Long-term Experience with ceiling-mounted Dose Rate Measurement Systems

Ziel/Aim: Ceiling-mounted dose rate measurement (cmDRM) systems represent an effective method for determining the dose rate and resulting effective half-life of radiopharmaceuticals in patients undergoing nuclear medicine therapy. In comparison to manually held measurement systems, they facilitate the implementation of consistent measurement conditions, irrespective of distribution geometry, and radionuclide.

Methodik/Methods: The Jena University Hospital uses the Dose Rate Monitor (DLMon) from STEP Sensortechnik, which includes a Geiger-Müller counter tube (type 70004; range 0.1-500 µSv/h) with a separate microcontroller and a lead collimator with an aperture angle of 60°. These components are installed above each patient bed, with probes and aperture focused to the upper third (thyroid disease) or/and the center (other diseases). Measurements are continuous, with data averaged and plotted every five minutes. For reliability, patients lie on the bed three times a day for 30 minutes each time with a flat bed position at the lowest bed height. The high frequency of measurements enables exact fitting of the effective half-life (eHL) and, if calibrated, dose/uptake calculations, all of which are stored in a database.

Ergebnisse/Results: Since the commissioning of the first ward in 2010 and the second ward in 2017, 8438 thyroid diseases (applied activity range I-131: 0.2-15.2 GBq;eHL range: 0.3-8.1d), 967 SIRT planning procedures (activity ranges: 148-252 MBq Tc-99m; 74-184 MBq Ho-166), 741 SIRT (activity range 0.2-7.7 GBq Y-90; 1.4-8.0 GBq Ho-166), 324 DOTATOC and 902 PSMA radioligand therapies (activity range 1.0-9.9 GBq Lu-177 with eHL range 0,4-5,9d; 2-12 MBq Ac-225) have been documented with the system.

Schlussfolgerungen/Conclusions: Compared with handheld devices, cmDRM offer several advantages, including continuous online monitoring (radiation protection for staff) with near real-time dose rate display. They ensure reproducible conditions when standardized protocols are used (e.g., measurements three times a day with a defined patient-detector distance). ). Additionally, integrated database management supports long-term analysis, reducing the risk of data manipulation and improving dose monitoring reliability.

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Artikel online veröffentlicht:
12. März 2025