Radiological Protection in Cone Beam Computed Tomography (CBCT)

Draft document: Radiological Protection in Cone Beam Computed Tomography (CBCT)
Submitted by Marie Claire Cantone, AIRP, Italian Association of Radiation Protection
Commenting on behalf of the organisation

Comments by the Italian Association of Radiation Protection, AIRP
ICRP draft : Radiological Protection in Cone Beam Computed Tomography (CBCT)

The document received the attention of our community with positive judgments about the objective, the structure and the contents of the document. However, it was observed a lack of attention to the dental CBCT that, even if it is motivated in the text, is perceived somehow disappointing. It was appreciated the emphasis given in reiterating that optimization refers not only to whole-body exposures, but also to specific tissues in view of the recent consideration on tissue reactions.

1) A specific comment refers to paragraph 9.4.Diagnostic reference levels.

The  first part:

“(216) DRLs have been established through government and professional organisations to guide users in optimising procedure performance for both image quality and radiation reduction. While these efforts have matured for MDCT imaging, little progress has been made toward setting DRLs for CBCT. SEDENTEXCT (EC, 2012) recommends a single reference level of 250 mGy.cm2 for the placement of an upper first molar implant in adults. “

appears not to take in full consideration the corresponding paragraph in the cited SEDENTEX (EC, 2012):

“6.3.2 Establishing Diagnostic Reference Levels -The UK’s Health Protection Agency have carried out a preliminary audit of DAP across 41 dental CBCT units and have proposed an achievable dose of 250 mGy cm2 for CBCT imaging appropriate for the placement of an upper first molar implant in a standard adult patient. It should be noted that large FOV units in the sample exceed this and the dose audit data had been normalised to an area corresponding to a 4cm x 4cm field of view at the isocentre of the equipment. It is for this reason that they have referred to this dose level as an “achievable dose” rather than a DRL. “

In particular, for what refers to the use of the concept “achievable dose” rather than DRL and to the  explanation that the dose value of 250 mGy cm2 is defined for a 4 cm x 4 cm FOV.
Existing equipment on the market have, for the larger part, higher values of FOV, for which the values of DAP related to them are higher than the indicated values.  It would be appropriate to define more than one LDR compatible with the technology actually present on the market.
It could be useful to remember in ICRP paragraph 9.4 (as already in SEDENTEX, in the 6.3.2 paragraph) that “Further work involving large scale audits is needed to establish robust DRLs for a range of dental CBCT applications that can aid in the optimization of exposures.”

2) Note that the Tables 7.1, 7.3, 7.4, 7.6 and 7.7  seem not explicitly cited in the text. Moreover  there is a suggestion to insert a footnote in Table 7.3  to make explicit, in the effective dose simulation for catheter ablation, the use of weighting factors from ICRP 60 and from ICRP 103.