Program Information
An Analytical Approach for Estimating Angular Change of a C-Arm Fluoroscope Necessary to Provide Discrete X-Ray Fields at the Plane of Patient Skin in Fluoroscopically Guided Interventions
A Zhao*, K Wunderle, Cleveland Clinic Foundation, Cleveland, OH
Presentations
SU-E-702-6 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 702
Purpose: To provide a methodology for estimating the angular change of a C-arm fluoroscope gantry that provides non-overlapping beams at the plane of patient skin in fluoroscopically guided interventions (FGIs) to assist in retrospective peak skin dose (PSD) estimation.
Methods: From previous works, the sizes of patient skin field area corresponding to nominal field of views were determined. In this work, calculation was based on an elliptical-shaped patient (32cm in AP direction, 46cm in mediolateral direction), and PA projection (0°) was assumed since it’s a very commonly used projection in FGIs. A coordinate system was established with patient center as the origin. The coordinate of gantry’s isocenter was then located in the coordinate system. The assumption that, for PA projections, the arc length of the elliptical skin profile of patient’s posterior in upper body equals to linear dimension was made. The arc length approximation was then calculated by integration technique in Excel using small angular increments. The intersection coordinate of the rotated beam’s virtual axis (from focal spot to isocenter) and patient elliptical skin profile was calculated. The angle between the axes of two non-overlapping beams was subsequently calculated by simple trigonometry.
Results: In PA projections, for a nominal field of view of 42cm, 32cm, 22cm, 11cm, with SID of 120cm and patient surface plane of 60cm from focal spot, minimum angular changes of 54.4°, 42.5°, 29.4°, 15.2°, respectively, have to be made to avoid beam overlapping. The angular changes are in nearly a linear relationship with sizes of different skin fields.
Conclusion: An analytical approach for angular change of the gantry of interventional fluoroscope was proposed to exclude beam overlapping at patient surface to assist in the estimation of PSD. In this approach, the actual SID, table height and patient size can be taken into account in calculation.
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