Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, USA.
RaySearch Laboratories AB, Stockholm, Sweden.
Med Phys. 2024 Oct;51(10):7047-7056. doi: 10.1002/mp.17307. Epub 2024 Jul 15.
Proton spatially fractionated RT (SFRT) can potentially synergize the unique advantages of using proton Bragg peak and SFRT peak-valley dose ratio (PVDR) to reduce the radiation-induced damage for normal tissues. Uniform-target-dose (UTD) proton GRID is a proton SFRT modality that can be clinically desirable and conveniently adopted since its UTD resembles target dose distribution in conventional proton RT (CONV). However, UTD proton GRID is not used clinically, which is likely due to the lack of an effective treatment planning method.
This work will develop a novel treatment planning method using scissor beams (SB) for UTD proton GRID, with the joint optimization of PVDR and dose objectives.
The SB method for spatial dose modulation in normal tissues with UTD has two steps: (1) a primary beam (PB) is halved with interleaved beamlets, to generate spatial dose modulation in normal tissues; (2) a complementary beam (CB) is added to fill in previously valley-dose positions in the target to generate UTD, while the CB is angled slightly from the PB, to maintain spatial dose modulation in normal tissues. A treatment planning method with PVDR optimization via the joint total variation and L1 (TVL1) regularization is developed to jointly optimize PVDR and dose objectives. The plan optimization solution is obtained using an iterative convex relaxation algorithm.
The new methods SB and SB-TVL1 were validated in comparison with CONV. Compared to CONV of relatively homogeneous dose distribution, SB had modulated spatial dose pattern in normal tissues with UTD and comparable plan quality. Compared to SB, SB-TVL1 further maximized PVDR, with comparable dose-volume parameters.
A novel SB method is proposed that can generate modulated spatial dose pattern in normal tissues to achieve UTD proton GRID. A treatment planning method with PVDR optimization capability via TVL1 regularization is developed that can jointly optimize PVDR and dose objectives for proton GRID.
质子空间分割调强放疗（SFRT）有可能利用质子布拉格峰和 SFRT 峰谷剂量比（PVDR）的独特优势协同作用，降低正常组织的辐射损伤。均匀靶区剂量（UTD）质子 GRID 是一种质子 SFRT 模式，由于其 UTD 类似于常规质子放疗（CONV）中的靶区剂量分布，因此在临床上是理想的，并且可以方便地采用。然而，UTD 质子 GRID 尚未在临床上使用，这可能是由于缺乏有效的治疗计划方法。
本研究旨在开发一种新的治疗计划方法，使用剪刀束（SB）进行 UTD 质子 GRID，联合优化 PVDR 和剂量目标。
用于具有 UTD 的正常组织空间剂量调制的 SB 方法有两个步骤：（1）通过交错的射束将主射束（PB）减半，以在正常组织中产生空间剂量调制；（2）添加互补射束（CB）以填充靶区中先前的谷剂量位置，从而产生 UTD，同时 CB 从 PB 略微倾斜，以维持正常组织中的空间剂量调制。通过联合全变分和 L1（TVL1）正则化的 PVDR 优化开发了一种治疗计划方法，以联合优化 PVDR 和剂量目标。使用迭代凸松弛算法获得计划优化解。
与 CONV 相比，对新方法 SB 和 SB-TVL1 进行了验证。与相对均匀剂量分布的 CONV 相比，SB 在具有 UTD 的正常组织中调制了空间剂量模式，并且具有可比的计划质量。与 SB 相比，SB-TVL1 进一步最大化了 PVDR，同时具有可比的剂量-体积参数。
提出了一种新的 SB 方法，该方法可以在正常组织中产生调制的空间剂量模式，从而实现 UTD 质子 GRID。开发了一种具有通过 TVL1 正则化的 PVDR 优化能力的治疗计划方法，该方法可以联合优化质子 GRID 的 PVDR 和剂量目标。
