Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847, USA.
Med Phys. 2011 Sep;38(9):4912-9. doi: 10.1118/1.3618736.
To propose an alternative radiation therapy (RT) planning and delivery scheme with optimal angular beam sampling and intrabeam modulation for improved dose distribution while maintaining high delivery efficiency.
In the proposed approach, coined as dense angularly sampled and sparse intensity modulated RT (DASSIM-RT), a large number of beam angles are used to increase the angular sampling, leading to potentially more conformal dose distributions as compared to conventional IMRT. At the same time, intensity modulation of the incident beams is simplified to eliminate the dispensable segments, compensating the increase in delivery time caused by the increased number of beams and facilitating the plan delivery. In a sense, the proposed approach shifts and transforms, in an optimal fashion, some of the beam segments in conventional IMRT to the added beams. For newly available digital accelerators, the DASSIM-RT delivery can be made very efficient by concatenating the beams so that they can be delivered sequentially without operator's intervention. Different from VMAT, the level of intensity modulation in DASSIS-RT is field specific and optimized to meet the need of each beam direction. Three clinical cases (a head and neck (HN) case, a pancreas case, and a lung case) are used to evaluate the proposed RT scheme. DASSIM-RT, VMAT, and conventional IMRT plans are compared quantitatively in terms of the conformality index (CI) and delivery efficiency.
Plan quality improves generally with the number and intensity modulation of the incident beams. For a fixed number of beams or fixed level of intensity modulation, the improvement saturates after the intensity modulation or number of beams reaches to a certain level. An interplay between the two variables is observed and the saturation point depends on the values of both variables. For all the cases studied here, the CI of DASSIM-RT with 15 beams and 5 intensity levels (0.90, 0.79, and 0.84 for the HN, pancreas, and lung cases, respectively) is similar with that of conventional IMRT with seven beams and ten intensity levels (0.88, 0.79, and 0.83) and is higher than that of single-arc VMAT (0.75, 0.75, and 0.82). It is also found that the DASSIM-RT plans generally have better sparing of organs-at-risk than IMRT plans. It is estimated that the dose delivery time of DASSIM-RT with 15 beams and 5 intensity levels is about 4.5, 4.4, and 4.2 min for the HN, pancreas, and lung case, respectively, similar to that of IMRT plans with 7 beams and 10 intensity levels.
DASSIS-RT bridges the gap between IMRT and VMAT and allows optimal sampling of angular space and intrabeam modulation, thus it provides improved conformity in dose distributions while maintaining high delivery efficiency.
提出一种新的放射治疗（RT）计划和实施方案，采用最佳角度采样和射束内调制，在保持高效传输的同时提高剂量分布的适形性。
在我们提出的方法中，我们称之为密集角度采样和稀疏强度调制放射治疗（DASSIM-RT），使用大量的射束角度来增加角度采样，从而可以获得比传统调强放射治疗（IMRT）更适形的剂量分布。同时，简化入射射束的强度调制，消除不必要的射束段，补偿因射束数量增加而导致的传输时间增加，并促进计划传输。从某种意义上说，该方法以最优的方式转移和转换了传统调强放射治疗（IMRT）中的一些射束段。对于新的数字加速器，通过串联射束，可以非常有效地进行 DASSIM-RT 传输，而无需操作人员干预，这些射束可以顺序传输。与容积旋转调强（VMAT）不同，DASSIM-RT 的强度调制水平是特定于射野的，并经过优化以满足每个射束方向的需求。使用三个临床病例（头颈部（HN）病例、胰腺病例和肺部病例）来评估所提出的 RT 方案。从适形性指数（CI）和传输效率两个方面对 DASSIM-RT、VMAT 和传统 IMRT 计划进行了定量比较。
随着入射射束的数量和强度调制的增加，计划质量普遍得到改善。对于固定数量的射束或固定的强度调制水平，在强度调制或射束数量达到一定水平后，改善就会达到饱和。观察到两个变量之间的相互作用，而饱和点取决于两个变量的值。对于研究中的所有病例，具有 15 个射束和 5 个强度水平（HN、胰腺和肺部病例分别为 0.90、0.79 和 0.84）的 DASSIM-RT 的 CI 与具有 7 个射束和 10 个强度水平（0.88、0.79 和 0.83）的传统 IMRT 的 CI 相似，并且高于单弧 VMAT（0.75、0.75 和 0.82）。还发现 DASSIM-RT 计划通常比 IMRT 计划更好地保护危及器官。估计具有 15 个射束和 5 个强度水平的 DASSIM-RT 的剂量传输时间分别约为 HN、胰腺和肺部病例的 4.5、4.4 和 4.2 分钟，与具有 7 个射束和 10 个强度水平的 IMRT 计划相似。
DASSIM-RT 弥补了 IMRT 和 VMAT 之间的差距，并允许对角度空间进行最佳采样和射束内调制，从而在保持高效传输的同时提供更好的剂量分布适形性。
