Every exposure is recorded twice: as a dose area product in the patient's record and as a count on the tube itself, which is a piece of hardware nobody can edit. Screening room 2 shows an eleven minute fluoroscopy at ten past four with no patient, and both records show it.
I am a radiographer and I hold the local rules for two screening rooms.
The two records, because their independence is the whole of this.
Dose area product is measured by a chamber in the beam and it is the number that goes on the patient's record and into the audit. It is in gray centimetres squared and it tells you how much radiation went into somebody.
Separately, the tube has counters. Exposure count, screening time, and the total energy through it, held in the generator's own service data. Those exist for the engineer, not for us, and they are not editable by any user account in this building.
Both of them have to be consistent, and the reason regulation is built this way is exactly so that a discrepancy shows up.
Room 2 records an eleven minute screening at about ten past four in the morning.
Roughly one week in three. The room is used for planned lists between eight and six, and there has not been an out of hours list in that room since 2019 because the emergency work goes to the other one.
There is no patient attached to it.
The record shows an exposure event with a dose area product, a screening time of eleven minutes and change, and no examination, no accession number, no operator login, and no patient.
The tube's counter goes up by the same eleven minutes.
Eleven minutes of screening is a lot. A straightforward diagnostic procedure is two or three. Eleven is a long interventional case, and the dose area product recorded is consistent with that: it is not a stray reading, it is the profile of somebody doing careful work for a quarter of an hour.
What has been done, and this went further up than anything else I have ever reported.
It was reported to the radiation protection adviser in 2021 and to the radiation protection supervisor, which is my consultant, and an entry was made under our incident procedure, because an unaccounted exposure is potentially a notifiable event and nobody was going to sit on it.
The investigation established, and I agree with all of it: no patient was in the department, the door interlock log shows the door shut and unopened between eleven at night and six in the morning, the card access to the room shows nobody entering, and the corridor camera shows nobody.
The X-ray warning light outside the room is wired to the generator and it comes on when the beam is on. Nobody was in the corridor to see it.
The adviser's report concludes that no person was exposed, that the event is therefore not notifiable, and that the equipment should be investigated for a fault causing spurious dose recording.
The engineer's report, which came back four months later.
The generator was tested and the tube was tested. Output, timing, filtration, all within specification.
The service data was downloaded and compared with the room's dose records.
His conclusion is that the tube has performed the exposures recorded, that the counters cannot be written to by the console or the network, and that in his opinion the equipment has been operated during those periods.
Two reports on the same file. One says nobody was in there. The other says the machine was used.
Neither of them is wrong about the thing it measured.
What we do about it.
The room is checked every morning as part of the daily quality assurance and the dose audit is done monthly and the unattributed events are listed in it under a heading of their own.
Our department's dose audit is otherwise excellent. My consultant made the point at the last radiation safety committee that a department whose numbers were sloppy would never have noticed this at all, which was kind of him and is true.
The room is locked out of hours now. That was the one action from the investigation and I asked for it. A key, not a card, and the key lives in the department safe, and nobody has taken it out at night.
It made no difference.
What I do.
I am usually first in and I unlock and do the warm up and the checks.
The change is that I do not do the four o'clock on call any more if it means being alone on that corridor, and the department has been decent about rostering it.
The last time was in October 2022, on call, and I came through the corridor at about twenty past four for something in the other room.
The warning light over room 2 was on.
I stood and looked at it for a while, which is the wrong thing to do, and I did what you are trained to do instead, which is not open the door.
It went off at twenty six minutes past. When I went in with the key in the morning the room was as I had left it the previous evening, and the console showed an eleven minute screening ending at 04:26, and the last patient on that machine had been at half past five the day before.