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Objective To discuss the application of digital simulation positioning machine in radiation oncology. Methods We used digital simulation positioning machine to shoot isocenter reset digital simulator images of 0 degrees direction and 90 degrees direction, 10 × 10 cm2 rectangular field and actual time radiation field with any field number. Compared the images taken with the TPS corresponding DRR image through bone marker matching to measure the error of isocenter and actual time radiation field , the linear accelerator Iview-GT system with the same method was shot in rectangular field simulator the same field number EPID image , and the TPS corresponding DRR image. Finally, we compared the measured error of the digital simulator positioning machine with the error of Iview-GT system image. Results The result of measured isocenter error of the digital simulator positioning machine was better than EPID image error (P=0.000). Conclusion The application of digital simulation positioning machine in radiation oncology can be more accurate to measure the error and correct the position deviation, however, it can also make the radiotherapy and the treatment more accurate.
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Objective:To discuss application of large aperture 16 row spiral CT in radiotherapy simulation positioning. Methods: To apply CT simulation positioning with large aperture 16 row spiral CT for the breast tangential field by early breast cancer after breast conserving surgery and radical radiotherapy. Compare CT-simulation and X-ray conventional positioning technique and Compare large aperture 16 row spiral CT and single row spiral CT image. Results: The application of large aperture 16 row spiral CT avoided the error because of body limited. Large aperture 16 row spiral CT simulation position validation error is superior to X-ray positioning. Its image quality is better than that of single row spiral CT. Conclusion:The application of large aperture 16 row spiral CT make simulation positioning more accurate, planned and treatment more accurate, it can provide guarantee of accurate simulation positioning for accurate plan and treatment.
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Objective To compare the errors of final isocenter marking method and reference point marking method for CT simulation positioning in intensity-modulated radiotherapy (IMRT).Methods From 2009 to 2012,327 patients with head and neck cancer for IMRT underwent CT simulation positioning using the Philips Brilliance CT Big Bore scanner and Philips Tumor LOC workstation and were divided into final isocenter marking group (n =208) and reference point marking group (n =119) according to positioning methods.Target volume delineation and treatment plan design were performed on the Varian Eclipse treatment planning system (TPS).Before treatment,kilovoltage cone-beam CT scans and registration were performed with the Varian EX on-board imager system to obtain beam position errors in the right-left (RL),superior-inferior (SI),and anterior-posterior (AP) directions,and then comparisons of errors between the two groups were made by independent-samples t test.Finally,the TPS was used to measure the changes in the doses to the organs at risk after moving isocenters in the RL,SI,and AP directions among 5 patients with nasopharyngeal carcinoma.Results The mean beam position errors in the three directions were less in the final isocenter marking group than in the reference point marking group (P =0.02,0.01,0.03).After moving isocenters in the three directions,the target dose was reduced and the dose to the normal tissue around the target tumor was increased significantly.The error in the AP direction had the maximum influence on the spinal cord and brainstem.Conclusions Final isocenter marking method leads to less beam position error than reference point marking method in CT simulation positioning.Small isocenter motion can cause large changes in the doses to the organs at risk.