A framework for defining FLASH dose rate for pencil beam scanning.
A framework for defining FLASH dose rate for pencil beam scanning.
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DOI：
10.1002/mp.14456
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发表时间：
2020-12
期刊：
影响因子：
3.8
通讯作者：
Ling CC
中科院分区：
文献类型：
--
作者：
Folkerts MM;Abel E;Busold S;Perez JR;Krishnamurthi V;Ling CC
开发一种方法(a)计算使用铅笔束扫描（PBS）传递的质子场内体素的剂量率，以及(b)报告PBS治疗场的代表性剂量率，使多种治疗方式之间能够对应。该方法考虑了PBS FLASH放射治疗独特的时空传递模式。PBS辐射场中每个体素的剂量率近似于该体素的剂量和“有效”照射时间的商。每个体素的“有效”照射时间开始于累积剂量超过选定的阈值时，并在其累积剂量达到其总剂量减去相同阈值时停止。上述计算产生PBS治疗场内所述体素的剂量率分布。为了报告PBS场的代表性剂量率，我们提出了一个用户可选择的剂量率分布的第p个百分位数参数，这样（100−p） %的场高于相应的剂量率。为了证明上述方法，我们设计了250 MeV质子的FLASH传输场，并在二维（2D）和三维（3D）模型中计算了PBS的剂量率分布。为了进一步评估形式主义，我们提供了一个临床PBS治疗领域的例子。利用二维PBS传输场，证明了在一个体素上累积总剂量的时间被限制为整个场传递时间的一小部分。此外，场内剂量和剂量率的空间分布也有较大差异。对于10 × 10 cm2的PBS场照射三维水影，在10 cm深度的规定剂量10 Gy在1.0 s内释放。由于库仑散射使光束光斑尺寸增大，辐照体积中的剂量率随深度的增加而减小（直到布拉格峰）。例如，在0 - 10 cm深度之间，95%的辐照体积接收> - 40 Gy/s，而在0 - 20 cm和0 - 30 cm深度之间，95%的辐照体积分别接收>36 Gy/s和>24 Gy/s。对于临床PBS治疗领域，扫描模式符合PTV。PBS剂量率数据显示PTV和邻近正常器官。我们开发了一种计算PBS质子场剂量率分布的方法，并推荐了报告PBS治疗剂量率的命名法。我们认为，标准化PBS治疗剂量率的计算和报告方法，以与其他治疗方式相对应的方式，将推动PBS FLASH放疗的研究和潜在应用。
To develop a method of (a) calculating the dose rate of voxels within a proton field delivered using pencil beam scanning (PBS), and (b) reporting a representative dose rate for the PBS treatment field that enables correspondence between multiple treatment modalities. This method takes into account the unique spatiotemporal delivery patterns of PBS FLASH radiotherapy. The dose rate at each voxel of a PBS radiation field is approximately the quotient of the voxel’s dose and “effective” irradiation time. Each voxel’s “effective” irradiation time starts when the cumulative dose rises above a chosen threshold value, and stops when its cumulative dose reaches its total dose minus the same threshold value. The above calculation yields a distribution of dose rates for the voxels within a PBS treatment field. To report a representative dose rate for the PBS field, we propose a user‐selectable parameter of pth percentile of the dose rate distribution, such that (100 − p) % of the field is above the corresponding dose rate. To demonstrate the method described above, we design FLASH transmission fields using 250 MeV protons and calculate the PBS dose rate distributions in both two‐dimensional (2D) and three‐dimensional (3D) models. To further evaluate the formalism, we provide an example of a clinical PBS treatment field. With the 2D PBS transmission field, it is demonstrated that the time to accumulate the total dose at a voxel is limited to a fraction of the delivery time of the entire field. In addition, the spatial distributions of dose and dose rate are quite different within the field. For the 10 × 10 cm2 PBS field irradiating a 3D water phantom, the prescribed dose of 10 Gy at 10 cm depth is delivered in 1.0 s. The dose rate decreases in the irradiated volume with increasing depth (until the Bragg peak) due to increase of beam spot size by Coulomb scattering. For example, 95% of the irradiated volume between 0 and 10 cm depth receive >40 Gy/s, whereas between 0–20 cm and 0–30 cm depth, 95% of the irradiated volume received >36 Gy/s and >24 Gy/s, respectively. For the clinical PBS treatment field, the scanning pattern conforms to the PTV. PBS dose rate data are presented for the PTV and adjacent normal organs. We have developed a method of calculating the dose rate distribution of a PBS proton field and have recommended nomenclature for reporting PBS treatment dose rate. We believe that standardizing the method for calculating and reporting PBS treatment dose rates, in a manner that corresponds with other treatment modalities, will advance the research and potential application of PBS FLASH radiotherapy.
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影响因子：
5.7
作者：
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