A Better Measure for Lesions
Novel quantitative assessment tools hold promise for future use in clinical practice.
Radiology is evolving into a more quantitative discipline, and unlike qualitative interpretation, which is prone to variability among radiologists, quantitative assessment can improve both the reproducibility of interpretations and the detail of information extracted from images.
This is particularly important for assessing tumor response to therapeutic interventions in patients with cancer. Quantitative assessment methods such as Response Evaluation Criteria In Solid Tumors (RECIST, formalized criteria for measuring tumor target lesions and for determining treatment response categories), are used in clinical research to provide clinicians with objective information about treatment response and clinical trial endpoints needed to make patient management decisions.1 However, these assessment methods are very time consuming, as they require the radiologist to draw lesion measurements by hand. Moreover, for serial imaging studies — often interpreted by different radiologists — identifying all the abnormalities seen on prior studies, determining how each abnormality was measured, and reviewing the specific measurements greatly hinders workflow. The lack of routine and systematic summarization of lesion measurements often leaves the referring oncologist with the difficult task of searching out measurement details within the radiology report.
To make quantitative interpretation more efficient and practical is the impetus behind the Electronic Physician Annotation Device (ePAD) initiative supported by ACRIN® and the ACR Imaging Core Laboratory and led by Daniel L. Rubin, MD, MS, assistant professor of radiology and medicine at Stanford University, and chair of the ACRIN Biomedical Informatics Committee. ePad is an open source, Web-based image viewing workstation that displays images and collects image annotations and quantitative measures derived from them in compliance with the National Cancer Institute's Annotation and Image Markup (AIM) standard for recording and storing information about lesions — including radiologist observations, measurements, and other quantitative information. "ePad will work with image assessments made on any other workstation so long as those interpretations are done using an AIM-compliant workstation. This is analogous to how the Digital Imaging and Communications in Medicine standard enabled interoperability among systems that work with image metadata," explains Rubin. While other lesion measurement and tracking applications are available, they require all image assessments to be made within that platform. If an image viewing tool is not AIM compliant, then every imaging time point to be interpreted must be done on the same system. Because patients can be imaged and evaluated at different facilities over time, it is important that software tools like ePAD support AIM to universally enable measurement rendering and other tool functionality. To date, a number of open source and commercial image viewing workstations support AIM, so the vision of AIM-enabled interoperability for image metadata is already becoming a reality.
“The nice thing about the ePAD platform is that it is not a silo.” — Daniel L. Rubin, MD, MS
Rubin reports that learning how to work with ePAD is very straightforward. "I showed radiologists here at Stanford how to use the tool in about 30 minutes and they were able to perform interpretations using ePAD without a problem," he explains. When images from an exam are opened, the tool presents a tabular summary of lesions recorded from a prior exam, to include showing the radiologist the specific abnormalities and how they were measured previously. By clicking on any of the measurements, the annotation and its associated image are presented. Any new measurements are automatically added to a summary table, and a summary quantitative report is generated along with a graphical summary of individual patient response to facilitate the decision-making process for the oncologist.
Verifying that ePAD adds efficiency to quantitative assessments is important for the technology's adoption. Prior to developing ePAD, Rubin and colleagues created an implementation of a tool called iPAD with Osirix, an open-source imaging-viewing workstation that runs on Mac computers (not to be confused with Apple's popular iPad tablet). Promising study results evaluating iPAD's impact on workflow in a real-world environment were presented at the 2012 RSNA Annual Meeting. Five radiologists from three institutions were recruited to interpret 20 cases (CT exams of the chest, abdomen, and pelvis) that included baseline and three follow-up imaging exams using RECIST (version 1.1). The exams were read initially with the aid of the iPAD tool and, after a 30-day memory "washout" period, reread unassisted by the tool. On average, across the five readers, the use of iPAD produced a savings of 2.9 minutes per case, representing a net increase in reader efficiency of 23 percent. Similar evaluation studies are now underway to confirm that the Web-based ePAD tool similarly enhances radiologist workflow in quantitative image interpretation.
"Give ePAD's ease of use and proven efficiency, further tool development, evaluation, and implementation will continue to be an important informatics and core lab initiative," says Mark Rosen, MD, PhD, associate professor of radiology at the University of Pennsylvania, and chair of the MRI/CT division of the ACR Imaging Core Laboratory.
To date, the ePAD tool has been tested with interpretations using RECIST measurements. For the next phase of testing, the ePAD research team is considering incorporating functionality for quantitative assessment with PET imaging. Rubin says,
Our current plan is to use one platform to implement many different quantitative measurements. The nice thing about the ePAD platform is that it is not a silo; it's fully expandable and can support plug-in software extensions that add functionality for performing other quantitative assessments.
It's beyond simply doing a good job with quantitative imaging within the core lab facilities. We hope to improve the practice of radiology by enabling a methodology in which this will ultimately be routine clinical practice, and we're doing it in a manner that promotes interoperability — which is a very different approach from that being used now.
Ultimately, it is patients who will benefit from their physicians have more objective information from imaging with which to make treatment decisions. "If the oncologist gets a report that says, 'Some lesions are slightly bigger and some are slightly smaller,' it's very difficult to make a decision," says Rubin. "On the other hand, if an oncologist gets a report that communicates the sum of the target lesions' linear dimensions have increased 22 percent, that's actionable, that means something specific to the oncologist and to the patient."
By Nancy Fredericks
1. Eisenhauera EA, et al. “New Response Evaluation Criteria in Solid Tumours: Revised RECIST Guideline (version 1.1).” European Journal of Cancer 2009;45:228–47.