Abstract
The technological development of Computed tomography (CT) makes it a powerful diagnostic tool, with the increasing utilization of CT, the rising population dose needs to be carefully considered. The stochastic effect of children caused by CT examinations worth more concern due to the pediatric population are more sensitive to radiation than adults, a lot of international organizations have been established to care about the children undergoing CT examination and recommendate scan parameters to achive ALARA (as low as reasonably achiveable) pricinple. There are two methods to estimate CT dose, one is physical measurement, the other is simulation, the latter commonly used mathematical phantoms or age-based voxel phantoms, both represent the general size of human anatomy, they have no ability to accurately depict the dose distribution of individual patient, therefore it is urgent and meaningful to establish a patient-specific dose evaluation system. Besides, more and more studies showed the individual body size has significance impact on dose distribution, it is important to investigate the relationship between body size and dose clinically from the perspective of optimization and radiation protection. This study retrospectively analyzed clinical pediatric chest CT images, quantified the image quality and body size, calculated the size-specific dose estimation (SSDE) and effective dose for each patient by various methods. To obtained patient-specific dose, we used BEAMnrc Monte Carlo system to establish a CT sanner model, validated the dose characteristics to match clinical application. On the other hand, we conducted the simulation and measurement of CTDI (computed tomography dose index) and MSAD (multi-slice average dose) of cylindrical PMMA phamtom to decide the absolute dose conversion factor. Finally the CT images of each patient were used to create voxel phantom, then individual organ doses and effective dose can be calculated. This study identified the appropriate body size index for clinical applications, and analyzed the function of current protocol, we provide the improved scan parameters by the result of phantom study. This study also established individual patient dose assessment system that can be served as dose tracking or dose monitoring; this study is highly valuable both for the academic research or practical applications.