Xu Qianyi, Kubicek Gregory, Mulvihill David, Eastwick Gary, Goldman Howard, Turtz Alan R, Fan Jiajin, Luo Dershan
Radiation Oncology, MD Anderson Cancer Center at Cooper, Mount Laurel, USA.
Radiation Oncology, Cooper University Hospital, Camden, USA.
Cureus. 2020 Aug 6;12(8):e9585. doi: 10.7759/cureus.9585.
Purpose We proposed a planning strategy that utilized tuning targets to guide GammaKnife (GK) Inverse Planning (IP) to deliver higher dose to the tumor, while keeping acceptable dose to the abutting organ at risk (OAR). Methods Ten patients with a large portion of brain tumor abutting the OAR previously treated with GK stereotactic radiosurgery (SRS) were selected. For each patient, multiple tuning targets were created by cropping the target contour from three-dimensional (3D) expansions of the OAR. The number of the tuning targets depended on the complexity of the planning process. To demonstrate dose sparing effect, an IP plan was generated for each tuning target after one round of optimization without shot fine-tuning. In the dose enhancement study, a more aggressive target dose was prescribed to the tuning target with a larger margin and one to two shots were filled in the region with missing dose. The resulting plans were compared to the previously approved clinical plans. Results For all 10 patients, a dose sparing effect was observed, i.e. both target coverage and dose to the OARs decreased when the margins of 3D expansion increased. For one patient, a margin of 6 mm was needed to decrease the maximum dose to the optical chiasm and optical nerve by 44.3% and 28.4%, respectively. For the other nine patients, the mean dropping rate of V12Gyto brain stem were 28.2% and 59.5% for tuning targets of 1 and 2 mm margins, respectively. In the dose enhancement study, the tuning-target-guided plans were hotter than the approved treatment plans, while keeping similar dose to the OARs. The mean of the treatment and enhancement dose was 15.6 ± 2.2 Gy and 18.5 ± 3.2 Gy, respectively. The mean coverage of the target by prescription dose was slightly higher in the enhancement plans (96.9 ± 2.6% vs 96.3 ± 3.6%), whereas the mean coverage of the enhancement dose was 20.1% higher in the enhancement plans (89.6 ± 9.0% vs 74.6 ± 19.9%). Conclusions We demonstrated that an inverse planning strategy could facilitate target dose enhancement for challenging GK cases while keeping acceptable OAR dose.
目的 我们提出了一种计划策略，该策略利用调谐靶点来指导伽玛刀（GK）逆向计划（IP），在使危及器官（OAR）接受可接受剂量的同时，向肿瘤输送更高剂量。方法 选择10例先前接受GK立体定向放射外科治疗（SRS）且大部分脑肿瘤毗邻OAR的患者。对于每位患者，通过从OAR的三维（3D）扩展中裁剪靶区轮廓来创建多个调谐靶点。调谐靶点的数量取决于计划过程的复杂性。为了证明剂量 sparing 效应，在一轮优化后且未进行射野微调的情况下，为每个调谐靶点生成一个IP计划。在剂量增强研究中，对具有较大边界的调谐靶点规定更高的靶区剂量，并在剂量缺失区域填充一到两个射野。将所得计划与先前批准的临床计划进行比较。结果 对于所有10例患者，均观察到剂量 sparing 效应，即当3D扩展边界增加时，靶区覆盖度和OAR所接受的剂量均降低。对于1例患者，需要6mm的边界才能分别将视交叉和视神经的最大剂量降低44.3%和28.4%。对于其他9例患者，对于边界为1mm和2mm的调谐靶点，脑干的V12Gy平均下降率分别为28.2%和59.5%。在剂量增强研究中，调谐靶点引导的计划比批准的治疗计划剂量更高，同时OAR所接受的剂量相似。治疗剂量和增强剂量的平均值分别为15.6±2.2Gy和18.5±3.2Gy。在增强计划中，处方剂量对靶区的平均覆盖度略高（96.9±2.6%对96.3±3.6%），而增强剂量的平均覆盖度在增强计划中高20.1%（89.6±9.0%对74.6±19.9%）。结论 我们证明了一种逆向计划策略可以在保持OAR剂量可接受的同时，促进具有挑战性的GK病例的靶区剂量增强。
