SCIENTIFIC SESSION ABSTRACT - Radiation Dose & Quality Safety

A RADIANCE-Based Alerting System for CT Radiation Dose Estimates

Author:

Seetharam Chadalavada, MD, MS, Hospital of the University of Pennsylvania; Anand Sundaram; Woojin Kim, MD; William W. Boonn, MD; Tessa Cook, MD, PhD

Background:

With growing interest in radiation dose monitoring for computed tomography (CT) over the past few years, it is critical to review CT dose estimates on a regular basis to promote protocol optimization and investigate outlier dose estimates that exceed reasonable thresholds. The American Association of Physicists in Medicine (AAPM) has published specific guidelines for volumetric CT dose index (CTDIvol) thresholds for CT scans of the adult and pediatric head and torso, as well as formCT brain perfusion and CT coronary angiographic studies [1]. The National Association of Electronics Manufacturers (NEMA) has specified an equipment feature for CT scanners (XR 25) to produce alert messages when dose thresholds are crossed. Furthermore, the Medical Imaging and Technology Alliance (MITA) has pledged to include this feature, as well as a safeguard that prevents scans from being performed at unsafe levels, in their CT scanners [2]. These new hardware-level alerting features will be available on newer CT scanners, however, older equipment may not be updated. Some work in developing an alerting system for multi-modality imaging has already been shown [3]. Just recently, the Joint Commission issued a Sentinel Event Alert regarding the radiation risks of diagnostic imaging [4]. In this work, we present a real-time monitoring system for CT exams which uses data collected by RADIANCE, an open-source CT dose monitoring and reporting system [5].

Evaluation:

At our institution, RADIANCE collects CT dose parameters in real time, within 5-10 minutes after the dose sheet is sent to the PACS and the performing technologist verifies the study. This data is available for review at the workstation at the time of study interpretation, and can also be used when protocoling a patient’s future imaging studies [6].

However, in situations where the CT dose estimate exceeds reasonable thresholds, no action has historically been taken to inform appropriate individuals of this event. In this RADIANCE update, we have introduced a three-tiered alerting system for a set of historically high-dose examinations, including CT urograms, CT colonograms, CT brain perfusion studies and coronary CT angiograms. The alerting system uses thresholds for whole-body effective CT dose estimates (in millisieverts) and dose-length product (DLP) for each study type. These thresholds are determined by performing a retrospective review of the extensive database (>160,000 CT exams for our primary hospital and >230,000 CT exams for our health system) within our internal RADIANCE installation. The average dose estimates and DLPs for the studies of interest are determined from this review.

Next, a three-tiered triggering system is designed and implemented within RADIANCE using thresholds of one, two or three standard deviations above the average. Any studies that exceed these predefined thresholds are flagged by RADIANCE upon insertion into the database. CT exams that exceed the threshold for either DLP or effective estimated dose by one standard deviation are recorded and transmitted in a batch email on a daily basis to a CT dose monitoring group. This group consists of CT physicists, the chief of the departmental section in which the study was performed, the modality chief for CT, the interpreting radiologist and an additional subset of radiologists focused on CT dose monitoring in our department. Depending on the type of study performed, the monitoring group varies slightly (i.e., the section chief and interpreting radiologist will typically differ from one study to the next). Those studies that exceed either threshold by two standard deviations are recorded and sent in an email to the monitoring group upon completion of the study. Finally, for any study in which a threshold is exceeded by three standard deviations, a text message is sent immediately upon study completion and automated dose review to the cell phones of the monitoring group.

The dose monitoring and alerting pipeline is summarized in Figure 1.

Figure 1
Figure 1

Discussion:

Having implemented this automated dose alerting system within RADIANCE, we seek to determine if it will change the number of CT exams that exceed the prescribed thresholds. In ongoing and future work, we are comparing the number of exams that trigger alerts now that the system is implemented to the number of exams that would have triggered these alerts previously. We anticipate that real-time dose alerting for outlier CT exams increases feedback to technologists involved in these studies as well as to the referring physicians for these patients about means to optimize these studies in the future or any patient or technical factors that may have contributed to the higher-than-desired doses. In the future, we may also include the referring physicians in the monitoring group for each study.

Conclusion:

As the need for regular and accurate CT dose monitoring continues to grow, this real-time alerting system for CT dose estimates will increase awareness about the issues surrounding CT-related radiation on the part of radiologists and technologists and ultimately also for referring physicians. Immediate feedback to the providers involved in CT exams that produce higher-than-desired dose estimates can help to decrease the number of instances of high-dose imaging studies in the future. This ultimately maximizes the benefit-to-risk ratio of ionizing radiation exposure for our patients and improves the care of radiology patients in the future.

References:

  1. AAPM Recommendations Regarding Notification and Alert Values for CT Scanners: Guidelines for Use of the NEMA XR 25 CT Dose-Check Standard. http://www.aapm.org/pubs/CTProtocols/documents/NotificationLevelsStatement_2011-04-27.pdf
  2. 'Dose Check' Designed to Improve CT Safety. https://www.asrt.org/Content%5CNews%5CIndustryNewsBriefs%5CCT%5Cdosecheckd100226.aspx. Published February 26, 2010; accessed September 8, 2011.
  3. S. Wang, W. Pavlicek et al. The “Dose Index Tracker”: An Automated Database of Patient Radiation Dose Records for Quality Monitoring. SIIM 2010.
  4. The Joint Commission Sentinel Event Alert, Issue 47: Radiation risks of diagnostic imaging. http://www.jointcommission.org/sea_issue_47/. Accessed September 9, 2011.
  5. TS Cook, SL Zimmerman, ADA Maidment, W Kim, WW Boonn. Automated Extraction of Radiation Dose Information for Computed Tomography Examinations. Journal of the American College of Radiology 7(11): 871-877, 2010.
  6. TS Cook et al. Integrated, On-demand Retrieval of Cumulative CT Dose Estimates at the Workstation during Image Interpretation. SIIM 2011.

Keywords:

Radiation dose monitoring
Dose alerting
Computed tomography