A Community Hospital's Experience With an Effective, Affordable, and Easily Implemented CT Radiation Dose Reduction Initiative

Abstract

c M m ( m t C m o u e RATIONALE CT has become an invaluable diagnostic tool, and its use has surged dramatically over the past decade. However, one of its main disadvantages is the significant dose of ionizing radiation required compared with other imaging modalities, such as ultrasound and MR. Increasing concern among both health care professionals and the public regarding the long-term carcinogenic effects of radiation exposure has stimulated efforts toward radiation dose reduction and the creation of several campaigns (Image Gently [1] and Image isely [2]) to promote the guiding rinciple of diagnostic radiation exosure: “as low as reasonably acievable.” Although new scanner echnologies and imaging processing echniques are continuously being eveloped to reduce doses, these inovations are often costly and not mmediately available to the wider edical community. Consequently, ore accessible techniques focused n controlling radiation exposure hrough the manipulation of patientpecific scanning parameters such as ube current and tube voltage have ncreasingly gained attention. A basic understanding of x-ray roduction is essential in appreciatng how adjustments in tube curent and tube voltage can affect adiation dosages. X-ray producion begins by heating a cathode, hich excites and releases elecrons from the cathode surface nto the x-ray tube. These elecrons constitute the tube current. ithin the tube, there also exists tube voltage, which serves to accelerate electrons toward the anode. As the electrons bombard the anode target, their kinetic energies are converted into a spectrum of x-rays released from the anode surface, forming the x-ray beam used for imaging. The rate of x-ray production can be roughly approximated as being directly proportional to the tube current and proportional to the square of the tube voltage [3]. Thus, changes in the tube voltage have a larger effect than changes in the tube current on the strength of the x-ray beam. The tube current and tube voltage can be adjusted for each examination. Modern CT scanners are equipped with automatic exposure software capable of tailoring tube current to patient body habitus. Additionally, tube voltage can be manually selected. The concept of decreasing tube voltage has been used in pediatric imaging to reduce radiation exposure for children, whose growing organs are more radiosensitive compared with those of adults. Although most adult examinations are typically carried out using tube voltages of 120 to 140 kVp, pediatric examinations are often performed at voltages less than 100 kVp. In recent years, the dose reduction advantage of decreasing tube voltage has also been shown in nonobese adults, primarily in cardiac CT imaging [4-6]. These findings have spurred interest in using tube voltage reduction to decrease radiation dosages in other CT examinations. On the basis of these reports, Scripps Mercy Hospital, an acute 2