ESTRO 2021 Abstract Book

S475

ESTRO 2021

Conclusion The contouring variances of OARs in the brain contoured on T1 MRI with contrast were low and consistent. This will facilitate consistent treatment plan comparisons across centers and aid in the decision making process where patients with brain cancer are referred to either photon or proton therapy. The data set is being prepared as a validation data set for auto segmentation algorithms for use within DCCC RT and potential collaborators.

Award lecture: K Breur Award

SP-0610 Value-based radiotherapy: turning evidence into practice. Y. Lievens 1 1 Ghent University Hospital and Ghent University, Radiation Oncology, Ghent, Belgium

Abstract Text Cancer incidence has been continuously on the rise over the past decades, and is predicted to reach over 5 million annually in Europe by 2035. Radiotherapy, one of the cornerstones of multidisciplinary cancer care, is crucial in the treatment of at least one out of two cancer patients, thereby improving local control, survival and quality-of-life. However, in contrast to the anticipated increase in radiotherapy needs in the years to come, suboptimal radiotherapy access and utilization has repeatedly been observed, even in high-income regions like Europe. This may negatively impact the outcome of our cancer patients. Meanwhile, innovative radiotherapy technologies and techniques show promise of better local control and toxicity profiles, and offer the potential to unlock new treatment opportunities such as a radical approach to oligometastatic disease or the routine integration of radiotherapy with novel systemic agents such as immunotherapy, further enhancing the needs. Yet, while certain new radiotherapy interventions may experience swift implementation, even if still of uncertain value, others may face barriers to translate into practice, regardless of a strong evidence-base. A debate between implementing radiotherapy innovation and providing broad access to radiation oncology as a whole cannot be the aim, but it is important to acknowledge this potential divide. With a plethora of novel interventions in a context of increasing needs, it will become ever more important to find common ground between optimizing our treatments and optimizing our health systems to secure access to proven and innovative interventions in real-life practice. Central in this endeavor is defining the real value of radiation treatments, in order to provide the best outcome to our patients, without wasting limited resources and budgets, further hampering access to and sustainability of our healthcare systems.

Award lecture: Honorary Physicist Award

SP-0612 Honorary what? C. Rasch

Abstract not available

Proffered papers: Proffered papers 35: Adaptive radiotherapy

OC-0613 Nine years of plan libraries for locally-advanced cervical cancer patients: what have we learned? D. Reijtenbagh 1 , J. Godart 1 , J. Penninkhof 1 , S. Quint 1 , A. Zolnay 1 , J.W. Mens 1 , M. Hoogeman 1 1 Erasmus MC, Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective Our center has been using a library-based plan of the day (PotD) strategy for EBRT for locally advanced cervical cancer patients since 2011. The goal of this strategy is to reduce dose to normal tissue. Since 2011, various adjustments have been made to the PotD and the treatment protocol. However, the performance of the PotD has not been assessed longitudinally. This study analyzes PotD performance over nine years and compares it to a maximum attainable normal tissue sparing based on daily replanning. Materials and Methods All patients clinically treated with the PotD protocol were included. As part of the protocol, patients were categorized as movers or non-movers based on tip-of-uterus displacement between an empty and full bladder CT scan. Non-movers and movers received one and two personalized library plans respectively, based on a motion model constructed from the full and empty bladder CT scan. An additional motion-robust plan (PTV BU ) was available for all patients. Starting date of radiotherapy, selected plans, and frequency and reason for full replanning were registered. Full replanning (new planning CT scans and plan library) was performed when PTV BU was selected three or more times during treatment. Planning structures were collected. Weighted PTV volumes (PTV w ) were calculated for all patients using the weighted sum of the PTV volumes from the library plans actually used for the fractions. This was considered representative for clinical practice. A fully-online adaptive strategy was simulated for each patient (PTV fully adapt. ), which comprised the full-bladder CTV and elective CTV with a 5-mm margin. The performance of the protocol was assessed by the percentage of patients requiring full replanning, the percentage of used motion-robust plans, and the comparison between the PTV w , PTV BU and PTV fully-adapt.