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Online and offline treatment plan adaptation (here defined as Adaptive Particle Therapy, APT) and intrafraction real-time respiratory motion management (RRMM) allow to account for anatomical changes and variations, resulting in more conformal target coverage and better sparing of organs at risk (OAR). Based on the POP-ART RT questionnaire*, the Patterns Of Practice for Adaptive and Real-Time Particle Therapy (POP-ART PT) questionnaire aims to determine the status of APT and RRMM implementation worldwide. Here we focus on APT for interfractional anatomical changes in European centers.

An institutional questionnaire was sent to particle therapy centers worldwide to determine the current extent of APT implementation in clinical practice. 25 European particle therapy centers as recorded by Particle Therapy Co-Operative Group were targeted. Respondents were asked if and which type of APT was used for selected treatment sites and details about the implemented workflow. Additionally, questions regarding the barriers to implementation and wishes for the future were addressed.

Here we present the results for 23 European particle therapy centers (13 countries), representing a 92% response rate for Europe (25 centers approached). All responding centers except one use APT for at least one treatment site with head and neck dominating. Other sites are shown in Table 1. Ad-hoc offline adaptation was the most prevalent and no center used online APT (plan libraries or daily adaptation). The plan adaptation was in all cases motivated by both, target and OAR dose considerations. Reasons for adaptation are presented in Figure 1.

Three of 23 centers are satisfied with their implemented adaptive workflows but would like to increase the number of treatment sites treated with APT. All other centers (20/23) would like to improve APT workflow for a treatment site already treated with APT and 13 of those centers would like to introduce APT to a new treatment site. One center explicitly stated that they would like to introduce an online adaptive workflow, first applied to skull base patients. Another center explicitly stated the aim to improve adaptive workflow efficiency. Other centers did not specify the type of improvement they wish for.  The main barriers for implementation of APT are presented in Figure 2. The biggest issues were the lack of integrated and efficient workflows and the lack of human resources.

96% of responding centers use offline APT for at least one tumor site. 70 % of centers would like to use APT for at least one additional site. Currently, no center uses online APT as efficient integrated workflows are missing. More research and development for integrated and efficient workflow is needed to bring it to clinical practice.  

Acknowledgement: The authors would like to thank all particle therapy centers that have answered the questionnaire.

* Bertholet & Anastasi, RO 2020