October JADA looks at reducing radiation exposure during intraoral imaging

October JADA cover image
A study published in the October issue of The Journal of the American Dental Association found the use of rectangular collimators during intraoral imaging significantly reduced levels of exposure to ionizing radiation in tissue models representing child and adult patients when compared with circular collimators.

The cover story, "Intraoral Radiographs: A Comparison of Dose and Risk Reduction With Collimation and Thyroid Shielding," examined effective radiation dose reductions using six rectangular intraoral collimators and one circular. Rectangular collimators shape the X-ray beam to correspond to the size and shape of the image receptor, therefore reducing the necessary exposure field, according to the study.

The study also looked at the effect of thyroid shielding when used with rectangular and circular collimators in children.

The study found the rectangular shape of the collimator alone will likely result in significant reductions in effective dose when compared with circular collimation, but these reductions can range from 2% to 51%, depending on the rectangular collimator used. Thyroid shielding on the child model produced significant dose reductions with all imaging modalities, but the use of an original equipment rectangular collimator without thyroid shielding yielded a lower dose to child thyroid tissues than any other modality with thyroid shielding present.

"Efforts to continually innovate dental imaging practices are driven by a two-part goal, to develop state-of-the-art equipment that will optimize the quality of care to our patients, and to do this in the safest way possible," said K. Brandon Johnson, corresponding author of the study and assistant professor of oral and maxillofacial radiology at the University of North Carolina Adams School of Dentistry in Chapel Hill, North Carolina. "Yet, rectangular collimation, a half-century-old technique, continues to be one of the simplest, cheapest, most effective and most underutilized techniques for reducing the potential risk burden to our patients from intraoral radiographic examinations."

The National Commission on Radiation Protection emphasizes the need for dental professionals to minimize both staff and patient doses by applying the As Low As Reasonably Achievable principle, according to the study. Introduced in the early 1960s, rectangular collimation became a well-known method for reducing patient exposure by the early 1980s, but the most implemented imaging technique for intraoral radiography uses circular collimation of the X-ray beam, the study stated.

The continued use of circular collimation may be because practitioners are concerned that the more restricted rectangular-collimated X-ray beam could lead to imaging errors, such as collimator centering issues, and ultimately result in increased patient exposure if essential anatomy is not captured and additional radiographs are needed, according to the study. Circular collimation, with its larger exposure field, may not require additional radiographs because of technical errors, but it has been shown to expose patients to as much as four times more radiation than rectangular collimation, the study stated.

Uncertainty remains regarding the cumulative effects of long-term exposure to low doses of ionizing radiation with respect to risks for cancer development, according to the study. Therefore, to adhere to the As Low As Reasonably Achievable principle and help ensure the safe use of ionizing radiation in dental practice, radiographers should be aware that the highest dose reduction will likely come from the collimator with the smallest field, the study stated.

"The decision to portray a rectangular collimator on the cover of the National Commission on Radiation Protection Report No. 177 was not a decision made by chance as the report strongly reemphasizes the importance and impact of the routine use of this dose reduction tool," Mr. Johnson said. "Regardless, introducing changes that run counter to the prevailing culture will eventually be undone. Therefore, the challenge ahead is 1) to disseminate high-quality evidence-based findings to dental providers to facilitate informed decision-making for their patients and 2) to establish an integrated mindset that will lead to real and lasting change in the promotion and implementation of the highest standards of care to our patients in practice."

Other articles in the October issue of JADA discuss patient aggression toward dentists, antibiotic prescribing in the dental practice and measuring sealant placement.

Every month, JADA articles are published online at JADA.ADA.org in advance of the print publication.