Limiting Exposure to Scattered Radiation From a CT System Installed in a Two-Sided Deployable ISO-Shelter.

INTRODUCTION: Diagnostic radiology in the deployed military environment (in-theater diagnostic radiology) was greatly improved in the early 1990s with the addition of CT systems installed in military-grade one-sided expandable ISO-shelters. These shelters were provided with limited radiation shielding by several flexible lead curtains covering only a small portion of the shelter walls, necessitating placement of deployed CT systems at substantial distances from the field medical facility to limit exposures to personnel from secondary radiation. The newest generation deployable CT system is housed in a two-sided ISO-shelter with radiation shielding applied to the shelter walls. To ensure compliance with military and national standards for protection against ionizing radiation, we developed a simple method to calculate safe distances based on workload, frequencies of the various CT exams performed, and occupancy of controlled and uncontrolled areas. MATERIALS AND METHODS: Calculation of radiation air kerma rates outside a two-sided CT ISO-shelter was developed using guidance from the National Council on Radiation Protection and Measurements Report No. 147. The simplified formula included measured radiation transmission factors for the ISO-shelter wall and installed shielding, occupancy factors, fraction of all CT exams that covered the chest, abdomen, and/or pelvis, total number of CT exams per week, and shielding design goals for controlled and uncontrolled areas. The formula was modified subsequently to account for whole-body CT exams expected during armed conflict. RESULTS: Calculated safe distances revealed that the shielded two-sided CT ISO-shelter can be positioned much closer to the surgical shelters of the field medical unit than the previously unshielded one-sided CT ISO-shelter. Tables of safe distances for controlled and uncontrolled areas for the two medical support environments of disaster relief/peacekeeping and combat are provided. For example, for a controlled area at 100% occupancy when 300 CT exams per week are performed and 50% of those exams are of the chest, abdomen, and/or pelvis, the safe distance between the nearest surgical shelter and the shielded CT ISO-shelter is 2.1 m. By comparison, the safe distance for an unshielded CT ISO-shelter is 8.5 m under the same conditions. For lower occupancy factors and lower weekly workload, safe distances from the nearest surgical shelter are often negligible. CONCLUSIONS: The shielding in the new deployable CT ISO-shelter substantially reduces the distance between it and the surgical shelters of the field medical unit necessary to ensure radiation safety. Safe distances depend on several factors including workload, types and frequencies of CT exams, occupancy factors, and classification of the area around the ISO-shelter, i.e., controlled and uncontrolled.

Cumulative effective radiation dose received by blunt trauma patients arriving to a military level I trauma center from point of injury and interhospital transfers.

BACKGROUND: Trauma patients sustaining blunt injuries are exposed to multiple radiologic studies. Evidence indicates that the risk of cancer from exposure to ionizing radiation rises in direct proportion to the cumulative effective dose (CED) received. The purpose of this study is to quantify the amount of ionizing radiation accumulated when arriving directly from point of injury to San Antonio Military Medical Center (SAMMC), a level I trauma center, compared with those transferred from other facilities. METHODS: A retrospective record review was conducted from 1st January 2010 through 31st December 2012. The SAMMC trauma registry, electronic medical records, and the digital radiology imaging system were searched for possible candidates. The medical records were then analyzed for sex, age, mechanism of injury, received directly from point of injury (direct group), transfer from another medical facility (transfer group), computed tomographic scans received, dose-length product, CED of radiation, and injury severity score. A diagnostic imaging physicist then calculated the estimated CED each subject received based on the dose-length product of each computed tomographic scan. RESULTS: A total of 300 patients were analyzed, with 150 patients in the direct group and 150 patients in the transfer group. Both groups were similar in age and sex. Patients in the transfer group received a significantly greater CED of radiation compared with the direct group (mean, 37.6 mSv vs 28 mSv; P=.001). The radiation received in the direct group correlates with a lifetime attributable risk (LAR) of 1 in 357 compared with the transfer group with an increase in LAR to 1 in 266. CONCLUSION: Patients transferred to our facility received a 34% increase in ionizing radiation compared with patients brought directly from the injury scene. This increased dose of ionizing radiation contributes to the LAR of cancer and needs to be considered before repeating imaging studies. LEVEL OF EVIDENCE: III.

CT radiation dose: current controversies and dose reduction strategies.

OBJECTIVE: The purpose of this article is to use clinical scenarios to explore aspects of ionizing radiation imparted to patients undergoing CT examinations. Examination appropriateness, effective doses, cancer risks, and pertinent dose reduction strategies are reviewed. CONCLUSION: CT accounts for the majority of radiation exposure related to medical imaging. Medical professionals should have a working knowledge of the benefits and risks of medical radiation and an understanding of strategies for reducing CT radiation dose.

Nontraumatic acute abdominal pain: unenhanced helical CT compared with three-view acute abdominal series.

PURPOSE: To prospectively evaluate and compare the diagnostic accuracy of unenhanced helical computed tomography (CT) for patients with nontraumatic acute abdominal pain with that of traditional abdominal radiography. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained; this study was completed before implementation of the HIPAA. Ninety-one patients (44 men; 47 women; age range, 18-84 years; mean age, 48.5 years) with acute nontraumatic abdominal pain over a 7-month period were referred by the emergency department of one institution. These patients underwent a three-view acute abdominal series (AAS) and unenhanced helical CT. AAS included an upright chest radiograph and upright and supine abdominal radiographs. Unenhanced helical CT images with 5-mm collimation were obtained from the lung bases to the pubic symphysis, without intravenous, oral, or rectal contrast material. AAS and unenhanced helical CT images were each separately and prospectively interpreted by a different experienced radiologist who was blinded to patient history and the images and interpretation of the other examination for each patient. Final diagnosis was established with surgical, pathologic, and clinical follow-up. The sensitivity, specificity, accuracy, positive predictive value, negative predictive value, and positive and negative likelihood ratios were calculated for AAS and unenhanced helical CT. Confidence intervals of 95% were calculated for each value with the standard equation for population proportions. Results of AAS and unenhanced helical CT examinations were compared with chi2 analysis. RESULTS: Among the 91 patients examined, unenhanced helical CT yielded an overall sensitivity, specificity, and accuracy of 96.0%, 95.1%, and 95.6%, respectively. The AAS interpretations yielded an overall sensitivity, specificity, and accuracy of 30.0%, 87.8%, and 56.0%, respectively. The accuracy of unenhanced helical CT was significantly greater than the accuracy of AAS (P < .05). CONCLUSION: AAS is an insensitive technique in the evaluation of nontraumatic acute abdominal pain in adults. Unenhanced helical CT is an accurate technique in the evaluation of adult patients with nontraumatic acute abdominal pain and should be considered as an alternative to radiography as the initial imaging modality.