Diagnostic Reference Levels in Medical Imaging

Draft document: Diagnostic Reference Levels in Medical Imaging
Submitted by JOHN DAMILAKIS, PiDRL Project
Commenting on behalf of the organisation

p.12, lines 9-10 state “Appropriate weight bands (generally with 10 kg intervals) are recommended for establishing paediatric DRLs and should be promoted for paediatrics.” This introduces an early assumption on the use of 10kg weight bands and should be avoided.

p. 92, line 5 it is the broad range of sizes of paediatrics but not the broad range of ages that makes paediatric DRLs more challenging than those for adults.

Section 6, Paediatrics

p. 92, lines 22-24 & p.94, lines 5-12: The main recommendations should be to use weight for body examinations, while age is still feasible for head examinations. Age can be used for all examinations in a transition period until data from the recommended weight based patient dose surveys become available. Due to the typical scarceness of paediatric patient dose data, the number of weight bands should be kept at minimum: not more than five groups should be recommended. Further, it is not advisable to define the weight bands in equal weight intervals. 

Recommended weight groups (intervals) for body examinations

Recommended age groups (intervals) for head examinations

         < 5 kg

5 - < 15 kg

15 - < 30 kg

30 - < 50 kg

50 - < 80 kg

0 - < 3 months

3 months - < 1 y

1- < 6 y

≥ 6 y


In the EC Guidelines, also the following   approximate equivalence of the weight and age groups have been given, for the purpose of comparing weight-based DRLs with age-based DRLs:



Weight group

Age group based on weight-for-age charts

Most common age groups used for the NDRLs (or equivalent)


< 5 kg

< 1 m

0 y

Infant, toddler and early childhood

5 - < 15 kg

1 m - < 4 y

1 y

Middle childhood

15 - < 30 kg

4 - < 10 y

5 y

Early adolescence

30 - < 50 kg

10 – < 14 y

10 y

Late adolescence

50 - < 80 kg

14 - < 18 y

15 y


p. 92, lines 33-34: effective diameter and patient equivalent thickness has been presented, and referred to in other parts of the document, in a way that does not make it clear that these are not synonyms but two different concepts. Further, water equivalent thickness defined by the AAPM Report 220 (2014) should also be mentioned in this connection. See also comment on p. 96. 

p.94, line 6: Reference “Järvinen et al., 2012”should be “Järvinen et al., 2015”. Please add more references besides this, e.g. Watson, D. J. and Coakley, K. S. Paediatric CT reference doses based on weight and CT dosimetry phantom size: local experience using a 64-slice CT scanner. Pediatr. Radiol. 40, 693–703 (2010).

p.94, lines 18-20: The given requirement is not clear. The “mean weight of the sample on which the DRLs were based” is not often known/available, unless the mean value of the weight band is meant here? Is this requirement needed if the samples (one for establishing a DRL and one for comparison with this DRL) include only data within a given weight band?

p.94, lines 29-31: Section 6.1 presents considerations relevant to paediatric DRLs; it is understood that these concern all paediatric examinations. “Weight” should be used for grouping patients also for CT and IR procedures; paragraph 250 is misleading as these two groups have not been mentioned. In general, in several parts of the document, it is not perfectly clear what examinations have been covered by given recommendations, e.g. sometimes the recommendations look like general ones, but nethertheless not applicable to paediatric examinations (e.g. p.101, lines 18-19 and p. 104, lines 30-37) . 

p. 95, lines 7-8: Reference for Fig. 6.1 should be only “Järvinen et al., 2015”. If desired, a sentence could be added: “The same principle has been applied to presenting DRLs for paediatric chest radiography, using patient thickness as a parameter (Kiljunen et al., 2007).”

p. 96, lines 24-25 and 37-39: “Patient equivalent thickness” is a term being developed by the IEC, and currently not yet published. The AAPM has introduced terms “effective diameter” and “water equivalent diameter”. Conceptually, “patient equivalent thickness” should be similar to “water equivalent diameter” (but different from “effective diameter”), as these two terms try to account for the differences in the attenuation in different parts of the body, while “effective diameter” is only a geometric concept. The three concepts should more precisely presented and discussed in the document with relevant references. 

p.97, lines 3-4: For clarity, add “to weight” after “alternative” (i.e. “as an alternative to weight”)

Section 7

p. 101, lines 4-5 and p.101-115 (whole Section 7): It is presented that “local surveys of DRL quantities should normally be carried out as part of the clinical audit …”. Clinical audit is a relatively new concept. In many departments, internal audit is not a continuous activity and external audit is not carried out at all. For these departments, the establishment or update of DRLs will be problematic if the local surveys of DRL quantities is considered to be part of the clinical audits.  While the local surveys of DRL quantities are appropriate for clinical auditing, it is important to emphasize that these surveys should be carried out even if no clinical audits are implemented. According to the EC Guidelines (RP 159, 2009), “In the audits of X-ray radiology and nuclear medicine, the patient dose or administered activity should be addressed in comparison with the given DRL …”. The EC recommendation should generally be interpreted in a way that local  surveys of DRL quantities would be requested before the audit, and the results of surveys compared with DRLs during the audit. This is the only way for external audits, whereby the whole local process of surveying DRL quantities and comparing the results with DRLs should be assessed (audited).  These principles of clinical audit should be briefly explained in the beginning, and thereafter several references to clinical audit would be more relevant and understandable.

p. 104, line 41: What is meant by “standard factors” (not clear)

p. 105, line 6: Should be “Fig. 7.1”.

p. 105, lines 10-13: This sentence is not clear and confusing. What is meant by “benchmark data”? If DRLs are referred to, then only median values should be compared.

p.105, line 15: The interquartile range should be explained.

p. 123, lines 1-4, requires revision in line with proposal for varying weight groupings