Radiation and radiofrequency safety assessment of a shared CT-MRI control room

Purpose: A shared control room for computed tomography (CT) and magnetic resonance imaging (MRI) systems presents a unique environment where ionizing and non-ionizing hazards such as CT exposure from scatter and leakage, alongside MRI electromagnetic interference and radiofrequency may overlap. This study aims to evaluate the adequacy of shielding in a shared control room for both ionizing radiation and radiofrequency fields. Methods: Shielding performance for CT was assessed following the guidelines of NCRP Report No. 147 for CTDI100 calculations. MRI radiofrequency shielding evaluation was conducted based on MR Safety recommendations outlined in the American College of Radiology manual. Calculated shielding requirements were compared with measured values obtained using a Bosean FS-600 survey meter and a Wintact WT3121. Specifically, measurements were acquired at a height of 120cm, wherein CT exposures were recorded at 120kVp, 350mA, and 20.82s, while magnetic field readings were taken with the MRI main field active. Results: Results indicate that the existing structural shielding exceeds the minimum required thickness for both machines. From the measured dose rates before and during CT exposure, the experimental barrier transmission factors for the control room and an adjacent controlled hallway were 2.09x10-4 and 2.00x10-4, respectively, which are lower than the calculated transmission factors, 2.96x10-2 and 1.61x10-3. Furthermore, the calculated annual dose in these selected areas were 1.38mSv and 1.77mSv, respectively, which indicates that the workers will not exceed the annual 20mSv dose limit. Similarly, the ratio of the magnetic field measurements along 1G and 3G lines were 5.60x10-4 and 4.67x10-4, respectively. Moreover, the measured values in the control room were below the 2mG limit of ICNIRP, indicating effective radiofrequency shielding. Conclusion: These findings demonstrate that the combined radiation and radiofrequency shielding in the shared control room is adequate, ensuring safety for both occupational workers and the public.