Paulu David, Alaei Parham
Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 55455, USA.
J Appl Clin Med Phys. 2017 May;18(3):9-15. doi: 10.1002/acm2.12060. Epub 2017 Mar 20.
There are an increasing number of radiation therapy patients with hip prosthesis. The common method of minimizing treatment planning inaccuracies is to avoid radiation beams to transit through the prosthesis. However, the beams often exit through them, especially when the patient has a double-prosthesis. Modern treatment planning systems employ algorithms with improved dose calculation accuracies but even these algorithms may not predict the dose accurately at high atomic number interfaces. The current study evaluates the dose calculation accuracy of three common dose calculation algorithms employed in two commercial treatment planning systems. A hip prosthesis was molded inside a cylindrical phantom and the dose at several points within the phantom at the interface with prosthesis was measured using thermoluminescent dosimeters. The measured doses were then compared to the predicted ones by the planning systems. The results of the study indicate all three algorithms underestimate the dose at the prosthesis interface, albeit to varying degrees, and for both low- and high-energy x rays. The measured doses are higher than calculated ones by 5-22% for Pinnacle Collapsed Cone Convolution algorithm, 2-23% for Eclipse Acuros XB, and 6-25% for Eclipse Analytical Anisotropic Algorithm. There are generally better agreements for AXB algorithm and the worst results are for the AAA.
接受放射治疗的髋关节假体患者数量日益增加。将治疗计划误差降至最低的常用方法是避免辐射束穿过假体。然而，辐射束常常会穿过假体射出，尤其是当患者有双侧假体时。现代治疗计划系统采用了剂量计算精度有所提高的算法，但即便这些算法在高原子序数界面处也可能无法准确预测剂量。本研究评估了两种商用治疗计划系统中使用的三种常见剂量计算算法的剂量计算精度。在圆柱形模体中塑造一个髋关节假体，使用热释光剂量计测量模体内部与假体界面处多个点的剂量。然后将测量得到的剂量与计划系统预测的剂量进行比较。研究结果表明，对于低能和高能X射线，所有三种算法均低估了假体界面处的剂量，不过低估程度有所不同。对于Pinnacle坍缩卷积算法，测量剂量比计算剂量高5% - 22%；对于Eclipse Acuros XB算法，高2% - 23%；对于Eclipse解析各向异性算法，高6% - 25%。一般来说，AXB算法的一致性更好，而AAA算法的结果最差。
