To analyze the differences between calculated and actual volumes of regions of interest (ROIs) in three treatment planning systems (TPSs): PrecisePlan, Xio, and Oncentra, to transfer different ROIs and compare their calculated volume between the three TPSs, and to provide a basis for clinical application.

Different sizes of ROIs were delineated on 5 sets of computed tomography (CT) images with different slice thickness. Square and round regions with different slice numbers were contoured in a homogeneous phantom. Three groups of patients (n=5) with head and neck tumor, chest and abdomen tumor, and pelvic tumor, respectively, were enrolled as subjects. All the ROIs were independently transferred back and forth between three TPSs and different workstations with the same system in DICOM RT format. The changes in actual and calculated ROI volumes were evaluated after back and forth transfer.

There was a significant positive linear correlation between the calculated volume, slice thickness, slice number, and actual volume of ROI in each TPS (PrecisePlan: R²=0.994, P<0.01; Xio: R²=0.997, P<0.01; Oncentra: R²=0.995, P<0.01). There were significant differences in all calculated ROI volumes of the head, chest and abdomen between the three TPS (P<0.05) except for the calculated ROI volumes of the chest and abdomen between Oncentra and Xio (P=0.114).

The variations in volume calculation algorithm and slice thickness are the main causes of differences in calculated ROI volume. Particularly, small-volume ROIs have the greatest variation in calculated volume. To avoid a secondary reconstruction of ROI volume, it is recommended to transfer ROI back and forth between dose calculation workstations with the same TPS.

Region of interest; Volume calculation; Image transmission; Treatment planning system