Dosimetry in CBCT with Different Protocols: Emphasis on Small FOVs Including Exams for TMJ.

Deborah Queiroz Freitas,Eduarda Helena Leandro Nascimento,Marcos Ely Almeida Andrade,Marco Antonio Gomes Frazão,Flavia Maria Moraes Ramos-Perez,Helena Aguiar Ribeiro Nascimento

doi:10.1590/0103-6440201701525

Deborah Queiroz Freitas, Eduarda Helena Leandro Nascimento + Show 4 more

Open Access

https://doi.org/10.1590/0103-6440201701525

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Abstract

This study aimed to estimate the absorbed dose in cone beam computed tomography (CBCT) exams according to different exposure parameters and size and position of the field of view (FOV). In addition was compared the absorbed dose of two smaller FOV scans with that of a larger FOV scan for evaluation of temporomandibular joint (TMJ), as it is a bilateral structure. CBCT scans were obtained on OP300 Maxio unit varying scanning mode (standard, high and endo) as well as size (5x5, 6x8 and 8x15 cm) and positioning of FOV. With a small FOV, different areas were scanned (maxilla or mandible, anterior or posterior and TMJ). Absorbed doses were determined using thermoluminescent dosimeters on the skin surface of sensitive organs of an anthropomorphic phantom. Endo mode showed the highest dose, followed by the high and standard modes in all FOV positions. With small FOV, doses were higher in the posterior region, especially in the mandible. Dose reduction occurred when small FOVs were used, but it was not proportional to FOV size reduction. For TMJ, the dose in a single acquisition with large FOV was greater than two acquisitions with small FOV, but lower than two acquisitions with medium FOV (6x8 cm). In conclusion, scanning mode, size and FOV position have great influence on the absorbed dose. Small FOV decreases the dose, but there is no linear relation between FOV size and dose. For bilateral exams of TMJ, double acquisition with small FOVs produces decrease in absorbed dose relative to a large FOV.

Highlights

Since the first reports on the cone beam computed tomography (CBCT) to dentistry, which occurred in the late 1990s [1,2], CBCT has become an integral part of the set of diagnostic tools for various dental specialties
Pioneering studies on CBCT dosimetry have used field of view (FOV) considered medium or large centered in the maxilla and mandible of anthropomorphic phantoms [8,17,18,19]
As CBCT units began to offer smaller FOVs, two questions derived from such innovation: how does FOV reduction and FOV positioning affect an exam’s total radiation dose? in this study, a device that is relatively new on the market and allows the choice of varied FOV sizes from small to large, was tested to enable the proposed comparisons

Summary

Introduction

Since the first reports on the cone beam computed tomography (CBCT) to dentistry, which occurred in the late 1990s [1,2], CBCT has become an integral part of the set of diagnostic tools for various dental specialties. That concern is justifiable in the head and neck imaging, since the irradiated field houses organs such as the thyroid, the salivary glands and the lens of the eyes [4]. The operator of a CBCT unit has several protocols available and selects the most appropriate setup according to the clinical requirements and the anatomical characteristics of the region of interest (ROI). As the radiation dose absorbed by the patient seems to depend primarily on the field of view (FOV) and on the exposure parameters, it is important to choose the protocol that provides the lowest dose to the patient while providing the necessary diagnostic information, according to the ALADA principle (“As low as diagnostically acceptable”) [5,6]

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