Ir-192 HDR Source Fails to Retract During Prostate Brachytherapy
A 67-year-old man with intermediate-risk prostate cancer is receiving the second of three HDR brachytherapy fractions, 15 Gy per fraction, with an iridium-192 source of about 10 Ci delivered through a transperineal template with 16 catheters. He is under spinal anesthesia with a Foley catheter in place. During the second dwell position the console displays a source transfer error and the treatment aborts. The therapist at the console presses the emergency stop, but the source position indicator still shows the source out of the safe. A survey meter placed at the maze entrance reads 90 mR/h, and the door interlock has not tripped. The radiation oncologist is at the console. The medical physicist is about 10 minutes away in another building. A nurse and an anesthesia provider are in the room with the patient, who is awake but sedated and asking what is happening.
1. List, in priority order, the actions the team should take in the first five minutes, and explain why each step comes where it does.
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- Declare the event and name a leader. The console therapist states plainly that the source is not shielded and the patient is in the room. Everyone then works from the same picture; undocumented assumptions are how people walk into a maze during an exposure.
- Do not open the door and do not move the patient. The patient is anesthetized and immobile, and the source is confined to a catheter at a fixed geometry. Moving him turns a calculable, stationary source into a moving one, adds staff dose, and may dislodge a catheter.
- Start a clock and record the alarm time. Dwell time drives any unintended dose estimate. Write it down; memory is unreliable under stress.
- Work through the engineered controls in order. Console emergency retract first, then the afterloader manual crank per the manufacturer's instructions, performed by the trained operator while another person watches the survey meter.
- Survey to confirm source position. A handheld meter at the door and in the maze tells you whether the source is out. If the reading at the maze entrance is elevated, assume it is out and keep everyone out.
- Call the physicist and RSO now, even though the physicist is 10 minutes away; phone guidance for manual retraction is valuable and the RSO must be notified regardless of outcome.
- Reassure and monitor the patient through the anesthesia team. Explain what is happening at a level he can absorb.
- Control entry. Nobody enters without a dosimeter and RSO approval; time, distance, and shielding govern staff dose, and the cheapest shield is the door.
2. The source still cannot be retracted with the console or the emergency retract. Describe how you would proceed, how you would confirm the source is back in the safe, how you would estimate the unintended dose, and what documentation and notifications follow.
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Retraction. Use the afterloader hand crank, turning slowly and watching the meter rather than the console display. Never pull, cut, or clamp a catheter to free a stuck source; a damaged catheter can leave the source in the patient or the room and creates a much larger event. If the crank does not retract the source, secure the room and call the vendor and the RSO; the patient stays in place under anesthesia monitoring until a controlled recovery is possible.
Confirmation. The source is shielded only when the meter at 1 m from the afterloader and at the maze entrance falls to background, confirmed with a second, independently checked meter. Then survey the patient over the perineum and the catheter ends, and wipe-test the template and catheters before they leave the room.
Dose estimate. Reconstruct the dwell time and position from the console log and the source strength corrected for decay. The physicist calculates dose at the prescription points and at nearby organs, using the measured exposure time rather than the planned one. The difference between planned and delivered dose is the number that determines reporting.
Documentation and notification. Notify the RSO, the radiation oncologist, the department head, and the regulatory body as required by the license. In the US, 10 CFR 35.3045 defines a medical event in part as a dose differing from the prescribed dose by 20% or more, or an organ dose at 50% or more of the threshold for deterministic effects. Inform and counsel the patient and his referring physician. File an incident report, and keep the unit out of service until the cause is found and the afterloader is tested.
3. The area monitor at the maze entrance did not alarm even though the source was out. What does this imply, and what should be done?
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The area monitor is a secondary layer of protection and is never a substitute for the source-position indicator, the door interlock, or the survey meter. Its failure means the room was being treated with one fewer barrier than the program assumed, and the same is true of the door interlock that did not trip.
Both failures must be treated as equipment faults with safety significance, not as coincidences. The room comes out of service, the physicist and service engineer test the monitor and the interlock circuit, and the results are documented before any further HDR treatment. The RSO reviews the event and the program's emergency procedures, because the staff response just tested them for real.
The therapist's practical lesson is to survey at the start of every fraction with a meter that is itself checked against a known source, and to treat an unexpected meter reading as a real source until proven otherwise.