Updated effective doses in radiology

In 2013 the European Council published the new Basic Safety Standards Directive regarding ionizing radiation [1]. The directive introduced several requirements for medical exposures and the associated doses, for example, providing the patient with adequate information relating to the benefits and risks associated with the radiation dose prior to the medical exposure, and taking into account radiation doses in referral guidelines. The evidence shows that clinicians nowadays lack awareness of the doses associated with the imaging tests they prescribe [2].

One of the different quantities used in radiological protection that could potentially fulfill at least part of those requirements is the effective dose. The international commission for radiological protection (ICRP) in its Publication 103 [3] warns that the effective dose should not be used for investigations of individual exposure and risk. But since it condenses in a single value the total detriment to the patient when the exposure has not been homogeneous (i.e. some organs were exposed while others were not), the effective dose holds a central position in the current system of radiological protection as the magnitude that allows comparisons between very different exposures, techniques and technologies, and thus, enables clinicians to discuss the risks and benefits of imaging tests with patients.

Increasing the knowledge of the typical effective dose of a certain procedure is, therefore, a basic starting point when communicating the risk that an imaging tests implies with a patient and also to help clinicians understand it.

The most recent review of the available evidence to identify the effective dose associated with each radiodiagnostic procedure was published in 2008 by Mettler et al [4]. They analyzed more than 150 peer-reviewed articles published between 1980 and 2007, which were included in a catalogue of estimated effective doses for a large number of common imaging tests. However, although this review is an essential reference, there was no specific mention of pediatric doses and the methodology to calculate each effective dose is not specified and, therefore, not reproducible. Moreover, it was developed before the updating of the ICRP Publication in 2007 and it does not include relevant initiatives, such as data from the dosedatamed project.

In 2004, the European Commission launched an international survey on collective effective doses from medical x-ray procedures, known as dosedatamed (DDM), which included 10 European countries with previous experience conducting surveys measuring the collective effective dose [5]. The project selected a set of 20 imaging tests that were among the highest contributors to the collective effective dose ('the top 20'). This project was updated with the dosedatamed2 (DDM2) that included 36 European countries [6]. In DDM2 the information from each country is based on national surveys that follow Report 154 of the European Commission [7], a protocol built on the experience from DDM1. Report 154 establishes that, if patient dose measurements are not available for a given country, data should be taken either from literature that matches as closely as possible the healthcare setting of the country or from the data provided by the DDM surveys.

Understanding the typical effective doses of the different imaging procedures performed at a hospital is a necessary step towards optimization and patient-risk minimization. Referral guidelines and protocols for communicating the risk-benefit balance to the patients could also benefit from updated information about effective doses. In light of all this, we reviewed recent literature in order to provide updated values of the typical effective doses associated with the top 20 imaging tests for adults and children and for the most widely used set of weights (ICRP60 [8]) as well as for the most recent one (ICRP103).

2.1. Search strategy and eligibility criteria

2.2. Study selection

2.3. Data extraction

2.4. Statistical analysis

3.1. Description of the studies included

As figure 1 shows, the literature searches identified a total of 902 potentially relevant abstracts. Of these, 65 studies were retrieved for full test review and finally, 27 papers fulfilled the eligibility criteria [8–34]. Out of 27 articles included, 11 (41%) were published in European countries, 5 (18%) in Asian countries, 5 (18%) in USA/Canada, 3 (11%) in Australia, 2 (8%) in Africa and 1 (4%) in Brazil.

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We also searched the web for potentially relevant studies backed by scientific organizations or national agencies. Of the five web references included in the study [35–38], 4 (80%) were based on European countries. Of the 33 sources (studies and web references), 17 (63%) were surveys. Moreover, 22 (67%) sources calculated values using ICRP 60; 7 (21%) using both ICRP 60 and ICRP 103 and 4 (12%) used ICRP 103.

The details of the 27 articles and 5 web references included are shown in Annex 1.

3.2. Description of the effective doses (mSv) for adults in the 20 selected examinations

A total of 378 values from the 20 procedures included were obtained, 280 (74%) using ICRP60 and 98 (26%) using ICRP103. Table 1 and figures 2–4 show the main results for adults using both sets weights.

Table 1. Description of the mean (minimum, maximum and standard deviation) effective dose (mSv) for the 20 selected examinations according to the two different sets of ICRP values used (ICRP60, from 1990, and ICRP103, from 2007) and the values of two references for comparison.

Category	Examination	ICRP 60			ICRP 103			References for comparison
		Mean	Min–max	Std dev	Mean	Min–max	Std. dev	Mettler FA [5]	DDM2 [4]
Computed tomography	CT abdomen	8.1	5.1–11.7	2.0	6.8	5.6–8	1.2	8.0	11.3
	CT chest	6.7	4.4–11.8	2.1	7.0	4.6–10.1	1.7	7.0	6.6
	CT head	1.8	1.4–2.6	0.4	1.7	0.9–2.6	0.5	2.0	1.9
	CT neck	3.2	1.8–6.0	1.3	3.0	1.7–5.8	1.9	3.0	2.5
	CT pelvis	8.3	4.0–11.9	2.4	7.4	5.7–9.9	2.2	6.0	7.3
	CT spine	10.3	4.0–16.7	5.3	7.0	1–12	0.0	6.0	7.7
	CT trunk	12.2	6.7–15.8	3.3	12.3	10–16	2.0	—	14.8
Interventional cardiology	PTCA	19.5	7.4–48.6	15.1	7.2	—	—	15.0	15.2
Plain radiography	Abdomen	0.92	0.21–2.1	0.6	0.5	0.14–0.75	0.25	0.7	0.9
	Cervical spine	0.08	0.02–0.18	0.06	0.05	0.01–0.11	0.05	0.20	0.19
	Chest/thorax	0.07	0.01–0.14	0.04	0.05	0.01–0.07	0.02	0.02	0.10
	Lumbar spine incl. LSJ	1.2	0.2–1.9	0.6	0.80	0.2–1.5	0.70	1.5	1.2
	Mammography	0.33	0.26–0.46	0.11	0.64	—	—	0.40	0.27
	Pelvis & hip	0.90	0.45–1.82	0.47	0.37	0.09–0.66	0.24	0.60	0.71
	Thoracic spine	0.60	0.23–1.22	0.43	0.50	0.1–1.2	0.40	1.00	0.64
Fluoroscopy	Ba enema	5.8	3.0–8.25	2.4	2.9	2.2–3.5	0.90	8.0	8.5
	Ba follow	3.5	1.2–7.7	3.7	1.3	1.2–1.3	0.10	5.0	7.3
	Ba meal	3.6	1.5–4.93	1.5	4.5	—	—	6.0	6.2
	Cardiac angiograpy	9.3	3.3–22.3	6.4	3.1	—	—	7.0	7.7
	Intra-venous urogram	3.5	2.3–6.5	2.0	2.1	—	—	3.0	2.9

Note: Minimum, maximum and standard deviations are only shown when more than one value was found.

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The values of the effective doses calculated using ICRP103 weights were lower than those calculated using ICRP60 weights for almost all procedures. The only exception is mammography, but this is due to the increase in weighting factor of the breasts (which has more than doubled, from 0.05 in ICRP60 to 0.12 in ICRP103).

3.3. Evaluation of the effective doses (mSv) for children

3.4. Comparison between the effective dose evaluated in this study (according to ICRP 60 and ICRP 103) and those evaluated previously (Mettler et al and DDM2) (table 1)

In this review we showed two sets of effective doses assessed for adults (using ICRP 60 and ICRP 103 weights) and a set of doses for pediatric patients (using only ICRP 60 weights) that could be used to estimate population exposure doses in clinical practice and in referral guidelines to help physicians to understand the variations between different examination techniques.

Ideally, only effective doses using the weights from ICRP 103, published in 2007, should have been included in the final estimations. However, we have found that most authors still use effective doses calculated using the weights from ICRP60. While the ICRP argues that the new definition of the effective dose is compatible with the previous one in terms of risk assessment, the difference between the values for Mettler et al, DDM2 and our ICRP60 and ICRP103 values described in this publication cannot be attributed solely to the change in weights. If we restricted our search to publications including values for both sets of weights, we would have found a ~5% decrease in effective doses, but our complete analysis shows a ~30% decrease. A similar comparison was previously made [11], where authors find a ~14% decrease across CT procedures.

In our opinion, this difference cannot be attributed solely to the change in ICRP weights, and thus, we also analyzed other parameters of interest such as the economic resources of the countries where each investigation was performed, the number of patients involved in the measuring process or the year of publication. We have found that none of these affected the results in a statistically significant manner.

The difference must be, therefore, related to the implications of using newer ICRP recommendations, which is probably related with a more current knowledge of all aspects involved in the calculation of the effective dose, including technology and dose-optimization techniques.

In our analysis we also wanted to find out if large country-wide surveys with complex sampling techniques or involving many patients were different to small local descriptive investigations. Neither the sample size nor the type of study proved to be a source of significant differences. While this is reassuring, a word of advice is needed.

Effective doses are calculated using mathematical phantoms modeling a standard man and woman, and studies often use patients fitting that standard to avoid non-standard patients skewing the data [34] or simply take the exposure parameters before the exposition is made (i.e. from the protocol) and calculate what the effective dose would have been if the patient had been standard. While this may be a reasonable method to avoid population doses being skewed, it would lead to individual reported doses being skewed. In other words, the reason descriptive studies and country wide surveys show no difference may very well be that the number of actual measurements and the way they are conducted (a selected group of 'standard' patients) is very similar in both cases.

To our knowledge, this is the first study proposing a complete set of typical effective doses for children. For occupational exposures (ages 18–70) it may be adequate to ignore age dependencies. However, given than medical exposures are nowadays the biggest contributor to the collective effective dose, we cannot ignore pediatric examinations. There were few studies estimating effective doses for children using ICRP103; thus, we calculated these data only using those studies applying ICRP60.

We performed a systematic search on several databases, and controlled observer concordance in both the study inclusion and during the data extraction. Nevertheless, it is possible that some articles with valid data could have been missed.

We have compiled and analyzed values of effective doses for the 20 procedures that typically contribute the most to the collective effective dose, using two sets of recommendations (ICRP60 and ICRP103), and the age groups recommended for the DDM2 project. Our results can be used for the purposes of optimization, comparison, to help clinicians in their daily practice in referral guidelines and also in communicating the risk-benefit of the procedures to the patients.

It is important to keep in mind that the effective dose was designed to estimate population risks and not individual risks. Two individuals with a different kind of irradiation (e.g. a Cardiac angiography versus a Pelvis CT) could have the same effective dose and contribute the same amount to the 'risk pool' but they will show different risks associated with their exposure. To calculate individual risks, the ICRP recommends using the absorbed and/or the equivalent organ dose and the individual risk factors of the patient.

We found that effective doses reported using ICRP103 weights were systematically smaller than those using ICRP60 weights, a difference that cannot be attributed solely to the difference in the weights itself. Therefore, if an institution carries out a dose survey and wants to compare its data with the literature, it will need the 'right' effective doses. To the best of our knowledge, this is the first time any attempt has been made to create a complete list of effective doses using ICRP103 weights for the most common procedures.

In conclusion, with this review, we provided the best available evidence from literature to evaluate the effective dose received by each patient for the most typical examinations. According to the recommendations from the Report 154 and from the European Council Directive [1, 7], these result could also be useful to estimate average exposure population to radiation.

Even though effective doses per examination are lower now than they were some years ago, population doses have increased steadily, because the number of examinations, especially the high-dose ones like CT, have increased [38, 39]. The knowledge of the typical effective dose of an individual examination in only a part of the integral approach proposed by the ICRP in its latest set of recommendations for the protection of patients. Radiological protection officers, medical physicists and all other health professionals involved must be aware of all aspects and always try to minimize exposures as much as possible.

Financial disclosures: This study was supported by the Fondo de Investigaciones Sanitarias, Instituto de Salud Carlos III (Plan Nacional de I+D+I) PI13/01576 and co-funded by the Fondo Europeo de Desarrollo Regional (FEDER)

Role of the sponsors: These funding organizations have not participated in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Explanation of each column:

• Reference: number of the reference in the bibliography of the main article
• Country: country where the study was conducted
• Year: year in which the study was published
• Type of study:
  • Survey: studies with a fully detailed and standardized sampling procedure in order to reduce the possibility of bias in order to calculate population doses.
  • Descriptive: studies in which the selection criteria and sampling procedure were not fully described or standardized, because the aim was not to calculate population dose but rather to evaluate doses in a set of carefully selected patients and exposure parameters.
• Sample: Total number of patients included in the study.
• Age: Adults, Pediatric patients of both
• Calculation Method:
  • Examination protocol: effective doses are calculated using the parameters that the equipment has pre-configured for each examination.
  • Equipment dosimetry: effective doses are calculated using dosimetry data (e.g. absorbed dose, dose area product, DLP...) reported by the equipment.
  • Equipment parameters: effective doses are calculated using the parameters used by the equipment for the individual patients. This is particularly relevant for equipment that uses automatic exposure compensation (AEC).
  • Measurements on the equipment: the same as the previous point (equipment dosimetry) but with data measured using external equipment.
  • Conversion Factor: effective doses where calculated using equipment dosimetry and a published conversion factor, specific to the imaging modality and/or the site
  • Following Report 154: Euratom Report 154 gives a detailed explanation on how to calculate the effective dose for each imaging modality, including appropriate number of samples, QA procedures that should be performed, etc...
• Calculation Sample: number of independent data points (e.g. patients, but also scanners or even technicians using the same equipment) used to calculate the effective dose of each examination.
• ICRP Weights: ICRP Report used for the calculation (either ICRP60 or ICRP103 or both).
• Included Procedures: type of procedures included in the study (RX, RX/Fluor, CT, Interventional or a combination of these