British Institute of Radiology [BIR] & Royal College of Radiology [RCR]
Comments on ICRP Draft Radiological Protection in Paediatric Diagnostic and Interventional Radiology
Radiation protection in Paediatric Radiology is an important topic. The greater radiation risk in children compared to adults, and the large variation in patient size, which leads to specific equipment requirements for paediatric procedures, provides a firm basis for such a publication.
However in quite a number of areas there are some minor typographical errors and it is felt that the report would benefit from improvements in phraseology in some instances. A few examples, and some further comments on specific areas are included below:-
Justification of examinations
In paragraph 27 advice is given concerning the irradiation of the potentially pregnant female. The final statement in this paragraph indicates that, in some cases, the referring clinician may have a final say regarding this advice. The implication is that a referring clinician may compel the undertaking of a medical exposure. The BIR & RCR strongly believe that the radiologist (or other responsible clinician who justifies the exposure) should act as the gatekeeper and have the final say on whether a medical exposure is undertaken or not. This may not be ICRP’s intention and we request that this paragraph is re-written.
Additional Beam Filtration
The physical rationale behind the use of additional filtration (ie in addition to that which would be used for adults) is something which can be confusing for radiographic operators, and it might be of benefit to the reader if this rationale could be set-out more clearly.
In paragraph 60, the reason for additional filtration is primarily to increase exposure time for certain X-ray generators which would otherwise not be capable of delivering the required shorter exposure times necessary for paediatric exposures. To assist in the reader’s understanding of why additional filtration is being used, this paragraph would perhaps be better placed at the end of the exposure-time section e.g. with paragraph 75 (which deals with adapting equipment to achieve the correct range of exposure times). If there is a further benefit in terms of dose reduction (eg by removing unproductive radiation) as implied by paragraph 59, the reason why this is appropriate for paediatrics, but not for adults, is not clearly explained.
Paragraph 61 states that “usually up to 1mm aluminium plus 0.1 (or 0.2) mm of copper as additional filtration is adequate”. However this seems to contradict the statement in the introductory paragraph (paragraph 38) which states that “adding a 0.3 mm copper filter in addition to the inherent aluminium filtration should be considered if not already provided”.
Also where variable copper filters are being added it is important that the status of the additional filtration is clear to the operator. For some current systems the operator cannot tell that additional copper has been added from either the console or from the tube-head operator positions. This can cause difficulties with CR or DR systems and ICRP could consider making a recommendation on this point; ie that those systems where the display of additional filtration is made clear to the operator, are preferred.
Protective Breast Shielding in CT Scanning
Paragraph 120 states that “local superficial protective devices using bismuth may be considered in girls to protect the breast tissue where possible”. BIR & RCR are not convinced about the over-all efficacy of such devices. Automatic-exposure-control and dose-modulation systems are increasingly available in CT, and ad-hoc in-beam shielding could interfere with such systems. In addition for a rotational scanning device the shielding will necessarily be between the patient and the detector for part of the scan. Logically therefore there must be some negative implications for image quality. Jacob Geleijns has recently provided a very clear summary of these points in the journal ‘Paediatric Radiology’ (2010), Volume 40, pages 1744 – 1747; and concluded “we strongly recommend against the use of selective bismuth shielding for all patients and especially for children. A far superior alternative for minimising dose in paediatric chest CT is reduction in the tube current to achieve the required image quality at the lowest possible dose, and the use of angular and z-axis tube current modulation, which has been shown to reduce dose to the region of the breast by approximately 50% without altering the accuracy of CT numbers or introducing streak and beam hardening artefacts”. BIR & RCR would recommend removing the current reference to bismuth breast shielding in paragraph 120 and replacing it with a statement similar to that above from Geleijns’ work. Failing this, the whole section’s emphasis should be altered to better reflect the balance of evidence in this area and to warn readings more explicitly regarding the dangers associated with in-beam shielding.
Adjustment in Scan Parameters and Optimising Dose Reduction in CT
Paragraph 122 mentions the likely future development of particular dose reduction features in CT, and this paragraph could be re-worded as many of these features are now available. For other equipment modalities, paragraph 38 states that “special consideration should be given to dose reduction measures when purchasing new radiographic or fluoroscopic equipment for paediatric use”. It would be good to have a similar recommendation for CT equipment.
Paragraph 114 states that “Radiation dose can be reduced without affecting diagnostic information obtained from the study”. This is unlikely to be true as a general statement, and the phraseology could be better at this point. The next sentence in paragraph 114 states that “image noise is proportional to the X-ray beam attenuation”. As it is not obvious that these two quantities are directly proportional, this statement would benefit from a reference.
Mobile Shielding
Paragraph 77 states that “regular use should be made of portable lead shielding to protect nearby patients during mobile radiography unless there is sufficient distance between the patients and the radiation source”. This may need clarification as there is potentially a considerable manual handling issue if the widespread-use of mobile lead-shielding were required. In many modern hospitals, beds on wards are arranged head-to-head separated by a lightweight stud-partition-wall; which provides neither distance nor the equivalent of lead shielding as protection, from say a chest X-ray on a patient propped-up in their bed. Sources of protection during mobile radiography in this scenario may include the patient themselves plus the (digital) detector as attenuators, together with low exposure factors and low workload at a given bed. Is it ICRP’s advice (as might be the conclusion from the current paragraph wording) that portable lead shielding should be used between bed-heads in such circumstances? (BIR doubts that this is currently consistent UK practice). On the other hand, if mobile lead-shielding for ward-based mobile radiography is not needed in this scenario, in what circumstances is it required?
Pulsed Fluoroscopy
Paragraph 64 concerns anti-scatter grids, but contains a sentence on pulsed fluoroscopy which appears misplaced. In addition it recommends always setting the lowest pulsed fluoroscopy setting. On occasion the lowest pulsed fluoroscopy setting may not always be the most appropriate, and in any event, the lowest pulsed setting might not always provide the lowest dose. Also paragraph 90 (page 35) may contradict this statement saying that in many instances 3 to 8 pulses per second is adequate.
Protective Shielding in Radiography
Paragraph 53 says that in abdominal or pelvic examinations gonad protection for girls is not possible. The text then goes on to give ‘justifiable reasons’ why it may be omitted in girls. ‘Justifiable reasons’ as to why it may be omitted could seem to contradict the earlier statement that it is not possible.
Equipment Features for Dose Reduction
Dose reduction features inherent to the equipment can provide great dose reduction opportunities. However, the report’s mention of many of these features is found tucked away in paragraph 38 under the heading 3.3.2 ‘adjustment in parameters’. Such features would reasonably merit their own paragraph or their own sub-section given their large potential contribution to dose reduction. To this list (in paragraph 38) of equipment features giving potential dose reduction could be added, virtual-collimation, low-attenuation table tops, and removable-grids. There is perhaps a slight preoccupation throughout the document with the grid-controlled aspect of pulsed fluoroscopy, in comparison with other dose reduction equipment features. For example in the report’s summary and recommendations (page 57) where only grid-controlled-fluoroscopy and last-image-hold are mentioned as significant equipment features leading to dose reduction.
There is also a risk that the report, by portraying justification and optimisation as especially important in the young, might inadvertently tend to downgrade their importance in the adult. In the summary and recommendations for example (page 56) it is stated that justification of every examination involving Ionising Radiation (followed by optimisation) is important especially in the young. In the UK justification and optimisation are legal requirements for every radiological examination and it could be seen as strange to imply that compliance with the law is more important in one patient than in another.
Overall however this is an important and useful document, and we hope these few comments prove useful to ICRP in developing the text.
BIR Radiation Protection Committee
July 2011
For and on behalf of BIR & RCR
[Andy Rogers, BIR RPC Secretary]