Résumé
Objective To analyze the discrepancies between position adjustments obtained with the stereoscopic 2DKV XGS-10 system and the Varian OBI system for head-and-neck region IMRT treatments,and to compare for image acquisition and registration time.Methods CBCT images were obtained with OBI system and 2DKV images were acquired by XGS-10 system for 30 head-and-neck patients prior to Varian21EX IMRT treatment.The images were registered with planning 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 different systems,the Pearson coefficient was used to analyzed the correlation and 95％ CI analysis to discern the consistence.Results Analysis of images acquired for the 30 patients yielded the following results:position adjustments with XGS-10 system were (-1.03 ± 2.15) mm,(0.86 ± 2.59) mm,(0.42 ± 1.66) mm in LR,SI and AP 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 and AP directions.The correlation coefficients between them were 0.817,0.731 and 0.495 in LR,SI and AP directions.95％ CI were (-1.47--0.59),(-1.32-0.04),(-0.26-0.90) mm.The average image acquisition and registration time were 10 s and ＜ 15 s in XGS-10 system,with 3 min and 8 min in OBI system.Conclusions Both of XGS-10 system and OBI system could be used to improve patient position accuracy,but XGS-10 system could cut down the total time.
Résumé
Objective Performing a daily quality assure (QA) program to get variation and error range of on board imager (OBI) system,so that the OBI system can meet the needs of clinical treatment.Methods The daily QA program including: mechanical accuracy,2D/2D Shift calculations accuracy,couch motion accuracy.Results The max deviation was-0.7 mm in lcft-right (LR) dircction and 0.8 mm in superior-inferior (S1) direction in Linac& OBI isocenter accuracy check.The max deviations in 4 blades (x1,x2,y2,y1) position accuracy check were:-2.1 mm,2.2 mm,± 1.7 mm,-2.1 mm.In OBI mechanical arms position accuracy check,31％ standard data was 85.2 cm with 0 mm deviation; 69％ standard data was 85.1 cm with 1 mm deviation.In LR,SI and anterior-posterior direction,2D/2D shift calculations accuracy was 0.46 mm,1.35 mm,-0.04 mm and couch motion accuracy was-0.1 mm,0.3 mm,0.2 mm,respectively.Conclusions By performing the daily QA program,it could be found whether OBI works properly and satisfies the clinical use.The physicist can pay more attention to the parameters which change frequently,and adjust the frequency of the parameters which are stable,so that working efficiently.
Résumé
PURPOSE: On-line image guided radiation therapy (on-line IGRT) and (kV X-ray images or cone beam CT images) were obtained by an on-board imager (OBI) and cone beam CT (CBCT), respectively. The images were then compared with simulated images to evaluate the patient's setup and correct for deviations. The setup deviations between the simulated images (kV or CBCT images), were computed from 2D/2D match or 3D/3D match programs, respectively. We then investigated the correctness of the calculated deviations. MATERIALS AND METHODS: After the simulation and treatment planning for the RANDO phantom, the phantom was positioned on the treatment table. The phantom setup process was performed with side wall lasers which standardized treatment setup of the phantom with the simulated images, after the establishment of tolerance limits for laser line thickness. After a known translation or rotation angle was applied to the phantom, the kV X-ray images and CBCT images were obtained. Next, 2D/2D match and 3D/3D match with simulation CT images were taken. Lastly, the results were analyzed for accuracy of positional correction. RESULTS: In the case of the 2D/2D match using kV X-ray and simulation images, a setup correction within 0.06degrees for rotation only, 1.8 mm for translation only, and 2.1 mm and 0.3degrees for both rotation and translation, respectively, was possible. As for the 3D/3D match using CBCT images, a correction within 0.03degrees for rotation only, 0.16 mm for translation only, and 1.5 mm for translation and 0.0degrees for rotation, respectively, was possible. CONCLUSION: The use of OBI or CBCT for the on-line IGRT provides the ability to exactly reproduce the simulated images in the setup of a patient in the treatment room. The fast detection and correction of a patient's positional error is possible in two dimensions via kV X-ray images from OBI and in three dimensions via CBCT with a higher accuracy. Consequently, the on-line IGRT represents a promising and reliable treatment procedure.