THE MEDICAL PHYSICS CONSULT MAHADEVAPPA MAHESH, MS, PHD, RICHARD L. MORIN, PHD
The DICOM Radiation Dose Structured Report: What It Is and What It Is Not Ioannis Sechopoulos, PhD, Annalisa Trianni, DMP, Donald Peck, PhD Although most radiologists and medical physicists have heard of the term “DICOM,” which stands for Digital Imaging and Communications in Medicine, many associate this term only with the format used to save radiographic images. However, the DICOM standard actually includes the specifications for communicating many types of medical-related data in an organized manner so that devices from different hardware and software manufacturers can talk to one another [1]. Examples of these different types of data, called nonimage information object definitions (IODs) in DICOMspeak, are treatment plans, waveforms, and structured reports, among others. Over the past few years, there has been an increasing awareness of the importance of the radiation dose used to acquire images with ionizing radiation, and with it there has been an increase in the efforts to optimize the levels of radiation used. For this, it is important to be able to store and analyze data regarding the exposure involved during these acquisitions in a standard format that can be machine read and interpreted. Although exposure information is recorded in the header of each image, this solution is not complete or ideal for various reasons. In the first place, there is no standard method to decouple the image itself from the exposure information. Therefore, to access and store the exposure information, it must be accompanied by the image data,
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resulting in vast increases in storage space and transmission time. In addition, if images are not stored for any reason (fluoroscopy frames not recorded, technical issues during acquisition, patient motion, etc), the information regarding that exposure is lost, although that irradiation event did take place and the patient was exposed. Furthermore, the exposure information included with the image is only related to the irradiation event used directly to create the data in the accompanying image. For example, the information on the low-dose preimage exposure in digital mammography used by the automatic exposure control process to determine the correct acquisition technique is not included in the header of the resulting mammographic image. Also, if an image is duplicated for any reason (eg, additional reconstructions or image processing), the exposure information in the image header is also duplicated, and therefore automated methods that gather all the exposure information could result in overestimates of exposure and dose. To address these and other issues and limitations, a nonimage IOD, the Radiation Dose Structured Report (RDSR) for projection x-ray angiography was added to the DICOM standard in 2005. The RDSR was developed to create a standardized format to record all the information related to the exposure parameters used for each irradiation event undergone by the patient, independent of the image data. Since its
initial inclusion in the standard, additional specific RDSR objects have been developed for CT, mammography, digital and computed radiography and recently nuclear medicine. Implementation of these objects by manufacturers is ongoing. The RDSR includes all information related to the x-ray tube output that has an impact on the radiation dose to the patient. In addition to data on tube voltage, tube current, exposure time, tube filtration, and so on, that is standard and applicable to all x-raybased modalities, modality-specific data are also included, such as doselength product and CT dose index (CTDI) for CT imaging. As can be seen from this example, the RDSR may include not only values for parameters that are directly set by the system (eg, exposure time) but also for parameters that are based on estimates from measurements (eg, CTDI, which is an estimate of dose to a specific phantom during the acquisition of a single axial CT scan). Information on the patient (name, identifier, etc), the procedure performed, the protocol used, and so on, is also included in the RDSR. As opposed to an image IOD, the RDSR includes information on each and every irradiation event. For example, a RDSR includes the information for any rejected and therefore repeated image acquisition. Also, an entire fluoroscopic sequence involving one pedal press will be included in the RDSR as a single irradiation event. The
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recording of exposure information after each irradiation event independent of any image creation avoids the issue of “lost” dose-related details due to image rejection or deletion and the creation of duplicate dose records due to copying of images. Because of the information it provides, the RDSR can be used for a wide range of applications. It could be a valuable tool during the optimization of image acquisition protocols. For example, after modification of CT protocols for a certain type of acquisitions (eg, contrastenhanced abdominal CT), followup by analysis of RDSR data on a number of patients spanning a certain time period can provide information on whether the expected optimization was achieved, considering the variability in patient size and imaging system models, capabilities, and manufacturers. In a similar fashion, RDSR data can be used to directly inform national dose registries such as the ACR Dose Index Registry [2], without relying on the information provided in image headers, with its previously discussed limitations. Other uses, such as providing clinical medical physicists with the information necessary to perform patient and fetal dose estimates, are also a possibility. It should be noted that the RDSR provides information on the parameters relevant to the x-ray exposure output by the imaging system but does not provide information on patientspecific radiation dose. It must be remembered that dose-related metrics
such as CTDI and dose-length product in CT and average glandular dose in mammography are estimates of dose to specific and standardized phantoms and do not take into account patient size, composition, orientation, and so on. As mentioned earlier, the data in a RDSR may allow, or at least provide part of the data necessary, for a physicist to estimate the dose to a patient. However, the RDSR does not include patient-specific dose estimates or all of the information needed to obtain these estimates. In addition, because the RDSR is created by the image acquisition system, it does not include a template for patient-specific dose data to be recorded after estimation. To accommodate this limitation, a new nonimage IOD, the Patient Radiation Dose Structured Report (P-RDSR), is being developed by the DICOM Standards Committee. It is envisioned that the P-RDSR will contain two key sets of information to perform patientspecific dose estimates. First, the P-RDSR will contain the information lacking in the RDSR that is related to the irradiation event that affects the patient-specific dose estimate (eg, patient size and position). Second, the P-RDSR will provide the archival tool for the medical physicist, or other person or computer system, performing the patient-specific dose estimation to record the methodology used to achieve the estimate. For example, data on the patient representation used (eg, a simple geometric phantom with size compensation, an anthropomorphic phantom model, a voxelized representation of an actual patient from CT
images), dose estimation method used (eg, Monte Carlo simulations, thermoluminescent dosimetric measurements in phantoms), and other relevant inputs to the dose estimation method will be recorded in the P-RDSR to ensure record keeping and reproducibility of methodology. Finally, the P-RDSR will include the resulting dose estimate, which may be a single number (eg, breast average glandular dose), a set of numbers (eg, organ absorbed dose to a number of organs), or a 2-D or 3-D image representation of dose data (eg, a skin dose map). When developed and implemented, the P-RDSR will not replace the RDSR or necessarily augment it; both are dose-related tools that are aimed at fulfilling different needs and tasks within radiology. Given the importance of awareness of radiation dose, the need to optimize and ensure the adequacy of image acquisition protocols, and the need to record at both the site and national levels the radiation exposure used to acquire clinical images with ionizing radiation, both clinical medical physicists and radiologists should be aware of the RDSR, its content, its meaning, and the possibilities it brings about.
REFERENCES 1. National Electrical Manufacturers Association. The DICOM Standard 2015b. Available at: http://dicom.nema.org/standard.html. Accessed May 5, 2015. 2. American College of Radiology. Dose Index Registry. Available at: http://www.acr. org/Quality-Safety/National-Radiology-DataRegistry/Dose-Index-Registry. Accessed May 5, 2015.
Ioannis Sechopoulos, PhD, is from the Departments of Radiology and Imaging Sciences, Hematology, and Medical Oncology and the Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia. Annalisa Trianni, DMP, is from the Department of Medical Physics, S. Maria Della Misericordia University Hospital, Udine, Italy. Donald Peck, PhD, is from the Department of Diagnostic Radiology, Henry Ford Health System, Detroit, Michigan. The authors have no conflicts of interest to disclose. Ioannis Sechopoulos, PhD: Emory University, Winship Cancer Institute, 1701 Upper Gate Drive NE, Suite 5018, Atlanta, GA 30322; e-mail: [email protected]. Journal of the American College of Radiology Sechopoulos, Trianni, Peck n The Medical Physics Consult
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The DICOM Radiation Dose Structured Report: What It Is and What It Is Not Ioannis Sechopoulos, PhD, Annalisa Trianni, DMP, Donald Peck, PhD Although most radiologists and medical physicists have heard of the term “DICOM,” which stands for Digital Imaging and Communications in Medicine, many associate this term only with the format used to save radiographic images. However, the DICOM standard actually includes the specifications for communicating many types of medical-related data in an organized manner so that devices from different hardware and software manufacturers can talk to one another [1]. Examples of these different types of data, called nonimage information object definitions (IODs) in DICOMspeak, are treatment plans, waveforms, and structured reports, among others. Over the past few years, there has been an increasing awareness of the importance of the radiation dose used to acquire images with ionizing radiation, and with it there has been an increase in the efforts to optimize the levels of radiation used. For this, it is important to be able to store and analyze data regarding the exposure involved during these acquisitions in a standard format that can be machine read and interpreted. Although exposure information is recorded in the header of each image, this solution is not complete or ideal for various reasons. In the first place, there is no standard method to decouple the image itself from the exposure information. Therefore, to access and store the exposure information, it must be accompanied by the image data,
712
resulting in vast increases in storage space and transmission time. In addition, if images are not stored for any reason (fluoroscopy frames not recorded, technical issues during acquisition, patient motion, etc), the information regarding that exposure is lost, although that irradiation event did take place and the patient was exposed. Furthermore, the exposure information included with the image is only related to the irradiation event used directly to create the data in the accompanying image. For example, the information on the low-dose preimage exposure in digital mammography used by the automatic exposure control process to determine the correct acquisition technique is not included in the header of the resulting mammographic image. Also, if an image is duplicated for any reason (eg, additional reconstructions or image processing), the exposure information in the image header is also duplicated, and therefore automated methods that gather all the exposure information could result in overestimates of exposure and dose. To address these and other issues and limitations, a nonimage IOD, the Radiation Dose Structured Report (RDSR) for projection x-ray angiography was added to the DICOM standard in 2005. The RDSR was developed to create a standardized format to record all the information related to the exposure parameters used for each irradiation event undergone by the patient, independent of the image data. Since its
initial inclusion in the standard, additional specific RDSR objects have been developed for CT, mammography, digital and computed radiography and recently nuclear medicine. Implementation of these objects by manufacturers is ongoing. The RDSR includes all information related to the x-ray tube output that has an impact on the radiation dose to the patient. In addition to data on tube voltage, tube current, exposure time, tube filtration, and so on, that is standard and applicable to all x-raybased modalities, modality-specific data are also included, such as doselength product and CT dose index (CTDI) for CT imaging. As can be seen from this example, the RDSR may include not only values for parameters that are directly set by the system (eg, exposure time) but also for parameters that are based on estimates from measurements (eg, CTDI, which is an estimate of dose to a specific phantom during the acquisition of a single axial CT scan). Information on the patient (name, identifier, etc), the procedure performed, the protocol used, and so on, is also included in the RDSR. As opposed to an image IOD, the RDSR includes information on each and every irradiation event. For example, a RDSR includes the information for any rejected and therefore repeated image acquisition. Also, an entire fluoroscopic sequence involving one pedal press will be included in the RDSR as a single irradiation event. The
1546-1440/15/$36.00
n
ª 2015 American College of Radiology http://dx.doi.org/10.1016/j.jacr.2015.04.002
recording of exposure information after each irradiation event independent of any image creation avoids the issue of “lost” dose-related details due to image rejection or deletion and the creation of duplicate dose records due to copying of images. Because of the information it provides, the RDSR can be used for a wide range of applications. It could be a valuable tool during the optimization of image acquisition protocols. For example, after modification of CT protocols for a certain type of acquisitions (eg, contrastenhanced abdominal CT), followup by analysis of RDSR data on a number of patients spanning a certain time period can provide information on whether the expected optimization was achieved, considering the variability in patient size and imaging system models, capabilities, and manufacturers. In a similar fashion, RDSR data can be used to directly inform national dose registries such as the ACR Dose Index Registry [2], without relying on the information provided in image headers, with its previously discussed limitations. Other uses, such as providing clinical medical physicists with the information necessary to perform patient and fetal dose estimates, are also a possibility. It should be noted that the RDSR provides information on the parameters relevant to the x-ray exposure output by the imaging system but does not provide information on patientspecific radiation dose. It must be remembered that dose-related metrics
such as CTDI and dose-length product in CT and average glandular dose in mammography are estimates of dose to specific and standardized phantoms and do not take into account patient size, composition, orientation, and so on. As mentioned earlier, the data in a RDSR may allow, or at least provide part of the data necessary, for a physicist to estimate the dose to a patient. However, the RDSR does not include patient-specific dose estimates or all of the information needed to obtain these estimates. In addition, because the RDSR is created by the image acquisition system, it does not include a template for patient-specific dose data to be recorded after estimation. To accommodate this limitation, a new nonimage IOD, the Patient Radiation Dose Structured Report (P-RDSR), is being developed by the DICOM Standards Committee. It is envisioned that the P-RDSR will contain two key sets of information to perform patientspecific dose estimates. First, the P-RDSR will contain the information lacking in the RDSR that is related to the irradiation event that affects the patient-specific dose estimate (eg, patient size and position). Second, the P-RDSR will provide the archival tool for the medical physicist, or other person or computer system, performing the patient-specific dose estimation to record the methodology used to achieve the estimate. For example, data on the patient representation used (eg, a simple geometric phantom with size compensation, an anthropomorphic phantom model, a voxelized representation of an actual patient from CT
images), dose estimation method used (eg, Monte Carlo simulations, thermoluminescent dosimetric measurements in phantoms), and other relevant inputs to the dose estimation method will be recorded in the P-RDSR to ensure record keeping and reproducibility of methodology. Finally, the P-RDSR will include the resulting dose estimate, which may be a single number (eg, breast average glandular dose), a set of numbers (eg, organ absorbed dose to a number of organs), or a 2-D or 3-D image representation of dose data (eg, a skin dose map). When developed and implemented, the P-RDSR will not replace the RDSR or necessarily augment it; both are dose-related tools that are aimed at fulfilling different needs and tasks within radiology. Given the importance of awareness of radiation dose, the need to optimize and ensure the adequacy of image acquisition protocols, and the need to record at both the site and national levels the radiation exposure used to acquire clinical images with ionizing radiation, both clinical medical physicists and radiologists should be aware of the RDSR, its content, its meaning, and the possibilities it brings about.
REFERENCES 1. National Electrical Manufacturers Association. The DICOM Standard 2015b. Available at: http://dicom.nema.org/standard.html. Accessed May 5, 2015. 2. American College of Radiology. Dose Index Registry. Available at: http://www.acr. org/Quality-Safety/National-Radiology-DataRegistry/Dose-Index-Registry. Accessed May 5, 2015.
Ioannis Sechopoulos, PhD, is from the Departments of Radiology and Imaging Sciences, Hematology, and Medical Oncology and the Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia. Annalisa Trianni, DMP, is from the Department of Medical Physics, S. Maria Della Misericordia University Hospital, Udine, Italy. Donald Peck, PhD, is from the Department of Diagnostic Radiology, Henry Ford Health System, Detroit, Michigan. The authors have no conflicts of interest to disclose. Ioannis Sechopoulos, PhD: Emory University, Winship Cancer Institute, 1701 Upper Gate Drive NE, Suite 5018, Atlanta, GA 30322; e-mail: [email protected]. Journal of the American College of Radiology Sechopoulos, Trianni, Peck n The Medical Physics Consult
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