Proposed Topic (Most preferred): :
Clinical Safety and Quality Service II (Projects aiming to enhance clinical safety and outcomes, clinical governance / risk management)
Proposed Topic (Second preferred): :
Clinical Safety and Quality Service I (Projects aiming to improve efficiency and effectiveness of care delivery to meet international standards)
Authors (including presenting author) :
LI KW(1)
Affiliation :
(1)Medical Physics Unit, Department of Clinical Oncology, Tuen Mun Hospital
Introduction :
Diagnostic medical x-ray imaging facilities must be shielded against ionizing radiation to protect employees and the general public. The radiation dose rate inside the control room is within the regulatory requirements. In general, operators are regarded as safe inside the control room during examinations. However, operators might need to be in the scanning room during computed tomography (CT)-guided interventional procedures depending on the institution’s protocol. In this case, operators are exposed to leakage radiation from the x-ray tube housing, secondary and tertiary radiation. Mobile lead shield can be placed between the operator and the scanner to attenuate leakage and secondary radiation scattered from patient to an acceptable level, but there is still a considerable amount of tertiary radiation scattered from the walls, floor, ceiling and surroundings over the top and round the side of the mobile shield that should not be neglected.
Objectives :
To quantify the tertiary radiation received by the operator behind a mobile shield and to evaluate the effectiveness of using a mobile shield during CT-guided lung biopsy.
Methodology :
The procedure of needle positioning during CT-guided lung biopsy was simulated on a 64-row CT scanner (Somatom Definition Edge, Siemens Healthineers) using a body phantom (CTDI, Sun Nuclear) placed on the couch at isocenter. Helical acquisitions for z-axis coverage of 80 mm were performed with low-dose scan parameters typically used in this procedure (Sn100 kVp, 90 effective mAs, 0.5 second rotation time, pitch factor of 1.2). Dose rates were measured using an ionization chamber radiation survey meter (451P, Fluke Biomedical) with and without a 2-mm lead equivalent mobile shield (size: 40” x 75”) placed between the operator and the scanner at 1 m and 1.5 m from the isocenter. The survey meter was placed at about the thorax level of the operator (height: 1.5 m).
Result & Outcome :
Mean dose rates were 3.1 mSv/h and 2.2 mSv/h at 1 m and 1.5 m, respectively. With a mobile shield, mean dose rates were 12.2 µSv/h and 20.2 µSv/h at 1 m and 1.5 m, respectively. The shielding ratios were 99.6% and 99.1% at 1 m and 1.5 m, respectively. A 0.5-mm lead equivalent apron will further attenuate the tertiary radiation by over 90%, leading to a low operator radiation dose close to the patient where rapid changes of needle position is highly facilitated.
