Monday, May 31, 2010

Dose Matters

Summary: Reducing the radiation exposure from diagnostic imaging is an increasing priority; standards exist for encoding dose information but are not yet widely adopted, though soon will be given regulatory pressure and industry commitments; few tools, commercial or open source, exist yet for monitoring and reporting radiation dose.

Long Version:

You would have to have been living on a desert island or under a rock to not be aware that there is a heightened sensitivity amongst the general populace and the regulatory authorities to the matter of radiation dose exposure from diagnostic imaging and the risk of cancer. Whether it be well publicized disasters like the Jacoby Roth or Cedars-Sinai incidents, or general concern related to dose from procedures like virtual colonoscopy, or articles evaluating the contribution of diagnostic imaging as a source of exposure, the need to deal with the matter is inescapable. This is true regardless of whether you are a "believer" in the linear no-threshold model, which says that no amount of radiation is safe, or not. The FDA is going to require that efforts be made to reduce the dose delivered by both CT and fluoroscopy, as discussed in their initiative white paper and reviewed at the recent public meeting, though they have been working on this for some time. Vendors are already delivering equipment incorporating dose saving technology. Attention is being drawn to the radiation dose caused by the ordering of repeat or low-yield procedures, as well as optimal strategies for pediatric imaging (image gently).

Yet so much remains in the hands of the user in terms of ordering as well as performance of the examination. If you cannot measure it, you cannot improve it (Lord Kelvin), so the question arises as to how one can track the amount of radiation being delivered, either to the population, or at a site, or to an individual, and hence benchmark one's own performance then make improvements to the process. Surprisingly, though devices have long been required to provide visual feedback to the operator at the console, it has proven remarkably difficult to get this information out of the scanners and into some sort of database or registry that can be searched or monitored.

DICOM has a number of ways that dose information can be encoded, but for the last few years has been focusing on the Radiation Dose Structured Report (SR), with the goal of having the modalities produce this directly. Many people expect that dose information would be in the image headers, but the image is the wrong place to encode this; images may be transmitted before the study is complete and hence not contain the cumulative information, and more than one image may be reconstructed from the same irradiation event, creating the risk that the dose may be counted more than once. Further, not all originally acquired images are necessarily retained (e.g., thin slices from CT), and a large volume of images is a poor means of communicating what is essentially a small amount of information. One upon a time, it was thought that the modality performed procedure step (MPPS) might be a suitable mechanism to communicate this information, but it was soon realized that there is no easy way to persist what is essentially a transient message, not to mention that MPPS is relatively poorly adopted.

To meet the users' immediate needs, some vendors have gone so far as to provide images that are saved screens containing the text of the delivered dose information. Both GE and Philips do this, and there is a large installed base of such scanners as well as archives full of such information. Though Philips had the foresight to also encode the same information in the header attributes of these images (albeit in a non-standard way), both as plain text and as individual elements, unfortunately GE did not, so many folks who want to perform a retrospective review of their dose information need to manually examine these images, or develop some optical character recognition (OCR) software.

For the time being, there is a relative paucity of tools available both to handle information from legacy devices, as well as to use more standard approaches, including that espoused in the IHE Radiation Exposure Monitoring (REM) profile, which is based on modalities producing DICOM Radiation Dose SR objects, and provides specific actors for consuming and reporting information, including transmission to registries, such as the ACR's Dose Index Registry. The good news is that there has been significant activity at recent IHE Connectathons with respect to implementing REM; you can review these yourself at the connectathon results page, where you can see which vendors have specific offerings in this field. MITA, the modality vendors' industry trade group, has made a strong commitment not only to dose reduction in general, and the CT Radiation Dose Check feature, but also to retrofitting at least the current platform in the installed base to produce DICOM SR objects .

At a recent teleconference of the newly convened Quality and Safety Subcommittee of the RSNA's Radiology Informatics Committee (RIC) , it was apparent that several academic groups have been working in this field, and the need to make available open source tools was highlighted, if for no other reason than to serve until the industry catches up and provides a robust infrastructure.

To this end I thought I would externalize some of my own primitive efforts, as extensions to my Pixelmed Java DICOM toolkit. Specifically, I put together a little application called DoseUtility, which brings together a number of components that I have been working on, including the construction and validation of Radiation Dose SR objects, as well as the ability to perform OCR on GE dose screen saved images. I have already used the validator to good effect during the last few connectathons, and the experience constructing and testing it has led to a number of proposed changes to the standard and the IHE profile.

Eventually I hope to extend this tool and its components to provide a complete infrastructure for dose management, at least from the DICOM and IHE side of the problem. Currently it focuses on CT, but it will be extended to fluoroscopy and projection X-ray soon, as well as injected dose from NM and PET, as those standards evolve.

I dare say that the various academic groups who have been working on the same types of problems may well have much more sophisticated tools, likely more easily integrated with their own PACS and RIS, perhaps taking advantage of proprietary APIs. As yet, I am unfamiliar with the specifics of most of them, but I will make a catalog of whatever becomes available.