HT系统兆伏级CT图像质量和剂量计算研究

Image quality and dose calculation of megavoltage computed tomography in helical tomotherapy

目的定量对HT系统兆伏级CT图像质量及剂量计算准确性进行评估。方法应用兆伏级CT扫描Cheese phantom模体，分别对图像成像几何精度、噪声、图像均匀性、空间分辨率、密度-CT值的转化及剂量计算准确性进行测试，并与常规千伏级CT进行对比分析。结果兆伏级CT图像的成像几何精度在三维方向均〈mm，MVCT图像噪声、均匀性、空间分辨率都差于千伏级CT。基于CT图像进行剂量重建的DVH均与千伏级CT计划的DVH有很好一致性。结论兆伏级CT图像几何尺寸精确，成像剂量低，剂量计算精确，满足于临床要求。

Objective To quantitatively investigate the image quality and dose calculation accuracy of megavohage computed tomography （CT） in helical tomotherapy. Methods The megavoltage CT was used to scan the Cheese phantom, and the geometric accuracy of images, noise, image uniformity, spatial resolution, density-CT value conversion, and dose calculation accuracy were analyzed and compared with conventional kilovohage CT. Results The geometric accuracy of megavohage CT images was within 2 mm in three directions. The megavoltage CT was inferior to kilovoltage CT in terms of image noise, uniformity, and spatial resolution. The dose-volume histogram （DVH） in dose reconstruction based on CT images was well consistent with DVH in the kilovoltage CT plan. Conclusions The megavohage CT can obtain images with accurate geometric dimensions and has a low imaging dose and accurate dose calculation, which meets clinical requirements.