Author(s): Saud. H . Allehyani , Huda A. S. Sharyan and Aida R. Tolba.
Purpose: The aim of the present study is to compare (3D-CRT) to RapidArc planning using (LNAC of 6 MV, 15 MV and 18 MV) in terms of dosimetric outcomes of iso-dose distribution, dose volume histog ram (DVH), PTV and at risk organs in 4 patients with Gastric Cancer. Methods: Plans were created for 4 patients with Gastric Cancer who had received radical RapidArc treatment from 2012 to 2014 at KAMC (King Abdullah Medical City). Dosimetric evaluation metrics were used to compare the two plans in terms of mean, maximum and minimum doses to PTV, Homogeneity Index (HI), Conformity Index (CI), Target Coverage Index (TCI) and mean and maximum doses to critical organs and normal tissue. Dose to 95% of the PTV (D95%) was used to quantify PTV coverage. Results: RapidArc plan achieved lower mean and maximum doses to the PTV. PTV dose coverage, as measured by the minimum dose and the dose to 95% of the volume, was higher in the RapidArc plan. RapidArc plan also showed a more homogeneous dose distribution in PTV, achieving an HI of 1.1202 compared with 1.2046 in the 3D-CRT plan. However, RapidArc and 3D-CRT achieved similar CI values and improvement in TCI value. Additionally, regarding OARs, the mean and maximum dose in liver was lower in RapidArc with a low percentage of the volume receiving low doses . The mean dose to right and left kidneys were within tolerance in RapidArc and 3D-CRT. Although the mean dose was better in 3D-CRT, critical structure was better in the RapidArc plan. The mean dose to right kidney was lower in 3D-CRT, while left kidney was lower in RapidArc. For the spinal cord, the maximum dose was higher achieving 34 Gy in RapidArc, compared to 18 Gy in 3D-CRTbut within the tolerance. Therefore VMAT achieved a better mean dose to central OARs: liver, spinal cord, Kidneys and heart. Conclusions: (VMAT) is superior to 3D-CRT in term of PTV, conformity and homogeneity and accepting the VMAT class solution over 3D-CRT treatment was preferred to be determined on a case by case basis Keywords: Planning Tumor Volume; Organs at Risk; Conformity Index; Heterogeneity Index; Gastric cancer