Annals of the ICRP,ICRP PUBLICATION IXX
Radiological protection in cone beam computed tomography (CBCT)
The report is written in addition to ICRP publications 87 and 102 dealing with computed tomography (CT) and multislice computed tomography (MSCT) because new applications of cone-beam computed tomography (CBCT) and the associated radiological protection issues are sufficiently different from those of conventional CT. The committee states that CBCT is now used widely by specialists who have little or no training in radiological protection. Advice on appropriate utilization of CBCT needs to be made widely available.
The draft report describes the general topics ‘’biological effects of radiation’’ and ‘’radiological protection for patients and workers’’ and focusses in 6 chapters on particular issues related to the use of CBCT mostly from the radiation physics point of view.
CBCT is widely used in various medical imaging tasks and in dentistry. Specific remarks on DentoMaxilloFacial Radiology (DMFR) are only made in chapter 7 (Radiation dose management in specific applications of CBCT), pp. 73-75. In chapter 1.6 ‘’scope of the document’’, the committee explains that the report is restricted to non-dental applications since ‘’a substantial amount of information is currently available on dental CBCT including a document issued by the European Commission’’.
Although justification is mentioned as one of the principles for radiological protection for patients and workers (Ch. 3) no specific attention is drawn to this subject with respect to all different applications of CBCT in the medical and/or dental field. In the specific remarks on dental use of CBCT (Ch. 7) the ICRP committee refers to the EC Guidelines 172 with respect to justification and optimization.
Comments / remarks of the EADMFR ‘’Selection Criteria and Radiation Protection- committee’’
- p. 11, lines 363-365 and p. 61, lines 2473-2475 “Dental CBCT scans should be justified, considering two-dimensional radiography as an alternative, and optimized through the use of small FOVs and application- and patient-specific exposure factors.”
Our committee prefers:
“Dental CBCT scans can be considered when two-dimensional radiography does not or is not expected to answer the diagnostic question. Dental CBCT should be optimized through the use of small FOVs and application- and patient-specific technique factors.” (see page 74, lines 2826-2827)
- p. 11, lines 370-372 and p. 82, lines 3180-3182: “All personnel intending to use CBCT for diagnostic purposes should be trained in the same manner as for diagnostic CT and for interventional CBCT same as interventional procedures using interventional CT.”
Remark from the committee:
This is not in accordance for the requirements for dental CBCT at least at the present.
“Personnel responsible for the use of CBCT for diagnostic purposes should be trained in the same manner as for diagnostic CT and for interventional CBCT same as interventional procedures using interventional CT.” For dental and maxillofacial applications basic training requirements have already been developed and published (See: Basic training requirements for the use of dental CBCT by dentists: a position paper prepared by the European Academy of DentoMaxilloFacial Radiology (EADMFR). Brown J, Jacobs R, Levring Jäghagen E, Lindh C, Baksi G, Schulze D, Schulze R 2014;43(1):20130291. doi:10.1259/dmfr.20130291).
- p. 16 (1.1 History of development): Nothing is said about the history of CBCT in dentomaxillofacial imaging (just various medical applications are mentioned).
The committee proposes to add:
‘’CBCT devices were introduced in DentoMaxilloFacial Radiology in the late nineties (Mozzo P, Procacci C, Tacconi A, Martini PT, Andreis IA (1998) A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results. Eur Radiol 8:1558-1564; Arai Y, Tammisalo E, Iwai K, Hashimoto K, Shinoda K (1999) Development of a compact computed tomographic apparatus for dental use. Dentomaxillofac Radiol 28:245-248)’’
- p. 38, line 1453 (5.4 A unified approach to CT dosimetry) and p. 87, line 3350 (9.3 Patient dose reporting): The ICRP recommends to display patient dose estimates on the console and transfer the dose data to a DICOM-structured dose report, as is standard in MDCT systems nowadays.
Comment of the committee:
We recommend adding a maximum error (%) that the displayed dose shall not exceed. According to the evidence based guidelines of the European Commission (EC), 2012. Radiation protection No. 162 this percentage should be 20%. (Reference IAEA 2011 & IEC 2011d)
- European Commission (EC), 2012. Radiation protection No. 162. Criteria for Acceptability of Medical Radiological Equipment used in Diagnostic Radiology, Nuclear Medicine and Radiotherapy and maxillofacial radiology. Evidence Based Guidelines. Directorate-General for Energy.
- IAEA (2011), Quality Assurance Programme for Computed Tomography: Diagnostic and Therapy Applications. Vienna
- IEC (2011d) International Electrotechnical Commission IEC 61223-3-5: Evaluation and routine testing in medical imaging departments – Part 3-5: Acceptance tests –Imaging performance of computed tomography X-ray equipment.
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2796-2798: “The images are used for diagnostic purposes, pre-operative planning, and image-guidance during navigated surgery in this region.”
The committee prefers:
“The images are used for diagnostic purposes, pre-operative planning, postoperative evaluation and image-guidance during navigated surgery in this region.”
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2798-2800: “Pathological changes such as fractures, periapical abscesses, caries and periodontal disease affect high-contrast structures and can therefore be imaged precisely using CBCT.”
Remark from the committee:
This sentence has to be modified!
CBCT is NOT the first choice for caries diagnosis. Suggestion is to remove caries from the list of pathological changes that can be imaged precisely using CBCT to prevent dental practitioners using CBCT for caries diagnosis while referring to this ICRP Report.
Periapical abscess is not a correct term and might be replaced for the more general periapical lesion.
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2802-2803: ‘’…very low radiation dose.’’
Compared to medical imaging tasks this is true, however compared to other dental radiological imaging the dose may not be stated as ‘’very low’’.
In their ‘’main points’’ (lines 363-365) the ICRP mentions 2D radiography in dental applications as an alternative to CBCT. And in their first ‘’main point’’ (line 259-263) ICRP emphasizes the importance of the report ‘’because CBCT extends the use of CT to areas that were not typically associated with CT in the past, e.g. dental’’
So ‘’very low dose’’ seems in contradiction with the general message of the report. Given the well known high number of dental radiographs in many countries in the world, the net (sum) dose has also to be considered here.
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2810-2812: ‘’dental CBCT is considered as a suitable substitute for MDCT for several applications (e.g. implant planning).
The use of MDCT for dental implant planning is not a widely used application of MDCT. The comparison of CBCT to MDCT as a substitute for implant planning is an old selling argument of dental CBCT manufacturer and therefore it should not have a prominent place in this report.
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2814: ‘’… detection of root pathology…’’
What does the ICRP mean with root pathology? If the ICRP aims at root fractures our committee believes there is not enough evidence to make this statement on superior diagnostic efficacy in this ICRP report.
- p. 73 (7.9 Dental (oral and maxillofacial)), lines 2815-16: ‘’… pre-operative evaluation of third molars, 2D radiographs often suffice.’’
Probably better to remove specific examples as presented here and just refer to general principles of justification and ALARA to avoid discussion on the example mentioned distracting from the point to be made.
- p. 74 (7.9 Dental (oral and maxillofacial)), lines 2828-2830: ‘’CBCT should not be used in soft tissue imaging since only MDCT and MRI provides the contrast resolution that is required.’’
This line is in contradiction with other lines in this ICRP report. The report learns that CBCT in medical radiology is used for soft tissue visualisation (main points, line 319-321). Despite this involves a higher dose then imaging of bony tissue, it seems that the second part of lines 2828-2830 ‘’since only MDCT and MRI….’’ is not correct.
We suggest to modify the sentence as follows: ‘’Dental and Maxillofacial CBCT should not be used in diagnostic soft tissue imaging’’
- p. 74 (7.9 Dental (oral and maxillofacial)), lines 2849-2851: ‘’ In addition, there is no standardization regarding the kVp used in dental CBCT, with values ranging between 70 and 120 kV. Clinically applied mAs values range more than 20-fold’’
The committee thinks that the observation of the ICRP on ranges of applied kVp and mAs should be followed by a recommendation for a better consensus of optimization in dental applications and maybe even the recommendation to establish DRL’s
- p. 9, line 267: “(MDCT))” -> (MDCT)
- p. 80, line 3104:Reference Alaei, P et al. is not in the correct place.
- P. 89, line 3469: Theusers -> The users
Page 86, Table 9.1. Proposed QA test and corresponding periodicity as recommended by international, national and professional societies
Here the German Standard DIN 6868-161 (acceptance testing) is missing. Here the following items are tested (according to the wording of this table):
-High contrast resolution
-Assess image artefacts
- field size
The corresponding periodicity testing standard (DIN 6868-15) is currently in the status of final approving and will periodically test
-High contrast resolution
-Assess image artefacts