Assessment of radiation dose awareness among pediatricians
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- Thomas, K.E., Parnell-Parmley, J.E., Haidar, S. et al. Pediatr Radiol (2006) 36: 823. doi:10.1007/s00247-006-0170-x
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There is increasing awareness among pediatric radiologists of the potential risks associated with ionizing radiation in medical imaging. However, it is not known whether there has been a corresponding increase in awareness among pediatricians.
To establish the level of awareness among pediatricians of the recent publicity on radiation risks in children, knowledge of the relative doses of radiological investigations, current practice regarding parent/patient discussions, and the sources of educational input.
Materials and methods
Of 220 respondents, 105 (48%) were aware of the 2001 American Journal of Roentgenology articles on pediatric CT and radiation, though only 6% were correct in their estimate of the quoted lifetime excess cancer risk associated with radiation doses equivalent to pediatric CT. A sustained or transient increase in parent questioning regarding radiation doses had been noticed by 31%. When estimating the effective doses of various pediatric radiological investigations in chest radiograph (CXR) equivalents, 87% of all responses (and 94% of CT estimates) were underestimates. Only 15% of respondents were familiar with the ALARA principle. Only 14% of pediatricians recalled any relevant formal teaching during their specialty training. The survey response rate was 40%.
Awareness of radiation protection issues among pediatricians is generally low, with widespread underestimation of relative doses and risks.
KeywordsPediatrician surveyRadiation dose awarenessALARA principle
Ionizing radiation in medical imaging is undoubtedly one of the most powerful diagnostic tools in medicine. Yet, as with all medical interventions, there are potential risks in addition to the clear potential benefits. The cancer risks associated with radiation exposure have long been known. Its potential for harm has been demonstrated by the deaths of early radiation workers , fetal radiation exposure , follow-up studies of patient groups exposed to repeated or high-dose radiological investigations [3–5], case control studies [6, 7] and data extrapolated from Japanese A-bomb victims exposed to high radiation doses [8, 9].
In February 2001, three papers were published in the American Journal of Roentgenology regarding radiation doses in pediatric CT that had a significant impact on both the radiological community and the public. Brenner et al.  estimated the lifetime cancer mortality associated with the radiation doses commonly involved in pediatric CT, using recently published data from the Japanese A-bomb survivors exposed to similar radiation levels . They suggested that a young child undergoing CT has an increased lifetime risk of fatal cancer of approximately 1 in 1,000 (0.18% for CT abdomen, 0.07% for CT head). The importance of adjusting CT technical parameters when performing pediatric examinations was emphasized by Paterson et al.  and Donnelly et al.  in two other papers published in the same issue. There was much attention in both the radiological literature and the lay press , with coverage on multiple television news programs .
The level of awareness concerning this issue has certainly increased among pediatric radiologists. But what about pediatricians? Studies from the UK [16, 17] and the United States  have suggested that there is widespread underestimation of radiation doses by physicians managing adult patients. Children are more radiosensitive than adults [19, 20]. However, the level of awareness among pediatricians, the health providers requesting examinations involving ionizing radiation on children, is not known.
The aim of our study was to survey a large cohort of pediatricians to establish the level of knowledge of the radiation doses and risks associated with radiological investigations in children and to assess the impact of the 2001 AJR articles on pediatricians and their patients. Questions were also included on radiation protection, the issue of informed consent and the sources and level of educational input during pediatric specialty training.
Materials and methods
The study was approved by the institutional Research Ethics Board. An anonymous two-page survey was distributed to 555 pediatric physicians and surgeons (Fig. 1). Of these, 224 (40%) were staff (attending physicians/surgeons) at a large pediatric teaching hospital in specialties involving regular use of the diagnostic imaging department, 186 (34%) were clinical or research fellows undergoing higher training but having completed their statutory specialty training, and 145 (26%) were other pediatricians identified from the records of the provincial College of Physicians and Surgeons practicing in local hospitals and/or clinics. All respondents were primarily involved in managing pediatric patients in medical or surgical specialties or general pediatric medicine. For the purposes of simplicity, we refer to our study group by the overall term “pediatricians”.
Data were entered into an Excel spreadsheet for statistical analysis using SAS 8.2 (SAS Institute, Cary, N.C.). Descriptive data were reported as charts, percentages, means and standard deviations. The association among categorical variables was determined by means of chi-squared tests. For contingency tables with small cell counts Fisher exact tests were used instead. The means of continuous measurements were compared by two sample t-test or analysis of variance. The normality of the continuous variables was assessed prior to the application of parametric methods. Statistical significance was defined as a P-value less than 0.05.
Of the 555 surveys distributed, 220 were returned, a response rate of 40% (staff pediatricians 47%, fellows 28%, local pediatricians 43%). Both early and later stages of career development were represented: 25% of the respondents had been practicing for <5 years, 22% for 5–10 years, 30% for 10–20 years and 23% for >20 years.
Impact of the 2001 AJR articles
Responses to questions on lifetime cancer risk from CT, discussion with parents and informed consent
No excess risk
1 in 1,000,000
1 in 10,000
1 in 1,000
1 in 100
No noticeable effect
I can’t remember the last time asked
1 in 1,000,000
1 in 10,000
1 in 1,000
1 in 100
1 in 10
The reported frequency of patients’ families inquiring of their pediatrician about radiation doses and risks was low (Q.9, Table 1). The majority of respondents were rarely (<1 in 100 patients) asked or could not remember the last time such questioning had occurred. Thirty one percent had noticed a sustained or transient increase in questioning after recent publicity, but the majority perceived no noticeable effect (Q.8, Table 1). There was no statistically significant difference among the teaching hospital, local hospital and community pediatrician groups.
Knowledge of relative radiation doses
Estimated effective doses for a 5-year-old child (19 kg) at our institution
Effective dose (mSv)
82 kVp, 5 mAs, 2.5 mm Al filtration
AP pelvis radiograph
68 kVp, 6.4 mAs, 2.5 mm Al filtration
83 mBq 99Tc-DMSA
1–2 min continuous fluoroscopy
90 mAs, 5 mm nominal slice thickness, effective pitch 1.35 (MSCT)
72 mAs, 5 mm nominal slice thickness, effective pitch 1.35 (MSCT)
chest 72 mAs, abdomen 90 mAs, 5 mm nominal slice thickness, effective pitch 1.35 (MSCT)
CT head (pre- and post-contrast medium)
240 mAs posterior fossa/200 mAs supratentorial, 5 mm slice thickness (axial acquisition)
Effective doses of CT were considerably underestimated, with a similar distribution of responses for each examination. For example, our estimated effective dose for CT abdomen/pelvis in a 5-year-old is 8.3 mSv, equivalent to approximately 1,300 CXR in a child of this age. The correct response (>900) was given by 3% of pediatricians, with only 16% answering within a factor of four of this (>300 CXR). The majority (58%) perceived the dose as approximately 10–50 times that of a CXR, with one-third (31%) estimating it as equivalent to 10 or fewer CXR. Only 1% of respondents correctly estimated the dose of a two-phase head CT (pre- and post-contrast medium), only 14% were within a factor of four, and 40% believed this frequently requested examination was equivalent to 10 CXR or less.
Eight pediatricians (4%) believed that US involves ionizing radiation (1–10 CXR) and 22 (12%) did not appreciate that DMSA scans do.
An overall accuracy score for Q.11 was generated for each respondent by weighting each response to subquestions a–h, excluding d (US). A correct response scored zero, underestimates scored 1–5 according to the number of boxes away from the correct response, and overestimates were similarly scored negatively. There was no statistically significant association between overall score and years of clinical experience, practice setting, familiarity with ALARA, awareness of the AJR articles or having received formal educational input. Fellows scored slightly better than practicing pediatricians (mean score 1.51 vs. 1.79, P=0.0001, two-sample t-test).
Of the 220 respondents, 33 (15%) were familiar with the ALARA principle regarding radiation doses in medical imaging (Q.5). The percentage of background radiation caused by medical radiation (Q.4, answer 15% ) was correctly identified by 10% of respondents, underestimated by 59%, and overestimated by 12%, with 19% responding “Don’t know.” More recent estimates of the average annual medical exposure in the USA suggest that the contribution of medical radiation might now be higher than the quoted figure from 1990 .
Multislice CT technology was considered by 51% of the respondents to involve a lower radiation dose than previous single-slice scanners, to involve a similar dose by 31% and a higher dose by 18% (Q.12). In general, multislice technology has increased the dose received by children [26, 27], and though some more recent technological advances such as mAs modulation offer hope for dose reduction , these are not yet in widespread use. Only 11% of pediatricians were aware that US government agencies were debating the addition of medical radiation to their list of known carcinogens (Q.13 ). This has subsequently occurred .
Respondents were asked at what level of excess lifetime cancer risk the radiation risks associated with CT should be routinely discussed with patients’ families (Q.10, Table 1). The largest number of respondents (43%) believed a risk level of 1 in 10,000 should be discussed, with an additional 15% discussing at 1 in 1,000,000. Twenty five percent believed 1 in 1,000 was a suitable level; 13% did not believe discussion was appropriate.
Level and sources of educational input
Recalled training regarding radiation doses in medical imaging (total no. of respondents 218)
Informal discussion with senior staff
The introduction of CT in the late 1970s has arguably revolutionised medical imaging. However, it involves radiation doses several orders of magnitude greater than most previous imaging modalities. CT currently represents 10% of procedures and almost 70% of the overall radiation burden . Its use in children is increasing, probably even more rapidly than in adults, with an estimated 2.7 million pediatric CT examinations per year in the USA, and 30% of patients undergo at least three scans .
Multiple factors are contributing to this worldwide increase, including advances in technology allowing faster scanning and less need for sedation or anesthesia in children, advances in software allowing ever more sophisticated applications and reconstructions, public perception and impatience, and perhaps medicolegal concerns.
CT is now being used on an increasing number of children for an increasing number of indications. Clearly the benefits to the patient are, in many cases, obvious and immediate. This does not, however, remove our responsibility to acquire a full knowledge of the potential risks involved and to do all we can to reduce these risks and to ensure that this powerful modality is used appropriately. In 1990 an NRPB survey estimated that up to half of the radiation dose resulting from diagnostic radiology in the UK was probably unnecessary . More recently, an informal survey at the SPR ALARA Conference estimated that up to 30% of pediatric CT requests were unlikely to benefit the individual or could be easily and effectively replaced by a non-ionizing imaging modality .
Our aim was to broaden the coverage of previous physician-based surveys, which have been largely limited to exploring knowledge of the relative radiation doses of radiological investigations in adults [16–18]. Our response rate of 40% is within the range expected of surveys of this magnitude, with 220 respondents exceeding the numbers involved in previous studies [16–18].
It was disappointing that only half of responding pediatricians were aware of the 2001 AJR articles and the surrounding publicity, given the perceived significance of these articles to pediatric radiologists and the press and TV coverage at the time. The story was apparently covered in 280 news programs throughout the world . The FDA issued a communication to all radiologists in the USA , and the SPR led more discussion by organizing the ALARA Conference . Either the initial impact beyond pediatric radiology was not as widespread as we perceived, or the message has been insufficiently reinforced. Even among those who believed they recalled the estimated lifetime cancer risk for a young child undergoing CT, the vast majority underestimated the risk and a small number believed the paper suggested there was no excess risk. It should be acknowledged that Brenner et al.  based their calculations on CT scans performed using adult technical parameters. Age-related reductions in mAs and other dose-reducing strategies can reduce doses and associated risks by 50%–80% in body CT and, to a lesser extent, in head CT. Even allowing for this, the perceived risk is a significant underestimate. Clinical scans often involve more than one body region and might be multiphase, further increasing dose. Finally, age-related dose reduction might not be as widespread as we hope .
The expression of effective doses in terms of CXR-equivalent units has proved useful in previous physician-based studies [16–18] and as a tool when discussing relative risks with patients and their families. Therefore, we decided to use this format. However, patient size must be taken into account in effective dose calculations. For the same exposure, there is an exponential increase in effective dose with decreasing age, which becomes particularly significant in children younger than 10 years [22, 37, 38]. Hence the increased lifetime cancer risk associated with a particular exposure will be higher in children. Following the recent A-bomb survivor data, risk estimates for young children have been revised upwards from three to four times [8, 9] to perhaps ten times the risk of an adult exposed under the same conditions .
Multiple factors contribute to this increased radiosensitivity [19, 20, 38]. As a consequence, though the measures of exposure such as entrance surface dose (radiography), dose-area-product (fluoroscopy), and dose length product (CT) will be lower in children than adults, the effective dose—from which an estimate of the future cancer risk associated with that exposure can be made—might be higher. In view of this inverse relationship of effective dose per energy imparted and age [22, 37, 38], it is necessary to state the age of the child being considered, and to use age-specific conversion factors when calculating effective doses . We chose a mid-range child (5 years old) with a radiosensitivity between that of infants and teenagers.
Respondents underestimated the relative effective doses of all investigations, regardless of modality, but particularly CT. Fewer than 20% of pediatricians were within 50% of the CT estimated doses, with 15%–40% believing such examinations are equivalent to 10 CXR or less. A large number of physicians are, therefore, submitting their patients to radiation doses significantly higher than they think.
Potential criticisms of our study include the nature of effective dose calculations in children, which are complex, involving estimates at several levels . With regard to the source data, our radiography, fluoroscopy and nuclear medicine doses were derived from our institution protocols and compare with published data and available diagnostic reference levels . Our age-related CT protocols compare with those of other pediatric institutions [13, 36], and the derived CT effective doses compare with those recently published from a large UK survey that included pediatric use . Further reductions in mAs for head CT have been achieved since the time of this study. It is hoped that dose reduction will continue with the advent of new software strategies . It is also true that a significant number of pediatric scans are performed in non-specialist centers or private clinics, where adult-type protocols might still be used, including multiphase imaging, higher mAs or lower effective pitch, and children could receive doses several times greater. Inevitably, therefore, the correct answers in surveys of this nature will always be estimates.
Some respondents might have been familiar with effective doses expressed in CXR-equivalents from previous adult-based sources [40, 41]. The higher relative number of CXR-equivalents in children, particularly for CT examinations, at least partially reflects the smaller denominator used—the effective dose of a PA CXR in an adult patient is 0.02 mSv, three times greater than that in a 5-year-old child (0.006 mSv). There are other inherent difficulties with the use of the CXR-equivalents method of expressing dose in children. As the effective dose of a CXR varies with age, so will the CXR-equivalent figures for higher-dose examinations, even if the mSv value is unchanged. Similarly, relatively small variations in CXR dose between institutions could create larger variability in CXR-equivalent data.
Nevertheless, the prevalence and degree of dose underestimation was such that if the CXR-equivalent estimates were reduced by over 50% for CT examinations, the result of widespread dose underestimation remains. Respondents estimating CT effective doses as equivalent to 10 CXR or less are of particular concern. Our results parallel those of previous studies demonstrating significant underestimation of adult radiation doses by physicians [16–18].
Some readers might believe our expectations of knowledge among pediatricians were high. Indeed, how would adult or pediatric radiologists score on our questionnaire? We do not have a gold standard of knowledge with which to compare. However, the study was performed as much to determine the general level of knowledge as a baseline and to aid future educational input as in the expectation of correct responses. We believe we should be aiming high in our efforts to disseminate knowledge that is of direct relevance and concern to practicing physicians.
Although there is undoubtedly a trend toward greater public knowledge and desire to be informed of both risks and benefits in medicine, the majority of pediatricians reported being asked about radiation doses and risks only rarely. However, approximately a quarter of respondents were asked sometimes or frequently, and a third reported a sustained or transient increase in questioning following the 2001 articles. We believe the demands of the public for informed discussion can only increase with time and that physicians must be able to provide balanced and accurate information to answer their concerns appropriately.
The question of obtaining formal informed consent to high-dose procedures such as CT has been raised recently by both radiologists and physicians [40, 42, 43]. The issue is generating widely differing views, and will no doubt develop over the coming years. We are not aware of any survey of pediatricians on this subject other than the single question included in our study. It is nevertheless interesting that, when asked at what level of excess lifetime cancer risk pediatricians believe we should be routinely discussing radiation risks with patients’ families, 58% chose 1 in 10,000 or 1 in 1,000,000—risks that are less than the current estimates associated with pediatric CT [9, 10]. Combined with the 25% who would discuss risks at 1 in 1,000, the implication is that the majority of pediatricians would at least consider a greater discussion of radiation risks with patients, though there remains a smaller minority (13%) who do not believe discussion is appropriate.
The difficulties of informed consent are numerous, including the lack of consensus on the true level of risk, the lack of readily available age-related effective dose information, and the future time period to which any risk relates. The greatest challenge is deciding the most meaningful way to express the level of risk and relating this to the potential benefit from an examination. Although each gives us some assessment of risk, there are limitations and potential difficulties in the use of numerical expressions of excess lifetime cancer risk, equivalent time periods of background radiation, and effective dose CXR-equivalents. All must be put in an appropriate context. For example, how many people would realize that annual natural background exposure is equivalent to approximately 150 CXR in an adult (3 mSv=150×0.02 mSv ) and 500 CXR in a 5-year-old (500×0.006 mSv)? The authors’ opinion is that while risk-versus-benefit assessments are challenging to both doctor and patient and though we do not wish to create a culture of fear, it is the responsibility of the medical community to promote parental and, arguably in the case of teenagers, patient understanding of this issue. Formal written consent is likely impracticable and may not be appropriate, but nevertheless, some form of discussion of potential radiation risks should be part of routine patient management in the same manner as potential adverse drug reactions.
Only one-third of practicing pediatric clinicians who responded recalled any specific teaching regarding radiation doses in medical imaging, and of these, less than half had attended a formal lecture, course or workshop, the remainder relying on personal reading or informal discussions with senior staff. This is clearly a major deficit.
But what is the most effective approach to correct this? Who should lead the educational process, what modality is most effective, and at what stage in training? We believe it is our role and responsibility as pediatric radiologists to take the lead in this with support from medical physicists. Input is necessary at all levels, starting in medical school, developing through pediatric medical and surgical training programs and continuing for our practicing colleagues with regular updated information as imaging technology advances. Approaches will vary with local programs and facilities but are likely to be most effective if a combination of formal lectures/rounds, opportunities for informal discussion such as workshops, and easily available reference data such as short information booklets can be combined. We were encouraged by the number of respondents (approximately 10%) acknowledging their relative lack of knowledge and/or requesting further information. We hope to continue the audit loop by distributing an information sheet. In our daily practice, pediatric radiologists have another opportunity for education through our gate-keeping role when receiving examination requests and also during reporting when there is opportunity to suggest other imaging studies and comment on why one modality might be preferred over another. Finally, contributions to the pediatric literature by radiologists can play an important role in increasing awareness .
There is increasing awareness among pediatric radiologists of the potential risks associated with ionizing radiation in medical imaging. However, this study suggests that there is still widespread underestimation of relative doses and risks by pediatricians. An important element of radiation protection is to ensure that physicians have sufficient knowledge to enable a balanced and accurate assessment of the risk-versus-benefit balance when considering radiological examinations. It is our responsibility to inform and educate our colleagues. Until this is addressed, our success at reducing or even maintaining the present radiation burden to the pediatric population is likely to be limited.
We thank the technical staff of the Department of Diagnostic Imaging at the Hospital for Sick Children for their help and support of this project.