APPLICATION OF THE MONTE CARLO METHOD FOR THE EVALUATION OF SCATTERED RADIATION DOSE DUE TO THE USE OF HANDHELD X-RAY IN DENTISTRY.

The object of this study was to evaluate the dose of scattered radiation in the organs of the operator and assistant located in different positions within a dental room when acquiring intraoral images with a portable handheld X-ray device, using Monte Carlo simulations for recommended and traditional techniques. A typical dental installation was modeled, where the operator and assistant were placed. The beam is represented by 60-kV spectrum. Ten scenarios were simulated, representing different positions and use of the lead apron. The results of the simulations were carried out with typical parameters of the annual workload, showing significant increases in dose in the organs of the operator due to the angulation. The minimum dose in the organs of the assistant occurred when he was located 2-m away and 45° from the direction of the beam. The dose received by the operator is significantly reduced with the use apron.

Effect of target/filter combination on the mean glandular dose and contrast-detail threshold: A phantom study.

INTRODUCTION: In mammography it is essential to combine aspects of image quality with compliance with glandular dose levels. The objective of this study was to combine the assessment of the contrast-detail threshold and the mean glandular dose for different target/filter combinations in digital mammography and to indicate the optimal combination through a figure of merit (FOM). METHODS: In a direct digital mammograph, performance and image quality standards were evaluated using a solid-state multidetector capable of measuring various parameters including kerma and standardized phantoms for image quality. After verifying the proper functioning of the mammograph, the contrast-detail detection threshold and the mean glandular dose values for thicknesses ranging from 20 mm to 70 mm in polymethylmethacrylate (PMMA) were evaluated. Combining these values, an FOM was defined to determine the optimal combination. RESULTS: The results indicated that the Mo/Rh and W/Rh combinations present mean glandular doses below the limit for all thicknesses. In contrast, using the Mo/Mo combination, the mean glandular doses were below the limit only up to 45 mm. However, when considering the FOM that combines dosimetric aspects and the contrast-detail threshold, the use of W/Rh is the most optimal option. CONCLUSION: The results obtained in this study demonstrate that the W/Rh combination in direct digital mammography is the option that presents the best trade-off between the mean glandular dose and the contrast-detail detection threshold. IMPLICATIONS FOR PRACTICE: The results demonstrate that the application of the W/Rh combination in direct digital mammography offers an optimized and applicable option, regardless of the thickness of the breast that will be radiographed.

Development and implementation of a low-cost phantom for quality control in cone beam computed tomography.

A phantom for quality control in cone beam computed tomography (CBCT) scanners was designed and constructed, and a methodology for testing was developed. The phantom had a polymethyl methacrylate structure filled with water and plastic objects that allowed the assessment of parameters related to quality control. The phantom allowed the evaluation of essential parameters in CBCT as well as the evaluation of linear and angular dimensions. The plastics used in the phantom were chosen so that their density and linear attenuation coefficient were similar to those of human facial structures. Three types of CBCT equipment, with two different technological concepts, were evaluated. The results of the assessment of the accuracy of linear and angular dimensions agreed with the existing standards. However, other parameters such as computed tomography number accuracy, uniformity and high-contrast detail did not meet the tolerances established in current regulations or the manufacturer's specifications. The results demonstrate the importance of establishing specific protocols and phantoms, which meet the specificities of CBCT. The practicality of implementation, the quality control test results for the proposed phantom and the consistency of the results using different equipment demonstrate its adequacy.

Development of a phantom and a methodology for evaluation of depth kerma and kerma index for dental cone beam computed tomography.

Basically, all modalities of diagnostic radiology require phantoms suitable for dosimetric evaluations. New technologies frequently arise unaccompanied of tools for dosimetric evaluations and quality control. In this study, a low-cost phantom and a consequent proposed methodology for dosimetric evaluations in cone beam computed tomography (CBCT) were presented. The developed phantom has typical dimensions of the human face, was built in polymethyl methacrylate and filled with water. Three devices with different technological concepts were evaluated and a proposed index, kerma index-height product (PKIH), was defined as an option to the use of air kerma-area product. The results of this study show relatively uniform kerma profiles for scanners with field of views (FOVs) of large diameters and non-uniform for FOVs of small diameters. With regard to the values obtained for the kerma indexes, much higher values were found for the equipment FOVs with small diameter compared with the values of the two other equipment that have larger diameters. The results indicate that (1) there is a need for special phantoms for use in CBCT, (2) the use of P(KA) in the evaluation of protocols on different equipment can lead to false interpretations and (3) the new index is a suitable alternative for the use of P(KA) in CBCT.

Effective doses in panoramic images from conventional and CBCT equipment.

Dental radiology is being extensively used especially after the consolidation of the dental implant technique. Although dental radiology has always been regarded as a low-dose technique, this scenario has changed with the introduction of volumetric techniques and consequent changes that have resulted from the use of the new technique. To compare dose values related to the use of different technologies used in the acquisition of dental panoramic images, the effective dose associated with this image technique was calculated using two different conversion factors for kerma-area product, P(KA), in the effective dose. Twenty-four pieces of equipment were evaluated and distributed into three categories: (1) 19 units of conventional equipment, (2) 3-cone beam computed tomography equipment (CBCT) which has a specific sensor to obtain panoramic images and (3) 2 items of CBCT equipment which only have sensors for volumetric acquisition, and the obtainment of panoramic images is through software reconstruction. The results show values of PKA and effective dose are higher for devices using digital image receptors. It is concluded that optimisation procedures and critical analysis should always be applied when adopting new technologies.