Liu Huan, Ye Jingjing, Kim John J, Deng Jun, Kaur Monica S, Chen Zhe Jay
Department of Therapeutic Radiology, Yale-New Haven Hospital and Yale School of Medicine, New Haven, CT.
Department of Therapeutic Radiology, Yale-New Haven Hospital and Yale School of Medicine, New Haven, CT.
Med Dosim. 2015 Spring;40(1):76-81. doi: 10.1016/j.meddos.2014.10.004. Epub 2014 Dec 10.
To compare the dosimetric and delivery characteristics of two arc-based stereotactic body radiotherapy (SBRT) techniques for early-stage lung cancer treatment. SBRT treatment plans for lung tumors of different sizes and locations were designed using a single-isocenter multisegment dynamic conformal arc technique (SiMs-arc) and a volumetric modulated arc therapy technique (RapidArc) for 5 representative patients treated previously with lung SBRT. The SiMs-arc plans were generated with the isocenter located in the geometric center of patient׳s axial plane (which allows for collision-free gantry rotation around the patient) and 6 contiguous 60° arc segments spanning from 1° to 359°. 2 RapidArc plans, one using the same arc geometry as the SiMs-arc and the other using typical partial arcs (210°) with the isocenter inside planning target volume (PTV), were generated for each corresponding SiMs-arc plan. All plans were generated using the Varian Eclipse treatment planning system (V10.0) and were normalized with PTV V100 to 95%. PTV coverage, dose to organs at risk, and total monitor units (MUs) were then compared and analyzed. For PTV coverage, the RapidArc plans generally produced higher PTV D99 (by 1.0% to 3.3%) and higher minimum dose (by 2.7% to 12.7%), better PTV conformality index (by 1% to 8%), and less volume of 50% dose outside 2cm from PTV (by 0 to 20.8cm(3)) than the corresponding SiMs-arc plans. For normal tissues, no significant dose differences were observed for the lungs, trachea, chest wall, and heart; RapidArc using partial arcs produced lowest maximum dose to spinal cord. For dose delivery, the RapidArc plans typically required 50% to 90% more MUs than SiMs-arc plans to deliver the same prescribed dose. The additional intensity modulation afforded by variable gantry speed and dose rate and by overlapping arcs enabled RapidArc plans to produce dosimetrically improved plans for lung SBRT, but required more MUs (by a factor > 1.5) to deliver. The dosimetric improvements, most notably in PTV minimum dose and in dose conformality for irregularly shaped PTVs, may outweigh the increased MUs in using RapidArc. For small and peripherally located tumors, SiMs-arc produces comparable dosimetric quality and could be more efficient in both treatment planning and dose delivery.
比较两种基于弧形的立体定向体部放射治疗（SBRT）技术在早期肺癌治疗中的剂量学和剂量传递特征。使用单等中心多段动态适形弧形技术（SiMs-arc）和容积调强弧形治疗技术（RapidArc），为5例先前接受过肺部SBRT治疗的代表性患者设计不同大小和位置的肺部肿瘤SBRT治疗计划。SiMs-arc计划的等中心位于患者轴向平面的几何中心（这允许机架围绕患者无碰撞旋转），6个连续的60°弧形段，范围从1°到359°。针对每个相应的SiMs-arc计划，生成2个RapidArc计划，一个使用与SiMs-arc相同的弧形几何形状，另一个使用典型的部分弧形（210°），等中心位于计划靶体积（PTV）内。所有计划均使用瓦里安Eclipse治疗计划系统（V10.0）生成，并将PTV V100归一化至95%。然后比较并分析PTV覆盖率、危及器官的剂量和总监测单位（MU）。对于PTV覆盖率，RapidArc计划通常产生更高的PTV D99（高1.0%至3.3%）和更高的最小剂量（高2.7%至12.7%），更好的PTV适形指数（高1%至8%），以及PTV外2cm处50%剂量的体积更小（小0至20.8cm³），比相应的SiMs-arc计划。对于正常组织，在肺、气管、胸壁和心脏方面未观察到显著的剂量差异；使用部分弧形的RapidArc对脊髓产生的最大剂量最低。对于剂量传递，RapidArc计划通常比SiMs-arc计划需要多50%至90%的MU来传递相同的处方剂量。可变机架速度和剂量率以及重叠弧形提供的额外强度调制使RapidArc计划能够为肺部SBRT产生剂量学上改进的计划，但传递需要更多的MU（系数>1.5）。剂量学上的改进，最显著的是在PTV最小剂量和不规则形状PTV的剂量适形性方面，可能超过使用RapidArc时增加的MU。对于小的和位于周边的肿瘤，SiMs-arc产生可比的剂量学质量，并且在治疗计划和剂量传递方面可能更有效。
