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

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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.