Investigating the Effect of mA Variation on Absorbed Dose to Salivary Glands and Mandible Body in CBCT

  Cone beam computed tomography (CBCT) has been broadly acceptable in recent years as a radiography modality for diagnosis, treatment planning and follow up in dentistry. Some important parameters such as radiation dose, image quality and field of view are considered as a criteria for deciding whether or not a CBCT dental unit is suitable for a particular application. This study aims to evaluate the effect of exposure levels on the absorbed dose of mandible and salivary glands according to various settings of milliamperage (mA) in CBCT. A very advanced multilayers head and neck phantom was constructed for this study. This phantom was built based on the CT images of a specific patient with an average size. This phantom was constructed using proper substitutes for soft tissue and bone according to their physical properties. Therefore, there was a high level of agreement with the patient's body. This phantom enables us to measure the absorbed dose inside the organs. Dosimetry has been performed by Soredex Cranex3d CBCT. For film dosimetry, AGFA films were used in various layers of the phantom. The mAs of the device was changed in the range of 2, 4, 6, 8, 10 and 12 mA. The maximum and the minimum absorbed dose was placed in the area related to the right mandible and the left submandibular gland. The increase of absorbed dose by mA increase was meaningful in the confidence level of 95% for all scanned areas. By changing mA from 2 to 12, the absorbed dose varied significantly with a maximum 5.44-fold variation between the highest and lowest dose for the parotid gland. This study has shown that there is a meaningful relationship between the increase of mA and increase of absorbed dose in different parts of the dentomaxillofacial area, including the mandible, submandibular and parotid glands. It is concluded that as long as the image quality is acceptable for diagnostic purposes, the mAs of the CBCT should be kept in a low range to minimize the absorbed dose.