Radiation Protection Dosimetry Advance Access published October 24, 2014 Radiation Protection Dosimetry (2014), pp. 1–6
doi:10.1093/rpd/ncu323
PREFECTURE-WIDE MULTI-CENTRE RADIATION DOSE SURVEY AS A USEFUL TOOL FOR CT DOSE OPTIMISATION: REPORT OF GUNMA RADIATION DOSE STUDY Yasuhiro Fukushima1,2,*, Ayako Taketomi-Takahashi2, Takahito Nakajima2 and Yoshito Tsushima2 1 Department of Radiology, Gunma University Hospital, 3-39-15 Showa, Maebashi, Gunma 371-8511, Japan 2 Department of Diagnostic Radiology and Nuclear Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511, Japan *Corresponding author: [email protected]
The aim of this study was to verify the usefulness for the dose optimisation of setting a diagnostic reference level (DRL) based on the results of a prefecture-wide multi-centre radiation dose survey and providing data feedback. All hospitals/clinics in the authors’ prefecture with computed tomography (CT) scanners were requested to report data. The first survey was done in July 2011, and the results of dose–length products (DLPs) for each CT scanner were fed back to all hospitals/clinics, with DRL set from all the data. One year later, a second survey was done in the same manner. The medians of DLP in the upper abdomen, whole body and coronary CT in 2012 were significantly smaller than those of the 2011 survey. The interquartile ranges of DLP in the head, chest, pelvis and coronary CT were also smaller in 2012. Radiation dose survey with data feedback may be helpful for CT dose optimisation.
INTRODUCTION In modern medicine, computed tomography (CT) has provided great benefits in clinical practice for determining treatment plan and follow-up after treatment. On the other hand, in the USA, 67 % of the collective effective dose in diagnostic radiology was due to CT examinations(1), whose relatively high-dose radiation exposure is an unavoidable drawback. After the estimates of cancer risk attributable to diagnostic Xrays in Japan have been reported in comparison with other developed countries(2), further efforts to reduce or optimise radiation dose have been encouraged. Usually in Japan, radiological technologists have sole discretion on the configuration of CT scanning parameters. The ICRP recommends the use of diagnostic reference level (DRL) for patients(3). Use of DRL is a method for evaluating whether the patient dose is unusually high or low for a particular medical imaging procedure(4). Several surveys for establishing DRLs for adults(5 – 7) and children(8, 9) have been reported in Europe and Korea. In Japan, calculated results on patient dose using simulation software have been reported, but so far, there has been no large-scale survey in Japan for establishing DRLs based on actual clinical data(10). Since 2008, the authors have been conducting prefecture-wide ‘Gunma radiation dose study (GRaD Study)’, which estimated the DRL for each anatomical region by surveying radiation dose that was collected from hospitals/clinics in Gunma prefecture (100 km north of Tokyo; population, two million) with CT
scanners. The authors previously reported that dose– length products (DLPs) were at comparable levels with DRLs previously reported from some countries, but the distribution of DLP had large variation and many outliers(11). In this study, the surveys of CT radiation dose were performed during the same month in two sequential years, 2011 and 2012. After analysing data of CT radiation dose in 2011, the results of this survey were sent to individual facilities. The results included distribution of DLPs for each anatomical region for each CT scanner and DRLs for each anatomical region. The 2011 survey provided only the data from their own CTs in comparison with other facilities and did not give any instructions or recommendations. The aim of this study was to verify the usefulness of prefecture-wide multi-centre radiation dose survey followed by the establishment of DRLs and data feedback to each institution for dose optimisation. MATERIALS AND METHODS This study was approved by the ethical committee of Gunma University Hospital, and informed consent from each patient was not necessary because this study was conducted under anonymity. CT radiation dose survey Surveys of CT radiation dose were performed twice, in July 2011 (first survey) and July 2012 (second
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at New York University on April 15, 2015
Received 21 June 2014; revised 26 September 2014; accepted 26 September 2014
Y. FUKUSHIMA ET AL.
Data analyses For the subjects of analysis, paediatric patients (0–15 y old) and examination type other than routine were excluded. Since a scanner usually does not provide the DLP for each individual anatomical region when two or more anatomical regions are scanned in a single session, only examinations of one anatomical region were sampled for the evaluation of DRL and DLP. If the number of scans for chest, upper abdomen and pelvis were same, the examinations were sampled as whole body (chest to pelvis). When a region was scanned two or more times (for instance, nonenhanced and enhanced scans), the obtained DLP
data were divided by the number of scans, as the authors analysed the dose in the method previously reported(11). The DLP data were expressed as median, 25th and 75th percentile (Q1 and Q3) values, and interquartile range (IQR; the difference between Q3 and Q1). The DRL was defined as Q1 and Q3 values (round off ) of DLP(11). Data feedback and evaluation of its effect After the first survey, DRLs estimated from the data of all hospitals/clinics along with the median and distribution of DLPs for each anatomical region for each CT scanner were sent to each hospital/clinic. This allowed radiological technologists to recognise the current condition of radiation exposure from CT. Each institution received individualised data sheets. On the individualised data sheets, data of the individual hospital/clinic were shown relative to those of other institutions, without showing the names of other institutions. Figure 1 is an example of the data sent (upper abdomen). The authors asked each institution to optimise CT scan parameters by comparing the distribution of DLPs in their own institution with those of other hospitals/clinics along with DRLs. One year later, the second survey was carried out in the same manner. The authors then compared the distribution of DLPs in the two studies to evaluate the change in DLPs. The authors also evaluated institutions with large changes in DLP between the two surveys for how they changed radiation dose and evaluated image quality, using the following method. The authors calculated the changes in DLP in each scanner for all anatomical regions. The change in DLPs was defined as (median DLP of second survey 2 median DLP of first survey)/median DLP of first survey (%). The authors found the five scanners with the greatest increase in radiation dose and five scanners with the greatest decrease in radiation dose for each anatomical region. From these data, the authors selected scanners that performed 10 or more scans for a given anatomical region on both the first and second surveys. The authors interviewed these institutions on the changes they made to their imaging parameters and how they evaluated the resulting changes in image quality. Statistical analysis Mann–Whitney U test and Mood test were employed for statistical analysis. The Mood test is a nonparametric test that tests a difference in distribution between two groups. A p-value of ,0.05 was considered statistically significant. Statistical analyses were performed using R (version 3.0.1., available via http:// www.r-project.org/).
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survey). The data concerning CT scanners and all individual patients undergoing CT examination in Gunma prefecture during a single month were collected. Datasheets were sent to all 187 hospitals/ clinics in Gunma prefecture with CT scanners. The data from CT scanners consisted of the vendor and model of the CT scanner, number of data acquisition channels and standard scanning protocols for each anatomical region. The data from each patient consisted of the patient’s age and sex, anatomical region of the CT examination, types of examinations if other than routine [for example, low-dose examination, CT perfusion or CT angiography (CTA)], number of scans for each anatomical region, volume CT dose index (CTDIvol) and total DLP as automatically displayed by the CT scanner. The authors chose to evaluate DRL for overall CT scanners with DLP instead of CTDIvol because some CT scanners display maximum CTDIvol instead of mean CTDIvol, whereas the definition of DLP is identical in all CT scanners. When a patient returned for a second or more CT sessions on a different day, the sessions were counted as two or more different patients with each undergoing a single CT session. The anatomical regions were divided into head (brain), face, neck, chest, upper abdomen, pelvis (lower abdomen) and coronary. When a patient was scanned in two or more anatomical regions during a single CT session, the number of examinations was counted as the number of anatomical regions scanned, and the number of scans was defined as the total number of scans for each anatomical region. For example, if a patient underwent unenhanced CT of the upper abdomen and enhanced CT of the chest and upper abdomen in a single CT session, the number of CT examinations was two, the number of scans of the chest was one and that of the upper abdomen was two. In coronary CT, low-dose non-enhanced scan for calcium scoring and high-dose enhanced scan for coronary CTA were routinely performed. To prevent underestimation of radiation dose for coronary CT in post-data processing, only DLPs and number of scans for coronary CTAwere obtained.
CT DOSE SURVEY FOR DOSE OPTIMISATION
RESULTS In the first survey (2011), CT dose data from 92 hospitals/clinics (102 CT scanners; single to 320 detector row CT) were obtained from data sheets sent to 187 institutions. The total data obtained were for 25 225 patients [male, 55.1 %; age, 64.6 + 19.4 y old (mean + SD); range, 0–105 y old], 43 779 examinations and 61 418 scans. Estimated DRLs of DLP for adult patients in each anatomical region were 810–1340 mGy cm for head CT examinations, 230 –460 mGy cm for face, 270– 650 mGy cm for neck, 260–540 mGy cm for chest, 280 –730 mGy cm for upper abdomen, 200–560 mGy cm for pelvis, 660 –1450 mGy cm for chest –pelvis and 390 –1320 mGy cm for coronary CT. This summary data were fed back to all hospitals/clinics with detailed dose distribution data for each anatomical region. In the second survey (2012), CT dose data were collected from 84 hospitals/ clinics (97 CT scanners) from data sheets sent to 187 hospitals, including 27 027 patients [male, 54.0 %; age, 64.4 + 19.4 y old (mean + SD); range, 0–105 y old], 46 346 examinations and 65 111 scans. Fifty-five hospitals/clinics (29.4 % of all facilities; 62 CT scanners) provided CT data in both the first and second surveys. Figure 2 briefly summarises CT scanners of 55 hospitals/clinics. To evaluate the changes in the DLPs between the two surveys, the authors reviewed data from these 55 hospitals, including 46 884 scans for the first survey (76.3 % of scans
Figure 2. The number of CT scanners according to the number of CT acquisition channels and vendors.
in the first survey) and 45 991 scans for the second survey (70.2 % of scans in the second survey). Thirtyfive institutions were hospitals with 100 or more beds (42.5 % of institution datasheet sent with 100 beds or more), and these hospitals performed the bulk of the scans in Gunma prefecture (87.0 % for the first survey and 84.9 % for the second survey). Of these scans, 12 761 scans from the first survey and 13 030 from the second survey were suitable for analysis. Table 1 and Figure 3 show the results of DLPs for each anatomical region along with outliers. In the upper abdomen,
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Figure 1. This is an example of a data sheet, which was fed back to each hospital/clinic after the first survey. This boxplot indicates the DLP in upper abdomen for each CT system, and the grey box indicates the results from all CT scanners. The dotted lines indicate DRL of abdomen (280–730 mGy cm). The height of the box displays IQR with the 25th (Q1) and 75th (Q3) percentiles representing the lower and upper edges of the box, respectively. The middle horizontal line is the median. Error bars extend from the box to show the range of non-outlying data points (whiskers). The lower whisker represents the Q1 2 1.5` IQR, and the upper whisker represents the Q3 þ 1.5` IQR. The outlier was defined as the value above Q3 þ 1.5` IQR, or below Q1 2 1.5` IQR (open circle, Q3 þ 1.5` IQR or Q1 2 1.5` IQR; asterisk, Q3 þ 3` IQR or Q1 2 3` IQR).
Y. FUKUSHIMA ET AL. Table 1. DLPs for each anatomical region. Anatomical region
Head Face Neck
Upper abdomen Pelvis Whole body Coronary
2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012
Number of CT scanners
61 23 28 54 39 29 44 15
Number of CT scanning
Statistical analysesa ( p-value)
DLP (mGy cm) 25th percentile
Median
75th percentile
IQRb
797 819 205 189 266 324 251 259 280 255 107 257 718 674 358 275
950 989 312 300 415 441 372 371 434 362 345 363 1010 910 722 606
1387 1262 402 419 616 678 544 519 694 590 556 549 1558 1343 1163 1031
590 443 197 230 350 354 293 260 414 335 449 292 840 669 805 756
4900 4997 399 464 385 319 3038 3138 1776 1592 180 161 1540 1814 543 545
Mann– Whitney U-test
Mood
0.167
,0.001
0.816
0.111
0.014
0.052
0.469
,0.001
,0.001
0.067
0.080
,0.001
,0.001
0.416
,0.001
0.041
a The Mann– Whitney U-test was used to evaluate the difference in median of DLP, and Mood test was used to evaluate the distribution. b IQR, interquartile range.
whole body and coronary CT, significant decreases in DLP were observed between 2011 and 2012 surveys ( p , 0.001, respectively). Although the number of scans was small, a significant increase in median DLP was observed in neck CT (6.3 %; p ¼ 0.014). The median DLPs decreased by 16.6 % for upper abdomen CT, 9.9 % for whole body CT and 16.1 % for coronary CT. Mood statistics revealed that the distributions of DLP in the head, chest, pelvis and coronary CT were smaller in 2012 survey compared with 2011 survey ( p ¼ 0.041 for coronary CT and p , 0.001 for head, chest and pelvis), resulting in the smaller IQRs. IQRs were decreased by 24.9 % for coronary CT, 11.3 % for head CT, 35.0 % for chest CT and 6.1 % for pelvic CT. Twenty-one institutions reported CT scanners with a large change in median DLP between the two surveys. Of these institutions, seven changed radiation dose by adjusting tube current or the noise index of auto exposure control (AEC). In these institutions, the radiologist or technologist evaluating the image made final decision of image quality and radiation dose. The other 14 institutions did not report a clear reason for the change in DLP. DISCUSSION The authors have shown that feedback of DRLs and DLP distribution data for each CT scanner derived
from the authors’ CT dose survey led to smaller distribution or reduction of radiation dose for head, chest, upper abdomen, pelvis, whole body and coronary CTs. Many competent radiologists and radiological technologists likely tried to optimise CT parameters based on the feedback data at their discretion, and the results fulfilled the authors’ expectations. The authors’ method of simply making competent radiologists and radiological technologists aware of how high or low DLP is in each CT system was surprisingly effective considering the limited resources involved, and at the same time, appropriate DRLs could be evaluated. Engel et al.(12) recently reported that weekly dose report feedback of site radiation doses of coronary CT angiography in a single institution resulted in significant overall dose reduction. It has also been reported that optimisation of CT acquisition protocol and a reduction of CT radiation dose delivered to patients by 39.2 % was achieved by radiological staff training(13). This is more effective than the results of the authors’ study. An intensive and comprehensive training course on CT acquisition protocol, emphasising the importance of optimising radiation dose is, of course, the ideal solution. However, it is not realistic to hope to enrol all radiologists and radiological technologists in the 187 hospitals/clinics in Gunma prefecture in training programmes and adequately cover the necessary material within a reasonable amount of time. Not all radiation technologists/medical physicists and
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Chest
Study year
CT DOSE SURVEY FOR DOSE OPTIMISATION
radiologists are enthusiastic about optimising image quality and radiation quality. The authors supposed that designing a retraining programme and requiring all professionals in the entire prefecture to attend would need enforcement by law to be successful. Outliers of DLP indicate unusually high or low radiation exposure for obtaining CT images. A large variation in DLP indicates that CT scan parameters vary greatly among facilities. The authors suspect that the lack of knowledge among radiological technologists on current standards of radiation exposure may be a reason for this variation. Data feedback to each radiology department and education of radiological technologists may be necessary for the optimisation and reduction of patient dose from CT. While optimal dose is the balance of radiation dose and image quality that may vary by facility, generally speaking, optimisation of patient dose in radiology departments means that distribution of DLP will have a low number of outliers and narrow distribution within the range of DRL. In neck CT, feedback of DRLs and DLP distribution data for each CT system did exceptionally not lead to reduction and narrowing of DLP variation.
One reason for the radiation dose increased was the original dose was too low for adequate image quality. The radiologist is responsible for obtaining images of quality sufficient for diagnosis while managing the dose to the patient so that it is commensurable to the clinical purpose(4). Radiologists and radiological technologists should consider not only reducing but also increasing radiation dose as needed to obtain image quality sufficient for diagnosis. Another possible reason was that the number of neck CTs in 2012 decreased by 22.3 % and these examinations were performed on only 23 units. This number was small compared with the number of units performing body CTs, making a change in the number of scans more likely to present as a change in overall dose distribution. These results may reflect the situation of diagnostic imaging in Japan. Japan is famous for its large (some may say excessive) number of CT scanners. In some smaller institutions, a limited number of radiology technologists may need to manage multiple modalities at the same time, and this large and varied workload may keep them from the chance, or perhaps even realising the need to discuss CT protocols and
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Figure 3. Anatomical region-specific and survey-specific DLP for the 62 CT scanners. The height of the box displays IQR with the 25th (Q1) and 75th (Q3) percentiles representing the lower and upper edges of the box, respectively. The middle horizontal line is the median. Error bars extend from the box to show the range of non-outlying data points (whiskers). The lower whisker represents the Q1 2 1.5` IQR, and the upper whisker represents the Q3 þ 1.5` IQR. The outlier was defined as the value above Q3 þ 1.5` IQR or below Q1 2 1.5` IQR (open circle, Q3 þ 1.5` IQR or Q1 2 1.5` IQR; asterisk, Q3 þ 3 ` IQR or Q1 2 3 ` IQR). * indicates Mann–Whitney U-test, ** indicates Mood test, *** indicates significant difference with both statistical analyses.
Y. FUKUSHIMA ET AL.
CONCLUSION A prefecture-wide multi-centre radiation dose survey in CT examinations with data feedback may be helpful for dose optimisation of CT examinations. While an intensive and comprehensive training course on radiation dose parameters would be ideal, surveys with data feedback may be a realistic alternative in environments where organisation of such courses is difficult. ACKNOWLEDGEMENTS The authors thank Hiroyuki Takei, RT, MS, Hidenori Otake, RT, MS, Takayuki Suto, RT, MS and many radiological technologists in Gunma prefecture for
cooperating with the GRaD Study. They also thank Keigo Endo, MD, PhD. FUNDING This study was supported by the Gunma Foundation for Medicine and Health Science. REFERENCES 1. Mettler, F. A., Wiest, P. W., Locken, J. A. and Kelsey, C. A. CT scanning: patterns of use and dose. J. Radiol. Prot. 20, 353–359 (2000). 2. Berrington de Gonza´lez, A. and Darby, S. Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries. Lancet 363, 345– 351 (2004). 3. International Commission on Radiological Protection. Radiological protection and safety in medicine. ICRP Publication 73. Ann. ICRP 26 (2007). 4. International Commission on Radiological Protection. Managing patient dose in multi-detector computed tomography (MDCT). ICRP Publication 102. Ann. ICRP 37 (2007). 5. Treier, R., Aroua, A., Verdun, F. R., Samara, E., Stuessi, A. and Trueb, P. R. Patient doses in CT examinations in Switzerland: implementation of national diagnostic reference levels. Radiat. Prot. Dosim. 142, 244– 254 (2010). 6. Choi, J., Cha, S., Lee, K., Shin, D., Kang, J., Kim, Y., Kim, K. and Kim, S. The development of a guidance level for patient dose for CT examinations in Korea. Radiat. Prot. Dosim. 138, 137–143 (2010). 7. Cho, P., Seo, B., Choi, T., Kim, J., Kim, Y., Choi, J., Oh, Y., Kim, K. and Choi, J. The development of a diagnostic reference level on patient dose for CT examination in Korea. Radiat. Prot. Dosim. 129, 463– 468 (2008). 8. Verdun, F. R., Gutierrez, D., Vader, J. P., Aroua, A., Alamo-Maestre, L. T., Bochud, F. and Gudinchet, F. CT radiation dose in children: a survey to establish agebased diagnostic reference levels in Switzerland. Eur. Radiol. 18, 1980–1986 (2008). 9. Pages, J. CT doses in children: a multicentre study. Br. J. Radiol. 76, 803– 811 (2003). 10. Tsushima, Y., Taketomi-Takahashi, A., Takei, H., Otake, H. and Endo, K. Radiation exposure from CT examinations in Japan. BMC Med. Imaging 10, 24 (2010). 11. Fukushima, Y., Tsushima, Y., Takei, H., TaketomiTakahashi, A., Otake, H. and Endo, K. Diagnostic reference level of computed tomography (CT) in Japan. Radiat. Prot. Dosim. 151, 51–57 (2012). 12. Engel, L.-C., Lee, A. M., Seifarth, H., Sidhu, M. S., Brady, T. J., Hoffmann, U. and Ghoshhajra, B. B. Weekly dose reports: the effects of a continuous quality improvement initiative on coronary computed tomography angiography radiation doses at a tertiary medical center. Acad. Radiol. 20, 1015– 1023 (2013). 13. Paolicchi, F., Faggioni, L., Bastiani, L., Molinaro, S., Caramella, D. and Bartolozzi, C. Real practice radiation dose and dosimetric impact of radiological staff training in body CT examinations. Insights Imaging 4, 239– 244 (2013).
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parameter optimisation with their colleagues. Simply providing these professionals with the chance to understand the need to optimise radiation dose and see how their current protocols compare with other institutions may have been sufficient encouragement to adjust their imaging parameters. In this study, all CT vendors and CT models were analysed together, so only DLP was analysed for radiation dose survey. Image quality was not objectively analysed. CT parameters were optimised at the discretion of each facility because of variations in manufacturer, number of detector-rows, model of CT system, CT image characteristics and also possible variation in image quality required for diagnosis among institutions. It is not realistic to expect all institutions, including community hospitals and clinics, to objectively evaluate image quality. In this study, some institutions reported changing tube current or AEC settings. These changes affect noise. Each institution has its own unique requirements, so experts in that institution (i.e. radiologists and radiologic technologists) should make decisions on image quality, and interviews showed that this was indeed the case in the institutions surveyed. This study had several limitations. First, the authors compared the data of only 29.4 % of facilities in Gunma prefecture. The authors did succeed in evaluating 42.5 % of hospitals with .100 beds, which is where most of the scans were performed. Second, only radiologists or radiologic technologists who were interested in quality improvement of their radiology department responded to these surveys. Additional strategies to achieve radiation dose optimisation and reduction in CT examinations may be necessary. Also, the authors cannot draw any conclusions about radiation dose optimisation in Japan, let alone the international medical community, from this data. Third, this study only surveyed DLP, not scan length, which is a factor influencing DLP. Fourth, the authors conducted both surveys in July. There might be effects of seasonality. Finally, this study did not include a control group (a group that does not receive feedback).
doi:10.1093/rpd/ncu323
PREFECTURE-WIDE MULTI-CENTRE RADIATION DOSE SURVEY AS A USEFUL TOOL FOR CT DOSE OPTIMISATION: REPORT OF GUNMA RADIATION DOSE STUDY Yasuhiro Fukushima1,2,*, Ayako Taketomi-Takahashi2, Takahito Nakajima2 and Yoshito Tsushima2 1 Department of Radiology, Gunma University Hospital, 3-39-15 Showa, Maebashi, Gunma 371-8511, Japan 2 Department of Diagnostic Radiology and Nuclear Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa, Maebashi, Gunma 371-8511, Japan *Corresponding author: [email protected]
The aim of this study was to verify the usefulness for the dose optimisation of setting a diagnostic reference level (DRL) based on the results of a prefecture-wide multi-centre radiation dose survey and providing data feedback. All hospitals/clinics in the authors’ prefecture with computed tomography (CT) scanners were requested to report data. The first survey was done in July 2011, and the results of dose–length products (DLPs) for each CT scanner were fed back to all hospitals/clinics, with DRL set from all the data. One year later, a second survey was done in the same manner. The medians of DLP in the upper abdomen, whole body and coronary CT in 2012 were significantly smaller than those of the 2011 survey. The interquartile ranges of DLP in the head, chest, pelvis and coronary CT were also smaller in 2012. Radiation dose survey with data feedback may be helpful for CT dose optimisation.
INTRODUCTION In modern medicine, computed tomography (CT) has provided great benefits in clinical practice for determining treatment plan and follow-up after treatment. On the other hand, in the USA, 67 % of the collective effective dose in diagnostic radiology was due to CT examinations(1), whose relatively high-dose radiation exposure is an unavoidable drawback. After the estimates of cancer risk attributable to diagnostic Xrays in Japan have been reported in comparison with other developed countries(2), further efforts to reduce or optimise radiation dose have been encouraged. Usually in Japan, radiological technologists have sole discretion on the configuration of CT scanning parameters. The ICRP recommends the use of diagnostic reference level (DRL) for patients(3). Use of DRL is a method for evaluating whether the patient dose is unusually high or low for a particular medical imaging procedure(4). Several surveys for establishing DRLs for adults(5 – 7) and children(8, 9) have been reported in Europe and Korea. In Japan, calculated results on patient dose using simulation software have been reported, but so far, there has been no large-scale survey in Japan for establishing DRLs based on actual clinical data(10). Since 2008, the authors have been conducting prefecture-wide ‘Gunma radiation dose study (GRaD Study)’, which estimated the DRL for each anatomical region by surveying radiation dose that was collected from hospitals/clinics in Gunma prefecture (100 km north of Tokyo; population, two million) with CT
scanners. The authors previously reported that dose– length products (DLPs) were at comparable levels with DRLs previously reported from some countries, but the distribution of DLP had large variation and many outliers(11). In this study, the surveys of CT radiation dose were performed during the same month in two sequential years, 2011 and 2012. After analysing data of CT radiation dose in 2011, the results of this survey were sent to individual facilities. The results included distribution of DLPs for each anatomical region for each CT scanner and DRLs for each anatomical region. The 2011 survey provided only the data from their own CTs in comparison with other facilities and did not give any instructions or recommendations. The aim of this study was to verify the usefulness of prefecture-wide multi-centre radiation dose survey followed by the establishment of DRLs and data feedback to each institution for dose optimisation. MATERIALS AND METHODS This study was approved by the ethical committee of Gunma University Hospital, and informed consent from each patient was not necessary because this study was conducted under anonymity. CT radiation dose survey Surveys of CT radiation dose were performed twice, in July 2011 (first survey) and July 2012 (second
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at New York University on April 15, 2015
Received 21 June 2014; revised 26 September 2014; accepted 26 September 2014
Y. FUKUSHIMA ET AL.
Data analyses For the subjects of analysis, paediatric patients (0–15 y old) and examination type other than routine were excluded. Since a scanner usually does not provide the DLP for each individual anatomical region when two or more anatomical regions are scanned in a single session, only examinations of one anatomical region were sampled for the evaluation of DRL and DLP. If the number of scans for chest, upper abdomen and pelvis were same, the examinations were sampled as whole body (chest to pelvis). When a region was scanned two or more times (for instance, nonenhanced and enhanced scans), the obtained DLP
data were divided by the number of scans, as the authors analysed the dose in the method previously reported(11). The DLP data were expressed as median, 25th and 75th percentile (Q1 and Q3) values, and interquartile range (IQR; the difference between Q3 and Q1). The DRL was defined as Q1 and Q3 values (round off ) of DLP(11). Data feedback and evaluation of its effect After the first survey, DRLs estimated from the data of all hospitals/clinics along with the median and distribution of DLPs for each anatomical region for each CT scanner were sent to each hospital/clinic. This allowed radiological technologists to recognise the current condition of radiation exposure from CT. Each institution received individualised data sheets. On the individualised data sheets, data of the individual hospital/clinic were shown relative to those of other institutions, without showing the names of other institutions. Figure 1 is an example of the data sent (upper abdomen). The authors asked each institution to optimise CT scan parameters by comparing the distribution of DLPs in their own institution with those of other hospitals/clinics along with DRLs. One year later, the second survey was carried out in the same manner. The authors then compared the distribution of DLPs in the two studies to evaluate the change in DLPs. The authors also evaluated institutions with large changes in DLP between the two surveys for how they changed radiation dose and evaluated image quality, using the following method. The authors calculated the changes in DLP in each scanner for all anatomical regions. The change in DLPs was defined as (median DLP of second survey 2 median DLP of first survey)/median DLP of first survey (%). The authors found the five scanners with the greatest increase in radiation dose and five scanners with the greatest decrease in radiation dose for each anatomical region. From these data, the authors selected scanners that performed 10 or more scans for a given anatomical region on both the first and second surveys. The authors interviewed these institutions on the changes they made to their imaging parameters and how they evaluated the resulting changes in image quality. Statistical analysis Mann–Whitney U test and Mood test were employed for statistical analysis. The Mood test is a nonparametric test that tests a difference in distribution between two groups. A p-value of ,0.05 was considered statistically significant. Statistical analyses were performed using R (version 3.0.1., available via http:// www.r-project.org/).
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survey). The data concerning CT scanners and all individual patients undergoing CT examination in Gunma prefecture during a single month were collected. Datasheets were sent to all 187 hospitals/ clinics in Gunma prefecture with CT scanners. The data from CT scanners consisted of the vendor and model of the CT scanner, number of data acquisition channels and standard scanning protocols for each anatomical region. The data from each patient consisted of the patient’s age and sex, anatomical region of the CT examination, types of examinations if other than routine [for example, low-dose examination, CT perfusion or CT angiography (CTA)], number of scans for each anatomical region, volume CT dose index (CTDIvol) and total DLP as automatically displayed by the CT scanner. The authors chose to evaluate DRL for overall CT scanners with DLP instead of CTDIvol because some CT scanners display maximum CTDIvol instead of mean CTDIvol, whereas the definition of DLP is identical in all CT scanners. When a patient returned for a second or more CT sessions on a different day, the sessions were counted as two or more different patients with each undergoing a single CT session. The anatomical regions were divided into head (brain), face, neck, chest, upper abdomen, pelvis (lower abdomen) and coronary. When a patient was scanned in two or more anatomical regions during a single CT session, the number of examinations was counted as the number of anatomical regions scanned, and the number of scans was defined as the total number of scans for each anatomical region. For example, if a patient underwent unenhanced CT of the upper abdomen and enhanced CT of the chest and upper abdomen in a single CT session, the number of CT examinations was two, the number of scans of the chest was one and that of the upper abdomen was two. In coronary CT, low-dose non-enhanced scan for calcium scoring and high-dose enhanced scan for coronary CTA were routinely performed. To prevent underestimation of radiation dose for coronary CT in post-data processing, only DLPs and number of scans for coronary CTAwere obtained.
CT DOSE SURVEY FOR DOSE OPTIMISATION
RESULTS In the first survey (2011), CT dose data from 92 hospitals/clinics (102 CT scanners; single to 320 detector row CT) were obtained from data sheets sent to 187 institutions. The total data obtained were for 25 225 patients [male, 55.1 %; age, 64.6 + 19.4 y old (mean + SD); range, 0–105 y old], 43 779 examinations and 61 418 scans. Estimated DRLs of DLP for adult patients in each anatomical region were 810–1340 mGy cm for head CT examinations, 230 –460 mGy cm for face, 270– 650 mGy cm for neck, 260–540 mGy cm for chest, 280 –730 mGy cm for upper abdomen, 200–560 mGy cm for pelvis, 660 –1450 mGy cm for chest –pelvis and 390 –1320 mGy cm for coronary CT. This summary data were fed back to all hospitals/clinics with detailed dose distribution data for each anatomical region. In the second survey (2012), CT dose data were collected from 84 hospitals/ clinics (97 CT scanners) from data sheets sent to 187 hospitals, including 27 027 patients [male, 54.0 %; age, 64.4 + 19.4 y old (mean + SD); range, 0–105 y old], 46 346 examinations and 65 111 scans. Fifty-five hospitals/clinics (29.4 % of all facilities; 62 CT scanners) provided CT data in both the first and second surveys. Figure 2 briefly summarises CT scanners of 55 hospitals/clinics. To evaluate the changes in the DLPs between the two surveys, the authors reviewed data from these 55 hospitals, including 46 884 scans for the first survey (76.3 % of scans
Figure 2. The number of CT scanners according to the number of CT acquisition channels and vendors.
in the first survey) and 45 991 scans for the second survey (70.2 % of scans in the second survey). Thirtyfive institutions were hospitals with 100 or more beds (42.5 % of institution datasheet sent with 100 beds or more), and these hospitals performed the bulk of the scans in Gunma prefecture (87.0 % for the first survey and 84.9 % for the second survey). Of these scans, 12 761 scans from the first survey and 13 030 from the second survey were suitable for analysis. Table 1 and Figure 3 show the results of DLPs for each anatomical region along with outliers. In the upper abdomen,
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Figure 1. This is an example of a data sheet, which was fed back to each hospital/clinic after the first survey. This boxplot indicates the DLP in upper abdomen for each CT system, and the grey box indicates the results from all CT scanners. The dotted lines indicate DRL of abdomen (280–730 mGy cm). The height of the box displays IQR with the 25th (Q1) and 75th (Q3) percentiles representing the lower and upper edges of the box, respectively. The middle horizontal line is the median. Error bars extend from the box to show the range of non-outlying data points (whiskers). The lower whisker represents the Q1 2 1.5` IQR, and the upper whisker represents the Q3 þ 1.5` IQR. The outlier was defined as the value above Q3 þ 1.5` IQR, or below Q1 2 1.5` IQR (open circle, Q3 þ 1.5` IQR or Q1 2 1.5` IQR; asterisk, Q3 þ 3` IQR or Q1 2 3` IQR).
Y. FUKUSHIMA ET AL. Table 1. DLPs for each anatomical region. Anatomical region
Head Face Neck
Upper abdomen Pelvis Whole body Coronary
2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012 2011 2012
Number of CT scanners
61 23 28 54 39 29 44 15
Number of CT scanning
Statistical analysesa ( p-value)
DLP (mGy cm) 25th percentile
Median
75th percentile
IQRb
797 819 205 189 266 324 251 259 280 255 107 257 718 674 358 275
950 989 312 300 415 441 372 371 434 362 345 363 1010 910 722 606
1387 1262 402 419 616 678 544 519 694 590 556 549 1558 1343 1163 1031
590 443 197 230 350 354 293 260 414 335 449 292 840 669 805 756
4900 4997 399 464 385 319 3038 3138 1776 1592 180 161 1540 1814 543 545
Mann– Whitney U-test
Mood
0.167
,0.001
0.816
0.111
0.014
0.052
0.469
,0.001
,0.001
0.067
0.080
,0.001
,0.001
0.416
,0.001
0.041
a The Mann– Whitney U-test was used to evaluate the difference in median of DLP, and Mood test was used to evaluate the distribution. b IQR, interquartile range.
whole body and coronary CT, significant decreases in DLP were observed between 2011 and 2012 surveys ( p , 0.001, respectively). Although the number of scans was small, a significant increase in median DLP was observed in neck CT (6.3 %; p ¼ 0.014). The median DLPs decreased by 16.6 % for upper abdomen CT, 9.9 % for whole body CT and 16.1 % for coronary CT. Mood statistics revealed that the distributions of DLP in the head, chest, pelvis and coronary CT were smaller in 2012 survey compared with 2011 survey ( p ¼ 0.041 for coronary CT and p , 0.001 for head, chest and pelvis), resulting in the smaller IQRs. IQRs were decreased by 24.9 % for coronary CT, 11.3 % for head CT, 35.0 % for chest CT and 6.1 % for pelvic CT. Twenty-one institutions reported CT scanners with a large change in median DLP between the two surveys. Of these institutions, seven changed radiation dose by adjusting tube current or the noise index of auto exposure control (AEC). In these institutions, the radiologist or technologist evaluating the image made final decision of image quality and radiation dose. The other 14 institutions did not report a clear reason for the change in DLP. DISCUSSION The authors have shown that feedback of DRLs and DLP distribution data for each CT scanner derived
from the authors’ CT dose survey led to smaller distribution or reduction of radiation dose for head, chest, upper abdomen, pelvis, whole body and coronary CTs. Many competent radiologists and radiological technologists likely tried to optimise CT parameters based on the feedback data at their discretion, and the results fulfilled the authors’ expectations. The authors’ method of simply making competent radiologists and radiological technologists aware of how high or low DLP is in each CT system was surprisingly effective considering the limited resources involved, and at the same time, appropriate DRLs could be evaluated. Engel et al.(12) recently reported that weekly dose report feedback of site radiation doses of coronary CT angiography in a single institution resulted in significant overall dose reduction. It has also been reported that optimisation of CT acquisition protocol and a reduction of CT radiation dose delivered to patients by 39.2 % was achieved by radiological staff training(13). This is more effective than the results of the authors’ study. An intensive and comprehensive training course on CT acquisition protocol, emphasising the importance of optimising radiation dose is, of course, the ideal solution. However, it is not realistic to hope to enrol all radiologists and radiological technologists in the 187 hospitals/clinics in Gunma prefecture in training programmes and adequately cover the necessary material within a reasonable amount of time. Not all radiation technologists/medical physicists and
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Chest
Study year
CT DOSE SURVEY FOR DOSE OPTIMISATION
radiologists are enthusiastic about optimising image quality and radiation quality. The authors supposed that designing a retraining programme and requiring all professionals in the entire prefecture to attend would need enforcement by law to be successful. Outliers of DLP indicate unusually high or low radiation exposure for obtaining CT images. A large variation in DLP indicates that CT scan parameters vary greatly among facilities. The authors suspect that the lack of knowledge among radiological technologists on current standards of radiation exposure may be a reason for this variation. Data feedback to each radiology department and education of radiological technologists may be necessary for the optimisation and reduction of patient dose from CT. While optimal dose is the balance of radiation dose and image quality that may vary by facility, generally speaking, optimisation of patient dose in radiology departments means that distribution of DLP will have a low number of outliers and narrow distribution within the range of DRL. In neck CT, feedback of DRLs and DLP distribution data for each CT system did exceptionally not lead to reduction and narrowing of DLP variation.
One reason for the radiation dose increased was the original dose was too low for adequate image quality. The radiologist is responsible for obtaining images of quality sufficient for diagnosis while managing the dose to the patient so that it is commensurable to the clinical purpose(4). Radiologists and radiological technologists should consider not only reducing but also increasing radiation dose as needed to obtain image quality sufficient for diagnosis. Another possible reason was that the number of neck CTs in 2012 decreased by 22.3 % and these examinations were performed on only 23 units. This number was small compared with the number of units performing body CTs, making a change in the number of scans more likely to present as a change in overall dose distribution. These results may reflect the situation of diagnostic imaging in Japan. Japan is famous for its large (some may say excessive) number of CT scanners. In some smaller institutions, a limited number of radiology technologists may need to manage multiple modalities at the same time, and this large and varied workload may keep them from the chance, or perhaps even realising the need to discuss CT protocols and
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Figure 3. Anatomical region-specific and survey-specific DLP for the 62 CT scanners. The height of the box displays IQR with the 25th (Q1) and 75th (Q3) percentiles representing the lower and upper edges of the box, respectively. The middle horizontal line is the median. Error bars extend from the box to show the range of non-outlying data points (whiskers). The lower whisker represents the Q1 2 1.5` IQR, and the upper whisker represents the Q3 þ 1.5` IQR. The outlier was defined as the value above Q3 þ 1.5` IQR or below Q1 2 1.5` IQR (open circle, Q3 þ 1.5` IQR or Q1 2 1.5` IQR; asterisk, Q3 þ 3 ` IQR or Q1 2 3 ` IQR). * indicates Mann–Whitney U-test, ** indicates Mood test, *** indicates significant difference with both statistical analyses.
Y. FUKUSHIMA ET AL.
CONCLUSION A prefecture-wide multi-centre radiation dose survey in CT examinations with data feedback may be helpful for dose optimisation of CT examinations. While an intensive and comprehensive training course on radiation dose parameters would be ideal, surveys with data feedback may be a realistic alternative in environments where organisation of such courses is difficult. ACKNOWLEDGEMENTS The authors thank Hiroyuki Takei, RT, MS, Hidenori Otake, RT, MS, Takayuki Suto, RT, MS and many radiological technologists in Gunma prefecture for
cooperating with the GRaD Study. They also thank Keigo Endo, MD, PhD. FUNDING This study was supported by the Gunma Foundation for Medicine and Health Science. REFERENCES 1. Mettler, F. A., Wiest, P. W., Locken, J. A. and Kelsey, C. A. CT scanning: patterns of use and dose. J. Radiol. Prot. 20, 353–359 (2000). 2. Berrington de Gonza´lez, A. and Darby, S. Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries. Lancet 363, 345– 351 (2004). 3. International Commission on Radiological Protection. Radiological protection and safety in medicine. ICRP Publication 73. Ann. ICRP 26 (2007). 4. International Commission on Radiological Protection. Managing patient dose in multi-detector computed tomography (MDCT). ICRP Publication 102. Ann. ICRP 37 (2007). 5. Treier, R., Aroua, A., Verdun, F. R., Samara, E., Stuessi, A. and Trueb, P. R. Patient doses in CT examinations in Switzerland: implementation of national diagnostic reference levels. Radiat. Prot. Dosim. 142, 244– 254 (2010). 6. Choi, J., Cha, S., Lee, K., Shin, D., Kang, J., Kim, Y., Kim, K. and Kim, S. The development of a guidance level for patient dose for CT examinations in Korea. Radiat. Prot. Dosim. 138, 137–143 (2010). 7. Cho, P., Seo, B., Choi, T., Kim, J., Kim, Y., Choi, J., Oh, Y., Kim, K. and Choi, J. The development of a diagnostic reference level on patient dose for CT examination in Korea. Radiat. Prot. Dosim. 129, 463– 468 (2008). 8. Verdun, F. R., Gutierrez, D., Vader, J. P., Aroua, A., Alamo-Maestre, L. T., Bochud, F. and Gudinchet, F. CT radiation dose in children: a survey to establish agebased diagnostic reference levels in Switzerland. Eur. Radiol. 18, 1980–1986 (2008). 9. Pages, J. CT doses in children: a multicentre study. Br. J. Radiol. 76, 803– 811 (2003). 10. Tsushima, Y., Taketomi-Takahashi, A., Takei, H., Otake, H. and Endo, K. Radiation exposure from CT examinations in Japan. BMC Med. Imaging 10, 24 (2010). 11. Fukushima, Y., Tsushima, Y., Takei, H., TaketomiTakahashi, A., Otake, H. and Endo, K. Diagnostic reference level of computed tomography (CT) in Japan. Radiat. Prot. Dosim. 151, 51–57 (2012). 12. Engel, L.-C., Lee, A. M., Seifarth, H., Sidhu, M. S., Brady, T. J., Hoffmann, U. and Ghoshhajra, B. B. Weekly dose reports: the effects of a continuous quality improvement initiative on coronary computed tomography angiography radiation doses at a tertiary medical center. Acad. Radiol. 20, 1015– 1023 (2013). 13. Paolicchi, F., Faggioni, L., Bastiani, L., Molinaro, S., Caramella, D. and Bartolozzi, C. Real practice radiation dose and dosimetric impact of radiological staff training in body CT examinations. Insights Imaging 4, 239– 244 (2013).
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parameter optimisation with their colleagues. Simply providing these professionals with the chance to understand the need to optimise radiation dose and see how their current protocols compare with other institutions may have been sufficient encouragement to adjust their imaging parameters. In this study, all CT vendors and CT models were analysed together, so only DLP was analysed for radiation dose survey. Image quality was not objectively analysed. CT parameters were optimised at the discretion of each facility because of variations in manufacturer, number of detector-rows, model of CT system, CT image characteristics and also possible variation in image quality required for diagnosis among institutions. It is not realistic to expect all institutions, including community hospitals and clinics, to objectively evaluate image quality. In this study, some institutions reported changing tube current or AEC settings. These changes affect noise. Each institution has its own unique requirements, so experts in that institution (i.e. radiologists and radiologic technologists) should make decisions on image quality, and interviews showed that this was indeed the case in the institutions surveyed. This study had several limitations. First, the authors compared the data of only 29.4 % of facilities in Gunma prefecture. The authors did succeed in evaluating 42.5 % of hospitals with .100 beds, which is where most of the scans were performed. Second, only radiologists or radiologic technologists who were interested in quality improvement of their radiology department responded to these surveys. Additional strategies to achieve radiation dose optimisation and reduction in CT examinations may be necessary. Also, the authors cannot draw any conclusions about radiation dose optimisation in Japan, let alone the international medical community, from this data. Third, this study only surveyed DLP, not scan length, which is a factor influencing DLP. Fourth, the authors conducted both surveys in July. There might be effects of seasonality. Finally, this study did not include a control group (a group that does not receive feedback).
