Radiation Exposure Monitoring

This article deals with a managerial control system for intended dose exposure of the human body for medical purposes due to ionizing radiation. For measurement of dose uptake within radiological protection, see Dosimetry.

Background

Studies^[1] have revealed that doses of ionizing radiation resulting from medical radiography procedures varies widely between equipment and facilities, suggesting that equivalent dose can be lowered to reduce their harmful effects without jeopardizing their diagnostic efficacy. In the majority of medical procedures involving radiation, the benefits to patients' health outweigh the risks.

The diagnostic procedures most commonly associated with avoidable radiation doses are CT scan, nuclear medicine, and fluoroscopy; however, all modalities delivering radiation can contribute to unnecessary risk. monitoring can 1) increase patient safety, 2) reduce unnecessary workload for radiologists, radiographers, and administrative and support staff, 3) reduce expenditures for inappropriate exams, 4) support better "best practice" radiology, and 5) assist clinical decision making by referring physicians.

Tracking the total radiation dose delivered over time can facilitate a number of activities that contribute to the goal of better patient care through reduced radiation doses.

Uses

Integrating the Healthcare Enterprise (IHE), an industry group, summarizes the benefits to a broad range of stakeholders:^[2]

For imaging physicians, monitoring exposures can assist in determining how changes in techniques and protocols impact radiation dose as well as image quality.
For facilities exposing patients to radiation, monitoring exposures can help ensure policies, procedures and protocols are adequate and being followed appropriately. This will enable them to maintain patient doses "as low as reasonably achievable" (ALARA).
For patients' physicians, overall data provided from monitoring exposures can help determine (in consultation with the imaging physician) if the benefit from the diagnostic information provided by an individual examination (or additional examinations) outweigh any small risk that may be associated with the imaging exam.
For medical physicists, having post-procedure information available for individual patients may help them make essential patient-specific dose estimates for pregnant patients or patients exhibiting skin erythema as a result of long fluoroscopy examinations.
For professional societies and regulatory agencies, a collection of exposure estimation data can be useful when setting or reviewing radiation dose related guidelines. Many groups have expressed a desire to establish standards of practice or dose reference levels based on a quantitative understanding of current practice, though to date it has proven prohibitively difficult to collect such data.
For physicists and physicians, this kind of data can be vital to answering some of the fundamental scientific questions that remain, and can contribute to a more detailed understanding of the health impacts of radiation exposure and how it should be measured and managed.

Collecting and utilizing dose data

A challenge in automating the reporting of radiation exposure estimations has traditionally been a function of whether the record of dose provided by a manufacturer is persistent (i.e. stored electronically) or transient (i.e. displayed on a read-out). Many current radiology devices provide only transient records, either in the form of human-readable dose screens that require manual intervention (i.e. pencil and paper) to permanently capture the patient exposure, or else in the equally perishable data generated by a modality-performed procedure step (MPPS) created to help manage the scheduling system.

MPPS is insufficient, having a limited ability to encode complex data, and no options for long-term storage or queries. Newer scanners are able to create DICOM Radiation Dose Structured Reports (RDSRs) alongside the images themselves. REM addresses perishable dose data by creating a persistent record that can be sent to a central repository, and then queried and analyzed by health information systems for either a specific patient's history or for analysis of radiation exposure levels among patient groups, platforms, or clinical operations.

ACR Dose Index Registry (DIR)

The American College of Radiology (ACR) operates the National Radiology Data Registry (NRDR), a warehouse of ACR registry databases that compare radiology facilities regionally and nationwide according to facility type. One of the registered databases is the Dose Index Registry (DIR),^[3] a data registry that allows facilities to compare their CT dose estimation indices to regional and national values. Information related to dose indices for all CT exams is collected, anonymized, transmitted to the ACR, and stored in a database. Institutions are then provided with periodic feedback reports comparing their results by body part and exam type to aggregate results. Data collected from the registry will be used to establish national benchmarks for CT dose indices.

Goals of the DIR are as follows:

Provide physicians and technologists with reference doses based on anatomy, purpose of the study, and patient size. Establish appropriate dose ranges for high-volume and high-dose diagnostic imaging studies.
Help radiologists and radiographers assure that the proper dosing protocol is in place for the patient being treated.
Institute a process for the review of all dosing protocols either annually or every two years to ensure that protocols adhere to the latest evidence.
Investigate patterns outside the range of appropriate doses. Track radiation doses from exams repeated due to insufficient image quality or lack of availability of previous studies to identify the causes. Address and resolve these problems through education and other measures.
Record the dosage or exposure as part of the study's summary report of findings.

Legislative activities mandating REM

As a result of the risks associated with ionizing radiation, there has been growing industry and legislative activities that encourage or mandate stricter oversight of radiation delivery. For example, the United States Department of Health and Human Services Centers for Medicare & Medicaid Services (CMS) will require the accreditation of facilities providing advanced imaging services (CT, MRI, PET, nuclear medicine) in non-hospital, freestanding settings beginning January 1, 2012.

The state of California has mandated that facilities furnishing CT X-ray services become accredited by July 1, 2013. The California law^[4] also requires documentation of the dose of each CT exam, annual verification of each dose by a medical physicist, and reporting of dose errors to patients and physicians. A fix-up bill AB-510 is likely to become law in the next few weeks. It contains a provision for dose information to be added to the radiologist's report where it would be routinely visible to referring physicians and patients. Finally, The Joint Commission has issued a Sentinel Event Alert, Issue 47 on radiation risks of diagnostic imaging.

A closer look at the California law

Beginning on July 1, 2012, facilities utilizing CT X-ray systems in the State of California will be required to record the dose of radiation on every CT study by either recording the dose within the patient's radiology report, or attaching the protocol page (that includes the dose of radiation) to the radiology report. The bill is limited to CT systems capable of calculating and displaying dose. Facilities conducting the CT studies will be required to send each CT study and protocol page that lists the technical factors and dose of radiation to the electronic picture archiving and communications system. The bill requires the displayed dose to be verified annually by a medical physicist to ensure the displayed doses are within 20 percent of the true measured dose, unless the facility is accredited.

The bill further mandates that health facilities—except for an event that results from patient movement or interference—be required to report to the Department of Public Health any event in which the administration of radiation resulted in any of the following:

Repeating of a CT examination, unless otherwise ordered by a physician or radiologist, if the following dose values are exceeded:

0.05 Sv (5 rem) effective dose equivalent;
0.5 Sv (50 rem) to an organ or tissue; or
0.5 Sv (50 rem) shallow dose equivalent to the skin.

CT X-ray irradiation of a body part other than that intended by the ordering physician or a radiologist if one of the following dose values are exceeded:

0.05 Sv (5 rem) effective dose equivalent;
0.5 Sv (50 rem) to an organ or tissue; or
0.5 Sv (50 rem) shallow dose equivalent to the skin.

Standards and Integrating the Healthcare Enterprise (IHE)

Integrating the Healthcare Enterprise (IHE) is an initiative by healthcare professionals and industry to improve the way computer systems in healthcare share information. IHE "Integration Profiles" help make systems easier to implement and integrate, and help care providers use information more effectively. The ultimate goal is more efficient delivery of optimal patient care. IHE Integration Profiles describe clinical information management use cases and specify how to use existing standards (HL7, DICOM, etc.) to address them. Systems that implement integration profiles solve interoperability problems. For equipment vendors, Integration Profiles are implementation guides. For healthcare providers, Integration Profiles are shorthand for integration requirements in purchasing documents. Integration Statements tell customers the IHE Profiles supported by a specific release of a specific product.

The REM Profile enables imaging modalities to export radiation exposure estimation details in a standard format. Radiation reporting systems can either query for these "dose objects" periodically from an archive, or receive them directly from the modalities. The radiation reporting system is expected to perform relevant dose QA analysis and produce related reports. The analysis methods and report format are not considered topics for standardization and are not covered in the profile. The profile also describes how radiation reporting systems can submit dose estimation reports to centralized registries such as might be run by professional societies or national accreditation groups. In the United States, the American College of Radiology DIR^[5] is one such registry. By profiling automated methods, the profile allows dose information to be collected and evaluated without imposing a significant administrative burden on staff otherwise occupied with caring for patients.

In addition to supporting profile quality assurance (QA) of the technical process at the local facility, (e.g. determining if the dose was appropriate for the procedure performed), the profile also supports population analysis performed by national registries. Compliant software products are capable of de-identifying and submitting dose reports to a national dose register securely, making it relatively simple for groups such as ACR to collect and process dose data from across the country once they have recruited participating sites.

Challenges

Fluoroscopy monitoring

Most fluoroscopic x-ray equipment can provide an estimate of the cumulative dose that would have resulted to a point on the skin if the x-ray beam was stationary during the complete procedure. Such an estimate is derived from the fluoroscopic technique factors and the total fluoroscopic exposure time, including any image recording, or from built-in dosimetry systems found on some newer equipment. However, these systems, known as dose-area-product meters (DAP meters), do not directly provide skin dose information without further knowledge of the sizes of the x-ray beam during the entire procedure. The relationship between cumulative skin dose and peak skin dose is highly variable, as has been demonstrated in a number of publications.^[6]

In Sentinel Alert 47,^[7] The Joint Commission specifically excludes fluoroscopy and radiation therapy. Individual facilities installing REM software may still choose to capture fluoroscopy dose information for internal use.

Limitations of dose monitoring

According to IHE, "It is important to understand the technical and practical limitations of dose monitoring and the reasons why the monitored values may not accurately provide the radiation dose administered to the patient":^[8]

The values provided by this tool are not "measurements" but only calculated estimates.
For computed tomography, "CTDI" is a dose estimate to a standard plastic phantom. Plastic is not human tissue. Therefore, the dose should not be represented as the dose received by the patient.
For planar or projection imaging, the recorded values may be exposure, skin dose or some other value that may not be patient's body or organ dose.
It is inappropriate and inaccurate to add up dose estimates received by different parts of the body into a single cumulative value.

Despite such limitations, interest in monitoring radiation dose estimates is clearly expressed in such documents as the European directive Euratom 97/43^[9] and the American College of Radiology Dose Whitepaper.^[10]