Feature | April 01, 2015 | Jeff Zagoudis

Monitoring Radiation Dose

New metrics and methods are helping radiologists keep dose down and share their successes with peers

Photo courtesy of Toshiba.

Radiation dose continues to be one of the hottest topics in radiology, as government mandates and public concern are forcing healthcare teams to find ways to achieve the same high image quality while reducing dose. The 2014 annual meeting of the Radiological Society of North America (RSNA) in December reflected those concerns, featuring sessions on the latest metrics for measuring dose and ways to keep dose down. 

Michael F. McNitt-Gray, Ph.D., professor of radiology at the David Geffen School of Medicine at UCLA, examined some of the metrics that can be used to calculate radiation dose. First and foremost was the computed tomography dose index (CTDI), a standardized measure of radiation dose output from a CT scanner that allows the user to compare radiation output between different scanners.

CTDI has been in use for decades and provides a number of advantages. It can provide a good measure of the scanner’s output, as well as how the scanner is being adjusted to accommodate the size of the patient. It doesn’t, however, factor in the size of the patient. The number may (and should) go up or down depending on patient size, but this is due to the scanner output being adjusted to compensate for different patients. 

Dose length product (DLP), also a staple on radiology reports, somewhat accounts for this discrepancy and is found by multiplying the CTDIvol by the length of the scan in mGy/cm, allowing for any overscan.

Various groups have worked on coordinating algorithms for CTDIvol or new metrics to compensate for varying patient sizes. In 2011, for example, the American Association of Physicists in Medicine (AAPM) released a report detailing a new metric called the size specific dose estimate (SSDE), which factors in the thickness of the patient’s torso to convert CTDIvol into an actual dose quantity. 

Change of Perspective 

While CTDIvol and DLP will likely continue to appear on image headers, the last several years have seen a push to dive deeper into the data. CT has been a primary focus but other modalities are making their way into the dose spotlight as well. With the healthcare landscape rapidly changing across the United States, dose reports and ways to minimize dose are fast on their way to becoming mandates at both the state and national levels, with accompanying financial incentives — or penalties. While many of these measures won’t take effect until at least 2016, “There’s no reason why everybody can’t be doing it this year,” said Kevin O’Donnell, senior manager with Toshiba.

The Medical Imaging and Technology Alliance (MITA) released one of the more prominent standards in recent years, publishing XR-25 in 2012. Known as Dose Check, XR-25 established a set of dose values which, when exceeded, will trigger a pre-scan alert from the machine; a notification will be sent if the scan is projected to exceed the prescribed dose value. In either case, the technologist must acknowledge the current setting or make adjustments before continuing with the exam.

Integrated Dose Reporting 

Most radiology departments and groups will have a variety of scanners from different manufacturers, which can make comparing dose information difficult if it is recorded and reported in different formats. As O’Donnell explained it, “The challenge comes when, for a feature to work, System A needs to do this, System B needs to do this and System C needs to handshake like this.”

The Integrating the Healthcare Enterprise (IHE) initiative has developed its own Radiation Exposure Monitoring (REM) profile to help implement and test functions that span multiple systems.

The basis of the IHE REM profile are Digital Imaging and Communications in Medicine (DICOM) radiation dose structured reports (RDSR), which capture the dose information without having to log the individual images. The RDSRs allow radiologists and physicians to evaluate the dose down to each individual irradiation event, or activation of the scanner.

The condensed data format makes it easier to examine reports from an extended time period, as opposed to having to pull individual images. At present, they have been applied to most imaging modalities with the exception of radiotherapy.

For those still using systems purchased prior to IHE REM, O’Donnell noted that there are legacy extractors to collect the same data and create partial REM objects complying with the RDSR format. The information collected is based on image header contents and the modality performed procedure step (MPPS) data, among other things. O’Donnell said that extractors are currently focused on CT and X-ray angiography (XA) but are expected to expand their reach in the future. 

Those not yet operating under XR-25 and/or IHE REM will need to get with the program by 2016, when the Centers for Medicare and Medicaid Services (CMS) start enforcing compliance with MITA’s XR-29, otherwise known as Smart Dose. Published in 2013, XR-29 bundles the requirement for compliant CT systems to provide: 

•  DICOM RDSR reports

•  XR-25

•  Automatic exposure control; and

•  Pediatric and adult reference protocols

The American College of Radiology (ACR) does have its own national Dose Index Registry compiling anonymized data submitted via IHE REM or legacy extractors. For a modest annual participation fee, users can access a plethora of dose statistics and compare their data to other sites. 

The Cost of Monitoring

As exciting and innovative as many of these tools are, figuring out where to start with REM software can be a daunting task. Tessa S. Cook, M.D., Ph.D., assistant professor of radiology and chief of 3-D and advanced imaging at the Hospital of the University of Pennsylvania, discussed the processes and considerations involved. 

Cook recommended forming a committee to take responsibility for REM procedures and software selection. Five practical considerations must be weighed when selecting software: cost, setup, features, data collection and reporting. 

The committee’s most important job, however, is to conduct regular reviews of REM procedures. Reviews should cover dose indices, protocols and any registry benchmarks to ensure the program is on track. 

Cook concluded that such reviews could turn up surprising results, such as old protocols that are still in use, default protocol settings that have been unexpectedly modified or vendor updates that lead to protocol changes. 

Ultimately, while the resources and tools available to radiologists to monitor radiation dose continue to grow, they must continue to take responsibility to act on the data and effect change. 

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