lab is normal. Undetected contamination is the failure. The distinction matters because departments sometimes treat a positive wipe as an embarrassment to be avoided, which quietly discourages people from taking wipes.
For short lived nuclides the disposal route is storage until the activity has fallen to background, followed by monitored release. That is simple in principle and goes wrong in one specific way: somebody adds a fresh item to a bin that was nearly ready for release. Label every container with the date of the last addition, not the date it was opened, and close a container to further additions once it starts its decay period.
| Waste stream | Handling | Release check |
|---|---|---|
| Sharps and used syringes | Shielded sharps container in the decay store, segregated by nuclide | Survey at contact and at distance, confirm background, record before release |
| Vials, generators and kit containers | Supplier return route where one exists, otherwise decay storage | Survey and wipe test, recorded against the item |
| Gloves, swabs and absorbent covering | Bagged, dated, sealed and stored by half life | Survey before release into the clinical waste stream |
| Liquid waste from dispensing | Dedicated sink and trap as designed, per your licence conditions | As specified in the design and licence |
| Patient toilet drainage | Routed as the design requires from the dedicated toilet | As specified in the design and licence |
Segregate by half life as well as by nuclide. A single bin mixing a short lived and a longer lived waste stream holds the whole volume hostage to the slowest item in it, and decay store volume is the thing every department runs out of first.
The hot lab should sit at negative pressure relative to the corridor, with dedicated extraction at the dispensing position and discharge above roof level, away from any air intake. That is standard. What is specific to this climate is what happens to the system through a Dhaka year.
Dust in the dry months and humidity in the monsoon foul filters faster than the maintenance schedule from the manufacturer assumes. Put filter changes on a calendar, keep a spare set in the department rather than in a central store, and record differential pressure so a blocked filter is a number rather than a complaint about the smell.
A second point applies to almost every retro-fitted hot lab in the country: a recirculating split air conditioner is not ventilation. It cools the room and it moves any airborne contamination around it. A split unit is acceptable for temperature control alongside a proper extract arrangement, and unacceptable as the only air handling in the room. Do not let the value engineering exercise delete the extract system on the grounds that the room already has an air conditioner.
Power to the extract system deserves the same treatment as power to the camera. If load-shedding stops the extract while dispensing continues, the room is at positive pressure to the corridor with the door being opened every few minutes. Put the extract fan on the same essential supply as the imaging equipment, and write into the procedure that dispensing stops when the extract stops.
Give every log a number, a retention period and a named owner. A hot lab whose logs are complete and signed answers most of an inspector's questions before they are asked, which shortens the visit considerably.