Assessment of radiation exposure in dental CBCT

Assessing the organ and effective dose resulting from dental cone-beam computerised tomography (CBCT) imaging.

This article aims to get readers thinking about the dose of their X-ray device and urge them to ask manufacturers to show their research when they claim that they have an ultra-low dose machine – without loss of image quality (Figure 1).

CBCT
Figure 1: Child (left) and adult (right) dosimetry phantoms

This paper is an abstract of a study by Kiovisto et al in 2012. He assessed radiation exposure in dental CBCT with the use of metal-oxide semi-conductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations.

The paper was written by J Koivisto PhLic, T Kiljunen PhD, M Tapiovaara MSc,  J Wolff DDS, PhD and M Kortesniemi PhD, of Helsinki and Tampere, Finland.

Objectives

The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerised tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and also to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations (Figure 2).

cbct
Figure 2: QUART phantom and analysis software display

Study design

Organ dose measurements were performed using 20 MOSFET dosimeters. These were then embedded in the eight most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations.

Results

The effective dose measurements using MOSFET dosimeters yielded, using 0.5cm steps, a value of 153 MSv and the PCXMC simulations resulted in a value of 136 MSv.

Conclusions

The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial effect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region.

The paper was published in Journal of Oral Surgery, Oral Medicine, Oral Pathology. Also, Oral Radiology, and Endodontics in 2012, volume 114 and pages 393-400.

Summary

Planmeca Ultra Low Dose (ULD) is the world’s leading method for acquiring CBCT images at low effective patient doses without a statistical reduction in image quality. It allows clinicians to gather more information. Compared to standard 2D panoramic images at an equivalent or even lower patient dose.

CBCT X-ray is acquired by taking several 2D frames of the patient by rotating the X-ray source and sensor around the anatomy of the patient. Each frame uses a short X-ray pulse with given kV and mA values. When applied, the Planmeca ULD protocol will alter the exposure values. It lowers the milliamperes and shortening the X-ray pulse needed for each frame. This will not only lower the patient dose but will also result in a faster rotation time making the scan less prone to patient movement artefacts.

Unlike competing low dose CBCT alternatives, the Planmeca ULD protocol does not take fewer frames or use a smaller rotation angle to lower the patient dose.

This is why we are therefore able to use the ULD protocol on any resolution or volume size.


Contact Julian English for references: [email protected].

This article first appeared in Endodontic Practice magazine. You can read the latest issue here.

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