Department of Radiation Oncology, Stanford University, Stanford, California 94305, USA.
Med Phys. 2011 Jan;38(1):57-66. doi: 10.1118/1.3521465.
Radiation therapy with high dose rate and flattening filter-free (FFF) beams has the potential advantage of greatly reduced treatment time and out-of-field dose. Current inverse planning algorithms are, however, not customized for beams with nonuniform incident profiles and the resultant IMRT plans are often inefficient in delivery. The authors propose a total-variation regularization (TVR)-based formalism by taking the inherent shapes of incident beam profiles into account.
A novel TVR-based inverse planning formalism is established for IMRT with nonuniform beam profiles. The authors introduce a TVR term into the objective function, which encourages piecewise constant fluence in the nonuniform FFF fluence domain. The proposed algorithm is applied to lung and prostate and head and neck cases and its performance is evaluated by comparing the resulting plans to those obtained using a conventional beamlet-based optimization (BBO).
For the prostate case, the authors' algorithm produces acceptable dose distributions with only 21 segments, while the conventional BBO requires 114 segments. For the lung case and the head and neck case, the proposed method generates similar coverage of target volume and sparing of the organs-at-risk as compared to BBO, but with a markedly reduced segment number.
TVR-based optimization in nonflat beam domain provides an effective way to maximally leverage the technical capacity of radiation therapy with FFF fields. The technique can generate effective IMRT plans with improved dose delivery efficiency without significant deterioration of the dose distribution.
高剂量率和无均整过滤器（FFF）射束的放射治疗具有显著缩短治疗时间和减少射野外剂量的潜在优势。然而，目前的逆向计划算法并没有针对非均匀入射分布的射束进行定制，因此生成的调强放射治疗计划在实施时往往效率低下。作者提出了一种基于全变分正则化（TVR）的方法，该方法考虑了入射射束分布的固有形状。
建立了一种新的基于 TVR 的非均匀射束分布调强逆向计划形式。作者在目标函数中引入了 TVR 项，鼓励在非均匀 FFF 通量域中实现分段常数通量。将所提出的算法应用于肺部和前列腺以及头颈部病例，并通过比较生成的计划与使用传统的基于射束单元（BBO）优化的计划来评估其性能。
对于前列腺病例，作者的算法仅使用 21 个射束段即可产生可接受的剂量分布，而传统的 BBO 需要 114 个射束段。对于肺部病例和头颈部病例，与 BBO 相比，所提出的方法在靶区覆盖和危及器官保护方面产生了相似的结果，但射束段数量明显减少。
基于 TVR 的非平坦射束域优化为充分利用 FFF 射束的放射治疗技术能力提供了一种有效的方法。该技术可以生成有效的调强放射治疗计划，提高剂量输送效率，而不会显著恶化剂量分布。
