Physics Institute, University of Zürich, Zürich, Switzerland; Department of Radiation Oncology, University Hospital Zürich, Zürich, Switzerland.
Department of Radiation Oncology, University Hospital Zürich, Zürich, Switzerland.
Int J Radiat Oncol Biol Phys. 2021 Sep 1;111(1):196-207. doi: 10.1016/j.ijrobp.2021.03.054. Epub 2021 Apr 20.
Proton therapy is a limited resource that is not available to all patients who may benefit from it. We investigated combined proton-photon treatments, in which some fractions are delivered with protons and the remaining fractions with photons, as an approach to maximize the benefit of limited proton therapy resources at a population level.
To quantify differences in normal-tissue complication probability (NTCP) between protons and photons, we considered a cohort of 45 patients with head and neck cancer for whom intensity modulated radiation therapy and intensity modulated proton therapy plans were previously created, in combination with NTCP models for xerostomia and dysphagia considered in the Netherlands for proton patient selection. Assuming limited availability of proton slots, we developed methods to optimally assign proton fractions in combined proton-photon treatments to minimize the average NTCP on a population level. The combined treatments were compared with patient selection strategies in which patients are assigned to single-modality proton or photon treatments.
There is a benefit of combined proton-photon treatments compared with patient selection, owing to the nonlinearity of NTCP functions; that is, the initial proton fractions are the most beneficial, whereas additional proton fractions have a decreasing benefit when a flatter part of the NTCP curve is reached. This effect was small for the patient cohort and NTCP models considered, but it may be larger if dose-response relationships are better known. In addition, when proton slots are limited, patient selection methods face a trade-off between leaving slots unused and blocking slots for future patients who may have a larger benefit. Combined proton-photon treatments with flexible proton slot assignment provide a method to make optimal use of all available resources.
Combined proton-photon treatments allow for better use of limited proton therapy resources. The benefit over patient selection schemes depends on the NTCP models and the dose differences between protons and photons.
质子治疗是一种有限的资源，并非所有可能从中受益的患者都能获得。我们研究了质子-光子联合治疗，其中一些分次采用质子治疗，其余分次采用光子治疗，作为一种在人群水平上最大限度地利用有限质子治疗资源的方法。
为了量化质子和光子之间正常组织并发症概率（NTCP）的差异，我们考虑了一组 45 名头颈部癌症患者，先前为这些患者制定了强度调制放射治疗和强度调制质子治疗计划，并结合了荷兰用于质子患者选择的口干和吞咽困难的 NTCP 模型。假设质子插槽的可用性有限，我们开发了方法来优化联合质子-光子治疗中的质子分次，以最大限度地降低人群水平上的平均 NTCP。将联合治疗与患者选择策略进行了比较，其中患者被分配到单一模式质子或光子治疗中。
与患者选择相比，联合质子-光子治疗具有优势，这是由于 NTCP 函数的非线性；也就是说，初始质子分次最有益，而当达到 NTCP 曲线较平坦的部分时，额外的质子分次的益处会逐渐减少。考虑到患者队列和 NTCP 模型，这种影响很小，但如果剂量-反应关系更明确，影响可能会更大。此外，当质子插槽有限时，患者选择方法面临着未使用插槽和为可能有更大获益的未来患者锁定插槽之间的权衡。具有灵活质子插槽分配的联合质子-光子治疗提供了一种优化利用所有可用资源的方法。
质子-光子联合治疗可以更好地利用有限的质子治疗资源。与患者选择方案相比，其优势取决于 NTCP 模型和质子与光子之间的剂量差异。
