Trager Michael, Salama Joseph, Yin Fang-Fang, Adamson Justus
Medical Physics Graduate Program, Duke University, Durham, North Carolina 27708, USA.
Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27708, USA.
J Radiosurg SBRT. 2017;4(4):265-273.
We address the challenges associated with applying a single isocenter treatment technique to extracranial oligometastases.
We propose a technique that uses a Single Isocenter with Distinct Optimizations (SIDO) in which all Volumetric Modulated Arc Therapy (VMAT) fields share an isocenter but each field treats only one target. When necessary, setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, and interplay is minimized using dynamic conformal arcs (DCA) as the starting point for inverse optimization. Using CBCTs from eleven previous SBRT cases we determined the likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties. We also compared SIDO and SIDO with DCA to single (VMAT) and dual (VMAT and DCA) isocenter plans for phantom (N=11) and patient (N=4) cases.
Spatial uncertainties from inter-fractional rotations were greatest for large target separation and small margins, with ~30% of fractions requiring a correction (3mm margin and 10cm separation). SIDO with DCA greatly decreased arc modulation, with approximately 20% more modulation than DCA, and similar conformity to conventional VMAT. SIDO and SIDO with DCA had comparable conformity to single and dual isocenter plans when separation between PTVs is >3cm, while traditional single isocenter VMAT had superior conformity for <3cm. SIDO with DCA had superior GI over other planning techniques for almost all cases.
SIDO for extracranial oligometastases allows flexibility to mitigate spatial uncertainties from rotation and deformation, and has comparable dosimetry to traditional VMAT with low modulation when inverse optimization begins with DCA.
我们探讨将单一等中心治疗技术应用于颅外寡转移瘤所面临的挑战。
我们提出一种使用具有不同优化的单一等中心（SIDO）的技术，其中所有容积调强弧形治疗（VMAT）射野共享一个等中心，但每个射野仅治疗一个靶区。必要时，通过在VMAT弧形射野之间应用治疗床平移来减轻旋转和变形引起的摆位不确定性，并使用动态适形弧形射野（DCA）作为逆向优化的起点来最小化相互作用。利用之前11例立体定向体部放疗（SBRT）病例的CBCT，我们确定了在SIDO弧形射野之间需要平移以校正旋转不确定性的可能性。我们还将SIDO以及结合DCA的SIDO与用于体模（N = 11）和患者（N = 4）病例的单（VMAT）等中心和双（VMAT和DCA）等中心计划进行了比较。
对于大的靶区间距和小的边界，分次间旋转引起的空间不确定性最大，约30%的分次需要校正（边界3mm，间距10cm）。结合DCA的SIDO大大降低了弧形射野调制，比DCA多约20%的调制，并且与传统VMAT具有相似的适形性。当计划靶体积（PTV）之间的间距>3cm时，SIDO以及结合DCA的SIDO与单等中心和双等中心计划具有相当的适形性，而传统的单等中心VMAT在<3cm时具有更好的适形性。在几乎所有病例中，结合DCA的SIDO比其他计划技术具有更好的胃肠道（GI）剂量分布。
用于颅外寡转移瘤的SIDO允许灵活减轻旋转和变形引起的空间不确定性，并且当逆向优化从DCA开始时，其剂量学与低调制的传统VMAT相当。
