Assessment of organ and effective dose when using region-of-interest attenuators in cone-beam CT and interventional fluoroscopy

In some medical-imaging procedures using cone-beam CT (CBCT) and fluoroscopy, only the center of the field of view (FOV) may be needed to be visualized with optimal image quality. To reduce the dose to the patient while maintaining visualization of the entire FOV, a Cu attenuator with a circular aperture for the region of interest (ROI) is used. The potential organ and effective dose reductions of ROI imaging when applied to CBCT and interventional fluoroscopic procedures were determined using EGSnrc Monte Carlo code. The Monte Carlo model was first validated by comparing the surface dose distribution in a solid-water block phantom with measurement by Gafchromic film. The dependence of dose reduction on the ROI attenuator thickness, the opening size of the ROI, the axial beam position, and the location of the different organs for both neuro and thoracic imaging was evaluated. The results showed a reduction in most organ doses of 45% to 70% and in effective dose of 46% to 66% compared to the dose in a CBCT scan and in an interventional procedure without the ROI attenuator. This work provides evidence of a substantial reduction of organ and effective doses when using an ROI attenuator during CBCT and fluoroscopic procedures.