Exposure to Head and neck CT radiation is associated with blood cancers.
About a year ago, I did a post on the incidence of brain cancer after CT examinations of children and young adults. This was a very controversial blog post, and there were many comments. Most of these supported the research, and others attempted to minimise the concerns raised by this paper. The study team have now published a further paper from this study. This addresses the incidence of blood cancers following CT radiation scans of children and young adults.
Before I get into this paper, I would like to highlight that the authors pointed out.
“There is no dose threshold below which the risk of radiation induced cancer is zero”.
A team based in Europe did this study. Nature Medicine published the paper. This is a highly-ranked journal with an impact factor of 82.9.
What did they ask?
They did this study to answer this question:
“What is the risk of hematoligical malignancies in relation to radiation exposure from CT examinations in childhood, adolescence, and early adulthood”.
It is clear that this is a very relevant question to all those practicing orthodontics.
What did they do?
This paper was one of the outputs for the EPI-CT study that includes data from 948,174 people from 9 European countries. The analysis includes data from 876,771 participants who underwent 1.3 million CT examinations. The team followed them up for at least two years following their first CT.
The team estimated radiation doses to the active bone marrow according to the body part scanned. Then they obtained data on 790 hematological malignancies. At the next stage they used complex modelling techniques to take into the account of confounding variables to calculate the relative risk of haematological malignancies following the CT scans.
At this point, I would like to remind readers that the relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.
What did they find?
The mean cumulative active bone marrow dose was 15.6 mGy in the whole cohort and 13.0 GmY in the cases. Importantly, they found increased risk for haematological malignancies across all the dose categories.
The excess relative risk per 100 mGy was 1.96 (95% CI=1.1-3.12).
These results suggest that for every 10,000 children examined with a CT (mean dose 8 mGY) 1-2 of them are expected to develop a haematological malignancy attributable to the radiation exposure in the subsequent 12 years.
What did they conclude?
Their overall conclusion was:
“There was a consistent and robust dose-related increased risk of radiation-induced haematological malignancies”
What did I think?
This was another paper that highlighted the risk of CT scans to children. In this respect, it is important and we cannot simply ignore the findings. However, I did find some aspects of this research a little difficult to fully understand. So, I asked my collegue Keith Horner to explain things to me. Keith is Emeritus Professor of Oral and Maxillofacial Imaging, at the University of Manchester. He was also the co-ordinator of the SEDENTEXT project and an author of the British Orthodontic Society Orthodontic Radiography Guidelines. This is what he explained to me.
“In this study, the scans were CT examinations and not CBCT. However, it is possible that the sample included some CBCT scans, as the classification depends on the hospital’s coding system. The study found that the cumulative doses were not evenly distributed, with a mean dose estimate of approximately 15mGy and a median of 10mGy. This represents an average of 1.5 scans per individual over the study period. Therefore, we could roughly estimate that the mean dose per scan was about 10mGy, and the median dose was approximately 7mGy. Most scans were of the head, so considering the study results in an orthodontic context is fair.
When we consider the possible CBCT scan doses to bone marrow (as opposed to CT). Ludlow et al. reported on this (2015;https://pubmed.ncbi.nlm.nih.gov/25224586/). They found enormous dose variations according to the particular manufacturer and model of the CBCT machine. However, they calculated that the mean bone marrow dose for a 10-year-old child for a single scan with “large” or medium-sized fields of view was 0.13mGy (+/- 0.08mGy sd). For small fields of view scans, they were 0.06 mGy (+/- 0.05mGy s.d.).
Paradoxically, for adults who have less active bone marrow, the doses were higher, which might be because more studies were available to include. Rather than quibbling over fractions of mGy, it’s reasonable to say that the CBCT bone marrow doses might be roughly in the range of 1-4% of those for CT.
We can conclude from this study that using a CT or CBCT scan does seem to carry a small risk of malignancy in irradiated organs and tissues. The risk is highest in children and in females. Some might argue that the risk is negligible, but the benefit must be considered. Most of the CT examinations in the epidemiological study would have been done for serious things – trauma, suspected or established intracranial pathosis, etc., some of which might have been life-threatening”.
I have given the paper and Keith’s comments a lot of thought. My feeling is that even though the risks maybe small. We need to consider the benefits of taking a CBCT. I am now going to be a bit controversial and blunt. I have published several posts on the research into the use of CBCT in orthodontics. This has shown the following.
- We do not know the incidence of clinically important incidental findings on CBCT images. When these are analysed few are clinically relevant.
- CBCT images do not meaningfully change treatment decisions on impacted canines.
- CBCT imaging is not reliable for airway assessment.
I have also thought about the reasons for taking routine CBCT images that proponents of this technology suggest. There is an absence of evidence for many of the supposed benefits. I certainly would not be exposing my patients to the additional radiation for the following:
- The need to measure the depth of the alveolar bone.
- To assess the 3D position of the teeth when deciding upon extractions.
- The 3D image providing information that we need to plan treatment
- The need to accurately check the position of the roots after treatment.
- The need to measure the airway and anatomy of the maxillary complex.
Currently, the evidence suggests that we should use CBCT as a secondary view for complex problems and the management of impacted teeth,
I will conclude with the BOS recommendation on using CBCT. This is clear and is similar to other organisations.
“There is little evidence to support routine CBCT use for orthodontic patients”
I know that I have posted about this subject several times and I must be sounding like a stuck record (for those who remember records). However, I cannot help thinking that these studies highlight the risks of CBCT imaging. Unfortunately, we will only know whether CBCT has harmed our patients after a gap of several years.
It would be terrible if a person had cancer because an orthodontist wanted to check on root paralleling or one of the many irrelevant claims that they are currently making. We need to consider whether this superficial information or the fees for the pretty pictures are worth any risk. As usual, lets have a debate in the comments below.
Emeritus Professor of Orthodontics, University of Manchester, UK.