Justification and optimisation of paediatric CT in prefectures around Tokyo

1. INTRODUCTION

It has become a global concern that medical radiation exposure during childhood, especially exposure to a high-dose CT scan, increases the future risk of cancer (Pearce et al., 2012). It is widely known that Japan has the largest number of CT scanners in the world, and according to UNSCEAR 2020/2021 Annex A Evaluation of medical exposure to ionising radiation, Japan has 222 computed tomography examinations per 1000 population, second only to the United States (UNSCEAR, 2022). Paediatric CT scans should only be performed when really necessary (justification) and at a radiation dose that takes the child's size into account (optimisation) (Frush, 2011; Ideguchi et al., 2018). Currently in Japan, there are two guidelines for diagnostic imaging in cases of paediatric acute appendicitis. One of them is ‘Diagnostic imaging guidelines (2016 edition)’ published by the Japan Radiological Society, and the other one is ‘Evidence-based guidelines for the emergency management of the abdomen in children 2017 edition’ published by the Japanese Society of Emergency Pediatrics (Japan Radiological Society, 2016; Japanese Society of Emergency Pediatrics, 2017). In both guidelines, when acute appendicitis is suspected, the first choice to be considered is an ultrasound examination. Also, ‘Evidence-based guidelines for the emergency management of the abdomen in children 2017 edition’ describes that if diagnosis is difficult based on an ultrasound examination, single-phase contrast-enhanced CT is desirable.

However, it is not known the degree to which the principles of justification and optimisation are applied to medical radiation exposure in children in everyday clinical settings.

Thus, from January to March 2021, a questionnaire survey was conducted in emergency hospitals in the Kanto-Koshinetsu area to ascertain the actual situation regarding diagnostic methods and radiation exposure dose in CT examination in cases of paediatric acute abdomen represented by acute appendicitis.

2. METHODS

This study was conducted under the approval of the IRB of the institution. The Tokyo area [the Kanto-Koshinetsu area, the centre of economic and political activity in Japan and where 35% of the total population lives and 38% of the gross domestic product (GDP) is generated] was selected as the subject area of the survey. The questionnaire was sent out to physicians and radiology technologists at 1194 emergency hospitals in the area. Responses were acquired through the Internet. The survey was conducted using Google Forms, which provided the necessary tools to design, distribute, and analyse the survey. The survey included both multiple-choice and open-ended questions, and survey respondents were able to enter a comment in the free text field. Respondents were asked to provide their name, affiliation, and email address, and no incentive was offered for completing the survey.

The questionnaire survey was divided into two main items. (1) To physicians examining paediatric patients, ‘diagnostic method used for acute appendicitis’ was asked to survey the justification of the examination. (2) To radiology technologists performing CT imaging, ‘CT imaging methods in childhood’ was asked to investigate optimisation.

3. RESULTS

3.1. Results of responses from physicians

Responses from physicians were obtained from 212 institutions (18%) out of 1194 institutions. Of these, 169 institutions have the possibility of examining paediatric acute abdomen. Questionnaire responses from 169 physicians who have the possibility of examining paediatric acute abdomen are summarised below. The results corresponding to the questions set out above are as follows:

Aware of ‘Diagnostic imaging guidelines 2016 edition’ in 34% (n = 57); aware of ‘Evidence-based guidelines for the emergency management of the abdomen in children 2017 edition’ in 43% (n = 73). Only about 30% to 40% of respondents knew the guidelines, so the level of awareness was low.

Clinical department which treats paediatric acute abdomen is paediatrics (n = 145), paediatric surgery (n = 31) during day shift on weekdays (Fig. 1, multiple responses allowed, n = 235). The percentage decreased during after-hours medical care to paediatrics (n = 99) and paediatric surgery (n = 21) (Fig. 2, multiple responses allowed, n = 229).

Only a few (17%, n = 28) are using the guidelines in actual medical care.

When acute appendicitis is listed in the differential diagnosis, the first examination to be conducted was ultrasound in 77% (n = 131) in day shift on weekdays (Fig. 3). Even during after-hours medical care, ultrasound was performed in 48% (n = 81), and the percentage for ultrasound was the highest (Fig. 4).

Ultrasound examination is performed mainly by a sonographer and paediatrician (Fig. 5, multiple responses allowed, n = 270).

When acute appendicitis was suspected, the CT imaging range was mainly ‘from the liver to pelvis’ (90%, n = 152).

When CT examination was performed, the imaging phase was ‘plain CT only’ in 30% (n = 51), ‘plain CT and contrast-enhanced CT’ in 33% (n = 55), and ‘contrast-enhanced single-phase CT only’ in 34% (n = 58), in approximately equal numbers.

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Fig. 1.

Departments which treat paediatric acute abdomen (day shift on weekdays) (multiple responses allowed, N = 235).

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Fig. 2.

Departments which treat paediatric acute abdomen (after-hours medical care) (multiple responses allowed, N = 229).

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Fig. 3.

What examination is performed first when acute appendicitis is listed in the differential diagnosis (during day shift)?

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Fig. 4.

What examination is performed first when acute appendicitis is listed in the differential diagnosis (during after-hours medical care)?

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Fig. 5.

Who performs ultrasound examinations (multiple responses allowed, N = 270)?

3.2. Results of responses from radiology technologists

Responses from radiology technologists were obtained from 172 institutions (14%) out of 1194 institutions. Of these, 123 institutions have the possibility of performing paediatric CT examinations. Questionnaire responses from 123 radiology technologists are summarised as follows:

The number of paediatric CT examinations in patients younger than 15 years of age was mainly at most 10 examinations in 79% (n = 97), and some institutions in 14% (n = 17) did not perform any examinations in the preceding 3 months.

As a percentage of abdominal CT examinations conducted in patients of all ages, those in patients younger than 15 years of age accounted for less than 1% in most of the institutions surveyed (76%, n = 93).

For the question Are you aware of the ‘Japan Network for Research and Information on Medical Exposure (J-RIME): National Diagnostic Reference Levels in Japan (2020)—Japan DRL 2020’?: At least 93% were aware of the DRL (n = 115).

Regarding whether CT examinations were optimised by imaging method, more than 80% (83%, n = 102) were optimised by age and/or weight.

Also, the basis of optimisation was the diagnostic reference level (DRL) in most institutions (69 institutions, multiple responses allowed n = 142) (Fig. 6).

Figs. 7 and 8 show boxplots of CTDI_vol (mGy) and DLP (mGy·cm) (values based on 32-cm CTDI phantom) by ages separated by 0 years, 1 to 5 years, 6 to 10 years, and 11 to 15 years. The median value in each age group was equal to the third quartile value or slightly less than that in the Japan DRL 2020.

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Fig. 6.

What is the basis for optimisation (multiple responses allowed, N = 142)?

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Fig. 7.

Boxplot of CTDI_vol (mGy) for each age (values based on 32-cm CTDI phantom).

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Fig. 8.

Boxplot of DLP (mGy·cm) for each age (values based on 32-cm CTDI phantom).

ICRP and WHO recommend the introduction of justification and optimisation to reduce medical radiation exposure in children (ICRP, 2013; WHO, 2017). The current guidelines in Japan recommend ultrasound as the first examination when paediatric acute appendicitis is suspected (Japan Radiological Society, 2016; Japanese Society of Emergency Pediatrics, 2017). Also, when CT examination is performed, contrast-enhanced single-phase CT of the abdomen is recommended (Japanese Society of Emergency Pediatrics, 2017). To survey and publish how much these guidelines are recognised and used in actual emergency hospitals in Japan and how much justification and optimisation are achieved in CT examinations are necessary to grasp the current situation and direct radiation exposure to reduction in the future.

This time, to survey these, the diagnosing methods by physicians and the imaging methods of abdominal CT by radiology technologists were surveyed in cases of paediatric acute abdomen represented by acute appendicitis in emergency hospitals in the Tokyo area.

In the survey for physicians, 30% to 40% of those surveyed were aware of the Japanese guidelines for paediatric acute appendicitis indicating that the level of awareness was low. The percentage of physicians actually using the guidelines was very low at 17%. However, when acute appendicitis is listed in the differential diagnosis, the first-choice examination was ultrasound (77% in the day shift on weekdays and 48% during after-hours medical care). The ratio of performing ultrasound examination reduced during after-hours medical care. This is probably because the chances of medical care being provided by a paediatrician and paediatric surgeon specialising in children are reduced, and sonographers who perform the ultrasound examination are often not on duty.

In the USA, when paediatric acute appendicitis was suspected, the examination performed in the child was an ultrasound examination (52%). This questionnaire survey revealed that ultrasound examination was performed more often in the Tokyo area than in the USA (Anderson et al., 2019). The results also revealed that in the emergency hospitals in the Tokyo area, the rationale for reducing childhood radiation exposure had been widely disseminated, as evidenced by selection of ultrasound to avoid unnecessary CT radiation exposure in paediatric acute abdomen without using the guidelines.

Regarding the scan range of performing CT examinations, many physicians selected the liver to the pelvis. However, for the imaging phase, ‘plain CT only’, ‘plain CT and contrast-enhanced CT’, and ‘single-phase contrast-enhanced CT only’ were selected on an equal basis. When the imaging phase was compared by the use and non-use of the guidelines, contrast-enhanced single-phase CT only was selected in many institutions using the guidelines, but ‘contrast-enhanced single-phase CT only’, ‘plain CT and contrast-enhanced CT’, and ‘plain CT only’ were selected on an equal basis in institutions not using the guidelines. Thus, it is considered that thorough and progressive notification of the guidelines can reduce unnecessary radiation exposure during CT imaging. This finding is also the actual situation as revealed by this survey.

On the other hand, in the survey on abdominal CT examinations in children targeting radiology technologists, many institutions conducted a few abdominal CT examinations in children representing less than 1% of all CT examinations. Nevertheless, the percentage of technologists who were aware of the DRL recommendations in paediatric CT imaging published by the J-RIME was very high at 93%. Although this survey was conducted at a short time, approximately half a year, after the publication of Japan DRL2020, at least 90% were aware of the recommended DRL, and awareness spread rapidly soon after publication of the DRL. It was revealed that many institutions conducted optimisation using the latest DRL.

From the median values of CTDI_vol (mGy) and DLP (mGy·cm) separated by 0 years, 1 to 5 years, 6 to 10 years, and 11 to 15 years, optimisation seems to be conducted in each age group. However, not a few institutions set both CTDI_vol and DLP above the DRL, and the distribution of the institutions showed a trend towards a long tail. This cannot be ignored, and the continuation of a grassroots movement to encourage the spread and use of DRL in Japan is necessary.

In the actual situation, radiation exposure in Japan is still higher than in other countries. Continuation of efforts to reduce radiation exposure dose in CT examinations is desired.

One of the limitations of this survey is the low response rate. Another limitation is that many of the responding facilities are centres of excellence that are fully aware of the importance of reducing exposure, and there is a concern that a bias may exist due to fewer responses from facilities where this awareness is absent.

5. CONCLUSION

When the justification of medical radiation exposure in childhood was considered, it was found that ultrasound examination was the first choice in many institutions in the Tokyo area. However, in abdominal CT examinations, ‘plain CT only’, ‘plain CT and contrast-enhanced CT’, and ‘contrast-enhanced single-phase CT only’ were selected on an equal basis, potentially resulting in a large amount of unnecessary radiation exposure. Thorough notification of the guidelines might reduce this unnecessary radiation exposure. Also, regarding the optimisation of radiation exposure in childhood, the technologists recognised DRL early and well. Optimisation by age and body weight according to DRL was also being achieved. In the future, it is desired to make efforts to lower the radiation exposure dose closer to the radiation exposure dose in each of the other countries in the world.