Yoon Kyoung Jun, Cho Byungchul, Kwak Jung Won, Lee Doheui, Kwon Do Hoon, Ahn Seung Do, Lee Sang-Wook, Kim Chang Jin, Roh Sung Woo, Cho Young Hyun
Radiosurgery Center, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
J Korean Neurosurg Soc. 2018 Nov;61(6):753-760. doi: 10.3340/jkns.2018.0075. Epub 2018 Oct 30.
We investigated the effect of optimization in dose-limiting shell method on the dosimetric quality of CyberKnife (CK) plans in treating brain metastases (BMs).
We selected 19 BMs previously treated using CK between 2014 and 2015. The original CK plans (CKoriginal) had been produced using 1 to 3 dose-limiting shells : one at the prescription isodose level (PIDL) for dose conformity and the others at lowisodose levels (10-30% of prescription dose) for dose spillage. In each case, a modified CK plan (CKmodified) was generated using 5 dose-limiting shells : one at the PIDL, another at intermediate isodose level (50% of prescription dose) for steeper dose fall-off, and the others at low-isodose levels, with an optimized shell-dilation size based on our experience. A Gamma Knife (GK) plan was also produced using the original contour set. Thus, three data sets of dosimetric parameters were generated and compared.
There were no differences in the conformity indices among the CKoriginal, CKmodified, and GK plans (mean 1.22, 1.18, and 1.24, respectively; p=0.079) and tumor coverage (mean 99.5%, 99.5%, and 99.4%, respectively; p=0.177), whereas the CKmodified plans produced significantly smaller normal tissue volumes receiving 50% of prescription dose than those produced by the CKoriginal plans (p<0.001), with no statistical differences in those volumes compared with GK plans (p=0.345).
These results indicate that significantly steeper dose fall-off is able to be achieved in the CK system by optimizing the shell function while maintaining high conformity of dose to tumor.
我们研究了剂量限制壳层法优化对射波刀（CK）治疗脑转移瘤（BMs）计划剂量学质量的影响。
我们选取了2014年至2015年间先前接受CK治疗的19例BMs。原始的CK计划（CKoriginal）使用1至3个剂量限制壳层生成：一个位于处方等剂量水平（PIDL）以保证剂量适形，其他位于低等剂量水平（处方剂量的10 - 30%）以防止剂量溢出。在每种情况下，使用5个剂量限制壳层生成改良的CK计划（CKmodified）：一个位于PIDL，另一个位于中间等剂量水平（处方剂量的50%）以实现更陡峭的剂量下降，其他位于低等剂量水平，并根据我们的经验优化壳层扩张尺寸。还使用原始轮廓集生成了伽玛刀（GK）计划。因此，生成并比较了三组剂量学参数数据集。
CKoriginal、CKmodified和GK计划之间的适形指数（分别为均值1.22、1.18和1.24；p = 0.079）和肿瘤覆盖率（分别为均值99.5%、99.5%和99.4%；p = 0.177）没有差异，而CKmodified计划产生的接受50%处方剂量的正常组织体积明显小于CKoriginal计划（p < 0.001），与GK计划相比，这些体积没有统计学差异（p = 0.345）。
这些结果表明，通过优化壳层功能，在射波刀系统中能够实现明显更陡峭的剂量下降，同时保持对肿瘤的高剂量适形性。
