A prospective study of OAR volume variations between two different treatment planning systems in radiotherapy

Abstract

Purpose: It has been seen that there is a clinically significant variation in the volume calculated across different planning systems for the same digital imaging and communication (DICOM) contours. The purpose of this study is to investigate the difference in volumes of organs at risk when the structure sets were exported from the Eclipse ((Palo Alto, USA Version 10.0) to XIO CMS (Electa, Crawley, UK Version 4.40.00) treatment planning system (TPS) and identify how the differences occur.   Methods: We prospectively analyzed the volumes of organs at risk from computerized tomography (CT) data of 54 patients. Head and neck and brain tumors were taken for this study and contoured on Eclipse treatment planning system (TPS) after importing images from CT. These contoured images were then exported using radiotherapy DICOM transfer facility to XIO CMS planning system and compared the contoured volumes with Eclipse TPS structured volumes. Results: Our analysis showed that the differences in calculated volumes of the contours for the patients between the two planning systems can be large. Mixed results are shown for different organs with the absolute volume difference ranging from -0.25 cc to 319.73 cc. These results clearly shown that the two TPS interprets the contours differently when calculating the volume, and there is a closer match with the theoretical calculated volumes with XIO CMS calculated volumes. Conclusion: Observed discrepancies were consistent between the two planning systems. This impact of contouring variability could play a role on plan quality metrics which is used as criteria for clinical trial protocol compliance.