RESUMO
Abstract Introduction Digital mammography present many advantages in comparison to conventional mammography, such as high dynamic range and the post-processing of acquired images. One problem is that protocols may not be optimized, resulting in higher absorbed doses to patients. The objective of this work is to evaluate image quality and to estimate mean glandular doses (MGD) in patients submitted to mammography examinations with three digital systems and one screen-film system in Recife, Brazil. Methods To estimate the MGD, the parameters used to acquire images of 5475 patients, with ages between 40 and 64 years and compressed breasts between 2 and 9 cm, were registered. The MGD was calculated by multiplying the incident air kerma with conversion coefficients depending on the anode/filter, breast glandularity and half-value layer. The image quality evaluation of the digital systems was made using objective and subjective European criteria. Results The results showed MGDs in the range of 0.4-10.3 mGy and the higher values were observed with digital systems. It was also observed that in the digital systems the use of compression force is not adequate and the irradiation parameters are not optimized. The images failed to reproduce the pectoral muscle and the contrast-to-noise ratio was not adequate for one system, indicating the need to improve the patient's positioning and the exposure parameters. Conclusion It can be concluded that the use of non-optimized irradiation parameters is causing the higher doses with digital systems, highlighting the insufficient compression force.
RESUMO
The objective of this work was to evaluate the air kerma-area product (PKA) and the skin absorbed dose in the region of the eyes, salivary glands and thyroid of the patient from mandible examinations performed with three cone-beam computed tomography (CBCT) scanners, i.e. i-CAT classic, Gendex CB-500 and PreXion 3D. For the dosimetric evaluation, an anthropomorphic head phantom (model RS-250) was used to simulate an adult patient. The CBCT examinations were performed using standard and high-resolution protocols for mandible acquisitions for adult patients. During the phantom's exposure, the PKA was measured using an ionising chamber and the absorbed doses to the skin in the region of the eyes, thyroid and salivary glands were estimated using thermoluminescence dosemeters (TLDs) positioned on the phantom's surface. The PKA values estimated with the CBCT scanners varied from 26 to 138 µGy m(2). Skin absorbed doses in the region of the eyes varied from 0.07 to 0.34 mGy; at the parotid glands, from 1.31 to 5.93 mGy; at the submandibular glands, from 1.41 to 6.86 mGy; and at the thyroid, from 0.18 to 2.45 mGy. PKA and absorbed doses showed the highest values for the PreXion 3D scanner due to the use of the continuous exposure mode and a high current-time product.
Assuntos
Tomografia Computadorizada de Feixe Cônico/normas , Mandíbula/diagnóstico por imagem , Doses de Radiação , Radiometria/normas , Ar , Antropometria , Tomografia Computadorizada de Feixe Cônico/métodos , Desenho de Equipamento , Olho/efeitos da radiação , Cabeça/efeitos da radiação , Humanos , Imageamento Tridimensional/métodos , Glândula Parótida/diagnóstico por imagem , Imagens de Fantasmas , Pele/efeitos da radiação , Glândula Submandibular/diagnóstico por imagem , Dosimetria Termoluminescente/métodos , Glândula Tireoide/diagnóstico por imagem , Tomógrafos ComputadorizadosRESUMO
The aim of this work was to perform a dosimetric evaluation of two cone-beam computed tomography scanners. The study was performed with two scanners: i-CAT classic and PreXion 3D. Air kerma-area product (PKA) was measured for all full-arch dental implant planning protocols. Surface air kerma was also estimated at the region of the eyes, salivary glands and thyroid using thermoluminescence dosemeters positioned on an anthropomorphic phantom. The PKA values for the i-CAT classic ranged from 24 to 180 µGy m(2) and, for the PreXion, from 70 to 138 µGy m(2). The large variation of these values was mainly caused by acquisition time and field of views. The surface air kerma values were from 0.08 to 3.39 mGy at the eyes, 0.50 to 3.96 mGy at the parotids, 0.11 to 2.95 mGy at the submandibular glands and 0.05 to 1.32 mGy at the thyroid. These values are comparable with those found in the literature.