Adaptation demand in proton beam therapy for head and neck tumour patients

头颈部恶性肿瘤分次放射治疗过程中，患者的解剖结构常发生较大的变化。由于质子束的范围可以受到组织变化的强烈影响，因此在没有定期伴随成像和合理的治疗计划适应的情况下进行质子治疗（PT）似乎对HNC患者至关重要。在能够建立适当的适应策略之前，需要估计标准分割PT期间对治疗计划适应的实际需求，由于仅针对常规光子治疗进行了全面的研究，因此仍然不确定（1）头颈部逐渐的解剖变化如何影响物理质子剂量分布，（2）考虑到整个治疗过程中的实际输送剂量，可以预期哪些生物后果，以及（3）是否存在必要的计划调整的指标或甚至某些时间间隔。在整个项目期间，需要从HNC患者的放射治疗过程中收集室内计算机断层扫描图像（CT）的数据库。将在初始临床描绘的CT图像上创建强度调制PT的治疗计划。将量化解剖结构变化及其对非适应性PT期间潜在剂量降解的影响。这些分析将考虑单次剂量以及总剂量分布，包括在估计的肿瘤控制和毒性概率方面的生物学评估。根据这些研究，应推导出治疗计划调整的适当时间点和潜在的一般和/或患者特异性指标。预期工作将使用治疗计划平台RayStation（RaySearch Laboratories AB，斯德哥尔摩瑞典）进行计算机模拟研究。将特别强调基于脚本的自动化，以使耗时的例行流程更快，更不易出错。这些脚本也将被要求减少时间和精力的一个可行的适应PT，这将被考虑在未来的研究中。关于适应需求的HNC患者在PT的分析结果将是进一步调查的基础上，例如，所需的控制CT的数量或强大的治疗计划的必要性和优势。此外，它们是德累斯顿质子治疗大学开发适应性PT实用概念的先决条件。

Considerable changes in patient's anatomy occur often during the course of fractionated radiotherapy of head-and-neck cancer (HNC). Since the range of proton beams can be strongly affected by tissue changes, the delivery of proton therapy (PT) without regular accompanying imaging and reasonable treatment plan adaptation seems to be critical for HNC patients. Before being able to establish appropriate adaptation strategies, the actual demand for treatment plan adaptation during standard-fractionated PT needs to be estimated.Since comprehensive investigations have been mainly performed for conventional photon therapy only, it is still uncertain(1) how the gradual anatomical changes in the head-and-neck region may affect the physical proton dose distribution,(2) which biological consequences can be expected considering the actually delivered dose during the whole treatment course and(3) whether there are indicators or even certain time intervals for a necessary plan adaptation.Consequently, the following objectives arise:A data pool of in-room computed tomography images (CTs), gathered from HNC patients during their radiotherapy treatment course, needs to be assembled throughout the project period. Treatment plans for intensity-modulated PT will be created on the initial, clinically delineated CT images. Anatomical changes and their impact on potential dose degradations during non-adapted PT will be quantified. These analyses will consider single fraction doses as well as the total dose distributions including their biological assessment in terms of estimated tumour control and toxicity probabilities. Based on these investigations, appropriate time points and potential general and/or patient-specific indicators for treatment plan adaptation shall be deduced.The envisaged work will be realized as in silico study using the treatment planning platform RayStation (RaySearch Laboratories AB, Stockholm Sweden). Particular emphasis will be placed on a script-bases automation to make time-consuming routine processes faster and less error-prone. Such scripts will also be required to reduce the time and effort of a practicable adapted PT which will be considered within future studies.The results of the analyses regarding the adaptation demand for HNC patients in PT will be the basis for further investigations concerning e.g. the amount of required control CTs or the necessity and advantage of robust treatment plans. Moreover, they are a prerequisite for the development of practicable concepts for adaptive PT at the UniversitätsProtonenTherapieDresden.