Evaluation of the stray radiation distribution around a mobile cone beam computed tomography system in a simulated operating room environment.

BACKGROUND: Radiation protection in the operating room (OR) environment is a subject of much discussion in both the surgery and medical physics communities. Radiation exposure is often infrequent during image-guided procedures, especially when only 3D imaging for navigation is used. This is accompanied by unique personnel considerations, including staff that rotate in and out of the OR and staff that are scrubbed in and do not have the opportunity to easily don and doff radioprotective garments. These communities seek clear guidance about the magnitude of stray radiation dose in the OR environment. However, prior studies have reported conflicting data on the topic and have used different methods and instruments. PURPOSE: To systematically measure the magnitude of stray radiation doses in a simulated OR environment in locations relevant to the placement of personnel during image-guided spine surgery and to make recommendations for radiation protection based on these data when using a mobile cone beam computed tomography (CBCT) system and a realistic anthropomorphic phantom on an actual spine surgery table. METHODS: Measurements of stray radiation dose were performed in a grid pattern in a simulated OR environment using pressurized ionization chamber survey meters and two configurations of a tissue-mimicking anthropomorphic phantom, large (L) and extra-large (XL). The phantom was imaged using "navigation" mode (i.e., CBCT) with standard and high definition (HD) protocols. Stray radiation dose was measured at heights corresponding to chest level (125 cm) and eye level (175 cm) of a typical operator and additional heights of 100 and 150 cm. RESULTS: The absolute per scan whole body dose in the shadow of the gantry console 2 m from isocenter at a height of 125 cm (chest level) was 1.26 µSv for an equal mix of L and XL patients, and at a height of 175 cm (eye lens level) the air kerma was 9.22 µGy. The dose at 2 m from isocenter on the head side of the patient at a height of 125 cm was 7.93 µSv and air kerma at a height of 175 cm was 14.7 µGy. Doses at the same distance from isocenter and same heights on the side of the gantry opposite the console were 13.5 µSv and 15.0 µGy. CONCLUSIONS: Stray radiation doses were lowest in the shadow of the gantry console and were higher at a height of 175 cm compared to a height of 125 cm. Based on measured stray radiation doses at a distance of 2 m from isocenter, multiple radiation protection strategies can be employed to maintain occupational doses as low as reasonably achievable for operating room personnel.