Medical Physics Seminar – Monday, September 17, 2012
Dosimetric Comparisons Between The Scanning Beam Digital X-ray (SBDX) System and a Conventional Flat-Panel Cardiac Fluoroscopic Imaging System
Bradley P. McCabe (student of Dr. Michael Van Lysel)
Research Assistant, Department of Medical Physics, UW-School of Medicine & Public Health, Madison, WI - USA -
The Scanning Beam Digital X-ray (SBDX) fluoroscopic system has great potential to become the next standard in cardiac fluoroscopic. This work consisted of a thorough dosimetric comparison between SBDX and a conventional flat-panel imaging system used for cardiac fluoroscopy. The investigation included NIST-traceable calibration of newly formulated radiochromic film designed for diagnostic x-ray beam qualities. Measurements and analysis of the x-ray fields of the SBDX and flat-panel systems were performed both free-in-air and at the surface of a phantom, and included measurements of free-in-air and on-phantom air kerma rates, x-ray field flatness and beam quality for both systems.
In vivo patient surface dosimetry was performed for fluoroscopically guided diagnostic and interventional cardiac procedures on the conventional flat-panel system. The film-measured air kerma was compared to the conventional system’s regional dosimetry calculations. From this investigation it as shown that the conventional system’s dosimetry values were approximately 23% lower than the film-measured air kerma. This difference was consistent with flat-field on-phantom film measurements which showed that the conventional system did not apply appropriate backscatter factors to the reported air kerma.
From the in vivo investigation one patient case was selected and replicated on the conventional system and SBDX systems using an adult anthropomorphic phantom as a substitute for a patient. It was shown that when operated with x-ray tube parameters that produced equivalent image quality, SBDX delivered approximately two times less dose to the phantom entrance surface than the conventional system for the same procedure time. The x-ray fields of SBDX were larger and more diffuse than the conventional system leading to lower dose in the overlapping “hot spot†regions.
A second phantom study investigated the dose reduction potential of SBDX’s unique Equalization feature. An adult anthropomorphic phantom was filled with high-sensitivity TLDs for this experiment. The TLD-filled phantom was exposed with the conventional system and SBDX both with and without Equalization to a single x-ray projection. The analysis showed that for equivalent phantom image quality, SBDX without Equalization produced average organ dose rates approximately one-quarter of the conventional system. With Equalization average organ dose rates were one-seventh of the conventional system.