Mihailidis D, Harmon M, Whaley L, Raja P, Kagadis G
Charleston Radiation Therapy Cons, Charleston, WV.
University of Patras, Greece.
Med Phys. 2012 Jun;39(6Part17):3811. doi: 10.1118/1.4735552.
This study shows that there is no clear dosimetric benefit of biological-based optimization for either fixed-beam IMRT or VMAT. Other than shorter delivery times, even VMAT does not offer additional advantage to fixed-beam IMRT.
A small number of patients for lung, pancreas, spine and brain CA were planned with fixed-beam IMRT, optimized with (gEUD) and without (DV) biological objectives and, also planned for VMAT with and without gEUD, for comparison. For the lung and brain cases, a non-coplanar 7-11 beam arrangement was used for fixed- beam IMRT and a coplanar 'hybrid' arc simulated VMAT with beams set every 5° spacing. For the other treatment sites, all beams were coplanar. For each case, the fixed-beam IMRT and VMAT plans were optimized with the same objectives. It is important to note that, only 2 segments/beam were allowed for each plan, in order to create small fluence modulation, appropriate for small target volumes during SBRT.
For all plans we noticed that there were minor or no dosimetric differences between fixed- beam IMRT and VMAT, whether DV or gEUD objectives were used or whether fixed-beam IMRT or VMAT is used. Keeping the level of beam modulation as-low-as possible, for small SBRT targets, one can show that VMAT with or without gEUD optimization does not offer any dosimetric advantage against fixed-beam IMRT with multiple non-coplanar beams. This is against the expectation that gEUD-optimization can Result superior plans than DV-optimization. The difference is that, for small target volumes like those encountered in SBRT, the complexity of the fluence is not as high as in large field intensity modulated cases.
The fact that VMAT with or without gEUD can produce as good plans as fixed-IMRT does not make VMAT a preferred treatment modality, other than the fact that requires reduced treatment time.
本研究表明，对于固定束调强放疗（IMRT）或容积调强弧形放疗（VMAT），基于生物学的优化在剂量学方面并无明显益处。除了治疗时间更短外，即使是VMAT相较于固定束IMRT也没有额外优势。
选取少量肺癌、胰腺癌、脊柱癌和脑癌患者，分别采用固定束IMRT进行计划，分别使用（广义等效均匀剂量，gEUD）和不使用（剂量体积，DV）生物学目标进行优化；同时也对VMAT进行计划，分别采用和不采用gEUD，以作比较。对于肺癌和脑癌病例，固定束IMRT采用非共面7 - 11野排列，VMAT采用共面“混合”弧形模拟，束间间隔5°。对于其他治疗部位，所有射野均为共面。对于每个病例，固定束IMRT和VMAT计划采用相同目标进行优化。需要注意的是，为了在立体定向体部放疗（SBRT）期间针对小靶体积产生小的注量调制，每个计划仅允许2个射野分段。
对于所有计划，我们注意到，无论使用DV还是gEUD目标，也无论使用固定束IMRT还是VMAT，固定束IMRT和VMAT之间在剂量学上的差异很小或不存在。对于小的SBRT靶区，将射野调制水平尽可能保持在低水平，可以看出，无论有无gEUD优化，VMAT相对于多非共面束固定束IMRT在剂量学上均无优势。这与gEUD优化能产生比DV优化更好计划的预期相悖。不同之处在于，对于SBRT中遇到的小靶体积，注量的复杂性不像大野调强病例那样高。
无论有无gEUD，VMAT都能产生与固定束IMRT一样好的计划，但这一事实并未使VMAT成为首选治疗方式，除了其所需治疗时间较短这一事实外。
