Evaluation of a low-dose protocol for cone beam computed tomography of the temporomandibular joint - ethical and methodological considerations

We read with great interest the recent paper entitled: “Evaluation of a low-dose protocol for cone beam computed tomography of the temporomandibular joint” published by Iskanderani and colleagues in Dentomaxillofacial Radiology.¹ In this article, the authors evaluated a low-dose protocol of cone-beam computed tomography (CBCT) to assess the visibility of temporomandibular joint (TMJ) bone components outlines, the subjective image quality and the presence of degenerative joint disease. We agree with the need to evaluate CBCT protocols for TMJ assessment; however, this study has some questions that must be raised for a better understanding.

Regarding study design, the evaluation was based in an in vivo study, in which patients were exposed to CBCT scanning of the same region twice, solely for research purposes. We acknowledge that the study was approved by the local ethics review board and that, apparently, this type of study is within the ethical standards in Sweden, such as the authors mentioned. Nevertheless, it is well known that the any ionizing radiation exposition should be properly justified, whereas any radiation dose is capable of inducing stochastic effects² and the probability of increased cancer risk is proportional to the exposure radiation dose.³ Taking into consideration ALARA (As Low as Reasonably Achievable), ALADA (As Low as Diagnostically Acceptable) and ALADAIP (As Low as Diagnostically Acceptable Being Indication-oriented and Patient-specific) principles,⁴ a supposed benefit to future clinical practice should not be the reason to submit patients to unnecessary radiation doses in the present. Another fact is that the patient’s general health status and how many examinations the patient will undergo during his life were not considered, so it does not seem appropriate to expose the patient without the proper indication. Moreover, this benefit cannot be predicted in the beginning of the study. It seems contradictory to emphasize the importance of dose optimization using an in vivo cross-sectional study. We believe that ex vivo or in vitro studies attend the purpose of which exposition protocols need to be tested and first validated. Therefore, for dose optimization, such laboratorial studies should be encouraged and in vivo studies, that expose patients to unnecessary radiation doses only for research purposes, should not become routine, and in fact, discouraged.

A diagnostic assessment of degenerative joint diseases was carried out and pointed out as “according to the Diagnostic Criteria of TMD (DC/TMD)”, citing Ahmad et al.⁵ However, the DC/TMD was only published in 2014, and in fact Ahmad et al study⁵ was based on the outdated DC/TMD predecessor (i.e. Research Diagnostic Criteria of TMD – RDC/TMD). Furthermore, the DC/TMD instrument is based on predominantly clinical diagnoses of TMDs, through the presence of noise (click or crepitus) detected during the clinical examination, or reported by the patient, and CBCT examination may be indicated only when necessary for confirmation.⁶

About the statistical analysis, as the test used considers the null hypothesis and the p-value differently from usual tests, we encourage an explanation for better comprehension. For example, it is stated that a p = 0.00 was not statistically significant. Also, there is a p-value for each observer and protocol in Table 1, and no clear explanation for which comparisons they refer to.

We would be grateful for the clarification of these points to improve the understanding of the research. We hope that this letter can be useful for future studies designs, as researchers must consider the need for scientific and biological justification for the development of in vivo studies employing ionizing radiation.

Evaluation of a low-dose protocol for cone beam computed tomography of the temporomandibular joint

^1,2Durer Iskanderani, ¹Mats Nilsson, ³Per Alstergren, ^1,4Xie-Qi Shi and ¹Kristina Hellén-Halme

¹Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden

²Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia

³Department of Orofacial Pain and Jaw Function, Faculty of Odontology, Malmö University, Malmö, Sweden

⁴Division of Oral Maxillofacial Radiology, Department of Clinical Dentistry, Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway

We are grateful to Dr Deborah Queiroz Freitas, and her colleagues Larissa de Oliveira Reis, Lucas P. Lopes Rosado and Hugo Gaêta-Araujo, for carefully reading and commenting on our paper.

We have the following comments to their letter to DMFR: We are indeed aware of the risks for late stochastic effects associated with ionizing radiation and the principle of keeping all exposures “As low as reasonably achievable.” This includes efforts to optimize cone beam CT (CBCT) examination protocols according to a given diagnostic purpose. In our case, the same diagnostic outcome was reached by means of reducing tube current while acquiring data for CBCT imaging. Clinical validation of diagnostic modality is warranted since pathological changes in temporomandibular joint (TMJ) could be difficult to mimic under in-vitro setups. The purpose of the paper was to confirm our hypothesis derived from testings on phantoms. Clinical translation of our hypothesis is needed since image quality captured on a phantom may not be directly interpreted in the same way under a clinical situation when taking into consideration the presence of pathological changes, possible motion artifacts, operator skill, and the observer’s clinical experience in image interpretation.

In accordance with the ICRP publication 62: Radiological Protection in Biomedical Research,¹ the Swedish national radiation protection regulations for medical exposure states (translation): “Medical exposure also includes persons participating in medical or biomedical exposure. In this context, justification means an assessment of whether the exposure results in a benefit to research that is greater than the estimated risk for the participating individual.”

The overall purpose of medical research is to provide new knowledge to society that can improve health care, including research in the field of dental radiology. In Sweden, the annual number of CBCT examinations is around 80,000. Given the facts that the nominal lifetime probability coefficients for late stochastic effects is 5% per Sv averaged over the whole population² and that the effective dose for one CBCT examination in Sweden is in the range of 50–200 μSv, the annual number of excess fatal cancers due to CBCT can be estimated to less than one case. Adding the additional 34 exposures with low tube current made in our study will not affect this estimation. This fact is the basis for the regional ethics committee´s decision to allow our study to be carried out. Based on experimental and clinical evidence, the study concluded that imaging of the TMJ can be done with the same diagnostic accuracy using 20% of the tube current that is normally used. This will, of course, affect the collective dose for CBCT imaging of the TMJ when this reduction is implemented clinically.

Concerning the p values in Table 1, they indicated that the observers performance were significantly different from the null hypotheses which were Az = 0.5, the diagonal lines in the figures.