Page 62 - ARNM-2-2

Advances in Radiotherapy
& Nuclear Medicine Optimal tube voltage for dental CBCT

conventional imaging techniques. Due to the growing uncertainty should be kept relatively as a high level could
demands of advanced technologies in treatment delivery affect the display of the images.
and the evolution of modern treatment techniques, the Quantum noise, which is determined by the
three-dimensional (3D) imaging technique was introduced amount of X-ray photons falling on the detectors, is
using the cone-beam computed tomography (CBCT). 1,2
the most significant factor influencing image quality in
Since its introduction into dental practices a few decades CBCT. 14,16-18 Furthermore, the tube current (milliampere)
ago, CBCT has developed to be an effective and widely used and the time of exposure (seconds) have a direct effect on
diagnostic technique in various kinds of head and neck image quality, radiation dose, and noise than the effect
medical and dental examinations. In recent times, this of tube voltage. This is because when the tube current-
3-5
dental practice has gradually emerged as an important and exposure time product (milliampere-seconds [mAs]) is
indispensable imaging modality with a variety of clinical reduced, it reduces the radiation exposure linearly, but at
applications in dentistry and related fields. 4,6-8 the expense of increased image noise. This is because the
CBCT in dentistry is a specialized X-ray technology signal of the detector also increases, and this will interfere
used when conventional facial or dental X-rays are not with the image interpretation. The transmitted X-photon
sufficient. Since the radiation exposure from this form of interacts with the receptor of an imaging system, leading to
scanning is far higher than that of ordinary dental X-rays, its detection as a signal. The detected photons are converted
it is no longer used regularly. From a single scan, a CBCT into images that can be viewed (radiograph). 6,8,16,17,19 Hence,
scanner can generate 3D images of dental structures, soft it will be important to decrease the tube current as much as
tissues, nerve paths, and bones in the craniofacial region. possible to adequately compensate for increasing the tube
The images of CBCT allow for more precise therapy voltage as this will ensure the noise produced remains at an
planning and improved diagnosis for diverse groups of acceptable level. 16
patients. Previously, exposure settings in CBCT were initially
Regarding the risk associated with patient radiation determined by the manufacturer, and as such, many CBCT
dose, concerns have been raised regarding the widespread models have pre-set exposure settings for various patient
application of CBCT to pediatric patients, who are three sizes and/or clinical applications, while some others permit
times more susceptible compared with adults to the the user to freely choose exposure parameters such as tube
adverse effects of ionizing radiation. If the children’s body voltage, tube current, and exposure time within a certain
size is taken into account in the exposure settings, they range. 6
would receive a higher radiation dose than required. 6,9-13 The results from a study by Zarb et al. revealed that a
Thus, this warrants the development of dose-reduction 50% reduction in mAs will result in a 40% rise in noise,
techniques to prevent unnecessary exposure to ionizing degrading the quality of the image but with a 50% dose
radiation. 14 reduction. A certain amount of noise is often present in
16
In accordance with the International Commission on an image, and noise levels above a certain threshold may
Radiological Protection and in compliance with the “as not be noticeable or affect diagnosis. The dose reduction
low as reasonably achievable” (ALARA) principle, patient methods introduced form the basis of image optimization
exposure should be kept as low as possible, after taking all of exposure parameters in dental CBCT, involving
other important factors into account for medical exposure the determination of the appropriate amount of noise
to radiation. Hence, to protect patients from radiation, produced which has no effect on diagnosis. 16
exposure optimization is of importance since no specific Furthermore, a study by Park et al. showed that the
amount of radiation is considered completely safe. 8,10-12 quality of an image is contingent on the image noise,
This optimization principle is usually direct, but its use can with the unacceptable images showing substantially
be complex due to the very wide range of doses found in more noises than the acceptable images. Thus, the aim
8
some dental CBCTs. 4,6,13 of this study was to investigate and optimize the exposure
The results from a recent research on a dental CBCT parameters for optimal tube voltage exposure for general
scanner showed that the highest tube voltage, ranging X-ray of dental CBCT by using a dose area product (DAP)
from 60 kV and 90 kV, offered the best compromise meter for noise reduction. This was achieved using a two-
between technical image quality, radiation exposure, and step method: identifying the tube voltage that produces the
15
reduced noise. The noise in dental CBCT refers to the least noise at a given mAs and then decreasing this mAs to
level of uncertainty in the assessment of the attenuation the least appropriate amount for clinical imaging using the
of the X-ray beam going through the patient. The level of identified optimal tube voltage. 9,10

Volume 2 Issue 2 (2024) 2 doi: 10.36922/arnm.2972