Evidence on radiation dose reduction using rectangular collimation: a systematic review

The goal of an intraoral radiograph is to be a valuable diagnostic tool while keeping the radiation exposure dose as low as reasonably achievable. The International Commission on Radiological Protection (ICRP) has strong recommendations for patient dose-reduction strategies.

To answer the following research question: 'In either patient or in phantoms, does rectangular collimation compared with other forms of collimation reduce the radiation absorbed dose during intraoral imaging?'

The search strategy was developed specifically for each electronic database. Information was collected from MEDLINE, all EBM Reviews including the Cochrane Library, EMBASE, LILACS, PubMed and Web of Science, and from a search of the grey literature via Google Scholar. Studies were included if they reported the radiation dose in intraoral imaging using rectangular collimation compared with any other type of collimation or the absence of it. Studies that did not involve comparison/control groups were excluded. A qualitative appraisal of the included studies was performed. The Methodological Index for NOn-Randomised Studies (MINORS) tool assessed the potential risk of bias among the studies, while the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach determined the level of available evidence.

Thirteen studies using different types of receptors, including D-speed film, E-speed film, phosphor storage plates (PSP) and direct digital sensors, were included. Different methods to access absorbed and effective dose by exploring distinct technical parameters, such as distance object-receptor, long- and short-cone, kVp and mA, exposure time and beam filtering, were used. High heterogeneity between the studies was found. The level of evidence was classified as moderate. The radiation dose reduction ranged from 40% to 92% compared with circular collimation. The limitations of the cross-sectional design and in vivo studies were discussed. As this systematic review applied validated tools and guidelines designed for population-based studies, the application for studies based on computer simulations and dosimetry measurements was challenging.

There is moderate evidence suggesting that rectangular collimation significantly reduces radiation dose when compared with round collimation, justifying its implementation in clinical settings/private practices while taking intraoral radiographs.