Comparison of lumbar spine metastasis plans involving different stereotactic radiotherapy devices

We compare plans involving two different stereotactic radiotherapy devices: Cyberknife (CK) and Helical Tomotherapy (HTT) and their results on the lumbarvertebra targets. 

 Ten simulation tomographs of the first lumbar vertebra were selected from among the tomographies of patients who had previously undergone SBRT for any reason. In each planning tomography, two separate clinical target volumes (CTV) were drawn at the first lumbar vertebra, we used 2%, 95% and 98% doses of the target volume (D2, D95, D98) in the plan evaluation. The 2% dose of the planning target volume (PTV) was used for comparison with the hot spot; the 95% dose coverage of CTV was used for the target coverage comparison, and the 98% dose of the target volume was used for the dose volume histogram "shoulder" metric definitionTheHomogeneity Index (HI), new Conformity Index (nCI) and Gradient Index (GI) were evaluated for each planning system and target. 

 In both groups, CTV1 and CTV2, when compared with D95, the coverage for HTT was found statistically significantly higher. D98 was found to be statistically significantly higher with HTT. In both targets, the CKplans were found to have a higher hot area (D2), and inhomogeneous plans were obtained when compared to HTT. The NCI results were similar, and GI was higher with HTT. 

In lumbar vertebra stereotactic radiotherapy, more inhomogeneous plans were obtained with Cyberknife than with the Helical Tomotherapy device. A better gradient index was achieved with Cyberknife, while better coverage was achieved on the HTT plan.