ESTRO 36 Abstract Book

S107 ESTRO 36 _______________________________________________________________________________________________

comprehensive study regarding follow-up after CovP based nodal boosting can be expected.

is well understood that suboptimal structure delineation (target or normal organs) can lead to suboptimal or unsafe treatment plans. Inaccuracies in structure delineation can translate to errors in treatment planning with OART more likely than with conventional RTP due the limited time available for quality assurance of segmented structures with OART. Many bodies have recommended that peer review process should be used as the second check of accuracy of organ delineation. With OART, prospective peer review will likely never be practical and the accuracy of auto-segmentation as well as the robustness of automatic evaluation of segmented structures will have to be able to compensate for limited ability for independent human checks. This presentation includes discussion of current practices in OART image segmentation with review of disease sites which are leading in the in the initial use of OART. Also discussed will be the image segmentation approaches for OART. Finally, efforts for development of automatic methods for verification of accuracy of segmented structures will be discussed. Now that OART is a practical reality, it is obvious that additional work is needed in development of image segmentation algorithms as well as development of automatic methods for verification of segmented structures. SP-0213 Ultra-fast treatment planning and dose reconstruction P. Ziegenhein 1 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Joint Department of Physics, Sutton, United Kingdom A new generation of hybrid MRI and linear accelerator machines, such as the MR-linac, is currently brought into practice which allows monitoring the changing patient anatomy during radiation delivery. The newly acquired images cannot only be used for real-time position verification but also to inform a re-planning strategy which adapts the treatment to the latest geometries. This new technique demands for a more interactive therapy workflow than it is used today. Treatment planning and dose verification steps need to be carried out more frequently and faster in order to make use of the continuously updated patient images. In this talk we will address two vital aspects of realizing an online therapy adaptation workflow: ultrafast treatment planning and dose reconstruction. Nowadays, with the help of modern computational hardware both operations can be performed in real-time. We will present state-of-the-art techniques designed especially for multi/many-core CPUs and discuss opportunities and challenges of their application. A proof of concept study on realistic patient data will be presented while alternative techniques and methods are analyzed and critically evaluated. SP-0214 Online tumour tracking – technology and quality assurance E. Colvill 1 1 Aarhus University Hospital, Radiation Oncology, Aarhus C, Denmark Intrafraction motion during radiotherapy delivery causes a blurring of the delivered dose distribution. For treatment sites affected by respiratory motion, including lung, liver and pancreas this effect can result in substantial deviations between planned and delivered dose, potentially compromising clinical goals. Treatment delivery accuracy may be increased through the implementation of adaptive delivery techniques. Online tumour tracking adapts the treatment to anatomical changes which may occur on the scale of seconds or minutes. It combines monitoring of the target motion and adaptation to that motion in real-time. In this talk a review of motion monitoring and treatment adaptation

Symposium: Ultra fast online therapy adaptation (replanning, dose accumulation QA)

SP-0212 Automatic image segmentation and structure evaluation for on-line adaptive RT S. Mutic 1 1 Washington University School of Medicine, Department of Radiation Oncology, St. Louis, USA The online adaptive radiotherapy (OART) has become a practical reality in recent years. Through experience, we have learned that the conventional radiotherapy planning (RTP) practices are not directly translatable to OART. With the OART, the entire planning process needs to be performed very quickly and generally can take no longer than 20-30 minutes for imaging, segmentation, planning, and quality assurance. The efficiency requirements of OART mean that each of the treatment planning steps needs to be performed in minutes rather than in hours or days, which can be afforded with the conventional RTP processes. This rate of efficiency demands a fundamental revisiting of the paradigms used in conventional RTP. One of the major differences between the OART and conventional RTP is image segmentation and processing of the segmented structures. For image segmentation, the OART efficiency needs mean that 1) there will be a significantly higher degree of reliance on auto-segmentation, 2) that few structures may be used\delineated, 3) that the conventional paradigms for structure creation will not be followed and that some structure will be contoured only to a limited extent, or 4) a combination of all three of these approaches. Unfortunate reality is that even the most sophisticated modern auto-contouring algorithms still have an unacceptably high degree of failure and inaccuracy and that these algorithms are almost always guaranteed to need some degree of manual editing. Additionally, many practical clinical cases are proving themselves to be not very good candidates for auto-contouring and that manual segmentation may be the best\most practical approach. The suboptimal performance of auto-contouring algorithms and use of a significant amount of available time on manual contouring or contour editing means that typically there is not much time left for contour validation. This lack of time for contour validation means that there is an increasing need for automatic evaluation of the segmented structures. It