Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, 30 Fruit Street, Boston, MA 02114, United States of America. Department of Radiation Therapy, Radiologie Vechta, Marienstraße 13, 49377 Vechta, Germany. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Jan 16;63(2):025023. doi: 10.1088/1361-6560/aaa36d.
We introduce a new method called NoVo (Noncoplanar VMAT Optimization) to produce volumetric modulated arc therapy (VMAT) treatment plans with noncoplanar trajectories. While the use of noncoplanar beam arrangements for intensity modulated radiation therapy (IMRT), and in particular high fraction stereotactic radiosurgery (SRS), is common, noncoplanar beam trajectories for VMAT are less common as the availability of treatment machines handling these is limited. For both IMRT and VMAT, the beam angle selection problem is highly nonconvex in nature, which is why automated beam angle selection procedures have not entered mainstream clinical usage. NoVo determines a noncoplanar VMAT solution (i.e. the simultaneous trajectories of the gantry and the couch) by first computing a [Formula: see text] solution (beams from every possible direction, suitably discretized) and then eliminating beams by examing fluence contributions. Also all beam angles are scored via geometrical considerations only to find out the usefulness of the whole beam space in a very short time. A custom path finding algorithm is applied to find an optimized, continuous trajectory through the most promising beam angles using the calculated score of the beam space. Finally, using this trajectory a VMAT plan is optimized. For three clinical cases, a lung, brain, and liver case, we compare NoVo to the ideal [Formula: see text] solution, nine beam noncoplanar IMRT, coplanar VMAT, and a recently published noncoplanar VMAT algorithm. NoVo comes closest to the [Formula: see text] solution considering the lung case (brain and liver case: second), as well as improving the solution time by using geometrical considerations, followed by a time effective iterative process reducing the [Formula: see text] solution. Compared to a recently published noncoplanar VMAT algorithm, using NoVo the computation time is reduced by a factor of 2-3 (depending on the case). Compared to coplanar VMAT, NoVo reduces the objective function value by 24%, 49% and 6% for the lung, brain and liver cases, respectively.
我们引入了一种名为 NoVo（非共面 VMAT 优化）的新方法，用于生成具有非共面轨迹的容积调制弧形治疗（VMAT）治疗计划。虽然非共面射束排列用于强度调制放射治疗（IMRT），特别是高分割立体定向放射外科（SRS），但对于 VMAT，非共面射束轨迹则不常见，因为能够处理这些射束的治疗机器的可用性有限。对于 IMRT 和 VMAT，射束角度选择问题本质上是高度非凸的，这就是为什么自动化射束角度选择程序尚未进入主流临床应用的原因。NoVo 通过首先计算[Formula: see text]解决方案（来自每个可能方向的射束，适当离散化），然后通过检查通量贡献来消除射束，来确定非共面 VMAT 解决方案（即机架和治疗床的同时轨迹）。此外，所有射束角度都仅通过几何考虑进行评分，以在很短的时间内了解整个射束空间的有用性。应用自定义路径查找算法，通过使用计算出的射束空间得分，找到最有前途的射束角度的优化、连续轨迹。最后，使用此轨迹优化 VMAT 计划。对于三个临床病例，肺、脑和肝病例，我们将 NoVo 与理想的[Formula: see text]解决方案、九个非共面 IMRT 射束、共面 VMAT 和最近发表的非共面 VMAT 算法进行了比较。就肺病例而言（脑和肝病例：第二），NoVo 最接近[Formula: see text]解决方案，并且通过使用几何考虑提高了解决方案的时间效率，然后通过有效的迭代过程减少了[Formula: see text]解决方案。与最近发表的非共面 VMAT 算法相比，使用 NoVo 可以将计算时间减少 2-3 倍（具体取决于病例）。与共面 VMAT 相比，NoVo 分别将肺、脑和肝病例的目标函数值降低了 24%、49%和 6%。
