Objective To identify the reasons why the monitored personal doses of radiation worker A in an institution exceeded the investigation level in 2023 and 2024, and remind workers to wear personal dosimeters in a standardized manner in scenarios such as work and business trips to ensure the authenticity and reliability of the monitoring data. Methods A thermoluminescence measurement system was used to read the personal dosimeters worn by radiation workers. Investigations were carried out on personnel whose doses exceeded the investigation level described in the “Specifications for individual monitoring of occupational external exposure” (GBZ 128—2019). The reasons for doses exceeding the investigation level were analyzed using additional dosimeters and conducting on-site experiments. Results In 2023 and 2024, radiation worker A recorded a total of 5 personal dose equivalents exceeding the investigation level (1.23 mSv) over a total of 8 monitoring cycles (each lasting 90 days). Following one cycle where the dose exceeded the investigation level, two additional dosimeters (each for a 30-day cycle) were issued to worker A, revealing readings below the investigation level for the 30-day monitoring cycle (0.41 mSv). The reading for the dosimeter was 2-3 μSv per time when passing through an X-ray security scanner, and approximately 2.10 mSv per time when passing through a computed tomography security scanner. Conclusion Within a 90-day monitoring cycle, a single exposure of a personal dosimeter to a computed tomography security scanner can result in a dose exceeding the investigation level. Radiation workers should avoid placing dosimeters in backpacks or suitcases that pass through computed tomography security scanners during business trips, so as to reduce the impact of security scanner irradiation on personal dose monitoring.