ESTRO 2020 Abstract Book

S424 ESTRO 2020

C. Hazelaar 1 1 MAASTRO Clinic, Radiotherapy, Maastricht, The Netherlands Abstract text Nowadays, several techniques exist that allow for tumor or organ-at-risk position monitoring during irradiation. This allows for the detection of patient motion and positional offsets, which can be accounted for using real-time tumor tracking techniques such as shifting the treatment source, shifting the treatment beam, or adjusting the patient position. This could help to accurately deliver high doses to the target with better OAR sparing. Some of these techniques require a dedicated treatment machine while others can be used on a conventional linear accelerator. However, the common aspect and first step required for real-time tumor tracking is accurate localization of the tumor position, which will be the focus of this talk. Currently, there is no universal and ready-to-use QA procedure for tumor position monitoring available. Therefore, it is important to focus on the application, challenges, and specific aspects of the tumor position monitoring technique that will be used in your clinic. In this talk, examples will be given of challenges that may be encountered, such as tumor visibility, differences in motion patterns, and patient-specific aspects. Based on this, QA procedures may be developed, for which suitable phantoms have to be used. However, one-size-fits-all phantoms do not yet exist, and therefore trade-offs have to be made, of which some examples will be shown. QA tests specific for tumor position monitoring, such as measurement of the static localization accuracy, dynamic localization accuracy for dedicated motion patterns such as free-breathing, breath-hold, prostate, and unexpected movements, and latency will be discussed. Finally, we will also briefly touch upon the subject of which accuracy is required for tumor position monitoring. SP-0776 Workflow aspects for markerless tumor tracking - from imaging to delivery A. Skrobala 1 1 Greater Poland Cancer Centre, Department of Medical Physics, Poznan, Poland Abstract text Radiotherapy workflows involve a lot of different professionals and different stages. Workflow can integrate daily imaging with the radiation therapy delivery process. This presentation will focus on workflow aspects for markerless tumor tracking. Characteristics and influence of tumor motion in different treatment sites (e. g. lung, prostate, and liver) should be considered at each radiotherapy stage starting from the initial planning CT scan and ending on image-guided radiotherapy. The most important element of appropriate realized markerless tumor tracking is identification of tumor position in real time, compensation of tumor motion, repositioning beam in real time and adaptive dosimetry, which verify PTV coverage and OARs sparing, using real time tumor tracking. The aims of this presentation will be (a) ways of prediction of tumor motion by different motion management system both during imaging and radiotherapy delivery, (b) presentation of existing technology (e. g. robotic system and integrated-MRI treatment) for markerless tumor tracking and their limitations, (c) description of practical obstacles in daily positioning of the markerless tumor motion during imaging. Finally, the aspects will be presented on how to improve the accuracy of markerless tumor tracking.

SP-0777 Clinical experience with markerless tumor tracking C. Bert 1 1 University Clinic Erlangen, Radiation Oncology, Erlangen, Germany Abstract text Dynamic tumor tracking (DTT) is one key feature of the Vero linear accelerator (Brainlab, Germany) that was developed dedicated to SBRT treatment. DTT can either be based on implanted fiducial markers which are in our case applied for liver cancer patients. Alternatively, DTT is used marker-less based on the image data only. This ML- DTT approach is in our clinic applied in lung cancer patients in particular since the implantation of fiducials bears the risk of causing a pneumothorax. The talk will cover a workflow description incl. treatment planning (margins), some data on delivery time, required personal, number of correlation models required, and the necessary imaging dose. These numbers are put into perspective to other DTT modalities in particular using the Cyberknife. SP-0778 Positioning and immobilisation- challenges in particle therapy from a clinical perspective P. Randers 1 , M. Fuglsang Jensen 1 , M. Giørtz 1 , A. Schouboe 1 , K. Seiersen 1 , A. Vestergaard 1 1 aarhus University Hospital, Danish Center For Particle Therapy, Aarhus N, Denmark Abstract text In January 2019 the Danish Center for Particle Therapy (DCPT) treated the first patient. Beforehand, a team of specialists with interdisciplinary qualifications was put together to evaluate different fixation equipment and methods specific to proton therapy. In this presentation, we will share our experiences with equipment selection and the challenges that we have met in the implementation process. Furthermore, we will show some of the tools we use to help pediatric patients cope with positioning and immobilization. SP-0779 Treatment planning considerations in particle therapy I. Kristensen 1 1 Skåne University Hospital, Dept of Hemathology- Oncology and Radiation Physics, Lund, Sweden Abstract text The main advantage of proton beam therapy is the finite range and sharp distal dose fall off in depth. However, compared to photons, protons have additional sources of uncertainties that should be analysed and understood. Range uncertainties in proton therapy can be substantial, i.e. several mm. Therefore, range uncertainties play a critical role in proton planning and has an impact on the entire planning process that differs from photons. The PTV margin recipes used in photon planning, are typically not sufficient in proton planning. In proton planning, two margins have to be considered, the lateral margin and the margin in depth i.e. range uncertainty. In principle, these two margins are of different nature. According to ICRU 78 [1] the PTVs are recommended to be used in proton planning for dose reporting purposes. Symposium: Particle Therapy - possibilities and limitations