1.

Introduction

In the past, population dose was an important factor for policymaking in radiation protection. The fraction of the dose to population that comes from different imaging modalities, such as computed tomography (CT) had an important place. The advent of multidetector computed tomography (MDCT) was a turning point not only for clinical imaging but also for radiation protection. It has necessitated a shift of focus from collective dose to the population from medical exposures to individual patient dose.¹ The MDCT made slice-by-slice scanning with interstice gap a thing of the past. Thinner slices with overlap and faster scanning that covered a larger area of the body, such as chest–abdomen–pelvis, increased the individual patient dose. Multiphase scanning became more common. In recent years, reports of overutilization of CT have emerged from the USA.² All these contribute to the need for tracking patient exposures.

The word tracking has been used to represent different situations, and this needs to be clarified. Essentially, tracking can fall into two categories, namely (a) for an individual patient or (b) for a group of patients. Furthermore, tracking can be of the number and type of radiological procedures an individual patient has undergone or of the doses of these examinations or both.³

Regarding terminology, initially, there was a lack of clarity in use of the terms ‘exposure’ and ‘dose’ concerning tracking. There is now a better understanding on this. When a patient undergoes multiple radiological examinations, accounting for all the examinations, but without any consideration of dose, this is referred to as exposure tracking. When the dose of each examination is also recorded, then this is termed dose tracking.⁴

In addition to overarching questions such as “Why track, what to track, and how to track?,” this paper discusses themes, such as attitudes toward tracking, review of practices in large parts of the world, description of various elements for exposure and dose tracking, how to use the information available from tracking, templates for implementation of tracking at different levels of health care, the role of picture archiving and communication systems (PACS) and eHealth, the role of tracking in justification and optimization of protection, comments on cumulative dose, how referrers can use this information, what dose indices to track, the role of smart cards, current provisions in international standards, and future actions.

Since the tracking of radiological examinations and dose is gaining momentum, the motivation for this review article is to delve into this topic in its wider context to review the current status of tracking with regard to radiation protection of patients.

2.

Tracking of Radiological Procedures and Dose of an Individual Patient

Tracking of radiological procedures of an individual patient is useful for individual patient protection as it provides clinical information that can avoid performing another radiological examination for that patient. Avoiding a repeat examination provides 100% dose reduction even when no account is made of dose from the previous examination.

Tracking of the dose of an individual patient is a concept that was established by the author through his work at the International Atomic Energy Agency (IAEA)^5,6 and led to the Smart Card project of the IAEA.⁷ It received wide attention globally and has been implemented in imaging through PACS. Many European countries have implemented this, and experience from one country (Finland) that documented the impact of tracking in strengthening the process of justification and optimization of the individual patient has been presented.⁸ Individual dose tracking helps in optimizing follow-up examination as the patient acts as his/her own standard or reference for comparison in due consideration of clinical indication and body part. The approach on optimization in previous years has been based on comparing average values of dose [such as computed tomography dose index (CTDI)/dose-length product (DLP)] of a facility with diagnostic reference level (DRL) values. The DRL value is taken as a standard value. DRL has a mix of body weights and is not valid for an individual patient. Templates for use by countries at different levels of development have been provided.⁴ Worldwide needs were assessed, and results have been published.⁹ Furthermore, a survey of availability and use of unique patient identification numbers (ID) in 40 countries around the world was studied.¹⁰ Challenges for tracking of radiation doses from nuclear medicine examinations have been presented.¹¹

Even though actions on tracking individual patient exposures have been pursued by the author of this paper since 2004, the first publicly available attempt to draw attention to cumulative radiation exposure to an individual patient by the author was in 2009 through an article in a nonindexed publication⁵ that received wide attention in the public and scientific media.^12–14 It drew attention to the increasing individual patient doses wherein CT was becoming a main contributor. It envisaged individual patient dose becoming a tool for directing actions on patient protection and a shift in focus from occupational protection to patient protection.

An article by Sodickson et al.¹⁵ reviewed the number of CT scans over the past 22 years in a cohort of 31,462 patients. In all, 33% of patients underwent five or more lifetime CT examinations, and 5% underwent between 22 and 132 examinations. About 15% of patients received estimated cumulative effective doses of $>100\mathrm{mSv}$, and 4% received between 250 and 1375 mSv. The authors concluded that the cumulative CT radiation exposure added incrementally to the baseline cancer risk in the cohort, and this subgroup is potentially at higher risk due to recurrent CT imaging. This was followed by a number of papers in subsequent years assessing multiple CT scans that a patient undergoes in different clinical conditions and reporting doses of a few tens of mSv or even 100 mSv that were received by the patient.^16,17

3.

Tracking of Radiation Doses of a Group of Patients

Tracking of radiation doses of a group of patients has become very prevalent in recent years. Many vendors have developed systems that provide dose information for every examination. This provides access to dose information, which helps in establishing DRLs, in comparing doses from time to time in the same institution, in making comparisons intrainstitution in different rooms to support the process of optimization. In previous years, it was common to establish the frequency of different radiological examinations and estimate collective dose to the population using the typical value of dose per examination. In addition, tracking of doses in a group of patients has been practiced by anonymizing patient data and results in patient dose registries.^18,19 This helps in comparing one’s own facility doses in any examination with dose with other facilities, which promotes optimization and can become a helpful tool in the accreditation process.

4.

Analysis of Attitudes Toward Tracking of Radiological Exposures and Dose

When the author started talking about developing mechanisms for radiological exposure history in 2004, the reaction of most colleagues was invariably negative. An analysis of attitudes revealed several distinct reservations

It is well known that managing any situation when the facts are known is better than managing it without any concrete information. It is widely taught that diagnosis is revealed in the patient’s history. “Listen to your patient, they are telling you the diagnosis” is a much-quoted aphorism.²⁰ Thus, looking into previous radiological examinations for clinical information is something that is natural but often missed in view of nonavailability or lack of easy access. It is here that specific concepts like that of tracking help. The concept has now reached the level of programs and gives impetus to solve traditional problems. On the issue of practicality (first point in the list above), it is amazing how many technological developments have occurred during the last decade. It was not possible in 2004 to think that listing of all examinations a patient has undergone will become possible with the click of a button in a few years. PACS systems were not talking to each other, although much had happened since 1995 through formal acceptance of Digital Imaging and Communications in Medicine (DICOM) standards. A high degree of variability of adoption of DICOM standards was responsible for integration difficulties. However, technology moved much faster than anticipated, probably due to the cancer risks from CT and impetus provided by a series of overexposures from CT scans during 2008 to 2009 with significant media attention where issues connected with safety became important.^21,22 Now, it is a reality in most PACS to be able to list all examinations against a patient ID along with respective images and even the dose in most cases. The second point of “why track” is discussed further later in this paper in relation to justification and optimization. The third point pertaining to transparency is a dynamic one. People get persuaded with time as transparency generates benefits of easy information that leads to reliability and legitimacy among the constituents. In recent decades, there has been a transparency rush. With regard to the fourth point, it took the author a long time to understand the need for mentioning procedure tracking (exposure) separately from dose tracking and delinking tracking from cumulative dose.

5.

Global Survey on Perceived Need for Tracking

We conducted the first-ever survey in 2010 that covered 76 countries including the six most populous countries and 16 of the 20 most populous ones. It addressed the availability of prior radiation tracking programs, the potential usefulness of such a program, and familiarity with IAEA efforts in this area.⁹

The survey⁹ showed that, although no country had yet implemented a patient exposure tracking program at a national level, there was increased interest in this issue. Eight countries (11%) indicated that such a program is actively being planned, and three (4%) stated that they have a program for tracking procedures only, but not for dose. Twenty-two (29%) felt that such a program will be “extremely useful,” 46 (60%) “very useful,” and eight (11%) “moderately useful,” with no respondents stating “mildly useful” or “not useful.” Ninety-nine percent of countries indicated an interest in developing and promoting such a program. There were successful examples at the subnational level where tracking had become possible within a few dozen hospitals covered by PACS systems and there were nascent efforts to extend coverage nationwide. These findings serve as a benchmark and stimulus for future radiation exposure and dose recording efforts, which offer the potential to create a data-rich environment that enables maximal global implementation.

The survey also included dose quantities that will be tracked. For projection radiography (x-ray, computed/digital/dental radiography), the most common choice was dose-area product (DAP)/kerma-area product (KAP) ($5/7=71\%$), whereas some also chose entrance surface air kerma ($2/7=28\%$), exposure index ($2/7=28\%$), organ absorbed dose, and effective dose.

For fluoroscopy, again, the most common choice was DAP/KAP ($7/7=100\%$), but some participants also chose fluoroscopy time ($4/7=57\%$), cine time ($4/7=57\%$), cine runs ($2/7=28\%$), and/or dose/air kerma at the interventional reference point ($4/7=57\%$).

For CT, the common choices were volume CTDI (${\mathrm{CTDI}}_{\mathrm{vol}}$) ($7/7=100\%$), DLP ($6/7=86\%$), and weighted CTDI (${\mathrm{CTDI}}_w$) ($2/7=28\%$); and one respondent also chose effective dose.

For mammography, three respondents only selected average glandular dose, whereas one also included incident air kerma.

For nuclear medicine, most selected administered activity (MBq) and organ absorbed dose; one also included effective dose.

Prior to 2006, when there was little international guidance on dosimetry in diagnostic radiology, there was a lack of clarity on what dose quantities to use in different imaging situations. The availability of guidance from ICRU and IAEA^24,25 remedied the situation, and now there is a high degree of stability on reference dose quantities.

6.

Elements of Patient Exposure and Dose Tracking

7.

Use of Radiation Dose Data

After achieving tracking of exposures and dose, the next question that arises is how to use this information. Imaging modalities deliver dose data in different quantities, mostly in reference dose quantities, such as ${\mathrm{CTDI}}_{\mathrm{vol}}$ and DLP in CT and KAP and cumulative air kerma in the case of fluoroscopy. These dose quantities can be used by experts, such as medical physicists, to consolidate dose information from various imaging modalities, convert them into effective dose, and communicate them to radiologists and clinicians as dose and risk estimates with due caution. It is the responsibility of the medical physicist to handle information in different units. It is not desirable for imaging systems to provide dose information in terms of effective doses, which normally have large variabilities and inaccuracies. Professionals not versed in these inaccuracies may overuse and misinterpret figures. A paper from our group has demonstrated how dose information of an individual patient from different imaging studies was useful in identifying scope for optimization.⁸ In a previous paper,⁴ we have provided a comprehensive list of potential benefits from patient exposure tracking, which is reproduced here in Table 1. These benefits include those to patients, to health-care providers who refer patients and who perform imaging studies, and to policymakers, regulators, and researchers.

Table 1

Potential benefits from patient radiation exposure tracking.4

8.

Role of Referrers

The referrers play a role in evaluating and comparing images with previous studies to contribute to the justification of radiological examination. This requires access through HIS, RIS, or eHealth systems. There are access control mechanisms usually in place to allow or forbid access to specified information. Invariably the referrer will need access to previous images, together with interpretation by an imaging professional, rather than dose. These days, there are possibilities for providing access for referrers through virtual private networks and intranet on mobile phones that facilitates decision-making to allow images to accompany the report from the radiation specialist. It is hoped that there will be increasing use of clinical information available in previous imaging studies, obviating the need for many repeat studies; thereby, tracking of procedures helps in strengthening the process of justification.

As indicated above, at this moment, it is not possible to provide guidelines on how referrers can use dose history for making judgments about subsequent examinations. With a lack of understanding about dose on part of referrers, there can be dangers in misinterpreting dose figures. Furthermore, there has been opposition to the use of cumulative dose received by the patient as part of the justification of the next examination. While such arguments may be valid in clear-cut situations, so-called black and white situations, there are a large number of situations where there are many shades of gray and it is not a clear-cut yes–no situation. Any amount of additional information can be very helpful, as is evident from the first-ever multinational survey among referrers that IAEA conducted.²³ The aim was to survey opinions of referrers on the importance of acquiring information about previous diagnostic exposures.²³ Seven hundred and twenty-eight referrers from 28 countries responded (52.3% from developed and 47.7% from developing countries). The vast majority (71.7%) of physicians feel that being aware of the previous history of CT scans would always or mostly lead them to a better decision on referring a patient for a CT scan, but only 43.4% often enquired about it. The majority of referrers (60.5%) stated that having a system that provides quick information about patient exposure history would be useful.

In future years, this issue needs to be further explored and debated.

9.

Templates for Implementation of Patient Radiation Exposure or Dose Tracking

There being wide variations in the global situation and increasing interest in this topic, we have previously provided templates that deal with different elements for implementation of exposure and dose tracking.⁴ We deliberated on various levels, such as practice, multipractice, national, and international. A template for less-resourced countries was also addressed. At the practice level, one needs primarily patient ID and a PACS system that connects all radiological imaging systems from all vendors within the practice with the capability to display all examinations of a patient when the patient ID is entered. At the multipractice level, PACS-interconnected hospitals must use the same patient ID with full connectivity including structured dose reports. Implementation at the national level is a matter of extension of principles from county/state level to national level. There are increasing issues of access controls needed when larger networks are encountered.

10.

Nuclear Medicine Exposures

Tracking mechanisms rely on the availability of structured dose reports, typically found in the DICOM header. While dosimetric information is currently readily available for many individual x-ray-based procedures, unfortunately, nuclear medicine, which constitutes a large part of radiation exposure to the patient population, currently lags behind x-ray-based procedures with respect to reporting of radiation dosimetric information electronically in patient files that are transmitted over a network. Currently, in nuclear medicine studies, one can include mention of administered activity. There is no system to give the dose to a representative phantom, if not to a patient. This is not to the same level as x-rays where the dose to a representative phantom is provided in a patient file based on the exposure factors employed. It is all the more important in hybrid imaging [positron emission tomography (PET)/CT and single-photon emission computed tomography (SPECT)/CT] where the doses from the PET and SPECT part are substantial. A paper by our group¹¹ discussed qualitative differences between nuclear medicine and x-ray-based procedures, including differences in the radiation source and measurement of its strength, the impact of biokinetics on dosimetry, and the capability of current scanners to record dosimetric information. These differences depict challenges in applying monitoring and reporting strategies used in x-ray-based procedures to nuclear medicine and integrating dosimetric information across modalities. The development of strategies to improve the reporting of radiation dosimetric data in nuclear medicine provides a challenge for the future. Some ideas on how to address this issue were suggested in that paper and are not repeated here.

11.

Consideration of Radiotherapy Exposures

In radiotherapy, the dose is deliberately delivered to kill or modify selected cells, unlike diagnostic exposures where the purpose is to obtain image and radiation exposure happens to be a part of the selected examination. When the purpose of tracking is to improve or strengthen the process of justification and optimization of patient protection in diagnostic studies, radiotherapy dose is not included in tracking. In the future, when practices get developed and there are models for better considerations of doses to organs not only for risk estimates but also for utilization of nontarget organ doses, one could think of the inclusion of that dose in tracking.

12.

Standards

Basic Safety Standards (BSS) of IAEA require that justification of medical exposure for an individual patient shall be carried out and account taken of relevant information from that patient’s previous radiological procedures, among other things.²⁹ The European BSS³⁰ defines that “clinical responsibility” means responsibility of a practitioner for individual medical exposures, in particular, justification; optimization; clinical evaluation of the outcome; cooperation with other specialists and staff, as appropriate, regarding practical aspects of medical radiological procedures; obtaining information, if appropriate, on previous examinations; providing existing medical radiological information and/or records to other practitioners and/or the referrer, as required; and giving information on the risk of ionizing radiation to patients and other individuals involved, as appropriate. Furthermore, the referrer and the practitioner, as specified by the member states, seek, where practicable, to obtain previous diagnostic information or medical records relevant to the planned exposure and consider these data to avoid unnecessary exposure. Thus, there is no doubt that there are requirements on using diagnostic information from previous examinations. There is no explicit mention of dose from previous examinations. To date, it has been left out in view of the absence of any dose limit for patients and no attempt has been made to provide guidelines when the individual patient dose has reached the level that we have today, for some patients. As a result, physicians are left with decision-making based on gut feelings, which explains the response to the survey among referrers.⁴ There is an urgent need to provide guidelines and clarity in standards to help in such situations.

13.

Future

With increasing access to radiological imaging, in particular, CT in many developing countries, it appears that this topic is going to become all the more important in coming years. In developed countries, where the problems pertain to overutilization of CT, such as in the USA,² tracking can be helpful not only in reducing the number of CT examinations but also in reducing inappropriate CT examinations through enhanced individual justification.^4,6,8

There will be a need in certain countries, where there has been a more rapid and less controlled expansion of the use of CT, to develop guidelines for patients who have received high doses of a few tens of mSv or a 100 mSv of effective dose where they need further imaging studies. The existing concept of a dose constraint that is currently not applicable to patients may need to be introduced. This will be yet another new step that will require crossing hurdles. The author has raised this issue within International Commission on Radiological Protection, but there is a lot of resistance, as is typical of anything that requires a change in the established frameworks. On the issue of cumulative dose, there have been considerations relating to the risk of radiation-induced carcinogenesis for utilization strategies.³¹ In another paper focusing on patient-centric actions, it is recommended that optimal methods to translate cumulative patient-centric dose to risk of malignancy need to be developed and validated to present to physicians and patients for adequate risk–benefit analysis in the context of decisions for further imaging in individual patients.³² Such risk analysis could similarly inform surveillance strategies in patients already exposed to some level of cumulative radiation dose. An action plan was developed by the “think tank” for cardiovascular imaging that recommended, in addition to others, robust dose assessment and longitudinal tracking.³³

Tracking will provide useful dose data for future epidemiological studies on patients who have been exposed to tens of mGy doses to organs or a few tens of mSv of effective dose, particularly during childhood.

14.

Summary

There are very few examples where so much has been achieved in so few years as in the case of patient exposure tracking. Some countries in Europe already have the capability of tracking radiological examinations and doses to an individual patient conducted nationwide. Many European countries are on the way to nationwide PACS systems that will instantaneously make tracking possible if the country uses permanent patient ID. The European Commission’s plans for cross-border health care will cross hurdles of confidentiality, data protection, access controls, information governance, and patient’s consent. It has been documented that patient-specific justification and optimization becomes possible using the tracking of radiological procedures and radiation dose of individual patients. There are many challenges that need to be addressed where future work will be needed, e.g., exploring utilization of cumulative dose in the context of decision-making for the next examination, the possibility of dose constraints for patients, and the extent to which referrers should be concerned with doses from examination. Tracking will provide useful dose data for future epidemiological studies on patients who have been exposed to tens of mGy doses to organs or a few tens of mSv of effective dose, particularly during childhood.