Effect of staff training on radiation dose in pediatric CT

AzadehHojrehaMichaelWeberb1PeterHomolkac2

aMedical University of Vienna, Department of Biological Imaging and Image-guided Therapy, Division of General and Paediatric Radiology, Waehringer Guertel 18–20, A-1090 Vienna, Austria
bMedical University of Vienna, Department of Biomedical Imaging and Image-guided Therapy, Division of General and Paediatric Radiology, Waehringer Guertel 18–20, A-1090 Vienna, Austria
cMedical University of Vienna, Centre for Medical Physics and Biomedical Engineering, Waehringer Guertel 18–20, A-1090 Vienna, Austria

Received 23 December 2014, Revised 22 March 2015, Accepted 23 April 2015, Available online 12 May 2015.

Highlights

•Pediatric patient CT doses were compared before and after staff training.
•Staff training increasing dose awareness resulted in patient dose reduction.
•Application of DRL reduced number of CT’s with unusually high doses.
•Continuous education and training are effective regarding dose optimization.

Abstract

Objective

To evaluate the efficacy of staff training on radiation doses applied in pediatric CT scans.

Methods

Pediatric patient doses from five CT scanners before (1426 scans) and after staff training (2566 scans) were compared statistically. Examinations included cranial CT (CCT), thoracic, abdomen–pelvis, and trunk scans. Dose length products (DLPs) per series were extracted from CT dose reports archived in the PACS.

Results

A pooled analysis of non-traumatic scans revealed a statistically significant reduction in the dose for cranial, thoracic, and abdomen/pelvis scans (p < 0.01). This trend could be demonstrated also for trunk scans, however, significance could not be established due to low patient frequencies (p > 0.05). The percentage of scans performed with DLPs exceeding the German DRLs was reduced from 41% to 7% (CCT), 19% to 5% (thorax-CT), from 9% to zero (abdominal–pelvis CT), and 26% to zero (trunk; DRL taken as summed DRLs for thorax plus abdomen–pelvis, reduced by 20% accounting for overlap). Comparison with Austrian DRLs – available only for CCT and thorax CT – showed a reduction from 21% to 3% (CCT), and 15 to 2% (thorax CT).

Conclusions

Staff training together with application of DRLs provide an efficient approach for optimizing radiation dose in pediatric CT practice.

Keywords

Pediatric computed tomography
Diagnostic reference levels
Radiation protection
Staff training
CT DRL

Abbreviations

ALARA

as low as reasonably achievable

CT

computed tomography

CCT

cranial computed tomography

CTDI

CT dose index

DLPs

dose length products

DRLs

diagnostic reference levels

NDRLs

national diagnostic reference levels

PACS

picture archiving and communication system

SPR

scan projection radiograph

SSDE

size specific dose estimate

1. Introduction

With ongoing technological developments in radiation protection, CT has become integral to pediatric radiology, and has established itself as an important part of the diagnostic algorithm [1–6]. Nevertheless, the awareness of the possible effects of ionizing radiation in the young and growing bodies of children requires that radiation dose and scan protocols be adapted to size, age, and clinical needs [6–9], according to the ALARA (as low as reasonably achievable) principles. In addition to stringent justification requirements, continuous optimization is imperative. Well-established radiation dose reduction methods are available for every modern CT scanner, such as automatic tube current modulation [10–12] and tube potential optimization [12,13]. In addition, correct patient positioning in the scanner isocenter [12–14], individually adjusted scan boundaries, the choice of an anterior–posterior or posterior–anterior supine projection, and appropriate reduction of the Scan Projection Radiograph (SPR) dose [12,15], must be considered. Another very important issue is avoiding multiple scan series in pediatric CT whenever possible. If necessary, clinically unstable and non-cooperative children should be sedated to reduce movement artifacts and prevent repeated scans [9]. One of the most powerful optimization tools is to compare the doses delivered to Diagnostic Reference Levels (DRLs), which are also now becoming available for pediatric CT [16–20]. In most cases, DRLs represent the 3rd quartile of doses from dose surveys, indicating a level of dose below which 75% of all institutions operate. However, especially in pediatric CT, these dose levels have been lowered quite a bit recently, indicating that there is still some more potential for optimization. Nevertheless, these values cannot be thought of as representing the optimum values. Rather, they are values which, when continuously exceeded, should trigger a process to determine the reasons these unusually high doses were used and an attempt should be made to lower them. To estimate doses to children from CT Dose Index (CTDI) readings, the concept of the Size Specific Dose Estimate (SSDE) [21] helps to visualize the relation of pediatric doses to doses delivered to adults, since, due to their reduced body diameter, the same CTDI values result in considerably higher organ and tissue doses in children.

Last but not least, radiation staff education is one of the most efficient ways to enforce scientific “good practice” in radiological institutes and to reduce the radiation dose to patients [22–25].

The purpose of our study was to evaluate the efficacy of staff training and continuous education on the radiation doses applied in pediatric CT scans.

2. Materials and methods

Pediatric CT scans were performed in the emergency department (Somatom Sensation Cardiac 64Siemens Medical, Erlangen, Germany), the divisions of musculoskelatal radiology (Brilliance 64Philips, The Netherlands), traumatology (Somatom Sensation Open, Siemens, Germany), neuroradiology (Somatom Sensation 4 until September 2010, Somatom Sensation 64 thereafter, both Siemens, Germany), and surgery (Somatom Definition Flash, Siemens, Germany). On the emergency and the surgical scanner, pediatric radiologists were in charge, and radiologists with pediatric radiology experience were present in the divisions of musculoskeletal radiology, neuroradiology, and traumatology. The technical staff consisted of licensed radiographers. On all scanners, quality control programs were performed, including regular (semi-annual) CTDI calibration and monthly image quality tests.

To avoid image quality loss below diagnostic requirements, the radiologists were made aware of the on-going optimisation and asked to report image quality issues immediately.

2.1. Data acquisition

Examination data from all pediatric and adolescent patients under 18 years of age, who underwent standard cranial, thoracic, abdomen–pelvis, and thoracic–abdomen–pelvis (trunk) scans between 2010 and 2012, were extracted retrospectively from the PACS system (IMPAX DS 3000, Agfa Healthcare, Mortsel, Belgium). Extracted dosimetric data included dose length product (DLP) values for each series obtained from the Dicom Structured Reports.

Standard ranges were defined as follows:

cranial scan (CCT): apex to skull base

thoracic scan: seventh cervical (or first thoracic vertebra) to sinus phrenicocostalis

abdomen–pelvis scan: diaphragmatic dome to symphysis

trunk scan: seventh cervical (or first thoracic vertebral) to symphysis.

All data were checked and excluded if the examination range indicated a non-standard range due to the patients’ individual indication, such as, e.g., a combined neck and thorax CT, a thorax including upper abdomen scan, or an abdomen–pelvis scan including the femora. CT examinations in which the dose report was not recorded in the PACS system were also excluded. Data evaluation was performed per series. If examinations consisted of more than one series (e.g., scans with and without contrast for oncological cases), every single series was treated as a separate scan.

2.2. Staff training

Staff training consisted of yearly obligatory radiation protection briefings, as stipulated by legislation, combined with continuing education elements. These sessions were organized as 90-min presentations, including a discussion part. During these training sessions, dosimetry concepts and optimization measures, including DRLs, were presented, together with new relevant publications and studies, as well as radiation protection rules for personnel and patients. Topics and presenters changed every year.

In 2010, the main topic was the newly published national DRLs (NDRLs) for pediatric examinations, including CT, since an amendment to the national medical radiation protection bylaw, which included pediatric DRLs for the first time, had been issued [20]. The presentation was offered three times in December 2010 to reach all radiologists and radiology technologists.

2.3. Data analysis

To extract longitudinal trends, data were evaluated and compared statistically for 2010 (i.e., before training dedicated to pediatric CT), 2011, and 2012. In order to be able to compare changes in dose applied as a result of optimization for the different examination types and age ranges in question, the percentages of examinations that exceeded the age- and procedure-specific DRLs were calculated. For this comparison, dose data from infants below one month of age were pooled in a group and compared to the DRL for newborns. Data from children between one and twelve months of age were compared to the DRLs for one-year-olds, from thirteen months to five years to five-year-olds, and so on, according to the usual instructions applied when comparing childrens’ exposures to DRLs using age banding and benchmarking against the upper limit of the appropriate age band. Since DRLs are different in most countries, the most comprehensive and complete European values from Germany, Austria, and Switzerland were used (Table 1). However, no reference levels were available for trunk scans. To still be able to make a valid comparison, the respective DLPs for chest and abdomen–pelvis scans were added and reduced by 20% to account for the overlap in the scan range. Twenty-percent has been shown to be an appropriate reduction for these combined scans in adults [26]. Dose optimization as a result of staff training was anticipated to result in a decrease in the relative number of patient scans that exceeded the appropriate DRLs.

Table 1. Dose reference levels (DRLs).

Cranial CT Thorax CT Abdomen–Pelvis CT Trunk CT
AUT GER CH AUT GER CH AUT GER CH AUT based on
GER* CH*
Newborn 300 300 290 80 20 12 n/a 45 27 n/a 52 31
1 year 400 400 390 100 30 28 n/a 85 70 n/a 92 78
5 years 600 500 520 150 65 55 n/a 165 125 n/a 184 144
10 years 750 650 710 180 115 105 n/a 250 240 n/a 292 276
15 years 900 850 920 200 230 205 n/a 500 500 n/a 584 564
*

Comparison values derived from thorax and abdomen/pelvis DRLs. AUT, GER, CH corresponds to Austrian, German, and Swiss values.

Statistical computations were performed using SPSS version 21.0 (IBM, New York, USA). In order to assess the association between age and DLP, linear and non-linear regression analyses were performed. Due to the intrinsically skewed nature of dose data, the DLP was described using median as well as 1st and 3rd quartiles. The percentages of scans with DLPs above diagnostic reference levels were determined. Data from the traumatology department were evaluated separately since trauma CT scan protocols differed from the protocols applied by the other departments due to diagnostic requirements.

Optimization, including retrospective anonymized evaluation of patient doses, and comparison of average doses applied with DRLs, is a legal requirement in Austria. Nevertheless, ethics board approval was obtained beforehand.

The authors have nothing to disclose and confirm that there are no conflicts of interest associated with this publication.

3. Results

Examination numbers were 1799 in 2010, 1582 in 2011, and 1525 in 2012. Dose reports were not included into the PACS for 79 series in 2010, 53 in 2011, and 31 in 2012. Another 477 series were excluded in 2010 because of a non-standard scan range; 407 in 2011; and 449 in 2012. Thus, in total, the rejection rate was 27.3% (1496 scan series). Table 1 shows how cases were distributed between the departments’ scanners.

No image quality issues were reported by staff (radiographers and radiologists) during optimisation.

DLP values exhibited the best correlation with age using an exponential model (R2 from 0.52 for CCT, 0.61 and 0.63 for abdomen–pelvis and thoracic scans, respectively, and 0.71 for trunk scans) and the least correlation when a linear model was applied (R2 from 0.34 to 4.49), with a quadratic model only fitting minusculely better than the linear model. Therefore, a linear correlation of log(DLP) with age was utilized to determine whether statistically significant dose reductions were achieved.

Table 3 summarizes the ANCOVA results that assessed whether the effects of dose reduction were statistically significant. Patient doses were significantly reduced for CCT both from 2010 to 2011, and 2012 with respect to 2011. The same was true for thoracic scans. For abdomen–pelvis scans, a reduction in the DLPs was significant for 2011 with respect to 2010. Average DLP values were also reduced slightly in the following year, but significance could not be demonstrated. For trunk scans, a slight reduction in average DLPs occurred; however, it was not significant (p > 0.05). This can also be seen in Fig. 1a–d, showing the box plots for the data. Case numbers (see also Table 2) for abdomen–pelvis, and, especially trunk scans, were quite low. Fig. 1a–d also clearly demonstrates a reduction in the range of variation within the age bands, seen from the widths of the boxes (1st to 3rd quartile) and the whiskers (10th to 90th percentile).

Fig. 1. (a–d): Box plots of dose length products (DLPs) distributions in age bands compared for 2010, 2011, and 2012.

Table 2. Case numbers per department and year.

Department Cranial CT Thorax CT Abdomen–Pelvis CT Trunk CT
2010 2011 2012 2010 2011 2012 2010 2011 2012 2010 2011 2012
Neuroradiology (old scanner) 589
Neuroradiology (new scanner) 202 684 707 1 2 2 2
Traumatology 119 109 63 2 4 2 8 15 5 40 42 15
Surgery 4 5 1 115 155 159 34 43 30 10 22 18
Musculoskeletal radiology 2 1 1 15 17 23 3 16 6 7
Emergency 174 132 125 54 39 30 38 32 33 10 20 5

Table 3. ANCOVA results for logarithms of dose reference level (DLP) values.

Average log (DLP) P
2010 2011 2012
CCT 6.43 6.29* 6.23* <0.01
Thorax CT 4.45 4.12* 3.97* <0.01
Abdomen–Pelvis CT 5.14 4.87* 4.76 <0.01
Trunk CT 5.15 5.10 4.67 >0.05
*

Indicates statistically significant reduction compared to preceding year.

Another measure designed to quantify optimization outcome is the number of scans that exceed the reference levels, as shown in Table 4. For all examinations, the relative number of these scans was reduced. Compared to the German reference levels, for example, there was a reduction of over 40% to approximately 6% in CCT scans, and from approximately 9% and 26% (abdomen–pelvis and trunk scans, respectively) to zero.

Table 4. Percentage of non-trauma and trauma scans performed that exceeded dose reference levels (DRL).

% Exceeding German DRL % Exceeding Austrian DRLs % Exceeding Swiss DRLs
2010 2011 2012 2010 2011 2012 2010 2011 2012
Cranial CT 41 16 6.7 21 6.4 3.4 29 12 4.1
Thorax CT 19 9.9 4.7 15 6.1 1.9 25 12 5.7
Abdomen–pelvis CT 9.3 4.3 0.0 n/a n/a n/a 6.7 4.3 0.0
Trunk CT 26 9.1 0.0 n/a n/a n/a 22 9.1 0.0
Traumatic cranial CT 76 88 83 50 50 37 68 68 75
Traumatic trunk CT 43 52 20 n/a n/a n/a 53 57 20

3.1. Trauma CT scans

An analysis of dose data was performed only for CCT and trunk scans, since examination numbers were too low for the other examinations.

No dose reduction was seen in traumatic CCT scans (Table 4), and the number of scans performed that exceeded DRLs increased from 76% in 2010 to 88% in 2011 and 83% in 2012, if the German values are used as a reference. For trunk scans, a reduction by a factor of two was observed, starting with 43% (compared to the German values) in 2010 to 20% in 2012. However, since the sample size in 2012 contained only 15 scans, and included no scans for children up to five years of age, this reduction cannot be considered credible.

4. Discussion

The application of Dose Reference Levels, in combination with staff education and awareness, has been demonstrated to be effective in dose optimization in pediatric computed tomography. The presentation of NDRL for pediatric cranial and body computed tomography to our already well-trained radiology technologists and radiologists enabled a radiation dose reduction for most pediatric CT examinations. This effect was also shown to be sustainable. This corresponds nicely to a rather recent publication indicating that one reason for unusually high doses in pediatric radiology was that radiation dose levels were never determined, and thus, not known [17].

Paolicchi et al. demonstrated the role of radiological staff training for adult chest, abdomen–pelvis, and whole body CT scans [25], indicating that training of radiologists and technologists is a key issue in optimizing CT protocols, and thus, can significantly reduce radiation dose [25]. They published also a radiation dose reduction while preserving diagnostic image quality in pediatric head CT examinations, after a radiologic staff training [27]. Schindera et al. reported the same effect for adult paranasal sinuses, brain, chest, pulmonary arteries, and abdomen CTs [24]. The authors reported that the largest decrease in radiation dose was reached for paranasal sinus and pulmonary arteries scans. No significant dose reduction for abdominal CTs was found; suboptimal image quality for low-contrast lesions in abdominal CTs was most likely identified as the reason. Education and training programs for radiological institutes was concluded to be effective in achieving substantial reduction in CT dose [24]. Sheyn et al. reported that staff radiation safety education can improve radiation safety practices in pediatric interventional radiology, and thus, decrease exposure to radiation for both staff and patients [22]. Georges et al. demonstrated in 2009 that training in radiation protection for interventional cardiologists, and the use of simple and cost-free dose-reduction techniques, were associated with a 50% reduction in radiation exposure to patients undergoing invasive cardiac procedures, without any loss of diagnostic information [23].

This work extends the scope of these studies, demonstrating the effects of continuing education and training on pediatric CT, and endorses the efficacy of the concept of DRLs. These two concepts complemented each other very well. We observed a significant decrease in DLP for all of our pediatric CT scans, including cranial, thoracic, abdomen–pelvis, and trunk CTs, during the observation interval from 2011 and 2012, compared to 2010, with the only exception being trauma CT scans. However, the DRLs are not directly applicable to trauma CT scans because of their specific requirements. This is most obvious in head scans, where the DRLs correspond to brain scans rather than the bony skull. Nevertheless, future work should be invested in imaging criteria including appropriate dose levels for trauma scans with special emphasis on pediatric examinations.

The relative number of scans performed at a dose exceeding the appropriate reference level was assessed. However, it must be noted that DRLs can only be applied on average doses and cannot be used on an individual basis. Therefore, it is inappropriate and misleading to argue that individual doses (DLPs in this case) that exceeded the DRLs indicated that too high a dose was used. If the values constantly exceeded that for standard patients and examinations, the dose level applied would be graded as “unusually high”, triggering the need to research the reasons for this higher level. Therefore, this type of assessment does not comply with the basic idea of reference Levels. However, if an unusual or rather high number of scans exceed the DRLs, and the rate decreases during optimization without any image quality issues arising, it seems reasonable to declare the education effort a success. Normally, doses quite below the appropriate DRLs can be applied since the actual values are not optimal values [28,29], but merely represent values below which 75% of institutions operate. However, care should be taken to ensure that patients and diagnostic requirements are comparable. In this work, DRLs from other countries were used, since a European consensus on values has not yet been reached, and Austrian levels do not cover all the indications we assessed in this work.

4.1. Limitations of this study

The scanner in the neuroradiology department has been replaced during this study (from a 4- to a 64-slice scanner) in September 2010. Most of the CCT scans in the study originated from this department. The protocols previously implemented at the four slice scanner were optimized before the scanner exchange, and transferred with only slight adjustments due to the new technology to the new machine. Scan protocols were individually adjusted to the patients’ physique at both, the old and the new machine. However, it cannot be ruled out completely, that the scanner change had an effect on the dose reduction, but this effect should have been minor. Another limitation was the low case number of trunk scans, due to which no statistically significant dose reduction in terms of DLP could be demonstrated. However, the effect can be seen in the reduction of the relative share of scans with doses greater than the DRLs (from approximately one quarter to zero). Last but not least, since the doses from traumatic scans did not change, future work should be dedicated to the definition of image quality requirements and optimization of these protocols.

5. Conclusion

Modern CT scanners provide numerous possibilities for optimizing radiation dose and applying it more efficiently, like automatic tube current modulation, individual kVp optimization, and iterative reconstruction, to name a few [30]. However, continuous education of personnel to ensure that they are familiar with these possibilities, in order to utilize the potential for dose reduction, must be emphasized.

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