Paediatric Diagnostic Reference Levels (DRLs)

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Recommendations and guidelines for the use of Paediatric DRLs.

By Raija Seuri , Paediatric Radiologist in Helsinki University Hospital and clinical consultant for the Radiation and Nuclear Safety Authority in Finland.

Editor’s note: the spelling of ‘paediatric’ used in this blog is the correct spelling in the European community.

An important change for DRLs for paediatric imaging is the recommendation to use grouping by weight rather than age.

Diagnostic Reference Levels (DRLs) are a useful tool for dose optimization – including in paediatric imaging. However, the relatively small number of paediatric patients in many institutions is a challenge for optimization of imaging parameters for children of different sizes. Optimization requires both time and expertise, which are not always easy to find in daily practice.

Fortunately, the focus on paediatric DRLs has increased during recent years. Recently (in 2017), the European Commission (EC) published European DRLs for the most common paediatric examinations for all modalities.

Based on my experience in this area, I have compiled those guidelines for DRLs for paediatric imaging that I believe are the most useful. I also explain when and how to apply national, European, and local DRLs.

DRLs – What are they?

Diagnostic Reference Levels are a tool for optimization. Optimization means keeping the dose “as low as reasonably achievable” (ALARA) for the required image quality to obtain the desired diagnostic information. The International Commission on Radiological Protection (ICRP) states, “the objective of a diagnostic reference level is to help avoid excessive radiation dose to the patient that does not contribute additional clinical information to the medical imaging task.” Several countries have begun to establish indication-based reference levels, but most are for adult procedures.

DRLs are not a dose constraint, nor a limit. They are not intended to classify “good” or “bad” practices. Rather, they are markers to help professionals identify abnormally high (or low) dose levels for the indication, and to make the optimization process easier. The dose should always be considered together with the indication of imaging and image quality needed.

DRLs – Where to find guidance?

Many international, national, and local authorities have published guidance for the use of DRLs. Following are the references for paediatric imaging that I believe are the most useful. I chose these because they are the most authoritative, are recently published, and give practical guidance for how to use DRLs for paediatric imaging.

International Atomic Energy Agency (IAEA) –I recommend this resource for everyone who has a role in paediatric imaging. The information is easy to find and in a compact form. Their Frequently Asked Questions (FAQs) section provides short and practical answers.

European Diagnostic Reference Levels for Paediatric Imaging (PiDRL) – This EC Publication includes European DRLs for the most common paediatric procedures on all modalities, and how to use them in everyday clinical practice. It also includes guidelines for collecting and comparing dose values to DRLs, and recommendations for collecting and processing data to establish national DRLs. I recommend the report to anyone interested in or responsible for paediatric imaging and paediatric dose. You can find them in Radiation Protection publication 185.

The International Commission on Radiological Protection (ICRP) Publication 135 (2017) –This is the most authoritative and thorough resource on DRLs in general. This will be of special interest for those responsible for radiation protection in their unit. The most recent publication- ICRP Publication 135 (2017) – includes a special chapter on paediatric procedures with detailed recommendations, including:

• Detailed and practical guidance on both the establishment and use of paediatric DRLs in clinical practice
• Recommendations on conducting surveys to establish DRLs
• Recommended quantities for DRLs for each modality
• All modalities including nuclear and hybrid imaging

The focus on paediatric DRLs has increased recently.

National, European and Local DRLs – Which ones to use?

When radiologists and other medical imaging professionals talk about DRLs, they are usually referring to national reference levels. However, European and local DRLs also can be used.

National DRLs (NDRL) – This will be the dominant reference – if one exists for your country. They are based on national dose surveys and are set by national authoritative bodies.

European DRLs (EDRLs) – EDRLs could play an important role in harmonizing the practises in the European countries by providing guidance for optimization until NDRLs are established. These DRLs should be considered when your country does not have national DRLs for paediatric patients, or if the NDRLs are higher than EDRLs or otherwise outdated.

They are based on national DRLs of the European countries. EDRLs can be found in the PiDRL Report.

Local DRL (LDRLs) – LDRLs can provide guidance on the institutional level for a hospital or a group of hospitals. Consider applying them if you feel the NDRLs are high for your local practice; or if your NDRLs are outdated or non-existent. In that case, your local DRLs can be the first step to establishing national DRLs in your country!

DRLs – How to use them?

When planning a dose survey, choose a procedure that is common in your institution. The recommended dose quantities are found in the guidelines, and should be easily available in the equipment console.

A recent and important change for many countries in DRLs for paediatric imaging is the recommendation to use grouping by weight rather than age. There can be a huge variation of sizes of paediatric patients within an age group, which might distort the results of dose collection especially with small sample sizes. The recommendation is to collect at least 10 patients for each weight group. In Finland, the national practice is to use a continuous DRL-curve, with which you only need 10 patients to compare your dose levels.

The calculated median dose of your collected sample is then compared to the DRL-value. If your value is higher than the DRL-value, you should have a closer look at your practices. Is there a problem in equipment function or optimization of parameters? Are you using the right protocol? Could there be a problem in staff performance (collimation, protocol/parameter selection)?

DRLs – When to use them?

Regular checks of dose levels should be part of your QC. Also, review dose levels when you:

• have changed your protocols;
• have a change in practice;
• purchase new equipment;
• or update existing equipment.

Also, remember to perform regular calibration or checks to ensure that you get accurate values of the dosimetric quantity from your console.

Dose always should be considered together with image quality. Good image quality in digital imaging is a result of multiple factors, and many of them do not relate to the dose parameters. To be able to know the dose used, you have to look at the dose indicators. With all PACS systems, it should be possible to get the dose indicators shown in the image display. The only way to know your dose levels is to collect actual patient doses. Comparison to existing DRLs shows where you stand with your dose levels, and where you should put your focus in quality improvement: dose optimization or image quality.

Remember that dose surveys are not only for comparison, but also to improve your practice.

Raija Seuri is a Paediatric Radiologist at HUS Medical Imaging, Children’s Hospital. She is also a clinical consultant for the Radiation and Nuclear Safety Authority STUK, Helsinki Finland. Radiation protection of patients and optimization of imaging practices in paediatric imaging are her special interest. She delivered a presentation on the topic of Paediatric DRLs at ECR 2018. #ALARA #pediatricdose #DRLs #ECR2018

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