Purpose: A real-time display of the scatter distribution in the fluoroscopic procedure room can provide valuable feedback to staff. Such a display system can utilize a pre-calculated database of distributions as a function of those parameters that vary during the procedure. This study investigates the error introduced by interpolating between parameter values in order to limit the number of distributions required in the database.
Methods: Room scatter distributions about a fluoroscopic C-Arm system were calculated using EGSnrc Monte-Carlo (MC) software and the Zubal computational phantom in a volume of 180 cm by 180 cm by 92 cm high centered on the gantry isocenter with a voxel size of 0.4 mm. Calculations were performed for LAO/RAO and CRA/CAU gantry angulation in increments of 5 degrees for head, chest and abdomen projections. Scatter profiles in vertical and horizontal profiles were compared between those calculated by MC and those interpolated to determine the error introduced by different degrees of interpolation. For this study, all MC simulations used 5 x 1010 photons with an 80 kVp spectrum beam.
Results: Comparisons between the interpolated distribution value and that calculated by MC generally showed better than 10% agreement between the interpolated distribution value and that calculated by MC. This was true for most RAO/LAO and CRA/CAU gantry angulation interpolations between +/- 15 degrees and interpolations between horizontal profiles over a 25 cm interval.
Conclusion: It would be difficult to have a separate scatter distribution in the database for every exposure parameter value due to memory and upload time considerations. Interpolation between those parameters available provides a viable alternative to matching the displayed distribution with the actual parameter value. Such interpolation methods can make a real-time scatter distribution display feasible for fluoroscopically-guided procedures.
Funding Support, Disclosures, and Conflict of Interest: This research is supported by Canon Medical Systems.