AAPM medical physics practice guideline 6.a.: Performance characteristics of radiation dose index monitoring systems

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: •Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. •Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States.
The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner.
Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.
The following terms are used in the AAPM practice guidelines: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline.
Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

| INTRODUCTION
Radiation dose index monitoring (RDIM) systems may generally be identified as software that retrospectively collects radiation dose indices (RDI) and other acquisition parameters from imaging studies that use ionizing radiation, and stores those indices in a relational database along with patient demographics. The software typically includes a graphical user interface, which allows the end user to visualize RDI by study type, patient or other category for quality assurance or patient-or study-specific investigations. When utilizing data from these RDIM systems, it is important to understand the applications and limitations of the recorded dose indices. 1

1.A | Overview
Many facilities are implementing RDIM software systems in part due to increasing public concern over the use of ionizing radiation in diagnostic examinations, in light of radiation injuries from diagnostic imaging equipment, [3][4][5] and to comply with applicable state regulations and accreditation requirements. The RDIM systems currently available from several vendors vary widely in their capabilities, degree of difficulty in implementing, ease of customizing the analyses of the data, and ability to grow with the change in clinical practice, imaging equipment, or regulatory requirements. It is therefore recommended that a facility considering the acquisition of a RDIM system create desired performance criteria just as for any other major piece of software such as voice recognition systems or picture archiving and communications systems (PACS). This practice guideline is intended to provide a guide to the minimum general and modality-specific requirements for RDIM systems.
Before embarking on an effort to develop or install an RDIM system, it is essential to identify how the data will be used, who will oversee and support the facility's RDIM effort, who will have access to the software and its data, and at what levels, who will implement the relevant aspects of the software within each modality, how often reviews of the collected data and of the program will occur, who is the audience of the reviews, and what the reviews will entail. The review process should also identify the necessary follow-up actions.

Specific questions include:
1. What is the primary goal of the project, e.g., regulatory or quality improvement (QI)?
2. What will be the reporting structure [

5.
Identifying the type of feedback that will be provided to physicians, (e.g., ordering and protocoling) and the mechanism for communicating that feedback.

1.B | Goals and rationale
The primary rationale for the acquisition and use of RDIM software is to enhance and expand existing QA and quality control (QC) efforts in a facility. When used for QA purposes, RDIM software may aid a QMP or other user in determining utilization practices by ordering physicians, identifying cases that are outliers compared to other similar cases, studies with parameters outside predefined reference levels, or image-guided interventions with exposures above a threshold for tissue reactions. With tracking of key patient-or study-specific RDI and imaging parameters, it is possible to enhance existing diagnostic imaging QA programs. 6 Comprehensive QA programs should address relevant critical aspects of patient imaging including positioning, motion, collimation or imaging extent, and overall image quality. Consequently, QA programs should consider the image acquisition and reconstruction parameters affecting dose and image quality performance across different systems within a given imaging modality, such as the various types of general radiography equipment used within a facility.
The ability to capture imaging parameters specific to the individual patient study varies considerably by modality and age of equipment. These will be addressed in the modality-specific sections below.
Additional approaches to QA are enabled by the use of RDIM software. The automated collection of large numbers of studies from modalities and protocol configurations allows QMPs to identify opportunities for radiation dose optimization, and analysis of practice characteristics by technologist, procedure code, or referring/performing physician, as examples.

1.C | Potential limitations and precautions
Care should be taken when purchasing RDIM systems to understand the features and capabilities, since some may not be relevant or valid for use in all situations. The appropriate use and interpretation of the data collected and generated by an RDIM system, especially in relationship to patient histories, is an essential role of the QMP. A number of situations describing potential limitations are highlighted below.

1.C.1 | Cumulative patient dose history
Assessing risk of deterministic skin injury is the most appropriate use for cumulative dose estimates. [7][8][9] However, predictions of hypothetical cancer incidence and deaths in patient populations exposed to doses encountered in imaging are highly speculative, may lead to inappropriate medical decision making and thus are strongly discouraged. Cumulative or longitudinal dose values obtained from summing RDI or RDI-derived quantities for an individual patient indicate stochastic risks that are based on hypothetical cancer incidence or death. Therefore, they should not be used as a basis for decisions regarding subsequent medical radiological procedures. 10,11

1.C.2 | RDIs are not patient dose
It is of utmost importance to understand that the RDI reported by modalities are not accurate reflections of the patient absorbed dose. 1,12 In certain cases, the use of Monte Carlo dose estimates, size-based corrections, or peak skin dose estimates may give a reasonable estimate of the patient dose. The methods used to generate these dose estimates must be transparent and based on peerreviewed scientific literature. A QMP should be involved in considering the appropriate use and interpretation of the dose estimates.
Furthermore, the summation of modality-generated RDIs from exposures to different areas of the body, even if the exposures occur during the same examination or within a short amount of time, may not produce a meaningful result.

1.C.3 | Patient dose estimates
Consideration and discussion of the stochastic risk associated with the low levels of ionizing radiation to which patients are exposed during diagnostic imaging studies is beyond the scope of this document. The use of effective dose estimates using population-based tissue-weighting factors to quantify risk for individual patients is not supported by current science. 2 There is substantial and convincing scientific evidence for health risks due to tissue reactions 13 from elevated or high radiation doses.
Alert levels can be established by modality, such as interventional fluoroscopy or dynamic computed tomography (CT) acquisitions (perfusion, CT-guided biopsy, etc.), to flag studies after they are completed for the possibility of tissue reactions. For estimation of tissue reactions, a peak skin dose estimate is usually desired. A QMP should review the individual patient record and the data associated with image acquisition parameters to make such assessments. 7   2. Radiation Dose Index (RDI) -A RDI is a descriptor of the radiation used to generate images for physician interpretation.

MONITORING SOFTWARE TEAM
Successful implementation of RDIM software requires a team effort.
At a minimum, this team must consist of a QMP, a lead radiologist, a lead technologist, and an individual from the PACS/IT department.
The team should include a senior administrator with authority over all departments that use radiation sources for imaging (such as a Chief Medical, Operating, or Administrative Officer, Vice President, or as determined by facility leadership). Alternatively, an administrator (manager, director, etc.) from each such department should participate. In addition, a physician from each other department using radiation-generating imaging equipment (e.g., cardiology, pain management, neurosurgery, vascular surgery) should participate. At many facilities, the RSO may be a key member of the team.
If the RDIM team does not include a senior administrator, there should be a clear delineation of its reporting structure. Facilities with a RSC should consider having the RDIM team report to the RSC. This team must be responsible for decisions regarding the selection of the software system. Each team member brings different expertise and may have a variety of responsibilities in the implementation and use of the RDIM software. To be successful, it is very important that the expectations of roles and responsibilities of each member are clearly described. The ability to work together in a team environment will be an important attribute of each member of this group.

| INFORMATICS RECOMMENDATIONS/ REQUIREMENTS
RDI monitoring is fundamentally an imaging informatics and medical physics effort, combining computer science, information technology, and networking with concepts and problems from medical imaging. A viable RDIM system must interface with a number of other clinical imaging information systems, possibly including, but not limited to, PACS, RIS, EMR, voice recognition and dictation systems, critical results reporting systems, and operational and quality dashboards.
Users evaluating RDIM technology should carefully consider a number of informatics-related system integration factors in selecting a solution and planning their budget and time needs for installation and integration. For example, some commercial RDIM solutions consist of hardware and software, while others consist of software and require the user to furnish server and workstation hardware to host the RDIM solution. The physical and logical architecture of the system must be examined to determine whether there are enough network ports in the right locations to connect all of the nodes that will send data to the RDIM solution or receive information from it. Each imaging modality might allow global configuration (at the imaging system console level) to send the desired type of RDI data to the RDIM system for all examinations, or information transfers may need to be configured within each individual preset imaging protocol. Likewise, each imaging system might automatically transmit the desired RDI data, or specific actions might be required of the operator to send the RDI data/file/object to the RDIM system. On some imaging modalities, the end user may have access to configure network settings and options to send RDI data, while on others, service passwords or special access may be needed to perform such configurations. This is a sampling of issues that require different approaches for the various combinations of RDIM and connected systems, which can lead to significant unforeseen costs and time delays if not planned for appropriately. Facilities should create performance expectations for these issues prior to system selection.
To ensure adequate interconnectivity, data security, and data integrity, the following informatics recommendations and requirements apply to all RDIM systems: 1. RDIM systems must communicate using appropriate DICOM and HL7 standards and conform with appropriate IHE integration profiles (e.g., REM).
2. RDIM systems must provide data portability, meaning that the RDI information database remains the property of and accessible to the healthcare institution (end user) after the termination of any RDIM software subscription or support agreement.
a. All RDI information, patient demographics, and other data transmitted to the RDIM system by the end user's systems must be made available to the end user in a format and medium that may be retained and accessed by the end user without proprietary tools associated with the RDIM system.  c. User documentation for RDIM systems should include a data portability summary describing the storage format and medium used for each type of data collected (and, if applicable, generated) by the system.

Patient PHI transmitted to and stored in RDIM systems is sub-
ject to the requirements of the HIPAA and HITECH laws and related regulations. The RDIM user must develop a written plan for data management and security. If PHI will be transmitted to any third party providing or supplying an RDIM solution, a written agreement with this party must be developed to address the data management and security responsibilities of both parties.   Backup data is subject to the information security requirements and considerations described above for PHI.

7.
A variety of means exist for collecting RDI data. Therefore, the end user of the RDIM system should carefully assess the type(s) of data that can be sent by each imaging device to be monitored and ensure that the RDIM system supports one or more data collection methods for all imaging devices. Examples of methods for RDI data collection are:  d. Determine whether each imaging system automatically transmits the desired data or whether specific actions must be taken by the operator to send the RDI data/file/object to the RDIM system. e. Determine whether the end user has the ability to configure the required connectivity settings or options on each imaging modality, RIS, PACS, or other connected system. Service engineers, applications specialists, or IT support personnel may need to be engaged to configure some transfers.

| RECOMMENDE D ELEMENTS COMMON TO ALL DOSE TR ACKING SOFTWARE INDE PEND ENT OF MOD ALITY
The following elements apply to all RDIM software and are independent of the specific imaging modality. As an essential tool for improving a QA program and ensuring regulatory compliance, RDIM software should provide users several fundamental functions that are available for all imaging modalities. (Table 1) 5.A | Common elements that are independent of modality 5.A.1 | Tracking of RDI For each imaging modality, its corresponding essential RDI must be recorded. There are often multiple irradiation events in a single patient examination (e.g., multiphase CT scans, irradiation from multiple views in fluoroscopic and other X-ray exams). The RDI of each irradiation event, including live fluoroscopy and rejected images must be recorded unambiguously if that information is transmitted to the RDIM software. In addition, available essential acquisition parameters should be recorded together with the corresponding RDI data. If the RDI information and/or acquisition parameters are not automatically recorded, the option of manual input of such information by the user must be provided.

5.A.2 | Notifications for RDI outside the defined range
It is often necessary to preset thresholds of RDI for different purposes, such as quality/safety assurance and regulatory compliance.
The RDIM software must allow users to set thresholds of RDI which may be based on a variety of criteria, including but not limited to modality, type of examination, and patient age. The users can determine the thresholds of RDI based on either their institution specific experience or publicly available resources such as published DRLs. In the scenario where the RDI of an examination exceeds its threshold, the predetermined target users must be notified in a timely manner.

If protected health information (PHI) is included in the notification, it
must be transmitted using a secure, HIPAA-compliant approach.

5.A.3 | Review or follow-up documentation
For each alert generated, the RDIM software must provide a means for users to document that the alert has been acknowledged, reviewed, or followed-up as appropriate. This should include a status flag or tag for each alert, so that alerts can be summarized by categories such as Needs Review, Under Review, Pending Follow-Up, Closed, etc. Each alert should also have input and storage for freetext notes to store information related to the alert and the followup. Since notes may contain PHI, review and follow-up documentation must be stored in a secure, HIPAA-compliant manner.

5.A.4 | User management
Access to the RDIM software must be limited to a group of authorized users, whose access is password protected. The level of data access and system configuration must be granted according to the specific role of each user or group of users as determined by the RDIM team.

5.A.6 | RDI analysis tools
The software should provide users tools to utilize the RDI information to assist with continuous practice quality improvement. Meaningful ways to analyze dose information should include but not be limited to comparing RDI of user-selected protocols across machines, analyzing the trending of RDI as a QA tool and reviewing patient history which could include examinations from multiple different imaging modalities.

5.A.7 | User interface elements
A user interface should provide a variety of functionalities for users to review the recorded RDI data, including but not limited to navigating examinations with customizable sorting options (e.g., chronologically, alphabetically, or by age), exploring detailed examination and RDI information of any user-selected examination, reviewing examination history of any user-selected patient, categorizing RDI T A B L E 1 Elements common to all modalities.

Elements Description
Essential RDI Essential RDI of the imaging modality must be recorded. If not automated, essential acquisition parameters must be able to be recorded with manual input capability.

Notifications for RDI outside a defined range
User-defined thresholds of RDI that trigger automatic notifications to a set of end users must be configurable in the RDIM software.

Review/follow-up documentation
User inputs for status tag and notes must be provided so that the user who reviews the alert can document acknowledgement of each alert and the status and outcome of any follow-up in the RDIM software.
User management Access to the RDIM software must be limited to a group of authorized users as determined by the facility.
Audit trails User identity, date and time stamp, and details of activity must be logged for all manual data inputs, edits, and deletions performed by RDIM software users.
RDI analysis tools RDI analysis tools should be provided to assist users in utilizing the collected information.

User interface elements
A user interface should provide key functionalities of reviewing the recorded RDI and imaging acquisition parameters. for capturing information about reviews of data other than alerts.
For example, users may find it beneficial to attach notes to a patient, examination, individual exposure event, or to a chart, plot, or table in the data review/analysis user interface.
The essential RDI for monitoring and notification for each modality are discussed in the modality-specific sections below.

| RECOMME NDED ELEMENTS SPECIFIC TO COMPUTED TOMOGRAPHY (CT)
CT provides the largest overall contribution to population radiation dose from medical imaging. 16 CT has been a particular area of focus for RDIM software 17,18 in part due to the number of highly publicized cases in which excessive amounts of radiation were delivered in CT examinations. 19,20 It is especially important to remember that the RDI associated with CT examinations are not the patient dose.
The minimum required elements apply to the collection of RDI from 3rd generation or "rotate-rotate" CT systems such as those found in diagnostic radiology departments, integrated with SPECT or PET systems and CT simulation systems found in Radiation Oncology If the modality includes a SSDE value in the DICOM metadata of a study, the software should be able to extract that information and WED and associate it with the examination in the database.

TO FLUOROSCOPY
The minimum requirements listed for fluoroscopy are applicable to all fluoroscopy-guided interventional (FGI) suites, general R/F rooms and mobile fluoroscopy units. Fluoroscopy time alone is not an T A B L E 2 Elements specific to CT.

Elements Description
Essential RDI CTDIvol, CTDI phantom, and DLP for each CT series must be recorded.

Notification of RDI outside of defined range
User-defined thresholds of RDI that trigger automatic notifications to a set of end users must be configurable.
Transmission of anonymized data to data repositories/ registries The software must possess the capability to transmit CT RDI to data repositories/registries.

Size-Specific Dose Estimate (SSDE) calculation
Calculation of the SSDE for applicable acquisitions should be available.
adequate quantity for assessing deterministic or stochastic risk to the patient. 23 General convention is to utilize air kerma at the reference point (K a,r ) 8 to assess examinations for deterministic risks such as skin erythema and desquamation, epilation, or dermal atrophy, and to use kerma-area product (P KA ) for stochastic risk assessment. 24,25 For this reason, examination time, K a,r and P KA must be recorded, and when possible detailed information for each irradiation event of a procedure (e.g., fluoroscopy as well as 2D and 3D acquisition events) should be recorded so a more thorough assessment of peak skin dose (PSD) can be performed. Given that the displayed K a,r may be inaccurate by as much as AE35%, a QMP should assess whether a correction factor should be applied to the displayed K a,r . 26,27 RDIM software should allow for unit-specific (by imaging system) correction factors to be assigned for accurate reporting of cumulative K a,r . (Table 3) 7.A | Elements specific to fluoroscopy

7.A.1 | Automated monitoring of essential RDI
The software should be able to extract fluoroscopy time, K a,r , P KA , and total number of irradiation events from the appropriate structured fields. When available, the software should also automatically extract technical factors for each event acquisition log (i.e., RDI and system geometry for fluoroscopy as well as 2D and 3D acquisition event). Acquisition (or exposure or run or serial fluoroscopy) logs provide a line-by-line review of the stored exposures. Fluoroscopy system vendors vary in the extent of information provided, including but not limited to the individual event(s) exposure time, tube position, tube angle, mode, filtration, and K a,r . Acquisition logs can be utilized by a QMP to assess cumulative and peak skin doses. 7

7.A.2 | Manual entry of RDI
For older fluoroscopy units, RDI may not be available or the system may lack the capability to export data to the RDIM server. In these instances, at minimum, a record of fluoroscopy time may be sufficient to meet federal and state requirements, and would require manual entry by the user. This option must be available.

7.A.3 | Exposure incidence map
The DICOM RDSR or acquisition logs (with line-by-line history of the tube position and individual event cumulative K a,r ) should be utilized to create an incidence map that can more appropriately identify the peak air kerma value. The peak air kerma value as reported by the vendor can then be used by a QMP to assess the risk of tissue reactions of the procedure by estimating the PSD. 7

Elements Description
Essential RDI Fluoroscopy time, K a,r and P KA must be recorded; for bi-plane imaging systems, RDI must be recorded separately for each X-ray tube (e.g., A/B or PA/lateral). Number of irradiation events and acquisition details (i.e., kV, filtration, mA, number of frames, gantry angle, etc.) should be recorded.
Manual entry of RDI data and fluoroscopy time Manual entry of fluoroscopy time and RDI data should be available for systems with no RDI information displays or those which have no ability to transfer such data electronically.

Exposure incidence map
A graphical indicator of cumulative K a,r distribution across a two-dimensional plane that intersects the patient entrance reference point (PERP), potentially highlighting areas of peak air kerma, which can be used to estimate peak skin dose (PSD) 7 should be available for systems connected using RDSR.

Notification of RDI outside of defined range
User-defined thresholds of RDI that trigger automatic notifications to a set of end users must be configurable.

IEC standard
In addition to RDI, the RDIM system must be able to capture image receptor exposure indicators. For CR and DR systems that have adopted the IEC standard, 28 the software must allow entry of protocol-specific target indices and protocol-specific acceptable values for DI, and must allow alert levels to be applied to imported DIs falling outside the acceptable values, as described below in iii.

Manufacturer-defined
For systems that employ proprietary EIs, the software should allow capture of these indices as well as the ability to apply alert levels as described below in iii. Systems that utilize nonstandard exposure indices might not employ a DI. In these cases, the alert values must allow for specification of both a high and low limit. to be a commonly employed procedure, again primarily in the oncology setting. NM is also seeing increased use in the pediatric population, driven primarily by the use of 18 F-FDG in pediatric oncology. 29 As a consequence, monitoring of radiation exposure from NM procedures as well as dose reduction strategies have become important concerns in the NM community (Table 5). 30-32 9.A | Elements specific to nuclear medicine 9.A.1 | Automated monitoring of essential RDI and

RDI-related parameters
The patient demographic data listed below may be automatically included in all imaging procedures stored in the RDIM software, depending on how the various hospital informatics and modality systems are configured to communicate with each other and the RDIM software. Specifically, for NM the patient demographics must be included in the exam data, because the estimated dose for a given radiopharmaceutical depends not only on the administered activity, but also on the patient's gender, age (e.g., pediatric versus adult) and body habitus. The software must support automatic recording of the T A B L E 4 Elements specific to projection radiographic X-ray AGD, Average Glandular Dose.

Elements Description
Essential RDI KAP, K a,r , and AGD (mammography only) must be recorded if available.
Exposure indices Exposure indices, whether the standard IEC definition or manufacturer-defined, must be imported and recorded.
Notification of RDI outside of defined range User-defined thresholds of RDI that trigger automatic notifications to a set of end users must be configurable.
T A B L E 5 Elements specific to nuclear medicine.

Elements Description
Essential RDI and RDIrelated parameters The software must record all essential RDI-related parameters. See 9.a below for list of elements specific to nuclear medicine.

Manual entry of RDI and RDI-related parameters
The software must support manual entry of procedure and patient RDI-related parameters.

Multiple radiopharmaceutical administrations
The software must support single procedures that involve multiple radiopharmaceutical administrations.
Organ and effective dose estimates The software should support calculation of reference organ and effective dose estimates.

Notification of RDI outside of defined range
User-defined thresholds of RDI that trigger automatic notifications to a set of end users must be configurable.
following essential NM RDI-related parameters, and should support The software must support manual entry of essential NM RDI and the RDI-related parameters listed above.

9.A.3 | Multiple radiopharmaceutical administrations
There exist procedures that involve two radiopharmaceutical administrations (e.g., stress-rest myocardial perfusion, simultaneous solidliquid gastric emptying). The software must be able to account for these multiple radiopharmaceutical procedures.

9.A.4 | Organ and effective dose estimates
It is standard practice to provide estimates of both organ and effective doses associated with NM procedures. The software should support calculation of organ and effective dose indices for a reference phantom or population representative of the patient, taking into account the patient's gender and age at the time of the procedure. and American Society of Nuclear Cardiology). 33,34 The RDIM software must allow the user to define thresholds for the monitored RDI for each procedure. Additionally, the software must have the capability to alert a set of users when a RDI from a completed procedure exceeds a defined threshold. The software must allow thresholds to be defined for either activity or dose, and should allow definition at a more granular level, such as by organ, or patient gender or age.

CONFLI CT OF INTERESTS
The authors declare no conflict of interest.