Yang J N, Mackie T R, Reckwerdt P, Deasy J O, Thomadsen B R
Department of Medical Physics, University of Wisconsin Medical School, Madison 53706, USA.
Med Phys. 1997 Mar;24(3):425-36. doi: 10.1118/1.597909.
Experimental simulations for tomotherapy beam delivery were performed using a computer-controlled phantom positioner, a cylindrical phantom, and a 6 MV x-ray slit beam. Both continuous helical beam and sequential segmented tomotherapy (SST) beam deliveries were evaluated. Beam junctioning problem due to couch indexing error or field width errors presented severe dose uniformity perturbations for SST, while the problem was minimized for helical beam delivery. Longitudinal breathing motions were experimentally simulated for helical and SST beam delivery. While motions reduced the dose uniformity perturbations for SST, small artifacts in dose uniformity can be introduced for helical beam delivery. With typical breath frequency and magnitude, for a slit beam of 2.0 cm width at 4 rpm, the dose uniformity perturbation was not significant. A running start/stop technique was implemented with helical beam delivery to sharpen the 20%-80% longitudinal dose fall-off from 1.5 to 0.5 cm. The latter was comparable to the corresponding dose penumbra of a conventional 6 MV 10 x 10 cm2 field. All together, helical beam delivery showed advantages over SST for tomotherapy beam delivery under similar delivery conditions.
使用计算机控制的体模定位仪、圆柱形体模和6兆伏X射线狭缝束进行了断层放射治疗束流传输的实验模拟。对连续螺旋束和序贯分段断层放射治疗（SST）束流传输都进行了评估。由于治疗床分度误差或射野宽度误差导致的束流衔接问题，给SST带来了严重的剂量均匀性扰动，而对于螺旋束流传输，该问题则被最小化。对螺旋束和SST束流传输进行了纵向呼吸运动的实验模拟。虽然运动减少了SST的剂量均匀性扰动，但对于螺旋束流传输，可能会引入剂量均匀性方面的小伪影。在典型的呼吸频率和幅度下，对于4转/分钟时宽度为2.0厘米的狭缝束，剂量均匀性扰动并不显著。采用螺旋束流传输时实施了一种运行启动/停止技术，以将20%-80%的纵向剂量下降从1.5厘米锐化至0.5厘米。后者与传统6兆伏10×10平方厘米射野相应的剂量半值层相当。总体而言，在类似的传输条件下，螺旋束流传输在断层放射治疗束流传输方面比SST显示出优势。
