模拟定位CT床板对放射治疗剂量的影响

The study of different CT bed boards on the effects of radiation therapy

目的研究不同定位CT床板对放射治疗剂量的影响。方法分别用碳纤床板、有机玻璃床板、普通CT凹形扫描床板、不用扫描床板对模体进行扫描,传输至计划系统,进行CT值采样,比较基于不同方法得到CT图像设计计划所得加速器输出量。结果与有机玻璃床板接触的模体部分CT值(如取样为1.25 cm及0.5 cm直径的圆相对偏差值分别为118.8%和205.6%),比不用扫描床板CT值大(P<0.01),其他扫描方法所得的CT值与不用扫描床板所得的CT值一致;在180°与有机玻璃床板接触的模体设射野时加速器输出量比不用扫描床板模体大0.9%,其他两种方法加速器输出量比不用扫描床板模体增大在0.5%内。结论射野穿过与有机玻璃床板接触的模体部位对剂量将有影响,而其他不同定位CT床板对放射治疗剂量的影响无临床意义;不同的治疗床板对剂量影响大小不一。

Objective To study the impact of different CT bed boards on radiotherapy dose distribution.Methods Phantom was scanned respectively with different bed boards which were carbon fiber bed board,plexiglass bed board,normal CT scan bed board and no bed board.Images of phantom were transferred to the planning system,and then CT values from different places of different bed boards were sampled,and the accelerator outputs obtained from different methods were compared.Results CT values of part in contact with the plexiglass bed board was 118.8% or 205.6%（sampling area was 1.25cm or 0.5cm diameter circle）higher than the part CT values with no bed.The results were statistically significant.In other locations the CT values were the same as other CT bed boards.The accelerator output with the images of plexiglass bed board was 0.9% bigger than the accelerator output with the images of no bed when gantry was 180°.Comparing with the other two methods which used carbon fiber bed board and normal CT scan bed board and the method which was with no bed board,the accelerator output error was within 0.5%.Conclusion The area in contact with the plexiglass bed board which is passed through by beam has some influence on the dose.Impact of different CT bed boards effects on radiation dose distribution will not cause clinically significant effect.Treatment of bed board has a certain impact on the dose.