ESTRO 2021 Abstract Book

S349

ESTRO 2021

plan’s quality using a number of qualitative and/or quantitative measures. The concept of plan quality can, however, encompass many different characteristics of the treatment plan and there is no global consensus on how exactly to define, measure, and report plan quality. For this reason, the 3rd Physics ESTRO Workshop held in Budapest in October 2019 included a track on ‘Plan quality assessment’. This presentation is based on the contents discussed during that Workshop and addresses different aspects that affect the quality of treatment plans: dose metrics, plan robustness, and plan complexity. We understand plan quality in radiotherapy as the clinical suitability of the delivered dose distribution that can be realistically expected from a treatment plan. Plan quality is commonly assessed by evaluating the dose distribution calculated by the treatment planning system (TPS). Evaluating the 3D dose distribution is not easy, however; dose-volume histograms do not take into account spatial information and it is hard to fully evaluate the spatial characteristics of the dose distribution. Furthermore, we still lack the knowledge for personalising the prediction of the clinical outcome based on individual patient characteristics. This advocates for standardisation and systematic collection of clinical data and outcomes after radiotherapy. Additionally, the calculated dose distribution is not exactly the dose delivered to the patient due to uncertainties in the dose calculation and the treatment delivery, including variations in the patient set-up and anatomy. Consequently, plan quality also depends on the robustness and complexity of the treatment plan. Robust evaluation and optimization address uncertainties explicitly, considering different treatment scenarios due to variations in the patient’s set-up and anatomy. In robust evaluation, the plan is evaluated across the different scenarios so that the impact of such uncertainties can be accounted for. In robust optimisation, the plan is optimised considering all of the scenarios (often the worst-case scenario, minimax approach) or for a combination of different scenarios, each one assigned a certain probability (probabilistic approach) in order to reduce the impact of those uncertainties on the dose delivered to the patient. Plan complexity also estimates the degree of dose uncertainty as a result of its calculation and delivery, which depends on all the machine parameters that make up the treatment plan. A high degree of plan complexity may compromise the overall accuracy and robustness of radiation treatments. Consequently, high degrees of plan complexity should be avoided to maximise the treatment quality. Future work and consensus on the best metrics for quality indices are required. Better tools are needed in TPSs for the evaluation of dose distributions, for the robust evaluation and optimisation of treatment plans, and for controlling and reporting plan complexity. Implementation of such tools and a better understanding of these concepts will facilitate the handling of these characteristics in clinical practice and be helpful to increase the overall quality of treatment plans in radiotherapy. What is plan quality in radiotherapy? The importance of evaluating dose metrics, complexity, and robustness of treatment plans. Radiotherapy and Oncology 153 (2020) 26–33.

Teaching lecture: Respiratory motion interventions for high precision radiotherapy

SP-0453 Respiratory motion interventions for high precision radiotherapy M. Josipovic 1 1 Rigshospitalet, Dept. of oncology, Copenhagen, Denmark

Abstract Text

In this teaching lecture, you will be guided through different approaches of respiratory motion interventions, used in modern radiotherapy. The first techniques have been developed around two decades ago and have both matured and evolved further. Many have become a standard of care in modern, high precision radiotherapy. The purpose of respiratory motion management in radiotherapy is twofold: • Improvement of the treatment delivery accuracy in very mobile targets and/or risk organs. This can be achieved by either use of sufficient, motion encompassing treatment margins, on-line tracking of the motion trajectory during treatment or mitigating the respiratory motion with breath hold. • Reduction of the dose delivered to the organs at risk, to minimise treatment related toxicity. In this case, the respiration is used to change the anatomy. The distance between the target and the risk organ can be maximised when treating during only a part of the respiratory cycle or in breath hold. In deep inspiration breath hold, the inflated lungs change the position of the heart and facilitate a dose reduction in both risk organs. Respiratory motion interventions will be presented for a range of treatment sites in the thorax and upper abdomen, addressing also stereotactic body radiotherapy (SBRT), MR-linac and proton radiotherapy. Uncertainties of the different solutions will be discussed.

Teaching lecture: Evidence-based approach for optimising clinical processes in radiotherapy

SP-0454 Evidence-based approach for optimising clinical processes in radiotherapy B. Soares Vieira Portugal

Abstract not available

Teaching lecture: Mental health prevention - Tips to stay healthy, recognise the signs of burnout

SP-0455 Mental health prevention - Tips to stay healthy, recognise the signs of burnout TBC