The Accuracy Of MRI In The Localization Of X(γ)-Stereotactic Radiotherapy

Porpuse: Stereotactic radiotherapy (SRT) is a precise treatment, and has high request to the precision of localization. The localization of SRT often takes CT and MRI as the foundation, and each of them has its advantage. Comparing to CT, MRI has more advantage in the resolution of soft organization, and can provide three-dimensional images; so many radiotherapy doctors are favor of it. But one weakness of MRI is the problem of image distortion, which causes the position of the targets to partial move, and then affecting the distribution of the doses and the result of the treatment. This experiment lies in the study of the MRI' s problem of image distortion, and its size of error in the localization of SRT, the influence factor and the corresponding methods etc., to make sure whether MRI can be used in the localization of SRT.Methods: This research adopted especially organic glass cylinder to make the phantom. The phantom was filled with the material, which had similar T1, T2 values with brain organizes. Six planes were marked to carry on the data processing. We imitated patient' s fixed method to fix the phantom and to acquire the MRI image data. Then we transmitted the data to the TPS. In the planning station, we measured the distance of the close and opposite points at the directions ofx, y; at the direction of z, the distance between arbitrarily two plane markings was measured. Finally, we compared these results with the actual value and confirmed the difference.Result: (1) Affected by the metal frame, the image distortion was a little more serious in a several planes near the frame than others. (2)To close points , at the direction of x, the error was in the range of 0.2- 1.4mm, and the average value was 0. 9mm; at the direction of y, the error was in the range of 0.3-1.5mm, and the average value was 0.9mm. Followed by the q test, there was no marked difference between the six planes at the two directions (P>0. 05) . To the distribution, the number that the error located in the range of 0. 5-1.0mm ( included 1. 0mm, not included 0. 5mm) was the most, but the number ^0. 5mm or ) 1. 0mm was a few.(3) To the opposite points, at the direction of x, the error was in the range of 0. 3-1.7mm, and the average value was 0.9mm; at the direction of y, the error was in the range of 0. 4-1.8mm, and the average value was 0.9mm. Followed by the q test, there was no marked difference between the six planes at the two directions (P>0. 05) . The number that the error was ^ 1.5mm was the most, and the number) 1.5mm was a few.(4) At the direction of z, the error was in the range of 0. 3~1.9mm, and the average value was 1.0mm. Many errors were ^1.5mm, and the number that the error was ) 1.5 mm was a few.Conclusion: To our MRI scanning system and SRT planning system, it is possible to use MRI alone in the localization of SRT in many locations of the brain and the head and neck. While using MRI for the localization of SRT, the operators must take the overall check...