European Journal of Radiology 84 (2015) 1574–1578

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Effect of staff training on radiation dose in pediatric CT Azadeh Hojreh a,∗ , Michael Weber b,1 , Peter Homolka c,2 a Medical 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 b Medical 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 c Medical University of Vienna, Centre for Medical Physics and Biomedical Engineering, Waehringer Guertel 18–20, A-1090 Vienna, Austria

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Article history: Received 23 December 2014 Received in revised form 22 March 2015 Accepted 23 April 2015 Keywords: Pediatric computed tomography Diagnostic reference levels Radiation protection Staff training CT DRL

a b s t r a c t 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. © 2015 Elsevier Ireland Ltd. All rights reserved.

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

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. ∗ Corresponding author. Tel.: +43 1 40400 48180; fax: +43 1 40400 48980. E-mail addresses: [email protected] (A. Hojreh), [email protected] (M. Weber), [email protected] (P. Homolka). 1 Tel.: +43 1 40400 48180; fax: +43 1 40400 48980. 2 Tel.: +43 1 40400 17130; fax: +43 1 40400 39880. http://dx.doi.org/10.1016/j.ejrad.2015.04.027 0720-048X/© 2015 Elsevier Ireland Ltd. All rights reserved.

requirements, continuous optimization is imperative. Wellestablished 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. Hojreh et al. / European Journal of Radiology 84 (2015) 1574–1578

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 64; Siemens Medical, Erlangen, Germany), the divisions of musculoskelatal radiology (Brilliance 64, Philips, 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

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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. 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.

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Table 1 Dose reference levels (DRLs). Cranial CT

Thorax CT

AUT

Newborn 1 year 5 years 10 years 15 years *

GER

300 400 600 750 900

CH

300 400 500 650 850

AUT

290 390 520 710 920

80 100 150 180 200

Abdomen–Pelvis CT GER

20 30 65 115 230

CH

12 28 55 105 205

GER

AUT

n/a n/a n/a n/a n/a

Trunk CT CH

45 85 165 250 500

AUT

27 70 125 240 500

n/a n/a n/a n/a n/a

based on GER*

CH*

52 92 184 292 584

31 78 144 276 564

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

Table 2 Case numbers per department and year. Department

Cranial CT

Neuroradiology (old scanner) Neuroradiology (new scanner) Traumatology Surgery Musculoskeletal radiology Emergency

Thorax CT 2012

2010

2011

2012

2010

2011

2012

2010

2011

2012

589 202 119 4 2 174

684 109 5 1 132

707 63 1 1 125

– 2 115 15 54

1 4 155 17 39

– 2 159 23 30

– 8 34 3 38

2 15 43 16 32

2 5 30 6 33

– 40 10 7 10

2 42 22 – 20

– 15 18 – 5

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

*

Trunk CT

2011

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). 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,

CCT Thorax CT Abdomen–Pelvis CT Trunk CT

Abdomen–Pelvis CT

2010

P

2010

2011

2012

6.43 4.45 5.14 5.15

6.29* 4.12* 4.87* 5.10

6.23* 3.97* 4.76 4.67

Effect of staff training on radiation dose in pediatric CT.

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