There are several factors that may contribute to the increase in radiation dose of CT including the use of unoptimized protocols and improper scanning technique. In this study, we aim to determine significant impact on radiation dose as a result of mis-centering during CT head examination. The scanning was performed by using Toshiba Aquilion 64 slices multi-detector CT (MDCT) scanner and dose were measured by using calibrated ionization chamber. Two scanning protocols of routine CT head; 120 kVp/ 180 mAs and 100 kVp/ 142 mAs were used represent standard and low dose, respectively. As reference measurement, the dose was first measured on standard cylindrical polymethyl methacrylate (PMMA) phantom that positioned at 104 cm from the floor (reference isocenter). The positions then were varied to simulate miscentering by 5 cm from isocenter, superiorly and inferiorly at 109 cm, 114 cm, 119 cm, 124 cm and 99 cm, 94 cm, 89 cm, 84 cm, respectively. Scanning parameter and dose information from the console were recorded for the radiation effective dose (E) measurement. The highest mean CTDIvol value for MCS and MCI were 105.06 mGy (at +10 cm) and 105.51 mGy (at -10 cm), respectively which differed significantly (p < 0.05) as compared to the isocenter. There were large significant different (p < 0.05) of mean Dose Length Product (DLP) recorded between isocenter to the MCS (85.8 mGy.cm) and MCI (93.1 mGy.cm). As the low dose protocol implemented, the volume CTDI (CTDIvol) were significantly increase (p < 0.05) for MCS (at +10 cm) and MCI (at -10 cm) when compared to the isocenter. The phantom study revealed a noticeable different in radiation dose between isocenter and experimental groups due to degradation of the bowtie filter performance. It is anticipated that these noteworthy findings may emphasize the importance of accurate patient centering at the isocenter of CT gantry, so that CT optimization practice can be achieved.
The increasing number of CT procedures owing to advanced CT technology requires careful monitoring by the personnel involved to ensure appropriate examinations and optimized procedures. For that reason, CT optimization is a crucial factor that could help to compensate for [[[AUTHOR: Could this sentence be clarified with more specific information? For example, you might say that optimization compensates for the poor image quality that can occur with low radiation. Thank you.]]] radiation dose and image quality. In current practice, optimization in CT is a complex procedure due to a wide range of acquisition parameters in imaging protocols. Diagnostic Reference Levels (DRLs) have been defined by the International Commission on Radiation Protection (ICRP) as a form of investigating the level of patient dose for a specified procedure used in medical imaging to indicate whether, in routine conditions, the patient dose is unusually high or low for that procedure. Hence, the Ministry of Health (MOH) has established a national DRL through a dose survey conducted from 2007 to 2009, and the project is called as NADS1. However, the study does not cover the effectiveness of image quality; in contrast, the current research focuses on both dose exposure and image quality to determine the level of effectiveness of the developed NADS1 data. This study involves several levels, including the acquisition of patient exposure data, image quality assessment, and effective dose measurement. Determination of acquisition of patient exposure data is based on the indicator of QAP CT Brain developed by the MOH, i.e., the total number of adult CT brain examinations for which the DLP value shall not exceed 10% of the national DRL values, 1050 mGy.cm. The outcome of this study can be used as a measure to optimize patients’ radiation exposures and can be a guide for implementing improvement measures. The results of this study allow radiology personnel to understand the concepts and mechanisms associated with managing patient radiation exposures. The outcome also provides the level of effectiveness of the developed QAP, which was implemented by the MOH and subsequently became a benchmark for improving the quality of healthcare services. Therefore, it is clear that this study has shown an impact on the level of optimization from the radiation exposure study, the NADS2 that is being implemented.
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