Center of Molecular Imaging, Radiotherapy and Oncology (MIRO), Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain, Louvain-La-Neuve, Belgium.
Ion Beam Applications SA, Louvain-La-Neuve, Belgium.
Med Phys. 2023 Sep;50(9):5784-5792. doi: 10.1002/mp.16607. Epub 2023 Jul 13.
FLASH proton therapy has the potential to reduce side effects of conventional proton therapy by delivering a high dose of radiation in a very short period of time. However, significant progress is needed in the development of FLASH proton therapy. Increasing the dose rate while maintaining dose conformality may involve the use of advanced beam-shaping technologies and specialized equipment such as 3D patient-specific range modulators, to take advantage of the higher transmission efficiency at the highest energy available. The dose rate is an important factor in FLASH proton therapy, but its definition can vary because of the uneven distribution of the dose over time in pencil-beam scanning (PBS).
Highlight the distinctions, both in terms of concept and numerical values, of the various definitions that can be established for the dose rate in PBS proton therapy.
In an in silico study, five definitions of the dose rate, namely the PBS dose rate, the percentile dose rate, the maximum percentile dose rate, the average dose rate, and the dose averaged dose rate (DADR) were analyzed first through theoretical comparison, and then applied to a head and neck case. To carry out this study, a treatment plan utilizing a single energy level and requiring the use of a patient-specific range modulator was employed. The dose rate values were compared both locally and by means of dose rate volume histograms (DRVHs).
The PBS dose rate, the percentile dose rate, and the maximum percentile dose are definitions that are specifically designed to take into account the time structure of the delivery of a PBS treatment plan. Although they may appear similar, our study shows that they can vary locally by up to 10%. On the other hand, the DADR values were approximately twice as high as those of the PBS, percentile, and maximum percentile dose rates, since the DADR disregards the periods when a voxel does not receive any dose. Finally, the average dose rate can be defined in various ways, as discussed in this paper. The average dose rate is found to be lower by a factor of approximately 1/2 than the PBS, percentile, and maximum percentile dose rates.
We have shown that using different definitions for the dose rate in FLASH proton therapy can lead to variations in calculated values ranging from a few percent to a factor of two. Since the dose rate is a critical parameter in FLASH radiation therapy, it is essential to carefully consider the choice of definition. However, to make an informed decision, additional biological data and models are needed.
FLASH 质子治疗技术有望通过在极短的时间内提供高剂量的辐射来降低传统质子治疗的副作用。然而，FLASH 质子治疗技术的发展仍需要取得重大进展。为了在保持剂量适形性的同时提高剂量率，可能需要使用先进的射束成型技术和专用设备，如 3D 患者特异性射程调制器，以利用最高可用能量下更高的传输效率。剂量率是 FLASH 质子治疗中的一个重要因素，但由于在铅笔束扫描（PBS）中剂量随时间的不均匀分布，其定义可能会有所不同。
重点介绍在 PBS 质子治疗中可以为剂量率建立的各种定义在概念和数值上的区别。
在一项计算机研究中，通过理论比较，首先分析了 PBS 剂量率、百分位数剂量率、最大百分位数剂量率、平均剂量率和剂量平均剂量率（DADR）这 5 种剂量率定义，然后将其应用于一个头颈部病例。为了进行这项研究，使用了一个单一能级的治疗计划，需要使用患者特异性射程调制器。通过局部比较和剂量率体积直方图（DRVH）对剂量率值进行了比较。
PBS 剂量率、百分位数剂量率和最大百分位数剂量是专门用于考虑 PBS 治疗计划传递的时间结构的定义。尽管它们看起来可能相似，但我们的研究表明，它们在局部可能相差 10%。另一方面，DADR 值比 PBS、百分位数和最大百分位数剂量率高约两倍，因为 DADR 忽略了一个体素没有接收到任何剂量的时间段。最后，如本文所述，可以以各种方式定义平均剂量率。平均剂量率比 PBS、百分位数和最大百分位数剂量率低约 1/2。
我们已经表明，在 FLASH 质子治疗中使用不同的剂量率定义会导致计算值的变化，从百分之几到两倍不等。由于剂量率是 FLASH 放射治疗中的一个关键参数，因此必须仔细考虑定义的选择。然而，为了做出明智的决策，还需要额外的生物学数据和模型。
