Room: Track 1
Purpose: Skin dose is dependent on the incident beam angle and corrections are needed for accurate estimation of the risk of deterministic effect on the skin. A method is described for applying such a correction in the skin-dose-tracking system (DTS) during fluoroscopically-guided procedures.
Methods: EGSnrc Monte-Carlo (MC) software was used to calculate the dose averaged over 0.1 cm depth into the entrance surface of a water phantom at the center of the field as a function of incident beam angle from 90-10 degrees for beam field sizes from 5-15 cm and for beam energies from 60-120 kVp. These values were normalized to the incident primary dose to obtain an angular-correction factor (ACF). The angle of beam incident at each intersection point at the surface of the patient graphic within the field was calculated by using the normal vector at each mesh vertex and the angle of a ray from the tube focal spot. Skin dose at each point of intersection was corrected using the ACF for the ray angle at each vertex for procedure projections saved in a DTS log file. The skin-dose values with and without angular correction were evaluated and these values were compared to those calculated using MC.
Results: The ACF reduces the skin dose for angled rays and the reduction can be substantial for small angles of incidence due to the curvature of the skin and beam angle. For example, a LAO projection of a cardiac procedure had a maximum percent dose difference of 17% and an averaged percent dose difference over the field of 10% for the DTS with and without angular correction.
Conclusion: Increased accuracy of skin-dose estimation during interventional fluoroscopic procedures can be obtained in the DTS by applying a correction factor for angle of x-ray incidence in real-time during the procedure.
Funding Support, Disclosures, and Conflict of Interest: Research support from Canon Medical Systems