Study Dose Information
The DICOM Standard has defined a set of Radiation Dose Structured Report (RDSR) data objects for recording and storing dose details in a DICOM study.
These templates have been developed in cooperation with medical physicists to incorporate common summary metrics such as CT Dose Index (CTDI), Dose Length Product (DLP), Dose Area Product (DAP), as well as detailed geometric and technique information that can be used to estimate the radiation dose to a patient.
Support for these RDSR objects will appear in a product's DICOM Conformance Statement (DCS) document which is generally available on vendor websites.
It should be noted that CTDIvol and DLP must be considered in the context of the phantom size (also recorded in the RDSR) used to calculated the metric. While these are good metrics to track and manage dose-related technique, using these scanner output metrics to estimate actual dose to a specific patient is complex and should be done in cooperation with a medical physicist.
Patient Dose Estimates
In addition to the above objects for recording the radiation details of an imaging study, the DICOM Standard has also defined an object for storing the results of an estimation of actual radiation dose to a patient. This P-RDSR object typically uses one or more RDSR objects as input.
IHE REM Profile
The IHE (Integrating the Healthcare Enterprise) initiative has developed a pair of Profiles that specify architecture and features for collecting and distributing DICOM RDSR data.
A variety of released products have implemented these Profiles and over 35 vendors have successfully demonstrated interoperability for the REM Profile at IHE Connectathon testing events. Some reporting systems may be capable of automatically extracting dose values directly from RDSR objects for insertion into radiology reports.
MITA XR-29 Dose Check
As a component of the MITA XR-29 Dose Check standard, DICOM CT RDSR is being made available in most new model CT Scanners since 2012.
Legacy Dose Reporting
Prior to the adoption of RDSR, many CT systems stored an image containing a screen capture of a dose report, listing CTDI and DLP values for each CT series. Although such reports contain much less information than the RDSR, and the values cannot be normally directly processed, the report can be displayed to a human, and there is commercial and open source software which will attempt to do optical character recognition and text parsing to partially populate an RDSR or other database with what values it can extract. Some CT systems provide DLP value as a private attribute within such images, or/and in the MPPS messages.
DICOM Image Headers
Finally, the headers of DICOM images may contain specific attribute tags with a subset of the dose information contained in an RDSR. For example, CTDIvol (0018,9345) describes the average dose for this image for the selected CT conditions of operation. Since DLP represents dose across multiple images, it does not belong in the header of individual images, although it is available in the RDSR for the exam. Estimation of study dose based on CTDI values in image headers is significantly complicated by the presence of multiple reconstructions from a single acquisition, issues like over-ranging, etc. Handling such issues is one reason for the introduction of RDSR.
Further information
For information on addressing the informatics, physics, and clinical practice issues around radiation dose, readers are encouraged to investigate seminars and materials provided by professional societies such as the Society of Imaging Informatics in Medicine, the American Association of Physicists in Medicine, and the American College of Radiology.