Evaluation of the accuracy of dose delivery in stereotactic radiotherapy using the Velocity commercial software

The purpose of this study was to evaluate the accuracy of dose delivery during stereotactic radiotherapy of the lung (SBRT) and brain (SRT) tumours by registered CT (rCT) images obtained from CT used for planning (pCT) and cone-beam CT (CBCT).The study is based on two groups of patients (10 patients each) undergoing SBRT and SRT. To assess the correctness of the propagation of the GTV (brain group) and ITV (lung group) contours, the volumes calculated on the pCT and rCT studies were analysed. The Dice-Sørensen similarity coefficient (DSC) was used to check the variability in the position of GTV/ITV observed between pCT and rCT. The dose recalculated on rCT was compared with the dose from pCT.GTV and ITV determined on pCT and rCT studies did not differ statistically (p = 0.770 for ITV and p = 0.086 for GTV). DSC obtained for the lung group was statistically smaller than that for the brain group (p < 0.001). Differences between doses obtained for 99% of the ITV/GTV on pCT and rCT studies were within ±10% and did not exceed the clinically acceptable tolerance.The observed changes in the volume (ITV/GTV) were within the area of the original PTV volume. The differences between the planned and delivered doses in the ITV/GTV were not clinically significant.