Analysis Of The Setup Errors Of A Stereoscopic Two-dimensional Kilo-voltage XGS-10System For Head-and-neck Region Intensity-modulated Radiotherapy

Objective To analyze the discrepancies between position adjustmentsobtained with a stereoscopic2DKV XGS-10system and a Varian CBCTsystem for head-and-neck region IMRT treatments, and to compare forimage acquisition and registration time.Methods CBCT images were obtained with OBI system and2DKVimages were acquired by XGS-10system for30head-and-neck patientsprior to Varian-21EX IMRT treatment. The images were registered withplanning image for localization, and position adjustments were given in LR,SI and AP directions, then the discrepancies between them were analyzed.On the comparison of the two diffferent systems, the Pearson coefficientwas used to analyzed the correlation and95%CI analysis to discern theconsistence.Results Analysis of images acquired for the30patients yielded thefollowing results: position adjustments with XGS-10system were（-1.03±2.15） mm,（0.86±2.59）mm,（0.42±1.66）mm in LR, SI andAP directions, whereas（0.00±1.68）mm,（1.53±2.12）mm,（0.10±1.54）mm with CBCT in LR, SI and AP directions. The discrepancies were（-1.03±1.24）mm,（-0.68±1.78）mm and （0.32±1.61）mm in LR, SI andAP directions. The correlation coefficients between them were0.817,0.731 and0.495in LR, SI and AP directions. The average image acquisition andregistration time were10seconds and <15s in XGS-10system, with3minand8min in OBI system.Conclusions More than95%of the discrepancies betweenadjustment given by XGS-10system and OBI system were less than3mm,indicating that there were high correlation and consistency between the twoand both could be used to improve patient position accuracy. Comparedwith OBI, the XGS-10system required much shorter time for acquisitionand registration, cutting down the total time.