Evaluation of Adaptive Planning of Lung Cases based on Cone Beam CT Images

The purpose of this study was to evaluate the accuracy of dose calculation based on Cone Beam Computed Tomography (CBCT) as adaptive planning for lung cancer. Dose calculation based on CBCT images was compared to Computed Tomography (CT) simulator images as references. Treatment planning was generated for 7 patients of lung using Intensity Modulated Radiotherapy (IMRT) technique and Volumetric Arc Therapy (VMAT) technique. Eclipse v13.6 Treatment Planning System (TPS) with Analytical Anisotropic Algorithm (AAA) and Acuros External Beam (AXB) algorithm were used to calculate the dose. This study was divided into three major parts: (1) Hounsfield Unit (HU) calibration for CBCT images by using CIRS 002LFC phantom; (2) analysis of Dose Volume Histogram (DVH); (3) analysis of Passing Rate Gamma with criteria Dose Difference (DD) 2%/Distance To Agreement (DTA) 2mm and DD 3%/DTA 3mm using Electronic Portal Imaging Device (EPID). The DVH analysis for D_98%, D_50% and D_2% deviation was evaluated and compared to the DVH for CT images with AAA algorithm as reference. The deviation of D_98%, D_50% and D_2% for lung cancer was less than 2%. The range of conformity index based on CBCT images for all planning was 0,923-0,999 and the homogeneity index was in the range of 0,042-0,197. The gamma criteria (DD/DTA) of dose difference and distance to agreement for 2%/2mm are 87% - 94% and for 3%/3mm were 96% -98% for IMRT techniques. Passing Rate Gamma for VMAT with 2%/2mm criteria were 87% -96% and 3%/3mm criteria were 96% - 98%. The results of this study showed that dose calculation based on CBCT image was similar to dose calculation using CT image with descrepancy less than 2%.